The Berkeley motes are a family of embedded sensor nodes sharing roughly the same architecture.
Let us take the MICA mote as an example. The MICA motes have a two-CPU design. The main microcontroller (MCU), an Atmel ATmega103L, takes care of regular processing. A separate and much less capable coprocessor is only active when the MCU is being reprogrammed. The ATmega103L MCU has integrated 512 KB flash memory and 4 KB of data memory. Given these small memory sizes, writing software for motes is challenging. Ideally, programmers should be relieved from optimizing code at assembly level to keep code footprint small. However, high-level support and software services are not free. Being able to mix and match only necessary software components to support a particular application is essential to achieving a small footprint. A detailed discussion of the software architecture for motes.
In addition to the memory inside the MCU, a MICA mote also has a separate 512 KB flash memory unit that can hold data. Since the connection between the MCU and this external memory is via a low-speed serial peripheral interface (SPI) protocol, the external memory is more suited for storing data for later batch processing than for storing programs. The RF communication on MICA motes uses the TR1000 chip set (from RF Monolithics, Inc.) operating at 916 MHz band. With hardware accelerators, it can achieve a maximum of 50 kbps raw data rate. MICA motes implement a 40 kbps transmission rate. The transmission power can be digitally adjusted by software through a potentiometer (Maxim DS1804). The maximum transmission range is about 300 feet in open space.
Like other types of motes in the family, MICA motes support a 51 pin I/O extension connector. Sensors, actuators, serial I/O boards, or parallel I/O boards can be connected via the connector. A sensor/actuator board can host a temperature sensor, a light sensor, an accelerometer, a magnetometer, a microphone, and a beeper. The serial I/O (UART) connection allows the mote to communicate with a PC in real time. The parallel connection is primarily for downloading programs to the mote.
It is interesting to look at the energy consumption of various components on a MICA mote. A radio transmission bears the maximum power consumption. However, each radio packet (e.g., 30 bytes) only takes 4 ms to send, while listening to incoming packets turns the radio receiver ON all the time. The energy that can send one packet only supports the radio receiver for about 27 ms. Another observation is that there are huge differences among the power consumption levels in the active mode, the idle mode, and the suspend mode of the MCU. It is thus worthwhile from an energy-saving point of view to suspend the MCU and the RF receiver as long as possible.
Source of Information : Elsevier Wireless Networking Complete 2010
Showing posts with label Wireless. Show all posts
Showing posts with label Wireless. Show all posts
Sensor Node Hardware
Sensor node hardware can be grouped into three categories, each of which entails a different
set of trade-offs in the design choices.
● Augmented general-purpose computers: Examples include low-power PCs, embedded PCs (e.g., PC104), custom-designed PCs (e.g., Sensoria WINS NG nodes), 1 and various personal digital assistants (PDAs). These nodes typically run off-the-shelf (OTS) operating systems such as Win CE, Linux, or real-time operating systems and use standard wireless communication protocols such as Bluetooth or IEEE 802.11. Because of their relatively higher processing capability, they can accommodate a wide variety of sensors, ranging from simple microphones to more sophisticated video cameras. Compared with dedicated sensor nodes, PC-like platforms are more power hungry. However, when power is not an issue, these platforms have the advantage that they can leverage the availability of fully supported networking protocols, popular programming languages, middleware, and other OTS software.
● Dedicated embedded sensor nodes: Examples include the Berkeley mote family, the UCLA Medusa family, Ember nodes, 2 and MIT μ AMP. These platforms typically use commercial OTS (COTS) chip sets with emphasis on small form factor, low power processing and communication, and simple sensor interfaces. Because of their COTS CPU, these platforms typically support at least one programming language, such as C. However, in order to keep the program footprint small to accommodate their small memory size, programmers of these platforms are given full access to hardware but barely any operating system support. A classical example is the TinyOS platform and its companion programming language, nesC.
● System-on-chip (SoC) nodes: Examples of SoC hardware include smart dust, the BWRC picoradio node, and the PASTA node. 3 Designers of these platforms try to push the hardware limits by fundamentally rethinking the hardware architecture trade-offs for a sensor node at the chip design level. The goal is to find new ways of integrating CMOS, MEMS, and RF technologies to build extremely low power and small footprint sensor nodes that still provide certain sensing, computation, and communication capabilities. Since most of these platforms are currently in the research pipeline with no predefined instruction set, there is no software platform support available.
Source of Information : Elsevier Wireless Networking Complete 2010
set of trade-offs in the design choices.
● Augmented general-purpose computers: Examples include low-power PCs, embedded PCs (e.g., PC104), custom-designed PCs (e.g., Sensoria WINS NG nodes), 1 and various personal digital assistants (PDAs). These nodes typically run off-the-shelf (OTS) operating systems such as Win CE, Linux, or real-time operating systems and use standard wireless communication protocols such as Bluetooth or IEEE 802.11. Because of their relatively higher processing capability, they can accommodate a wide variety of sensors, ranging from simple microphones to more sophisticated video cameras. Compared with dedicated sensor nodes, PC-like platforms are more power hungry. However, when power is not an issue, these platforms have the advantage that they can leverage the availability of fully supported networking protocols, popular programming languages, middleware, and other OTS software.
● Dedicated embedded sensor nodes: Examples include the Berkeley mote family, the UCLA Medusa family, Ember nodes, 2 and MIT μ AMP. These platforms typically use commercial OTS (COTS) chip sets with emphasis on small form factor, low power processing and communication, and simple sensor interfaces. Because of their COTS CPU, these platforms typically support at least one programming language, such as C. However, in order to keep the program footprint small to accommodate their small memory size, programmers of these platforms are given full access to hardware but barely any operating system support. A classical example is the TinyOS platform and its companion programming language, nesC.
● System-on-chip (SoC) nodes: Examples of SoC hardware include smart dust, the BWRC picoradio node, and the PASTA node. 3 Designers of these platforms try to push the hardware limits by fundamentally rethinking the hardware architecture trade-offs for a sensor node at the chip design level. The goal is to find new ways of integrating CMOS, MEMS, and RF technologies to build extremely low power and small footprint sensor nodes that still provide certain sensing, computation, and communication capabilities. Since most of these platforms are currently in the research pipeline with no predefined instruction set, there is no software platform support available.
Source of Information : Elsevier Wireless Networking Complete 2010
Sensor Network Platforms and Tools
We discussed various aspects of sensor networks, including sensing and estimation, networking, infrastructure services, sensor tasking, and data storage and query. A real-world sensor network application most likely has to incorporate all these elements, subject to energy, bandwidth, computation, storage, and real-time constraints. This makes sensor network application development quite different from traditional distributed system development or database programming. With ad hoc deployment and frequently changing network topology, a sensor network application can hardly assume an always-on infrastructure that provides reliable services such as optimal routing, global directories, or service discovery.
There are two types of programming for sensor networks, those carried out by end users and those performed by application developers. An end user may view a sensor network as a pool of data and interact with the network via queries. Just as with query languages for database systems like SQL, a good sensor network programming language should be expressive enough to encode application logic at a high level of abstraction, and at the same time be structured enough to allow efficient execution on the distributed platform. Ideally, the end users should be shielded away from details of how sensors are organized and how nodes communicate.
On the other hand, an application developer must provide end users of a sensor network with the capabilities of data acquisition, processing, and storage. Unlike general distributed or database systems, collaborative signal and information processing (CSIP) software comprises reactive, concurrent, distributed programs running on ad hoc, resource-constrained, unreliable computation and communication platforms. Developers at this level have to deal with all kinds of uncertainty in the real world. For example, signals are noisy, events can happen at the same time, communication and computation take time, communications may be unreliable, battery life is limited, and so on. Moreover, because of the amount of domain knowledge required, application developers are typically signal and information processing specialists, rather than operating systems and networking experts. How to provide appropriate programming abstractions to these application writers is a key challenge for sensor network software development. In this chapter, we focus on software design issues to support this type of programming.
To make our discussion of these software issues concrete, we first give an overview of a few representative sensor node hardware platforms. We present the challenges of sensor network programming due to the massively concurrent interaction with the physical world. TinyOS for Berkeley motes and two types of nodecentric programming interfaces: an imperative language, nesC, and a dataflow-style language, TinyGALS. Node-centric designs are typically supported by node-level simulators such as ns-2 and TOSSIM. State-centric programming is a step toward programming beyond individual nodes. It gives programmers platform support for thinking in high-level abstractions, such as the state of the phenomena of interest over space and time.
Source of Information : Elsevier Wireless Networking Complete 2010
There are two types of programming for sensor networks, those carried out by end users and those performed by application developers. An end user may view a sensor network as a pool of data and interact with the network via queries. Just as with query languages for database systems like SQL, a good sensor network programming language should be expressive enough to encode application logic at a high level of abstraction, and at the same time be structured enough to allow efficient execution on the distributed platform. Ideally, the end users should be shielded away from details of how sensors are organized and how nodes communicate.
On the other hand, an application developer must provide end users of a sensor network with the capabilities of data acquisition, processing, and storage. Unlike general distributed or database systems, collaborative signal and information processing (CSIP) software comprises reactive, concurrent, distributed programs running on ad hoc, resource-constrained, unreliable computation and communication platforms. Developers at this level have to deal with all kinds of uncertainty in the real world. For example, signals are noisy, events can happen at the same time, communication and computation take time, communications may be unreliable, battery life is limited, and so on. Moreover, because of the amount of domain knowledge required, application developers are typically signal and information processing specialists, rather than operating systems and networking experts. How to provide appropriate programming abstractions to these application writers is a key challenge for sensor network software development. In this chapter, we focus on software design issues to support this type of programming.
To make our discussion of these software issues concrete, we first give an overview of a few representative sensor node hardware platforms. We present the challenges of sensor network programming due to the massively concurrent interaction with the physical world. TinyOS for Berkeley motes and two types of nodecentric programming interfaces: an imperative language, nesC, and a dataflow-style language, TinyGALS. Node-centric designs are typically supported by node-level simulators such as ns-2 and TOSSIM. State-centric programming is a step toward programming beyond individual nodes. It gives programmers platform support for thinking in high-level abstractions, such as the state of the phenomena of interest over space and time.
Source of Information : Elsevier Wireless Networking Complete 2010
Ad Hoc Wireless Sensor Networks
Advances in microelectronics technology have made it possible to build inexpensive, low-power, miniature sensing devices. Equipped with a microprocessor, memory, radio, and battery, such devices can now combine the functions of sensing, computing, and wireless communication into miniature smart sensor nodes , also called motes . Since smart sensors need not be tethered to any infrastructure because of on-board radio and battery, their main utility lies in being ad hoc, in the sense that they can be rapidly deployed by randomly strewing them over a region of interest. Several applications of such wireless sensor networks have been proposed, and there have also been several experimental deployments. Example applications are:
● Ecological Monitoring: wild-life in conservation areas, remote lakes, forest fi res.
● Monitoring of Large Structures: bridges, buildings, ships, and large machinery, such as turbines.
● Industrial Measurement and Control: measurement of various environment and process parameters in very large factories, such as continuous process chemical plants.
● Navigation Assistance: guidance through the geographical area where the sensor network is deployed.
● Defense Applications: monitoring of intrusion into remote border areas; detection, identification, and tracking of intruding personnel or vehicles.
The ad hoc nature of these wireless sensor networks means that the devices and the wireless links will not be laid out to achieve a planned topology. During the operation, sensors would be difficult or even impossible to access and hence their network needs to operate autonomously. Moreover, with time it is possible that sensors fail (one reason being battery drain) and cannot be replaced. It is, therefore, essential that sensors learn about each other and organize into a network on their own. Another crucial requirement is that since sensors may often be deployed randomly (e.g., simply strewn from an aircraft), in order to be useful, the devices need to determine their locations. In the absence of a centralized control, this whole process of self-organization needs to be carried out in a distributed fashion. In a sensor network, there is usually a single, global objective to be achieved. For example, in a surveillance application, a sensor network may be deployed to detect intruders. The global objective here is intrusion detection. This can be contrasted with multihop wireless mesh networks , where we have a collection of source – destination pairs, and each pair is interested in optimizing its individual performance metric. Another characteristic feature of sensor networks appears in the packet scheduling algorithms used. Sensor nodes are battery-powered and the batteries cannot be replaced. Hence, energy-aware packet scheduling is of crucial importance.
