Sunday, March 27, 2005

IEEE 802 Family

IEEE 802 refers to a family of IEEE standards about local area networks and metropolitan area networks. More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. (By contrast, in cell-based networks data is transmitted in short, uniformly sized units called cells. Isochronous networks, where data is transmitted as a steady stream of octets, or groups of octets, at regular time intervals, are also out of the scope of this standard.)

The services and protocols specified in IEEE 802 map to the lower two layers (Data Link and Physical) of the seven-layer OSI networking reference model. In fact, IEEE 802 splits the OSI Data Link Layer into two sub-layers named Logical link control (LLC) and Media Access Control, so that the layers can be listed like this:

  • Data link layer
  • LLC Sublayer
  • MAC Sublayer
  • Physical layer

The LLC Sublayer of this architecture can optionally be replaced by an ethernet sub-layer. (Alternatively the ethernet frames may be encapsulated into LLC frames as described by RFC 1042, RFC 1390 and the IEEE 802.1H standard.)

The IEEE 802 family of standards is maintained by the IEEE 802 LAN/MAN Standards Committee (LMSC). The most widely used standards are for the Ethernet family, Token Ring, Wireless LAN, Bridging and Virtual Bridged LANs. An individual Working Group provides the focus for each area.

Tuesday, March 22, 2005


ZigBee is a published specification set of high level communication protocols designed to use small, low power digital radios based on the IEEE 802.15.4 standard for wireless personal area networking. The relationship between IEEE 802.15.4 and ZigBee is analogous to that existing between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specifications were ratified on December 14, 2004, and are available to members of the ZigBee Alliance. An entry level membership in the ZigBee Alliance costs $3500 and provides access to the specifications.

The technology is designed to be simpler and cheaper than other WPANs such as Bluetooth. The most capable ZigBee node type is said to require only about 10% of the software of a typical Bluetooth or Wireless Internet node, while the simplest nodes are about 2%.

As of 2004, the estimated cost of the radio for a ZigBee node is about $6 to the manufacturer.

ZigBee is aimed at applications with low data rates and low power consumption. ZigBee's current focus is to define a general-purpose, inexpensive self-organizing mesh network that can be shared by industrial controls, medical devices, smoke and intruder alarms, building-automation and home automation. The network is designed to use very small amounts of power, so that individual devices might run for a year or two with a single alkaline battery. The killer app is probably meter-reading, although other applications, such as wireless light controls, should also be popular.

Device types
There are three different types of ZigBee devices: The most capable is a "ZigBee coordinator." It might bridge to other networks, and forms the root of the network tree. It is able to store information about the network. There is exactly one ZigBee coordinator in each network. A "full function device" (FFD) can act as an intermediate router, passing data from other devices. A "reduced function device" (RFD) is just smart enough to talk to the network; it cannot relay data from other devices. An RFD requires less memory, and therefore should be less expensive to manufacture, than an FFD. Similarly, an FFD requires less memory, and therefore should be less expensive to manufacture, than a ZigBee coordinator.

The protocols build on recent algorithmic research to automatically construct a low-speed ad-hoc network of nodes. In most large cases, the network is a cluster of clusters. It can also form a mesh or a single cluster.

The ZigBee protocols support both beaconing and non-beaconing networks. In beaconing networks, the network nodes transmit beacons to confirm their presence to other network nodes, and to allow nodes to sleep between beacons, thereby lowering their duty cycle and extending their battery life. Beacon intervals may range from 15.36 milliseconds to 15.36 ms * 2^14 = 251.65824 seconds; to obtain the benefits of low duty cycle operation with long beacon intervals, however, precise timing is needed, which can conflict with the need for low product cost. In non-beaconing networks, most devices typically have their receivers continuously active, requiring a more robust power supply; however, this enables heterogeneous networks, in which some devices receive continuously while some remain asleep, transmitting only when an external stimulus is detected. The typical example of a heterogeneous network is the wireless light switch: The ZigBee node at the lamp may receive constantly, since it is connected to the mains supply, while the battery-powered light switch remains asleep until the switch is thrown. The switch then wakes up, sends a command to the lamp, receives an acknowledgement, and returns to sleep. In such a network the lamp node is at least an FFD, if not the ZigBee coordinator; the switch node is typically an RFD.

In general, the ZigBee protocols minimize the time the radio is on in order to reduce the power used by the radio. In beaconing networks the network synchronizes nodes to talk and listen at particular times when they have anything to hear or say. In non-beaconing networks, power consumption is more asymmetrical; some devices are constantly active, while others (if present) are almost always asleep.