A smart sensor may have only modest computing power, but the ability to communicate allows a group of sensors to collaborate to execute tasks more complex than just sensing and forwarding the information, as in traditional sensor arrays. Hence, they may be involved in online processing of sensed data in a distributed fashion so as to yield partial or even complete results to an observer, thereby facilitating control applications, interactive computing, and querying. A distributed computing approach will also be energy-efficient as compared to mere data dissemination since it will avoid energy consumption in long haul transport of the measurements to the observer; this is of particular importance since sensors could be used in large numbers due to their low cost, yielding very high resolutions and large volumes of sensed data. Further, by arranging computations among only the neighboring sensors the number of transmissions is reduced, thereby saving transmission energy. A simple class of distributed computing algorithms would require each sensor to periodically exchange the results of local computation with the neighboring sensors. Thus the design of distributed signal processing and computation algorithms, and the mapping of these algorithms onto a network, is an important aspect of sensor network design.
Design and analysis of sensor networks must take into account the native capabilities of the nodes, as well as architectural features of the network. We assume that the sensor nodes are not mobile . Further, nodes are not equipped with position-sensing technology , like the Global Positioning System (GPS). However, each node can set its transmit power at an appropriate level — each node can exercise power control . Further, each node has an associated sensing radius ; events occurring within a circle of this radius centered at the sensor can be detected.
In general, a sensor network can have multiple sinks, where the traffic generated by the sensor sources leaves the network. We consider networks in which only a single sink is present. Further, we will be concerned with situations in which sensors are randomly deployed . In many scenarios of practical interest, preplanned placing of sensors is infeasible, leaving random deployment as the only practical alternative; e.g., consider a large terrain that is to be populated with sensors for surveillance purposes. In addition, random deployment is a convenient assumption for analytical tractability in models. Our study will also assume a simple path loss model , with no shadowing and no fading in the environment.
Source of Information : Elsevier Wireless Networking Complete 2010
● Ecological Monitoring: wild-life in conservation areas, remote lakes, forest fi res.
● Monitoring of Large Structures: bridges, buildings, ships, and large machinery, such as turbines.
● Industrial Measurement and Control: measurement of various environment and process parameters in very large factories, such as continuous process chemical plants.
● Navigation Assistance: guidance through the geographical area where the sensor network is deployed.
● Defense Applications: monitoring of intrusion into remote border areas; detection, identification, and tracking of intruding personnel or vehicles.
The ad hoc nature of these wireless sensor networks means that the devices and the wireless links will not be laid out to achieve a planned topology. During the operation, sensors would be difficult or even impossible to access and hence their network needs to operate autonomously. Moreover, with time it is possible that sensors fail (one reason being battery drain) and cannot be replaced. It is, therefore, essential that sensors learn about each other and organize into a network on their own. Another crucial requirement is that since sensors may often be deployed randomly (e.g., simply strewn from an aircraft), in order to be useful, the devices need to determine their locations. In the absence of a centralized control, this whole process of self-organization needs to be carried out in a distributed fashion. In a sensor network, there is usually a single, global objective to be achieved. For example, in a surveillance application, a sensor network may be deployed to detect intruders. The global objective here is intrusion detection. This can be contrasted with multihop wireless mesh networks , where we have a collection of source – destination pairs, and each pair is interested in optimizing its individual performance metric. Another characteristic feature of sensor networks appears in the packet scheduling algorithms used. Sensor nodes are battery-powered and the batteries cannot be replaced. Hence, energy-aware packet scheduling is of crucial importance.
A smart sensor may have only modest computing power, but the ability to communicate allows a group of sensors to collaborate to execute tasks more complex than just sensing and forwarding the information, as in traditional sensor arrays. Hence, they may be involved in online processing of sensed data in a distributed fashion so as to yield partial or even complete results to an observer, thereby facilitating control applications, interactive computing, and querying. A distributed computing approach will also be energy-efficient as compared to mere data dissemination since it will avoid energy consumption in long haul transport of the measurements to the observer; this is of particular importance since sensors could be used in large numbers due to their low cost, yielding very high resolutions and large volumes of sensed data. Further, by arranging computations among only the neighboring sensors the number of transmissions is reduced, thereby saving transmission energy. A simple class of distributed computing algorithms would require each sensor to periodically exchange the results of local computation with the neighboring sensors. Thus the design of distributed signal processing and computation algorithms, and the mapping of these algorithms onto a network, is an important aspect of sensor network design.
Design and analysis of sensor networks must take into account the native capabilities of the nodes, as well as architectural features of the network. We assume that the sensor nodes are not mobile . Further, nodes are not equipped with position-sensing technology , like the Global Positioning System (GPS). However, each node can set its transmit power at an appropriate level — each node can exercise power control . Further, each node has an associated sensing radius ; events occurring within a circle of this radius centered at the sensor can be detected.
In general, a sensor network can have multiple sinks, where the traffic generated by the sensor sources leaves the network. We consider networks in which only a single sink is present. Further, we will be concerned with situations in which sensors are randomly deployed . In many scenarios of practical interest, preplanned placing of sensors is infeasible, leaving random deployment as the only practical alternative; e.g., consider a large terrain that is to be populated with sensors for surveillance purposes. In addition, random deployment is a convenient assumption for analytical tractability in models. Our study will also assume a simple path loss model , with no shadowing and no fading in the environment.
Source of Information : Elsevier Wireless Networking Complete 2010
IEEE 802.11n
In response to growing market demand for higher-performance WLANs, the IEEE formed the task group 802.11n. The scope of this task group is to defi ne modifi cations to the PHY and MAC layer to deliver a minimum of 100 Mbps throughput at the MAC service AP (SAP).
802 .11n employs an evolutionary philosophy reusing existing technologies where practical, while introducing new technologies where they provide effective performance improvements to meet the needs of evolving applications. Reuse of legacy technologies such as OFDM, FEC coding, interleaving, and quadrature amplitude modulation mapping have been maintained to keep costs down and ease backward compatibility.
There are three key areas that need to be considered when addressing increases in WLAN performance. First, improvements in radio technology are needed to increase the physical transfer rate. Second, new mechanisms implementing the effective management of enhanced PHY performance modes must be developed. Third, improvements in data transfer efficiency are needed to reduce the improvements achieved with an increase in physical transfer rate.
The emerging 802.11n specification differs from its predecessors in that it provides for a variety of optional modes and configurations that dictate different maximum raw data rates. This enables the standard to provide baseline performance parameters for all 802.11n devices, while allowing manufacturers to enhance or tune capabilities to accommodate different applications and price points. WLAN hardware does not need to support every option to be compliant with the standard.
The first requirement is to support an OFDM implementation that improves upon the one
employed in 802.11a/g standards, using a higher maximum code rate and slightly wider bandwidth. This change improves the highest attainable raw data rate to 65 Mbps from
54 Mbps in the existing standards.
Multi -input, multi-output (MIMO) technology is used in 802.11n to evolve the existing OFDM physical interface presently implemented with legacy 802.11a/g. MIMO harnesses multipath with a technique known as space-division multiplexing (SDM). The transmitting WLAN device splits a data stream into multiple parts, called spatial streams, and transmits each spatial stream through separate antennas to corresponding antennas on the receiving end. The current 802.11n provides for up to four spatial streams, even though compliant hardware is not required to support that many.
Doubling the number of spatial streams from one to two effectively doubles the raw data rate. There are trade-offs, however, such as increased power consumption and, to a lesser extent, cost. The 802.11n specification includes an MIMO power-save mode, which mitigates power consumption by using multiple paths only when communication would benefit from the additional performance. The MIMO power-save mode is a required feature in the 802.11n specification.
There are two features in the specification that focus on improving MIMO performance: (1) beam-forming and (2) diversity. Beam-forming is a technique that focuses radio signals directly on the target antenna, thereby improving range and performance by limiting interference. Diversity exploits multiple antennas by combining the outputs of or selecting the best subset of a larger number of antennas than required to receive a number of spatial streams. The 802.11n specification supports up to four antennas.
Another optional mode in the 802.11n effectively doubles data rates by doubling the width of a WLAN communications channel from 20 to 40 MHz. The primary trade-off is fewer channels available for other devices. In the case of the 2.4-GHz band, there is enough room for three nonoverlapping 20-MHz channels. A 40-MHz channel does not leave much room for other devices to join the network or transmit in the same air space. This means intelligent, dynamic management is critical to ensuring that the 40-MHz channel option improves overall WLAN performance by balancing the high-bandwidth demands of some clients with the needs of other clients to remain connected to the network.
One of the most important features in the 802.11n specifi cation to improve mixed-mode performance is aggregation. Rather than sending a single data frame, the transmitting client bundles several frames together. Thus, aggregation improves effi ciency by restoring the percentage of time that data is being transmitted over the network.
The 802.11n specification was developed with previous standards in mind to ensure compatibility with more than 200 million Wi-Fi (802.11b) devices currently in use. An 802.11n AP will communicate with 802.11a devices on the 5-GHz band as well as 802.11b and 802.11g hardware on 2.4-GHz frequencies. In addition to basic interoperability between devices, 802.11n provides for greater network efficiency in mixed mode over what 802.11g offers.
Because it promises far greater bandwidth, better range, and reliability, 802.11n is advantageous in a variety of network configurations. And as emerging networking applications take hold in the home, a growing number of consumers will view 802.11n not just as an enhancement to their existing network, but as a necessity. Some of the current and emerging applications that are driving the need for 802.11n are voice over IP (VoIP), streaming video and music, gaming, and network attached storage.
Source of Information : Elsevier Wireless Networking Complete
802 .11n employs an evolutionary philosophy reusing existing technologies where practical, while introducing new technologies where they provide effective performance improvements to meet the needs of evolving applications. Reuse of legacy technologies such as OFDM, FEC coding, interleaving, and quadrature amplitude modulation mapping have been maintained to keep costs down and ease backward compatibility.
There are three key areas that need to be considered when addressing increases in WLAN performance. First, improvements in radio technology are needed to increase the physical transfer rate. Second, new mechanisms implementing the effective management of enhanced PHY performance modes must be developed. Third, improvements in data transfer efficiency are needed to reduce the improvements achieved with an increase in physical transfer rate.
The emerging 802.11n specification differs from its predecessors in that it provides for a variety of optional modes and configurations that dictate different maximum raw data rates. This enables the standard to provide baseline performance parameters for all 802.11n devices, while allowing manufacturers to enhance or tune capabilities to accommodate different applications and price points. WLAN hardware does not need to support every option to be compliant with the standard.
The first requirement is to support an OFDM implementation that improves upon the one
employed in 802.11a/g standards, using a higher maximum code rate and slightly wider bandwidth. This change improves the highest attainable raw data rate to 65 Mbps from
54 Mbps in the existing standards.
Multi -input, multi-output (MIMO) technology is used in 802.11n to evolve the existing OFDM physical interface presently implemented with legacy 802.11a/g. MIMO harnesses multipath with a technique known as space-division multiplexing (SDM). The transmitting WLAN device splits a data stream into multiple parts, called spatial streams, and transmits each spatial stream through separate antennas to corresponding antennas on the receiving end. The current 802.11n provides for up to four spatial streams, even though compliant hardware is not required to support that many.
Doubling the number of spatial streams from one to two effectively doubles the raw data rate. There are trade-offs, however, such as increased power consumption and, to a lesser extent, cost. The 802.11n specification includes an MIMO power-save mode, which mitigates power consumption by using multiple paths only when communication would benefit from the additional performance. The MIMO power-save mode is a required feature in the 802.11n specification.
There are two features in the specification that focus on improving MIMO performance: (1) beam-forming and (2) diversity. Beam-forming is a technique that focuses radio signals directly on the target antenna, thereby improving range and performance by limiting interference. Diversity exploits multiple antennas by combining the outputs of or selecting the best subset of a larger number of antennas than required to receive a number of spatial streams. The 802.11n specification supports up to four antennas.
Another optional mode in the 802.11n effectively doubles data rates by doubling the width of a WLAN communications channel from 20 to 40 MHz. The primary trade-off is fewer channels available for other devices. In the case of the 2.4-GHz band, there is enough room for three nonoverlapping 20-MHz channels. A 40-MHz channel does not leave much room for other devices to join the network or transmit in the same air space. This means intelligent, dynamic management is critical to ensuring that the 40-MHz channel option improves overall WLAN performance by balancing the high-bandwidth demands of some clients with the needs of other clients to remain connected to the network.
One of the most important features in the 802.11n specifi cation to improve mixed-mode performance is aggregation. Rather than sending a single data frame, the transmitting client bundles several frames together. Thus, aggregation improves effi ciency by restoring the percentage of time that data is being transmitted over the network.
The 802.11n specification was developed with previous standards in mind to ensure compatibility with more than 200 million Wi-Fi (802.11b) devices currently in use. An 802.11n AP will communicate with 802.11a devices on the 5-GHz band as well as 802.11b and 802.11g hardware on 2.4-GHz frequencies. In addition to basic interoperability between devices, 802.11n provides for greater network efficiency in mixed mode over what 802.11g offers.
Because it promises far greater bandwidth, better range, and reliability, 802.11n is advantageous in a variety of network configurations. And as emerging networking applications take hold in the home, a growing number of consumers will view 802.11n not just as an enhancement to their existing network, but as a necessity. Some of the current and emerging applications that are driving the need for 802.11n are voice over IP (VoIP), streaming video and music, gaming, and network attached storage.
Source of Information : Elsevier Wireless Networking Complete
IEEE 802.11b — High-Rate DSSS
In September 1999, IEEE ratified the 802.11b high-rate amendment to the standard, which added two higher speeds (5.5 and 11 Mbps) to 802.11. The key contribution of the 802.11b addition to the WLAN standard was to standardize the PHY support to two new speeds, 5.5 and 11 Mbps. To accomplish this, DSSS was selected as the sole PHY technique for the standard, since frequency hopping (FH) cannot support the higher speeds without violating current FCC regulations. The implication is that the 802.11b system will interoperate with 1 and 2 Mbps 802.11 DSSS systems, but will not work with 1 and 2 Mbps FHSS systems.
The original version of the 802.11 specifi es in the DSSS standard an 11-bit chipping, called a Barker sequence, to encode all data sent over the air. Each 11-chip sequence represents a single data bit (1 or 0), and is converted to a waveform, called a symbol, that can be sent over the air. These symbols are transmitted at a one million symbols per second (Msps) rate using binary phase shift keying (BPSK). In the case of 2 Mbps, a more sophisticated implementation based on quadrature phase shift keying (QPSK) is used. This doubles the data rate available in BPSK, via improved efficiency in the use of the radio bandwidth.
To increase the data rate in 802.11b standard, advanced coding techniques are employed. Rather than the two 11-bit Barker sequences, 802.11b specifi es complementary code keying (CCK). CCK allows for multichannel operation in the 2.4 GHz band by using existing 1 and 2 Mbps DSSS channelization schemes. CCK consists of a set of 64 8-bit code words. As a set, these code words have unique mathematical properties that allow them to be correctly distinguished from one another by a receiver even in the presence of substantial noise and multipath interference. The 5.5 Mbps rate uses CCK to encode four bits per carrier, while the 11 Mbps rate encodes eight bits per carrier. Both speeds use QPSK modulation and a signal at 1.375 Msps. This is how the higher data rates are obtained.
To support very noisy environments as well as extended ranges, 802.11b WLANs use dynamic rate shifting, allowing data rates to be automatically adjusted to compensate for the changing nature of the radio channel. Ideally, users connect at a full 11 Mbps rate. However, when devices move beyond the optimal range for 11 Mbps operation, or if substantial interference is present, 802.11b devices will transmit at lower speeds, falling
back to 5.5, 2, and 1 Mbps. Likewise, if a device moves back within the range of a higherspeed transmission, the connection will automatically speed up again. Rate shifting is a PHY mechanism transparent to the user and upper layers of the protocol stack.
Source of Information : Elsevier Wireless Networking Complete
The original version of the 802.11 specifi es in the DSSS standard an 11-bit chipping, called a Barker sequence, to encode all data sent over the air. Each 11-chip sequence represents a single data bit (1 or 0), and is converted to a waveform, called a symbol, that can be sent over the air. These symbols are transmitted at a one million symbols per second (Msps) rate using binary phase shift keying (BPSK). In the case of 2 Mbps, a more sophisticated implementation based on quadrature phase shift keying (QPSK) is used. This doubles the data rate available in BPSK, via improved efficiency in the use of the radio bandwidth.
To increase the data rate in 802.11b standard, advanced coding techniques are employed. Rather than the two 11-bit Barker sequences, 802.11b specifi es complementary code keying (CCK). CCK allows for multichannel operation in the 2.4 GHz band by using existing 1 and 2 Mbps DSSS channelization schemes. CCK consists of a set of 64 8-bit code words. As a set, these code words have unique mathematical properties that allow them to be correctly distinguished from one another by a receiver even in the presence of substantial noise and multipath interference. The 5.5 Mbps rate uses CCK to encode four bits per carrier, while the 11 Mbps rate encodes eight bits per carrier. Both speeds use QPSK modulation and a signal at 1.375 Msps. This is how the higher data rates are obtained.
To support very noisy environments as well as extended ranges, 802.11b WLANs use dynamic rate shifting, allowing data rates to be automatically adjusted to compensate for the changing nature of the radio channel. Ideally, users connect at a full 11 Mbps rate. However, when devices move beyond the optimal range for 11 Mbps operation, or if substantial interference is present, 802.11b devices will transmit at lower speeds, falling
back to 5.5, 2, and 1 Mbps. Likewise, if a device moves back within the range of a higherspeed transmission, the connection will automatically speed up again. Rate shifting is a PHY mechanism transparent to the user and upper layers of the protocol stack.
Source of Information : Elsevier Wireless Networking Complete
Security of IEEE 802.11 Systems
The IEEE 802.11 provides for MAC access control and encryption mechanisms. Earlier,
the wire line equivalent privacy (WEP) algorithm was used to encrypt messages. WEP uses a Rivest Cipher 4 (RC4) pseudo-random number generator with two key structures
of 40 and 128 bits. Because of the inherent weaknesses of the WEP, the IEEE 802.11i committee developed a new encryption algorithm and worked on the enhanced security and authentication mechanisms for 802.11 systems.
For access control, ESSID (also known as a WLAN service area ID) is programmed into each AP and is required in order for a wireless client to associate with an AP. In addition, there is provision for a table of MAC addresses called an access control list to be included in the AP, restricting access to stations whose MAC addresses are not on the list.
Beyond layer-2, 802.11 WLANs support the same security standards supported by other 802 LANs for access control (such as network operating system logins) and encryption (such as IPSec or application-level encryption). These higher-level technologies can be used to create end-to-end secure networks encompassing both wired LAN and WLAN components, with the wireless piece of the network gaining additional security from the IEEE 802.11i feature set.
Source of Information : Elsevier Wireless Networking Complete
the wire line equivalent privacy (WEP) algorithm was used to encrypt messages. WEP uses a Rivest Cipher 4 (RC4) pseudo-random number generator with two key structures
of 40 and 128 bits. Because of the inherent weaknesses of the WEP, the IEEE 802.11i committee developed a new encryption algorithm and worked on the enhanced security and authentication mechanisms for 802.11 systems.
For access control, ESSID (also known as a WLAN service area ID) is programmed into each AP and is required in order for a wireless client to associate with an AP. In addition, there is provision for a table of MAC addresses called an access control list to be included in the AP, restricting access to stations whose MAC addresses are not on the list.
Beyond layer-2, 802.11 WLANs support the same security standards supported by other 802 LANs for access control (such as network operating system logins) and encryption (such as IPSec or application-level encryption). These higher-level technologies can be used to create end-to-end secure networks encompassing both wired LAN and WLAN components, with the wireless piece of the network gaining additional security from the IEEE 802.11i feature set.
Source of Information : Elsevier Wireless Networking Complete
WLAN Technologies
The technologies available for use in a WLAN include IR, UHF (narrowband), and SS implementation. Each implementation comes with its own set of advantages and limitations.
IR Technology
IR is an invisible band of radiation that exists at the lower end of the visible electromagnetic spectrum. This type of transmission is most effective when a clear line-of-sight exists between the transmitter and the receiver.
Two types of IR WLAN solutions are available: diffused-beam and direct-beam (or line-of-sight). Currently, direct-beam WLANs offer a faster data rate than the diffused-beam networks. Direct-beam is more directional since diffused-beam technology uses reflected rays to transmit/receive a data signal. It achieves lower data rates in the 1 – 2 Mbps range.
IR is a short-range technology. When used indoors, it can be limited by solid objects such
as doors, walls, merchandise, or racking. In addition, the lighting environment can affect
signal quality. For example, loss of communication may occur because of the large amount of sunlight or background light in an environment. Fluorescent lights also may contain large amounts of IR. This problem may be solved by using high signal power and an optimal bandwidth filter, which reduces the IR signals coming from an outside source. In an outdoor environment, snow, ice, and fog may affect the operation of an IR-based system.
UHF Narrowband Technology
UHF wireless data communication systems have been available since the early 1980s.
These systems normally transmit in the 430 – 470 MHz frequency range, with rare systems using segments of the 800 MHz range. The lower portion of this band — 430 – 450 MHz — is referred to as the unprotected (unlicensed), and 450 – 470 MHz is referred to as the protected (licensed) band. In the unprotected band, RF licenses are not granted for specific frequencies and anyone is allowed to use any frequencies, giving customers some assurance that they will have complete use of that frequency.
Because independent narrowband RF systems cannot coexist on the same frequency, government agencies allocate specific RFs to users through RF site licenses. A limited amount of unlicensed spectrum is also available in some countries. In order to have many
frequencies that can be allocated to users, the bandwidth given to a specific user is very small.
The term narrowband is used to describe this technology because the RF signal is sent in a very narrow bandwidth, typically 12.5 or 25 kHz. Power levels range from 1 to 2 W for
narrowband RF data systems. This narrow bandwidth combined with high power results in larger transmission distances than are available from 900 MHz or 2.4 GHz SS systems, which have lower power levels and wider bandwidths. Table 5.4 lists the advantages and disadvantages of UHF technology.
Many modern UHF systems are synthesized radio technology. This refers to the way channel frequencies are generated in the radio. The crystal-controlled products in legacy UHF products require factory installation of unique crystals for each possible channel frequency. Synthesized radio technology uses a single, standard crystal frequency and drives the required channel frequency by dividing the crystal frequency down to a small value, then multiplying it up to the desired channel frequency. The division and multiplication factors are unique for each desired channel frequency, and are programmed into digital memory in the radio at the time of manufacturing. Synthesized UHF-based solutions provide the ability to install equipment without the complexity of hardware crystals. Common equipment can be purchased and specific UHF frequency used for each device can be tuned based upon specific location requirements. Additionally, synthesized UHF radios do not exhibit the frequency drift problem experienced in crystal-controlled UHF radios.
Modern UHF systems allow APs to be individually configured for operation on one of the several preprogrammed frequencies. Terminals are programmed with a list of all frequencies used in the installed APs, allowing them to change frequencies when roaming. To increase throughput, APs may be installed with overlapping coverage but use different frequencies.