ZigBee uses the IEEE 802.15.4 Low-Rate Wireless Personal Area Network (WPAN) standard to describe its lower protocol layers--the physical layer (PHY), and the medium access control (MAC) portion of the data link layer (DLL). This standard specifies operation in the unlicensed 2.4 GHz, 915 MHz and 868 MHz ISM bands. The radio uses DSSS which is managed by the digital stream into the modulator. Conventional DSSS is employed in the 868 and 915 MHz bands, while an orthogonal signaling scheme that transmits four bits per symbol is employed in the 2.4 GHz band. The raw, over-the-air data rate is 250 kb/s per channel in the 2.4 GHz band, 40 kb/s per channel in the 915 MHz band, and 20 kb/s in the 868 MHz band. Transmission range is between 10 and 75 metres (33~246 feet).

The basic mode of channel access specified by IEEE 802.15.4 is "carrier sense, multiple access" (CSMA), that is, the nodes talk in the same way that people converse--they briefly check to see that no one is talking before they start. Beacons, however, are sent on a fixed timing schedule, and do not use CSMA. Message acknowledgements also do not use CSMA.

Software and Hardware
The software is designed to be easy to code for small, cheap microprocessors. The radio design utilized by ZigBee has been carefully optimized for low cost. It has few analog stages and uses digital circuits wherever possible. Most vendors plan to put the radio on a single chip.

ZigBee-style networks began to be conceived near 1998, when many engineers realized that both WiFi and Bluetooth were going to be unsuitable for many applications. In particular, many engineers wanted to design self-organizing ad-hoc networks of digital radios. The simple one-chip design of Bluetooth digital radios was also inspirational for many engineers. The IEEE 802.15.4 standard was completed in May 2003. In the summer of 2003, Philips Semiconductors, a major promoter, ceased its investment. Philips Lighting has, however, continued Philips' participation, and Philips remains a promoter member on the ZigBee Alliance Board of Directors. The ZigBee Alliance announced in October 2004 that its membership had more than doubled in the past year and had grown to more than 100 member companies, in 22 countries. The ZigBee specifications were ratified on 14 December 2004.


IEEE 802.15 is the working group 15 of the IEEE 802 which specializes in Wireless PAN standards. It includes four task groups (numbered from 1 to 4).

  1. Task group 1 (WPAN/Bluetooth) deals with Bluetooth, having produced the 802.15.1 standard, published on June 14, 2002. It includes a medium access control and physical layer specification adapted from Bluetooth 1.1.
  2. Task group 2 (Coexistence) deals with coexistence of Wireless LAN (802.11) and Wireless PAN.
  3. Task group 3 is in fact two groups: 3 (WPAN High Rate) and 3a (WPAN Alternate Higher Rate), both dealing with high-rate WPAN standards (20 Mbit/s or higher).
  4. Task group 4 (WPAN Low Rate) deals with low rate but very long battery life (months or even years)

Friday, March 18, 2005

Metropolitan Area Network (MAN)

Metropolitan area networks or MANs are large computer networks usually spanning a campus or a city. They typically use optical fiber connections to link their sites.

For instance a university or college may have a MAN that joins together many of their local area networks (LANs) situated around site of a fraction of a square kilometer. Then from their MAN they could have several wide area network (WAN) links to other universities or the Internet.
Some technologies used for this purpose are ATM, FDDI and SMDS. These older technologies are in the process of being displaced by Gigabit Ethernet-based MANs in most areas. MAN links between LANs have been built without cables using either microwave, radio, or infra-red free-space optical communication links.

Several notable networks started as MANs, such as the Internet peering points MAE-West and MAE-East and the Sohonet media network.

Thursday, March 17, 2005

WiMAX - IEEE 802.16

IEEE 802.16 is working group number 16 of IEEE 802, specialising in point-to-multipoint broadband wireless access. It also is known as WiMAX, an acronym that stands for Worldwide Interoperability for Microwave Access.

The current 802.16 standard is 802.16d-2004, which was approved late 2004. It obsoletes the previous (and first) version 802.16-2001, and its amendments 802.16a and 802.16c. The 802.16d standard only addresses fixed systems. An amendment 802.16e is in the works which adds mobility components to the standard. This amendment is expected to be completed in mid 2005.

Similar technologies
What differentiates WiMAX from earlier broadband wireless access (BWA) iterations is standardization. Chipsets are currently custom-built for each broadband wireless access vendor, adding time and cost to the process.