Spread Spectrum Technology
Most WLANs use SS technology, a wideband RF technique that uses the entire allotted
spectrum in a shared fashion as opposed to dividing it into discrete private pieces (as with
narrowband). The SS system spreads the transmission power over the entire usable spectrum. This is obviously a less efficient use of the bandwidth than the narrowband approach. However, SS is designed to trade off bandwidth efficiency for reliability, integrity, and security. The bandwidth trade-off produces a signal that is easier to detect, provided that the receiver knows the parameters of the SS signal being broadcast. If the receiver is not tuned to the right frequency, a SS signal looks like background noise.
By operating across a broad range of radio frequencies, a SS device could communicate clearly despite interference from other devices using the same spectrum in the same physical location. In addition to its relative immunity to interference, SS makes eavesdropping and jamming inherently difficult.
In commercial applications, SS techniques currently offer data rates up to 2 Mbps. Because the FCC does not require site licensing for the bands used by SS systems, this technology has become the standard for high-speed RF data transmission. Two modulation schemes are commonly used to encode SS signals: direct sequence SS (DSSS) and frequency-hopping SS (FHSS).
FHSS uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be a short-duration impulse noise.
DSSS generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a spreading code . The longer the code, the greater the probability that the original data can be recovered (and, of course, the more bandwidth will be required). To an unintended receiver DSSS appears as low-power wideband noise and is rejected by most narrowband receivers.
Source of Information : Elsevier Wireless Networking Complete
IR Technology
IR is an invisible band of radiation that exists at the lower end of the visible electromagnetic spectrum. This type of transmission is most effective when a clear line-of-sight exists between the transmitter and the receiver.
Two types of IR WLAN solutions are available: diffused-beam and direct-beam (or line-of-sight). Currently, direct-beam WLANs offer a faster data rate than the diffused-beam networks. Direct-beam is more directional since diffused-beam technology uses reflected rays to transmit/receive a data signal. It achieves lower data rates in the 1 – 2 Mbps range.
IR is a short-range technology. When used indoors, it can be limited by solid objects such
as doors, walls, merchandise, or racking. In addition, the lighting environment can affect
signal quality. For example, loss of communication may occur because of the large amount of sunlight or background light in an environment. Fluorescent lights also may contain large amounts of IR. This problem may be solved by using high signal power and an optimal bandwidth filter, which reduces the IR signals coming from an outside source. In an outdoor environment, snow, ice, and fog may affect the operation of an IR-based system.
UHF Narrowband Technology
UHF wireless data communication systems have been available since the early 1980s.
These systems normally transmit in the 430 – 470 MHz frequency range, with rare systems using segments of the 800 MHz range. The lower portion of this band — 430 – 450 MHz — is referred to as the unprotected (unlicensed), and 450 – 470 MHz is referred to as the protected (licensed) band. In the unprotected band, RF licenses are not granted for specific frequencies and anyone is allowed to use any frequencies, giving customers some assurance that they will have complete use of that frequency.
Because independent narrowband RF systems cannot coexist on the same frequency, government agencies allocate specific RFs to users through RF site licenses. A limited amount of unlicensed spectrum is also available in some countries. In order to have many
frequencies that can be allocated to users, the bandwidth given to a specific user is very small.
The term narrowband is used to describe this technology because the RF signal is sent in a very narrow bandwidth, typically 12.5 or 25 kHz. Power levels range from 1 to 2 W for
narrowband RF data systems. This narrow bandwidth combined with high power results in larger transmission distances than are available from 900 MHz or 2.4 GHz SS systems, which have lower power levels and wider bandwidths. Table 5.4 lists the advantages and disadvantages of UHF technology.
Many modern UHF systems are synthesized radio technology. This refers to the way channel frequencies are generated in the radio. The crystal-controlled products in legacy UHF products require factory installation of unique crystals for each possible channel frequency. Synthesized radio technology uses a single, standard crystal frequency and drives the required channel frequency by dividing the crystal frequency down to a small value, then multiplying it up to the desired channel frequency. The division and multiplication factors are unique for each desired channel frequency, and are programmed into digital memory in the radio at the time of manufacturing. Synthesized UHF-based solutions provide the ability to install equipment without the complexity of hardware crystals. Common equipment can be purchased and specific UHF frequency used for each device can be tuned based upon specific location requirements. Additionally, synthesized UHF radios do not exhibit the frequency drift problem experienced in crystal-controlled UHF radios.
Modern UHF systems allow APs to be individually configured for operation on one of the several preprogrammed frequencies. Terminals are programmed with a list of all frequencies used in the installed APs, allowing them to change frequencies when roaming. To increase throughput, APs may be installed with overlapping coverage but use different frequencies.
Spread Spectrum Technology
Most WLANs use SS technology, a wideband RF technique that uses the entire allotted
spectrum in a shared fashion as opposed to dividing it into discrete private pieces (as with
narrowband). The SS system spreads the transmission power over the entire usable spectrum. This is obviously a less efficient use of the bandwidth than the narrowband approach. However, SS is designed to trade off bandwidth efficiency for reliability, integrity, and security. The bandwidth trade-off produces a signal that is easier to detect, provided that the receiver knows the parameters of the SS signal being broadcast. If the receiver is not tuned to the right frequency, a SS signal looks like background noise.
By operating across a broad range of radio frequencies, a SS device could communicate clearly despite interference from other devices using the same spectrum in the same physical location. In addition to its relative immunity to interference, SS makes eavesdropping and jamming inherently difficult.
In commercial applications, SS techniques currently offer data rates up to 2 Mbps. Because the FCC does not require site licensing for the bands used by SS systems, this technology has become the standard for high-speed RF data transmission. Two modulation schemes are commonly used to encode SS signals: direct sequence SS (DSSS) and frequency-hopping SS (FHSS).
FHSS uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be a short-duration impulse noise.
DSSS generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a spreading code . The longer the code, the greater the probability that the original data can be recovered (and, of course, the more bandwidth will be required). To an unintended receiver DSSS appears as low-power wideband noise and is rejected by most narrowband receivers.
Source of Information : Elsevier Wireless Networking Complete
WLAN Equipment
There are three main links that form the basis of the wireless network. These are:
● LAN adapter : Wireless adapters are made in the same basic form as their wired counterparts: PCMCIA, Card bus, PCI, and USB. They also serve the same function, enabling end-users to access the network. In a wired LAN, adapters provide an interface between the network operating system and the wire. In a WLAN, they provide the interface between the network operating system and an antenna to create a transparent connection to the network.
● AP : The AP is the wireless equivalent of a LAN hub. It receives, buffers, and transmits data between the WLAN and the wired network, supporting a group of wireless user devices. An AP is typically connected with the backbone network through a standard Ethernet cable, and communicates with wireless devices by means of an antenna. The AP or antenna connected to it is generally mounted on a high wall or on the ceiling. Like cells in a cellular network, multiple APs can support handoff from one AP to another as the user moves from area to area. APs have a range from 20 to 500 m. A single AP can support between 15 to 250 users, depending on technology, configuration, and use. It is relatively easy to scale a WLAN by adding more APs to reduce network congestion and enlarge the coverage area. Large networks requiring multiple APs deploy them to create overlapping cells for constant connectivity to the network. A wireless AP can monitor movement of a client across its domain and permit or deny specific traffic or clients from communicating through it.
● Outdoor LAN bridges : Outdoor LAN bridges are used to connect LANs in different
buildings. When the cost of buying a fiber optic cable between buildings is considered, particularly if there are barriers such as highways or bodies of water in the way, a WLAN can be an economical alternative. An outdoor bridge can provide a less expensive alternative to recurring leased-line charges. WLAN bridge products support fairly high data rates and ranges of several miles with the use of line-of-sight directional antennas. Some APs can also be used as a bridge between buildings of relatively close proximity.
Source of Information : Elsevier Wireless Networking Complete
● LAN adapter : Wireless adapters are made in the same basic form as their wired counterparts: PCMCIA, Card bus, PCI, and USB. They also serve the same function, enabling end-users to access the network. In a wired LAN, adapters provide an interface between the network operating system and the wire. In a WLAN, they provide the interface between the network operating system and an antenna to create a transparent connection to the network.
● AP : The AP is the wireless equivalent of a LAN hub. It receives, buffers, and transmits data between the WLAN and the wired network, supporting a group of wireless user devices. An AP is typically connected with the backbone network through a standard Ethernet cable, and communicates with wireless devices by means of an antenna. The AP or antenna connected to it is generally mounted on a high wall or on the ceiling. Like cells in a cellular network, multiple APs can support handoff from one AP to another as the user moves from area to area. APs have a range from 20 to 500 m. A single AP can support between 15 to 250 users, depending on technology, configuration, and use. It is relatively easy to scale a WLAN by adding more APs to reduce network congestion and enlarge the coverage area. Large networks requiring multiple APs deploy them to create overlapping cells for constant connectivity to the network. A wireless AP can monitor movement of a client across its domain and permit or deny specific traffic or clients from communicating through it.
● Outdoor LAN bridges : Outdoor LAN bridges are used to connect LANs in different
buildings. When the cost of buying a fiber optic cable between buildings is considered, particularly if there are barriers such as highways or bodies of water in the way, a WLAN can be an economical alternative. An outdoor bridge can provide a less expensive alternative to recurring leased-line charges. WLAN bridge products support fairly high data rates and ranges of several miles with the use of line-of-sight directional antennas. Some APs can also be used as a bridge between buildings of relatively close proximity.
Source of Information : Elsevier Wireless Networking Complete
imode Versus WAP
imode is available only in Japan, whereas Europe and other big markets for 3G mobile service providers are completely WAP-based. In the United States, most service providers have chosen WAP.
The most basic difference between imode and WAP is the different graphic capabilities; imode only supports simple graphics, which is far more than what WAP allows. The imode packet-switched data network is more suited for transferring data than the WAP CS network.
Another major difference is the “ always-on ” capabilities of imode. Since users are not charged for the time they spend on-line, it is more convenient and also less expensive. Since there is no need to dial up before using the various IP-based services, e-mail becomes as instant as SMS. imode uses cHTML, a subset of HTML, while WAP uses WML, a subset of XML. cHTML, while certainly easier to develop from a web-designer standpoint, has its limitations. The downside of WML, on the other hand, is similarly obvious — currently a WAP gateway is required to translate between HTML and WML for almost every data transfer. On the other hand, since WML is derived from XML, it is much more extensible. XML allows for more dynamic content and various different applications. In the future, a WML-based service will be of more advantage than an HTML-based one. So while WAP may currently require more complicated technology, in the long run, it may enable the user to do more with his or her device.
Source of Information : Elsevier Wireless Networking Complete
The most basic difference between imode and WAP is the different graphic capabilities; imode only supports simple graphics, which is far more than what WAP allows. The imode packet-switched data network is more suited for transferring data than the WAP CS network.
Another major difference is the “ always-on ” capabilities of imode. Since users are not charged for the time they spend on-line, it is more convenient and also less expensive. Since there is no need to dial up before using the various IP-based services, e-mail becomes as instant as SMS. imode uses cHTML, a subset of HTML, while WAP uses WML, a subset of XML. cHTML, while certainly easier to develop from a web-designer standpoint, has its limitations. The downside of WML, on the other hand, is similarly obvious — currently a WAP gateway is required to translate between HTML and WML for almost every data transfer. On the other hand, since WML is derived from XML, it is much more extensible. XML allows for more dynamic content and various different applications. In the future, a WML-based service will be of more advantage than an HTML-based one. So while WAP may currently require more complicated technology, in the long run, it may enable the user to do more with his or her device.
Source of Information : Elsevier Wireless Networking Complete
imode
imode is a proprietary mobile ISP and portal service from NTT DoCoMo, Japan, with about 50 million subscribers. For imode, DoCoMo adopted the Internet model and protocol. imode uses compact HTML (cHTML) as a page description language. The structure of cHTML means that the user can view traditional HTML and imode sites can be inspected with ordinary Internet web browsers. This is in contrast to WAP, where HTML pages must be translated to WML. imode provides Internet service using personal digital cellular-packet (PDC-P) and a subset of HTML 3.0 for content description.
imode is a packet-switched service (always connected, as long as the user’s handset is reached by imode signal) which includes images, animated images, and colors. In imode, users are charged per packet of downloaded information. imode allows application/content providers to distribute software to cellular phones and also permits users to download appilets (e.g., games). imode uses packet-switched technology for the wireless part of the communication. The wired part of the communication is carried over TCP/IP.
Packet -switched services send and receive information by dividing messages into small blocks called packets and adding headers containing address and control information to each packet. This allows multiple communications to be carried on a communication channel, giving efficient channel usage with low cost. Dopa, DoCoMo’s dedicated data communications service, offers connections to location area network (LAN) and ISPs.
The mobile packet communications system has a network configuration in which a packet communications function is added and integrated into PDC, the digital system for portable and automobile telephones. DoCoMo has developed a data transmission protocol specific to imode. This protocol is used with the PDC-P system. The PDC-P network includes a mobile message packet gateway (M-PGW) to handle conversions between the two protocol formats. Connection between the imode server and the Internet uses TCP/IP. The imode server is regular web server which can reside at NTT DoCoMo or at the enterprise. DoCoMo has been acting as a 1717 portal and normally maintains the imode server.
imode relies on Internet security as provided by SSL/TLS and does not have the ability to
handle server-side authenticated SSL sessions. imode phones are preconfigured with root
collision avoidance keys from public key infrastructure. This will allow for establishment of a server-side authenticated SSL session between the imode device and imode server hosted by the enterprise. imode does not have the capability of handling client-side certifi cates which means that nonrepudiation is not possible with the current implementation of imode.
imode is a packet-switched service (always connected, as long as the user’s handset is reached by imode signal) which includes images, animated images, and colors. In imode, users are charged per packet of downloaded information. imode allows application/content providers to distribute software to cellular phones and also permits users to download appilets (e.g., games). imode uses packet-switched technology for the wireless part of the communication. The wired part of the communication is carried over TCP/IP.
Packet -switched services send and receive information by dividing messages into small blocks called packets and adding headers containing address and control information to each packet. This allows multiple communications to be carried on a communication channel, giving efficient channel usage with low cost. Dopa, DoCoMo’s dedicated data communications service, offers connections to location area network (LAN) and ISPs.
The mobile packet communications system has a network configuration in which a packet communications function is added and integrated into PDC, the digital system for portable and automobile telephones. DoCoMo has developed a data transmission protocol specific to imode. This protocol is used with the PDC-P system. The PDC-P network includes a mobile message packet gateway (M-PGW) to handle conversions between the two protocol formats. Connection between the imode server and the Internet uses TCP/IP. The imode server is regular web server which can reside at NTT DoCoMo or at the enterprise. DoCoMo has been acting as a 1717 portal and normally maintains the imode server.
imode relies on Internet security as provided by SSL/TLS and does not have the ability to
handle server-side authenticated SSL sessions. imode phones are preconfigured with root
collision avoidance keys from public key infrastructure. This will allow for establishment of a server-side authenticated SSL session between the imode device and imode server hosted by the enterprise. imode does not have the capability of handling client-side certifi cates which means that nonrepudiation is not possible with the current implementation of imode.
Applications of WAP
The first and foremost application of WAP is accessing the Internet from mobile devices.
This is already in use in many mobile phones. This application is gaining popularity daily,
and many web sites already have a WAP version of their site. An application, which is out, is sending sale offers to mobile customers through WAP. The user’s phone will be able to receive any sale prices and offers from the web site of a store.
Games can be played from mobile devices over wireless devices. This application has been implemented in certain countries and is under development in many others. This is an application which has been predicted to gain high popularity. Application to access time sheets and filing expenses claims via mobile handsets are currently being developed. These applications, when implemented, will be a breakthrough in the business world.
Applications to locate WAP customers geographically have been developed. Applications to help users who are lost or stranded by guiding them using their locations are under
consideration. WAP also provides short messaging, e-mail, weather, and traffic alerts based on the geographic location of the customer. These applications are available in some countries but will soon be provided in all countries. One of the biggest applications of WAP under consideration is banking from mobile devices.
These applications will be very popular if they are implemented in a secure manner. The mobile industry appears to be moving forward, putting aside the issues of network and air interface standards, and instead concentrating on laying the foundations for service development, regarded by many as the key driver to multimedia on the move and third generation mobile systems. From that point of view, in the near future WAP and Bluetooth will play fundamental roles.
Source of Information : Elsevier Wireless Networking Complete
This is already in use in many mobile phones. This application is gaining popularity daily,
and many web sites already have a WAP version of their site. An application, which is out, is sending sale offers to mobile customers through WAP. The user’s phone will be able to receive any sale prices and offers from the web site of a store.
Games can be played from mobile devices over wireless devices. This application has been implemented in certain countries and is under development in many others. This is an application which has been predicted to gain high popularity. Application to access time sheets and filing expenses claims via mobile handsets are currently being developed. These applications, when implemented, will be a breakthrough in the business world.
Applications to locate WAP customers geographically have been developed. Applications to help users who are lost or stranded by guiding them using their locations are under
consideration. WAP also provides short messaging, e-mail, weather, and traffic alerts based on the geographic location of the customer. These applications are available in some countries but will soon be provided in all countries. One of the biggest applications of WAP under consideration is banking from mobile devices.
These applications will be very popular if they are implemented in a secure manner. The mobile industry appears to be moving forward, putting aside the issues of network and air interface standards, and instead concentrating on laying the foundations for service development, regarded by many as the key driver to multimedia on the move and third generation mobile systems. From that point of view, in the near future WAP and Bluetooth will play fundamental roles.
Source of Information : Elsevier Wireless Networking Complete
WAP Advantages and Disadvantages
The following are the advantages of WAP:
● Implementation near to the Internet model;
● Most modern mobile telephone devices support WAP;
● Real-time send/receive data;
● Multiplatform functionality (little change is needed to run on any web site since XML is used);
● No hardware obsolescence.
The following are some of the advantages of using WAP CSS on mobile Internet sites:
● Because of WAP 2.0 (XHTML MP/WAP CSS), web programming and WAP programming converge. Learning WAP programming does not require much effort if you already know how to program the web. Web developers can continue to use their familiar web authoring tools and PC web browsers for building mobile Internet sites. This is one major advantage of XHTML MP/WAP CSS over WML.
● You can have greater control on the appearance of WAP pages with WAP CSS than with WML. For example, you can specify the colors, fonts, background, borders, margins, and padding of various elements with WAP CSS.
● If you apply a single CSS to the whole mobile Internet site, a mobile device will download the CSS only once the fi rst time the mobile Internet site is visited. The CSS will then be stored in the cache and it can be accessed later without connecting to the server.
● The file sizes of XHTML MP documents can become smaller if the layout and formatting information is moved to an external WAP CSS style sheet. A small fi le
size has the advantage of a shorter download time.
● Using WAP CSS has the advantage that the content and presentation can be separated. This means you can:
1. Match the layout and style of the same content to the characteristics of different wireless devices easily.
2. Match the layout and style of the same content for different user agents easily.
3. Minimize the effort to maintain a WAP site. When new mobile phone models come onto the market, you can write new WAP CSS style sheets to optimize the layout of the WAP site on these new mobile phones. The content files do not need to be modifed.
4. Apply a single WAP CSS style sheet to multiple WAP pages. Later if you want to change the look and feel of the whole WAP site, just modify the WAP CSS.
5. Reuse the style code in multiple projects.
6. Remotely divide work — someone can focus on look and feel WAP, whereas others can concentrate on contents.
Some of the disadvantages of the WAP are the following:
● Low speeds, security, and very small user interface;
● Not very familiar to the users;
● Business model is expensive;
● Forms are hard to design;
● Third party is included.
Some of the disadvantages of using WAP CSS style sheets on mobile Internet sites are:
● Different WAP browsers have varied levels of support for WAP CSS. One property supported on one WAP browser may not be available on another WAP browser.
● An external WAP CSS style sheet can increase the time required for a page to be
completely loaded the fi rst time the WAP site is visited because of the following
reasons:
1. The external WAP CSS style sheet does not exist in the cache of the mobile phone at the first visit, which means the mobile phone has to download it from the server.
2. An XHTML MP document and its external WAP CSS style sheet have to be downloaded in separate requests.
3. If you make use of a single WAP CSS file to specify all the presentation
information about the mobile Internet site, the fi le size of the WAP CSS file can be quite large.
4. The WAP browser needs to parse the CSS in addition to the XHTML MP document.
Source of Information : Elsevier Wireless Networking Complete
● Implementation near to the Internet model;
● Most modern mobile telephone devices support WAP;
● Real-time send/receive data;
● Multiplatform functionality (little change is needed to run on any web site since XML is used);
● No hardware obsolescence.
The following are some of the advantages of using WAP CSS on mobile Internet sites:
● Because of WAP 2.0 (XHTML MP/WAP CSS), web programming and WAP programming converge. Learning WAP programming does not require much effort if you already know how to program the web. Web developers can continue to use their familiar web authoring tools and PC web browsers for building mobile Internet sites. This is one major advantage of XHTML MP/WAP CSS over WML.
● You can have greater control on the appearance of WAP pages with WAP CSS than with WML. For example, you can specify the colors, fonts, background, borders, margins, and padding of various elements with WAP CSS.
● If you apply a single CSS to the whole mobile Internet site, a mobile device will download the CSS only once the fi rst time the mobile Internet site is visited. The CSS will then be stored in the cache and it can be accessed later without connecting to the server.
● The file sizes of XHTML MP documents can become smaller if the layout and formatting information is moved to an external WAP CSS style sheet. A small fi le
size has the advantage of a shorter download time.
● Using WAP CSS has the advantage that the content and presentation can be separated. This means you can:
1. Match the layout and style of the same content to the characteristics of different wireless devices easily.
2. Match the layout and style of the same content for different user agents easily.
3. Minimize the effort to maintain a WAP site. When new mobile phone models come onto the market, you can write new WAP CSS style sheets to optimize the layout of the WAP site on these new mobile phones. The content files do not need to be modifed.
4. Apply a single WAP CSS style sheet to multiple WAP pages. Later if you want to change the look and feel of the whole WAP site, just modify the WAP CSS.
5. Reuse the style code in multiple projects.
6. Remotely divide work — someone can focus on look and feel WAP, whereas others can concentrate on contents.
Some of the disadvantages of the WAP are the following:
● Low speeds, security, and very small user interface;
● Not very familiar to the users;
● Business model is expensive;
● Forms are hard to design;
● Third party is included.
Some of the disadvantages of using WAP CSS style sheets on mobile Internet sites are:
● Different WAP browsers have varied levels of support for WAP CSS. One property supported on one WAP browser may not be available on another WAP browser.
● An external WAP CSS style sheet can increase the time required for a page to be
completely loaded the fi rst time the WAP site is visited because of the following
reasons:
1. The external WAP CSS style sheet does not exist in the cache of the mobile phone at the first visit, which means the mobile phone has to download it from the server.
2. An XHTML MP document and its external WAP CSS style sheet have to be downloaded in separate requests.
3. If you make use of a single WAP CSS file to specify all the presentation
information about the mobile Internet site, the fi le size of the WAP CSS file can be quite large.
4. The WAP browser needs to parse the CSS in addition to the XHTML MP document.
Source of Information : Elsevier Wireless Networking Complete
The WAP Programming Model
Before presenting the WAP programming model, we briefl y discuss the WWW model that is the basis for the WAP model.
The WWW Model
The Internet WWW architecture provides a fl exible and powerful programming model. Applications and content are presented in standard data formats, and are browsed by
applications known as web browsers. The web browser is a network application, i.e., it sends requests for named data objects to a network server and the network server responds with encoded data using the standard formats.