Its equivalent or competitor in Europe is HIPERMAN. WiMAX Forum, the consortium behind the standardization, is working on methods to make 802.16 and HIPERMAN interoperate seamlessly. Products developed by the WiMAX Forum members need to comply to pass the certification process.

Korea's telecoms industry has developed its own standard, WiBro. In late 2004, Intel and LG Electronics have agreed on interoperability between WiBro and WiMAX.

Technical advantages
WiMAX does not conflict with WiFi but complements it. Because IEEE 802.16 networks use the same Logical Link Controller (standardized by IEEE 802.2) as other LANs and WANs, it can be both bridged and routed to them. So the comment about complementarity to WiFi also includes all flavors of wired ethernet (802.3), token ring (802.5) and non-IEEE standards that use the same LLC including FDDI and cable modem (DOCSIS).

WiMAX is a wireless metropolitan area network (MAN) technology that will connect IEEE 802.11(WiFi) hotspots to the Internet and provide a wireless extension to cable and DSL for last mile (last km) broadband access. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows users connectivity without a direct line of sight to a base station. Note that this should not be taken to mean that users 50 km (31 miles) away without line of sight will have connectivity. The technology also provides shared data rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity.

An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings.

The MAC is significantly different than in WiFi (and ethernet from which WiFi is derived). In WiFi, the ethernet uses contention access -- all subscriber stations wishing to pass data through an access point are competing for the AP's attention on a random basis. By contrast, the 802.16 MAC is a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription (unlike 803.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations.

What is important for business using this technology is to ensure that it is managed correctly.

WiMAX is referred to as "WiFi on steroids". It has the potential to enable even more millions to access the Internet wirelessly, cheaply and easily. Proponents say that WiMAX wireless coverage will be measured in square kilometers/miles while that of WiFi is measured in square meters/yards. According to WiMAX promoters, a WiMAX base station would beam high-speed Internet connections to homes and businesses in a radius of up to 50 km (31 miles); these base stations will eventually cover an entire metropolitan area, making that area into a WMAN and allowing true wireless mobility within it, as opposed to hot-spot hopping required by WiFi. The proponents are hoping that the technology will eventually be used in notebook computers and PDAs. True roaming cell-like wireless broadband, however, is IEEE standard 802.20, which is compatible with WiMAX.

It should be duly noted that claims of 50 km (31 mile) range, especially claims that such distances can be achieved without line of sight, respresents, at best, a theoretical maximum under ideal circumstances. The technical merit of this claim has yet to be tested in the real world. No test has demonstrated the technical or practical feasibility of this number.

WiMAX standard relies mainly on spectrum in the 2 to 11 GHz range. The WiMAX specification improves upon many of the limitations of the WiFi standard by providing increased bandwidth and stronger encryption. It also aims to provide connectivity to network endpoints without direct line of sight in some circumstances. The details of performance under non line of sight circumstances, however, are unclear, as they have yet to be demonstrated.

Product release
Products are expected to be announced second quarter of 2005. As of 2004, major cities such as Los Angeles , New York , Boston , Providence RI, Seattle in the U.S.,and Dalian and Chengdu in China are already implementing WiMax.

Beyond the metro area rollouts (prev paragraph), WiMax is like WiFi in that you can 'roll your own'. Several vendors have some form of product now (2004), usually in a pre-standards-compliance stage so you can't reasonably expect multivendor interoperability within a single network segment. Several companies are planning rollouts of compliant chipsets in FPGAs in 2005 and ASICs the following year which will shrink the digital electronics suitable for PCMCIA type of form factors. Along with the physical shrinkage, we can reasonably expect some price shrinkage as economies of scale and amortization on non-recurrent engineering costs take place.

Tuesday, March 15, 2005

Wireless Community Network

Wireless community networks or wireless community projects are the largely hobbyist-led development of interlinked computer networks using wireless LAN technologies, taking advantage of the recent development of cheap, standardised 802.11b (Wi-Fi) devices to build growing clusters of linked, citywide networks. Some are being used to link to the wider Internet, particularly where individuals can obtain unmetered ADSL and/or cable modem internet connections at fixed costs and share them with friends. Where such access is unavailable or expensive, they can act as a low-cost partial alternative, as the only cost is the fixed cost of the equipment.

Such projects started to evolve in 1998 with the availability of 802.11 equipment, and are gradually spreading to cities and towns around the world. As of mid-2002, most such networks remain embryonic, with small groups of people experimenting and gradually interconnecting with each other and thus expanding the domain and utility of the networks.