The WWW standards specify several mechanisms necessary to build a general-purpose
application environment which includes:
● Standard naming model. All servers and content on the WWW are named with an Internet-standard Uniform Resource Locator ( URL ).
● Content typing. All content on the WWW is given a specific type, thereby allowing web browsers to correctly process the content based on its type.
● Standard content formats. All web browsers support a set of standard content formats. These include (HTML), JavaScript scripting language (ECMAScript, JavaScript), and a large number of other formats.
● Standard protocols. Standard networking protocols allow any web browser to communicate with any web server. The most commonly used protocol on the WWW
is the HTTP. This infrastructure allows users to easily reach a large number of thirdparty
applications and content services. It also allows application developers to easily create applications and content services for a large community of clients.
The WWW protocols defi ne three classes of servers:
1. Origin server: The server on which a given resource (content) resides or is to be created.
2. Proxy: An intermediary program that acts as both a server and a client for the purpose of making requests on behalf of other clients. The proxy typically resides between clients and servers that have no means of direct communication (e.g., across a firewall). Requests are ither serviced by a proxy program or passed on with possible translation to other servers. A proxy must implement both the client and the server requirements of WWW specifications.
3. Gateway: A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the origin server for the requested resource. The requesting client may not be aware that it is communicating with a gateway.
The WAP Model
The WAP programming model is similar to the WWW programming model. This provides several benefits to the application developer community, including a familiar programming model, a proven architecture, and the ability to leverage existing tools (e.g.,
web servers, XML tools, etc.). Optimization and extensions have been made in order to match the characteristics of the wireless environment. Wherever possible, existing standards have been adopted or have been used as the starting point for the WAP technology.
WAP content and applications are specified in a set of well-known content formats based on WWW content formats. Content is transported using a set of standard communication
protocols based on WWW communication protocols. A microbrowser in the wireless terminal coordinates the user interface and is analogous to a standard web browser. WAP defines a set of standard components that enable communication between mobile terminals and network servers, including:
● Standard naming model : WWW-standard URLs are used to identify WAP content on origin servers. WWW-standard URLs are used to identify local resources in a device (e.g., call control functions).
● Content typing : All WAP content is given a specifi c type consistent with WWW typing. This allows WAP user agents to correctly process the content based on its type.
● Standard content formats : WAP content formats are based on WWW technology
and include display markup, calendar information, electronic business card objects,
images, and scripting language.
● Standard protocols : WAP communication protocols enable the communication of
browser requests from the mobile terminal to the network web server. The WAP
content types and protocols have been optimized for mass market, hand-held wireless
devices. WAP utilizes proxy technology to connect between the wireless domain and
the WWW.
The WAP proxy typically comprises the following functionality:
● Protocol gateway : The protocol gateway translates requests from the WAP protocol stack to the WWW protocol stack (HTTP and TCP/IP).
● Content encoders and decoders : The content encoders translate WAP content into compact encoded formats to reduce the size of data over the network. This infrastructure ensures that mobile terminal users can browse a wide variety of WAP content and applications, and that the application author is able to build content services and applications that run on a large base of mobile devices. The WAP proxy allows content and applications to be hosted on standard WWW servers and to be developed using proven WWW technologies such as cell global identity (CGI) scripting. While the nominal use of WAP includes a web server, WAP proxy, and WAP client, WAP architecture can easily support other confi gurations. It is possible to create an origin server that includes WAP proxy functionality. Such a server might be used to facilitate end-to-end security solutions, or applications that require better access control or a guarantee of responsiveness.
Source of Information : Elsevier Wireless Networking Complete 2010
The WWW Model
The Internet WWW architecture provides a fl exible and powerful programming model. Applications and content are presented in standard data formats, and are browsed by
applications known as web browsers. The web browser is a network application, i.e., it sends requests for named data objects to a network server and the network server responds with encoded data using the standard formats.
The WWW standards specify several mechanisms necessary to build a general-purpose
application environment which includes:
● Standard naming model. All servers and content on the WWW are named with an Internet-standard Uniform Resource Locator ( URL ).
● Content typing. All content on the WWW is given a specific type, thereby allowing web browsers to correctly process the content based on its type.
● Standard content formats. All web browsers support a set of standard content formats. These include (HTML), JavaScript scripting language (ECMAScript, JavaScript), and a large number of other formats.
● Standard protocols. Standard networking protocols allow any web browser to communicate with any web server. The most commonly used protocol on the WWW
is the HTTP. This infrastructure allows users to easily reach a large number of thirdparty
applications and content services. It also allows application developers to easily create applications and content services for a large community of clients.
The WWW protocols defi ne three classes of servers:
1. Origin server: The server on which a given resource (content) resides or is to be created.
2. Proxy: An intermediary program that acts as both a server and a client for the purpose of making requests on behalf of other clients. The proxy typically resides between clients and servers that have no means of direct communication (e.g., across a firewall). Requests are ither serviced by a proxy program or passed on with possible translation to other servers. A proxy must implement both the client and the server requirements of WWW specifications.
3. Gateway: A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the origin server for the requested resource. The requesting client may not be aware that it is communicating with a gateway.
The WAP Model
The WAP programming model is similar to the WWW programming model. This provides several benefits to the application developer community, including a familiar programming model, a proven architecture, and the ability to leverage existing tools (e.g.,
web servers, XML tools, etc.). Optimization and extensions have been made in order to match the characteristics of the wireless environment. Wherever possible, existing standards have been adopted or have been used as the starting point for the WAP technology.
WAP content and applications are specified in a set of well-known content formats based on WWW content formats. Content is transported using a set of standard communication
protocols based on WWW communication protocols. A microbrowser in the wireless terminal coordinates the user interface and is analogous to a standard web browser. WAP defines a set of standard components that enable communication between mobile terminals and network servers, including:
● Standard naming model : WWW-standard URLs are used to identify WAP content on origin servers. WWW-standard URLs are used to identify local resources in a device (e.g., call control functions).
● Content typing : All WAP content is given a specifi c type consistent with WWW typing. This allows WAP user agents to correctly process the content based on its type.
● Standard content formats : WAP content formats are based on WWW technology
and include display markup, calendar information, electronic business card objects,
images, and scripting language.
● Standard protocols : WAP communication protocols enable the communication of
browser requests from the mobile terminal to the network web server. The WAP
content types and protocols have been optimized for mass market, hand-held wireless
devices. WAP utilizes proxy technology to connect between the wireless domain and
the WWW.
The WAP proxy typically comprises the following functionality:
● Protocol gateway : The protocol gateway translates requests from the WAP protocol stack to the WWW protocol stack (HTTP and TCP/IP).
● Content encoders and decoders : The content encoders translate WAP content into compact encoded formats to reduce the size of data over the network. This infrastructure ensures that mobile terminal users can browse a wide variety of WAP content and applications, and that the application author is able to build content services and applications that run on a large base of mobile devices. The WAP proxy allows content and applications to be hosted on standard WWW servers and to be developed using proven WWW technologies such as cell global identity (CGI) scripting. While the nominal use of WAP includes a web server, WAP proxy, and WAP client, WAP architecture can easily support other confi gurations. It is possible to create an origin server that includes WAP proxy functionality. Such a server might be used to facilitate end-to-end security solutions, or applications that require better access control or a guarantee of responsiveness.
Source of Information : Elsevier Wireless Networking Complete 2010
Standardization in the Wireless World
The advent of next-generation mobile computing calls for open standards and platforms to enable interoperability. As has been discussed in this chapter, a full spectrum of wireless technologies is set to be integrated to allow roaming in on unprecedented levels. Proprietary technologies do not fit into this new era of convergence, as it would be difficult for them to gain ground to a great extent due to the limited number of vendors and compatible products. On the contrary, open, well-crafted standards for the technology will enable and encourage any interested business parties to engage in developing and manufacturing products or offering services that are guaranteed to be interchangeable or compatible. Open standards essentially provide a solid foundation of framework of a technology as well as design constraints, thereby boosting the spread and acceptance of the technology.
A standard is a specification or definition that has been approved by a recognized standards organization such as ITU, IEEE, and ETSI, or is generally accepted as a de facto model by the industry. In the context of computing, standards exist for computer hardware, communication protocols, programming languages, operating systems, and some applications. Network communications have a wide range of standards, such as IEEE 802.3 Ethernet standard for LANs, IEEE 802.11 and ETSI HIPERLAN for wireless LANs, GSM, and IS-95 and IS136.
In addition to communication standard bodies such as ITU, IEEE, and ETSI, some other standard bodies have been founded for specialized technological fields. The American
National Standards Institute (ANSI) is primarily responsible for software and programming language standardization; it has created ANSI C and C _ _ . HTML and XML have been adopted by the International Organization for Standardization (ISO) and the World Wide Web Consortium (W3C). The Internet Engineering Task Force (IETF) has released a number of requests for comments (RFCs) that serve as the basis of many network protocols. Many computer peripheral standards such as the PCMCIA, Universal Serial Bus (USB), and compact flash have been created by industrial forums or associations.
Cellular Standard Groups
The two standard bodies behind competing cellular technologies are the Third Generation
Partnership Project (3GPP) and Third Generation Partnership Project 2 (3GPP2). 3GPP is an international organization supporting the development of UMTS/WCDMA systems.
3GPP partners include ETSI of Europe, ATIS of the United States, ARIB and TTC of Japan, TTA of Korea, and CCSA of China. 3GPP has released two versions of UMTS standards, namely Release 99 and Release 2000. 3GPP2 is the parallel partnership project for cdma2000 technology. It consists of TIA of the United States, ARIB and TTC of Japan, TTA of Korea, and CCSA of China. ITU is a United Nations organization responsible for maintaining and extending worldwide coordination of different governments and private sectors and managing the radio-frequency spectrum. 3GPP and 3GPP2 are formed under ITU.
IEEE Standards
The Institute of Electrical and Electronic Engineers (IEEE) has been the key standards organization in promoting networking technologies for many years. For wireless technologies, IEEE has established several working groups, mainly under the 802 standard committee.
» IEEE 802.1: LAN/MAN architecture with emphasis on internet working and link security (inactive).
» IEEE 802.2: Logical link control, part of the data-link layer protocol of a LAN.
» IEEE 802.3: Ethernet, the dominating LAN technology.
» IEEE 802.4: Token bus, a LAN technology utilizing token rings over coaxial cables.
» IEEE 802.5: Token ring, another token ring LAN technology (inactive).
» IEEE 802.6: Metropolitan area networks, a specification of MANs using Distributed Queue Dual Bus (DQDB) (inactive).
» IEEE 802.7: Broadband TAG (Technical Advisory Group), a broadband LAN.
» IEEE 802.8: Fiberoptic TAG, a fiber-optic LAN standard (inactive).
» IEEE 802.9: Isochronous LAN, an Isochronous Ethernet (IsoEnet) (inactive).
» IEEE 802.10: Security, specifying key management, access control, and data integrity for LANs and WANs (inactive).
» IEEE 802.11: Wireless LAN, a set of protocols for wireless LANs operating on unlicensed 2.4-GHz and 5-GHz bands.
» IEEE 802.12: Demand priority, 100BaseVG-AnyLAN (inactive).
» IEEE 802.13: Not used (for some reason).
» IEEE 802.14: Cable data, a MAC layer specification for multimedia traffic over hybrid fiber and coaxial networks.
» IEEE 802.15: Wireless PAN, a set of protocols for short-range wireless networks, including Bluetooth (802.15.1).
» IEEE 802.16: Broadband wireless access, PHY and MAC layer protocols for PTM broadband wireless access; WiMax is based on 802.16.
» IEEE 802.17: Resilient packet ring (RPR), a protocol to improve resilience for packet data traffic over fiber rings.
» IEEE 802.20: Mobile Broadband Wireless Access, PHY and MAC layer protocols for mobile data access.