These projects are in many senses an evolution of amateur radio and, more specifically packet radio, as well as an outgrowth of the free software community (which in itself substantially overlaps with amateur radio), and share their freewheeling, experimental, adaptable culture. The key to using standard wireless networking devices designed for short-range use for multi-kilometre linkups is the use of high-gain antennas. Commercially-available examples are relatively expensive and not that readily available, so much experimentation has gone into homebuilt antenna construction. One striking design is the cantenna, which performs better than many commercial antenna designs and is constructed from a steel food can.

Most wireless community network projects are coordinated by citywide user groups who freely share information and help using the Internet. They often spring up as a grassroots movement offering free, anonymous Internet access to anyone with WiFi capability.

Monday, March 14, 2005


Wardriving is an activity consisting of driving around with a laptop or a PDA in one's vehicle, detecting Wi-Fi wireless networks. It is also known (as of 2002) as WiLDing (Wireless Lan Driving), originating in the USA with the Bay Area Wireless Users Group (BAWUG). It is similar to using a scanner for radio. Many wardrivers will use GPS devices to find the exact location of the network found and log it on a website. For better range, antennas are built or bought, and vary from omnidirectional to fully directional. Software for wardriving is freely available on the internet, notably, NetStumbler for Windows, MacStumbler for Macintosh, and Kismet for Linux.

Wardriving shares similarities to Wardialing in name only.

Wardrivers do not engage in malicious activity, the average wardriver is typically only out to log and collect information from the Access Points (APs) they find while driving.

In the USA, accessing the files on an open network is illegal under both Federal and State laws, as is using the internet connection of an open wireless network. (the law differs in other countries - for example in UK you would be caught by the 'use of a computer for a purpose for which you do not have permission' clause). This is a commonly misunderstood concept. Wardrivers do not in fact use services without authorization.

Ethical considerations
Wardriving is frequently pointed out as an example of questionable activity. However, from a technical viewpoint, everything is working as designed: a radio is transmitting data accessible by anyone with a suitable receiver. In cases of listen-only software, such as kismet, wardriving can be likened to listening to a radio station that happens to be broadcasting in your area - however again, this may differ in other countries - for example in UK it is actually illegal to listen on some radio frequencies or to some transmissions (such as those used by the Police or Armed forces). With other types of software, such as Netstumbler, the wardriver sends probes, and the access point responds per design. Most access points, when using default settings, are intended to provide wireless access to all who request it. In this sense, those who set up access points without adding security measures are offering their connection (most likely unintentionally) to the community. In fact, when people unfamiliar to wardriving see how many unsecured access points there are and how easy it is to find them, they often want to make their own access points more secure. However, there are many wardrivers who, while securing their own networks, are delighted to offer wireless internet access to whomever wants it, with the exception of those who use too much bandwidth.

Wireless network security
More security-conscious network operators may choose from a variety of security measures to limit access to their wireless network, including:

  • MAC address authentication in combination with discretionary DHCP server settings allow a user to set up an "allowed MAC address" list. Under this type of security, the access point will only give an IP Address to computers whose MAC address is on the list. Thus, the network administrator would obtain the valid MAC addresses from each of the potential clients in their network. Disadvantages to this method include the additional setup. Methods to defeat this type of security include MAC address spoofing, detailed on the MAC address page, whereby network traffic is observed, valid MACs are collected, and then used to obtain DHCP leases.
  • IPsec can be used to encrypt traffic between network nodes, reducing or eliminating the amount of Plaintext information transmitted over the air. This security method addresses privacy concerns of wireless users, as it becomes much more difficult to observe their wireless activity. Difficulty of setting up IPsec is related to the brand of Access Point being used. Some access points may not offer IPsec at all, while others may require firmware updates before IPsec options are available. Methods to defeat this type of security are computationally intensive to the extent that they are infeasible using readily-available hardware, or they rely on social engineering to obtain information (keys, etc) about the IPsec installation.
  • WEP can be used on many Access Points without cumbersome setup, but offers little in the way of practical security. It is cryptologically very weak, so an access key can easily be stolen (see WEP for more information). Its use is often discouraged in favor of other more robust security measures, but many users feel that any security is better than none. In practice, this may simply mean your neighbors' non-WEP networks are more accessible targets.
  • Wi-Fi Protected Access or WPA is more secure than WEP but isn't very wide spread yet. Many Access Points will support WPA after a firmware update.
  • VPN options such as tunnel-mode IPSec or OpenVPN can be the (respectively) most difficult to set up, but often provide the most flexible, extendable security, and as such are recommended for larger networks with many users.