Standards War
Emerging innovational technologies usually imply huge business opportunities. Different groups of industry alliances always attempt to influence the standardization of these technologies in favor of their own business interests. This sometimes leads to serious conflicts within a standardization body which inevitably puts the technology in stalemate and affects the promotion of the underlying technology with respect to providing a unified, interoperable solution framework for interested parties. For instance, the IEEE standardization of UWB (802.15.3) has been deadlocked due to proposals from two rivalry groups: the MBOA Alliance (Intel and TI lead) and UWB Forum (Motorola leads). Each side claims its proposal is superior to the other. Seeing no immediate ratification of a standard, both groups are moving forward to advance their approaches in commercial developments, effectively creating a segmented UWB market. The evolution of cellular networks is another example of a standards war. The lack of a global standard of cellular networks has resulted in two dominating 2G GSM and CDMA systems and two ongoing 3G deployments: UMTS/WCDMA and cdma2000, backed up by two organizations, 3GPP and 3GPP2, respectively. If a united standard agreement cannot be reached by the different groups, it is very likely the market will make the final decision. The standards body will supposedly pick the approach that is the most popular in the marketplace. Interestingly and understandably, it is not always the technically superior approach or system that eventually wins the majority of the market. We have seen this happen with Betamax versus VHS, two competing videotape standards back in the 1990s. It would be interesting to see what will happen to those emerging wireless technology standards.
Source of Information : Elsevier Wireless Networking Complete 2010
A standard is a specification or definition that has been approved by a recognized standards organization such as ITU, IEEE, and ETSI, or is generally accepted as a de facto model by the industry. In the context of computing, standards exist for computer hardware, communication protocols, programming languages, operating systems, and some applications. Network communications have a wide range of standards, such as IEEE 802.3 Ethernet standard for LANs, IEEE 802.11 and ETSI HIPERLAN for wireless LANs, GSM, and IS-95 and IS136.
In addition to communication standard bodies such as ITU, IEEE, and ETSI, some other standard bodies have been founded for specialized technological fields. The American
National Standards Institute (ANSI) is primarily responsible for software and programming language standardization; it has created ANSI C and C _ _ . HTML and XML have been adopted by the International Organization for Standardization (ISO) and the World Wide Web Consortium (W3C). The Internet Engineering Task Force (IETF) has released a number of requests for comments (RFCs) that serve as the basis of many network protocols. Many computer peripheral standards such as the PCMCIA, Universal Serial Bus (USB), and compact flash have been created by industrial forums or associations.
Cellular Standard Groups
The two standard bodies behind competing cellular technologies are the Third Generation
Partnership Project (3GPP) and Third Generation Partnership Project 2 (3GPP2). 3GPP is an international organization supporting the development of UMTS/WCDMA systems.
3GPP partners include ETSI of Europe, ATIS of the United States, ARIB and TTC of Japan, TTA of Korea, and CCSA of China. 3GPP has released two versions of UMTS standards, namely Release 99 and Release 2000. 3GPP2 is the parallel partnership project for cdma2000 technology. It consists of TIA of the United States, ARIB and TTC of Japan, TTA of Korea, and CCSA of China. ITU is a United Nations organization responsible for maintaining and extending worldwide coordination of different governments and private sectors and managing the radio-frequency spectrum. 3GPP and 3GPP2 are formed under ITU.
IEEE Standards
The Institute of Electrical and Electronic Engineers (IEEE) has been the key standards organization in promoting networking technologies for many years. For wireless technologies, IEEE has established several working groups, mainly under the 802 standard committee.
» IEEE 802.1: LAN/MAN architecture with emphasis on internet working and link security (inactive).
» IEEE 802.2: Logical link control, part of the data-link layer protocol of a LAN.
» IEEE 802.3: Ethernet, the dominating LAN technology.
» IEEE 802.4: Token bus, a LAN technology utilizing token rings over coaxial cables.
» IEEE 802.5: Token ring, another token ring LAN technology (inactive).
» IEEE 802.6: Metropolitan area networks, a specification of MANs using Distributed Queue Dual Bus (DQDB) (inactive).
» IEEE 802.7: Broadband TAG (Technical Advisory Group), a broadband LAN.
» IEEE 802.8: Fiberoptic TAG, a fiber-optic LAN standard (inactive).
» IEEE 802.9: Isochronous LAN, an Isochronous Ethernet (IsoEnet) (inactive).
» IEEE 802.10: Security, specifying key management, access control, and data integrity for LANs and WANs (inactive).
» IEEE 802.11: Wireless LAN, a set of protocols for wireless LANs operating on unlicensed 2.4-GHz and 5-GHz bands.
» IEEE 802.12: Demand priority, 100BaseVG-AnyLAN (inactive).
» IEEE 802.13: Not used (for some reason).
» IEEE 802.14: Cable data, a MAC layer specification for multimedia traffic over hybrid fiber and coaxial networks.
» IEEE 802.15: Wireless PAN, a set of protocols for short-range wireless networks, including Bluetooth (802.15.1).
» IEEE 802.16: Broadband wireless access, PHY and MAC layer protocols for PTM broadband wireless access; WiMax is based on 802.16.
» IEEE 802.17: Resilient packet ring (RPR), a protocol to improve resilience for packet data traffic over fiber rings.
» IEEE 802.20: Mobile Broadband Wireless Access, PHY and MAC layer protocols for mobile data access.
Standards War
Emerging innovational technologies usually imply huge business opportunities. Different groups of industry alliances always attempt to influence the standardization of these technologies in favor of their own business interests. This sometimes leads to serious conflicts within a standardization body which inevitably puts the technology in stalemate and affects the promotion of the underlying technology with respect to providing a unified, interoperable solution framework for interested parties. For instance, the IEEE standardization of UWB (802.15.3) has been deadlocked due to proposals from two rivalry groups: the MBOA Alliance (Intel and TI lead) and UWB Forum (Motorola leads). Each side claims its proposal is superior to the other. Seeing no immediate ratification of a standard, both groups are moving forward to advance their approaches in commercial developments, effectively creating a segmented UWB market. The evolution of cellular networks is another example of a standards war. The lack of a global standard of cellular networks has resulted in two dominating 2G GSM and CDMA systems and two ongoing 3G deployments: UMTS/WCDMA and cdma2000, backed up by two organizations, 3GPP and 3GPP2, respectively. If a united standard agreement cannot be reached by the different groups, it is very likely the market will make the final decision. The standards body will supposedly pick the approach that is the most popular in the marketplace. Interestingly and understandably, it is not always the technically superior approach or system that eventually wins the majority of the market. We have seen this happen with Betamax versus VHS, two competing videotape standards back in the 1990s. It would be interesting to see what will happen to those emerging wireless technology standards.
Source of Information : Elsevier Wireless Networking Complete 2010
ZigBee
One of the emerging applications of WSN is wireless monitoring and control. ZigBee is such an application that uses low-power and low-data-rate networked sensors. It was developed by the ZigBee Alliance, an industry association of semiconductor companies and network equipment companies such as Ember, Honeywell, Mitsubishi Electric, Motorola, Samsung, and Philips. It has to be noted that the term ZigBee refers to the silent communication between honeybees where the bee dances in a zig-zag pattern to tell others the location, distance, and direction of some newly found food. WSN communication somewhat resembles the ZigBee principle in that they must be simple and effective.
The idea is to take advantage of wireless sensors to monitor environments, objects, and human beings and control devices, appliances, and facilities. Wireless sensors make it possible to remotely and conveniently monitor or be notified of operational states or crucial state change of an object, such as a dying battery in a smoke detector and rapidly increasing temperature in a truck carrying frozen goods. WSNs in ZigBee are not designed to carry large data transfer due to the limited capability of wireless communication; however, these sensors are able to form a fully functional network, self-organize for efficient data routing and in-network processing, and self-heal in the case of node failure. The initial target markets of ZigBee products are home control, building control, industrial automation, personal healthcare, consumer electronics, PC and peripherals control, etc. Key specs of ZigBee include the following:
» Frequency bands: 868 MHz, 915 MHz, and 2.4 GHz;
» Data transfer rate up to 250 Kbps;
» Signal transmission range of 10 to 100 m, depending on the sensors being used;
» AES encryption of data;
» Various ZigBee applications can work with each other;
» Low power usage.
Unlike UWB or Bluetooth, ZigBee specifications do not define radio interface and data-link layer protocols; ZigBee simply uses the IEEE 802.15.4 physical radio standard. The ZigBee network application support layer and application profile are the major components that make up the ZigBee specification. Because ZigBee is a proprietary protocol rather than an open standard like those ratified by IEEE, its fate hinges on how it refines itself to become the de facto industry standard. To this end, standardization battles seem inevitable.
Source of Information : Elsevier Wireless Networking Complete 2010
The idea is to take advantage of wireless sensors to monitor environments, objects, and human beings and control devices, appliances, and facilities. Wireless sensors make it possible to remotely and conveniently monitor or be notified of operational states or crucial state change of an object, such as a dying battery in a smoke detector and rapidly increasing temperature in a truck carrying frozen goods. WSNs in ZigBee are not designed to carry large data transfer due to the limited capability of wireless communication; however, these sensors are able to form a fully functional network, self-organize for efficient data routing and in-network processing, and self-heal in the case of node failure. The initial target markets of ZigBee products are home control, building control, industrial automation, personal healthcare, consumer electronics, PC and peripherals control, etc. Key specs of ZigBee include the following:
» Frequency bands: 868 MHz, 915 MHz, and 2.4 GHz;
» Data transfer rate up to 250 Kbps;
» Signal transmission range of 10 to 100 m, depending on the sensors being used;
» AES encryption of data;
» Various ZigBee applications can work with each other;
» Low power usage.
Unlike UWB or Bluetooth, ZigBee specifications do not define radio interface and data-link layer protocols; ZigBee simply uses the IEEE 802.15.4 physical radio standard. The ZigBee network application support layer and application profile are the major components that make up the ZigBee specification. Because ZigBee is a proprietary protocol rather than an open standard like those ratified by IEEE, its fate hinges on how it refines itself to become the de facto industry standard. To this end, standardization battles seem inevitable.
Source of Information : Elsevier Wireless Networking Complete 2010
Self-Organized Networks
The physical layer of a WSN is nothing new: radio-frequency transmission at unlicensed bands. LOS is not required. The data-link layer monitors the channels and transmits frames only when the channel is idle. The network layer and transport layer require more discussion. Like ad hoc networks, the routing paths between each two nodes cannot be determined and configured prior to deployment because there is no predefined fixed infrastructure in WSNs. Sensor nodes have to discover multihop routes to relevant nodes themselves. This is often done via routing data dissemination, in which packets that contain the transmitter and the distance to the root are flooded in the network. A sensor node, upon receiving such packets, will be able to find a “ parent ” who is closer to the root; hence, a distribution tree can be generated. Data collection from sensor nodes can be routed back to the root following the distribution tree.
Task or query dissemination throughout a sensor network is data-centric in association with data aggregation, a routing scheme known as directed diffusion. Sensor nodes are not addressed uniformly using numeric identifications; instead, the addressing and naming schemes are correlated with the application. They are identified by “ attribute – value ” pairs in their data. A task in the form of some attribute inquiry is sent out from some nodes in the hope of obtaining relevant data from other nodes, and then all participating nodes form a routing gradient toward the originators. In the case where a WSN is used as a platform of the sensory database, the applications and underlying routing schemes must support declarative queries, thereby making the detail of in-network query processing and optimization transparent to the user. Power consumption is another crucial factor when it comes to in-network aggregation support of query processing. Sophisticated power-aware query processing and packet routing schemes have been devised to reduce the overall power consumption of a WSN.
Sensory data delivery can be performed in several ways. Sensor node can actively report readings periodically to its parent or only report when an event occurs. The delivery procedure can also be initiated by a user issuing a command that is diffused across the network. Depending on the design objectives, a WSN may apply different data delivery models to different sensor nodes. For example, some high-level roots in the distribution tree may employ a request-and-response mechanism for queries, whereas some low-level sensor nodes may simply report data continuously.
Compared with mobile ad hoc network, network communication over WSNs imposes additional constraints other than node mobility and power consumption. Sensors node are more prone to failure, and their computational capability and memory capacity are greatly limited. When designing a protocol stack of a WSN, these constraints have to be taken into account. Specifically, because complete raw data forwarding is not necessary in many circumstances, data aggregation may be conducted at various levels of the distribution tree to reduce the amount of data being transferred upward to the gateway while still providing sufficient information to other nodes. Furthermore, data aggregation can be combined with applications of the WSN to further improve the efficiency of data collection and dissemination schemes. This reflects one of the most important characteristics of WSNs: cross-layer design. The well-known sensor operating system is TinyOS, which is an open-source, event-based embedded operating system developed at the University of California, Berkeley. TinyOS provides a set of components for networking, memory management, and power management, as well as data acquisition and query processing tools. The programming language supported by TinyOS is nesC, a C-like language for embedded network system development.
Source of Information : Elsevier Wireless Networking Complete 2010
Task or query dissemination throughout a sensor network is data-centric in association with data aggregation, a routing scheme known as directed diffusion. Sensor nodes are not addressed uniformly using numeric identifications; instead, the addressing and naming schemes are correlated with the application. They are identified by “ attribute – value ” pairs in their data. A task in the form of some attribute inquiry is sent out from some nodes in the hope of obtaining relevant data from other nodes, and then all participating nodes form a routing gradient toward the originators. In the case where a WSN is used as a platform of the sensory database, the applications and underlying routing schemes must support declarative queries, thereby making the detail of in-network query processing and optimization transparent to the user. Power consumption is another crucial factor when it comes to in-network aggregation support of query processing. Sophisticated power-aware query processing and packet routing schemes have been devised to reduce the overall power consumption of a WSN.
Sensory data delivery can be performed in several ways. Sensor node can actively report readings periodically to its parent or only report when an event occurs. The delivery procedure can also be initiated by a user issuing a command that is diffused across the network. Depending on the design objectives, a WSN may apply different data delivery models to different sensor nodes. For example, some high-level roots in the distribution tree may employ a request-and-response mechanism for queries, whereas some low-level sensor nodes may simply report data continuously.
Compared with mobile ad hoc network, network communication over WSNs imposes additional constraints other than node mobility and power consumption. Sensors node are more prone to failure, and their computational capability and memory capacity are greatly limited. When designing a protocol stack of a WSN, these constraints have to be taken into account. Specifically, because complete raw data forwarding is not necessary in many circumstances, data aggregation may be conducted at various levels of the distribution tree to reduce the amount of data being transferred upward to the gateway while still providing sufficient information to other nodes. Furthermore, data aggregation can be combined with applications of the WSN to further improve the efficiency of data collection and dissemination schemes. This reflects one of the most important characteristics of WSNs: cross-layer design. The well-known sensor operating system is TinyOS, which is an open-source, event-based embedded operating system developed at the University of California, Berkeley. TinyOS provides a set of components for networking, memory management, and power management, as well as data acquisition and query processing tools. The programming language supported by TinyOS is nesC, a C-like language for embedded network system development.
Source of Information : Elsevier Wireless Networking Complete 2010
Wireless Sensor Node
A sensor node is made up of four basic components: sensing unit, processing unit, transceiver unit, and power unit. The sensing unit usually consists of two components: a sensor and an analog-to-digital converter (ADC). The processing unit acts as a tiny computer: a microprocessor and some RAM. The processing unit runs an embedded operating system and executes WSN applications that control the operations of the sensor and communication between sensor nodes. The transceiver unit is a low-power radio operating on an unlicensed frequency band. The power unit is a battery for regular sensor nodes. Note that in most cases a WSN will have a special sensor node that acts as the gateway for other sensor nodes with respect to ultimate data delivery. The gateway node interfaces to computers via RS232 or Ethernet links. As a result, the gateway node is different from other regular nodes, in both size and processing functionality, thus requiring more power supply.
Following is a list of sensor node characteristics that affect the design of WSN system architectures and applications:
» Size: Sensor nodes are very small, due to advancements in semiconductor technologies.
» Low power: Sensor nodes are expected to operate for a long time before the battery drains out. In many cases, it is prohibitive to replace batteries.
» Autonomous, unattended operations: Once deployed, sensor nodes should selforganize to work as programmed. Remote reprogramming is sometimes possible.
» Inexpensive: Their low cost makes it possible to deploy a large number of sensor notes at a moderate cost.
» Adaptive to environments and themselves: Sensor nodes are able to adapt to environmental and status changes.
Source of Information : Elsevier Wireless Networking Complete 2010
Following is a list of sensor node characteristics that affect the design of WSN system architectures and applications:
» Size: Sensor nodes are very small, due to advancements in semiconductor technologies.
» Low power: Sensor nodes are expected to operate for a long time before the battery drains out. In many cases, it is prohibitive to replace batteries.
» Autonomous, unattended operations: Once deployed, sensor nodes should selforganize to work as programmed. Remote reprogramming is sometimes possible.
» Inexpensive: Their low cost makes it possible to deploy a large number of sensor notes at a moderate cost.
» Adaptive to environments and themselves: Sensor nodes are able to adapt to environmental and status changes.
Source of Information : Elsevier Wireless Networking Complete 2010
WSN Applications
The wide range of sensors and collective instrumental functionality of WSNs, coupled with the underlying wireless networks, make it possible to provide unprecedented levels of data access and associated intelligence, bringing about a new dimension of application for different industry sectors. WSN applications can be divided into three categories: monitoring space, including objects as part of the space; monitoring operation states of objects; and monitoring interactions between objects and space. The first category represents the most common and basic use of WSNs (dealing with physical environments), whereas the second is mainly concerned with a specific entity rather than its surroundings. The third category encompasses more sophisticated monitoring and control over communications and interactions between objects and between an object and its surroundings. Some pilot projects have explored WSNs for a number of different application scenarios. Many potential applications are being developed to leverage WSNs. Some examples are introduced as follows.
Environmental Sensing
Using a large number of sensor nodes deployed in a target geographic location, it is possible to derive useful patterns and trends based on datasets collected over time. Examples of environmental sensing are light sensing, microclimate monitoring, traffic monitoring, pollution level monitoring, indoor climate control, and habitat monitoring. Very often users are only concerned with independent characteristics of an entity, such as the number of vehicles passing by during a time period or the propagation speed of some contaminant in a river.
Object Sensing
Aside from environmental sensing, sensors can be attached to objects and collect data regarding motion, pressure, or any mechanical, electronic, or biological characteristics of the host. Object sensing is predominantly used in industrial control and maintenance. Examples include structural monitoring of buildings, bridges, vehicles, and airplanes; sensing machinery wear in a factory; industrial asset tracking in warehouses and stores; surveillance in parking lot and streets; crop monitoring; and military-related object sensing in battlefields. In particular, RFID, a scaled-down wireless sensing technology, utilizes small tags of very limited local computing power and storage to identify and inventory objects. Section 13 has presented a detailed introduction to RFID.
Sensing with Intelligence
More challenging application scenarios require embedded intelligence that goes beyond raw data sensing, thus requiring the simultaneous sensing of multiple related quantities and in-network processing so as to detect internal interactions between objects. Examples of this category are monitoring wildlife habitats, telemedicine sensing, context-aware pervasive computing using sensors, and disaster management. For instance, researchers at the University of California, Berkeley, and Intel have developed a successful experimental WSN to monitor petrels on an uninhabited island off the coast of Maine. The birds being observed are Leach’s store petrels, a type of tiny reclusive seabird that burrows in sandy soil and emerges only at night. To ornithologists, monitoring and understanding the comings and goings of these birds in a wild area are not simple tasks, as they would have to dig into the birds ’ burrows for more information. The WSN deployed on the island consists of 190 wireless sensor nodes called motes , some of which are located in burrows and others on the ground, and a solar-powered central computer station that collects sensory data from a gateway mote and reports back to a remote site in real-time via satellite links. Sensors on the motes monitor temperature, humidity, barometric pressure, and ambient light. The temperature reading within a burrow can be used to infer if a petrel is present or not. Other data also contribute to our understanding of the behavior of these petrels and their responses to changes in their surroundings.
Source of Information : Elsevier Wireless Networking Complete 2010
Environmental Sensing
Using a large number of sensor nodes deployed in a target geographic location, it is possible to derive useful patterns and trends based on datasets collected over time. Examples of environmental sensing are light sensing, microclimate monitoring, traffic monitoring, pollution level monitoring, indoor climate control, and habitat monitoring. Very often users are only concerned with independent characteristics of an entity, such as the number of vehicles passing by during a time period or the propagation speed of some contaminant in a river.
Object Sensing
Aside from environmental sensing, sensors can be attached to objects and collect data regarding motion, pressure, or any mechanical, electronic, or biological characteristics of the host. Object sensing is predominantly used in industrial control and maintenance. Examples include structural monitoring of buildings, bridges, vehicles, and airplanes; sensing machinery wear in a factory; industrial asset tracking in warehouses and stores; surveillance in parking lot and streets; crop monitoring; and military-related object sensing in battlefields. In particular, RFID, a scaled-down wireless sensing technology, utilizes small tags of very limited local computing power and storage to identify and inventory objects. Section 13 has presented a detailed introduction to RFID.
Sensing with Intelligence
More challenging application scenarios require embedded intelligence that goes beyond raw data sensing, thus requiring the simultaneous sensing of multiple related quantities and in-network processing so as to detect internal interactions between objects. Examples of this category are monitoring wildlife habitats, telemedicine sensing, context-aware pervasive computing using sensors, and disaster management. For instance, researchers at the University of California, Berkeley, and Intel have developed a successful experimental WSN to monitor petrels on an uninhabited island off the coast of Maine. The birds being observed are Leach’s store petrels, a type of tiny reclusive seabird that burrows in sandy soil and emerges only at night. To ornithologists, monitoring and understanding the comings and goings of these birds in a wild area are not simple tasks, as they would have to dig into the birds ’ burrows for more information. The WSN deployed on the island consists of 190 wireless sensor nodes called motes , some of which are located in burrows and others on the ground, and a solar-powered central computer station that collects sensory data from a gateway mote and reports back to a remote site in real-time via satellite links. Sensors on the motes monitor temperature, humidity, barometric pressure, and ambient light. The temperature reading within a burrow can be used to infer if a petrel is present or not. Other data also contribute to our understanding of the behavior of these petrels and their responses to changes in their surroundings.
Source of Information : Elsevier Wireless Networking Complete 2010
Wireless Sensor Networks
Data communication continues to expand in both scope and complexity, from internal communication among the hardware components of an individual computer to intercomputer network communication via wired or wireless BANs, PANs, LANs, MANs, and WANs. At the same time, computers are becoming more closely related to the physical world and human beings, gathering, monitoring, processing, and analyzing data to allow instrumentation and automation and to facilitate decision-making. Wireless sensor networks (WSNs) represent networks that are embedded into our physical environments. A sensor is a tiny electronic device that can respond to a physical stimulus and convert it into numeric data. A WSN is composed of many low-power, low-cost, autonomous sensor nodes interconnected with wireless communication of sensory data. A myriad of measurements can be done by sensors, including environmental properties such as temperatures, humidity, and air pressure; presence, vibration, and motion detection of objects; chemical properties; radiation levels; GPS; light; and acoustic and seismic activities. Data gathering is conducted intermittently at a specified frequency. A sensor node in a WSN possesses sufficient computing power to process sensory data gathered locally or transmitted from other sensor nodes via wireless links. Furthermore, sensor nodes in a WSN self-organize into a network topology, thereby improving robustness and reducing maintenance costs.
Source of Information : Elsevier Wireless Networking Complete 2010
Source of Information : Elsevier Wireless Networking Complete 2010
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