Sunday, March 13, 2005


Bluetooth is an industrial specification for wireless personal area networks (PANs) first developed by Ericsson, later formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on May 20, 1999. It was established by Sony Ericsson, IBM, Intel, Toshiba and Nokia, and later joined by many other companies as Associate or Adopter members.

The system is named after a Danish king Harald Blåtand (Harold Bluetooth in English), King of Denmark and Norway from 935 and 936 respectively, to 940 known for his unification of previously warring tribes from Denmark, Norway and Sweden. Bluetooth likewise was intended to unify different technologies like computers and mobile phones. The Bluetooth logo merges the Nordic runes for H and B. This is the official story: however, the actual Harald Blåtand that was referred to in naming Bluetooth was most probably the liberal interpretation given to him in The Long Ships by Frans Gunnar Bengtsson, a Swedish best-selling Viking-inspired novel.
Bluetooth provides a way to connect and exchange information between devices like personal digital assistants (PDAs), mobile phones, laptops, PCs, printers and digital cameras via a secure, low-cost, globally available short range radio frequency.

Bluetooth lets these devices talk to each other when they come in range, even if they're not in the same room, as long as they are within 10 metres (32 feet) of each other.

General information
A typical Bluetooth mobile phone headsetThe latest version currently available to consumers is 2.0, but few manufacturers have started shipping any products yet. Apple Computer, Inc. offered the first products supporting version 2.0 to end customers in January 2005. The core chips have been available to OEMs (from November 2004), so there will be an influx of 2.0 devices in mid-2005. The previous version, on which all earlier commercial devices are based, is called 1.2.

Bluetooth is a wireless radio standard primarily designed for low power consumption, with a short range (up to 10 meters) and with a low-cost transceiver microchip in each device.
It can be used to wirelessly connect peripherals like printers or keyboards to computers, or to have PDAs communicate with other nearby PDAs or computers.

Cell phones with integrated Bluetooth technology have also been sold in large numbers, and are able to connect to computers, PDAs and, specifically, to handsfree devices. BMW was the first motor vehicle manufacturer to install handsfree Bluetooth technology in its cars, adding it as an option on its 3 Series, 5 Series and X5 vehicles. Since then, other manufacturers have followed suit, with many vehicles, including the 2004 Toyota Prius and the 2004 Lexus LS 430. The Bluetooth car kits allow users with Bluetooth-equipped cell phones to make use of some of the phone's features, such as making calls, while the phone itself can be left in a suitcase or in the boot/trunk, for instance.

The standard also includes support for more powerful, longer-range devices suitable for constructing wireless LANs.

A Bluetooth device playing the role of "master" can communicate with up to 7 devices playing the role of "slave". At any given instant in time, data can be transferred between the master and one slave; but the master switches rapidly from slave to slave in a round-robin fashion. (Simultaneous transmission from the master to multiple slaves is possible, but not used much in practice). These groups of up to 8 devices (1 master and 7 slaves) are called piconets.
The Bluetooth specification also allows connecting two or more piconets together to form a scatternet, with some devices acting as a bridges by simultaneously playing the master role in one piconet and the slave role in another piconet. These devices have yet to come, though are supposed to appear within the next two years.

Any device may perform an "inquiry" to find other devices to which to connect, and any device can be configured to respond to such inquiries.

Pairs of devices may establish a trusted relationship by learning (by user input) a shared secret known as a "passkey". A device that wants to communicate only with a trusted device can cryptographically authenticate the identity of the other device. Trusted devices may also encrypt the data that they exchange over the air so that no one can listen in.

The protocol operates in the license-free ISM band at 2.45 GHz. In order to avoid interfering with other protocols which use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels and changes channels up to 1600 times per second. Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s. Version 2.0 implementations feature Bluetooth Enhanced Data Rate (EDR), and thus reach 2.1 Mbit/s. Technically version 2.0 devices have a higher power consumption, but the three times faster rate reduces the transmission times, effectively reducing consumption to half that of 1.x devices (assuming equal traffic load).
Bluetooth differs from Wi-Fi in that the latter provides higher throughput and covers greater distances but requires more expensive hardware and higher power consumption. They use the same frequency range, but employ different multiplexing schemes. While Bluetooth is a cable replacement for a variety of applications, Wi-Fi is a cable replacement only for local area network access. A glib summary is that Bluetooth is wireless USB whereas Wi-Fi is wireless Ethernet.

Many USB Bluetooth adapters are available, some of which also include an IrDA adapter.
Embedded BluetoothBluetooth devices and modules are increasingly being made available which come with an embedded stack and a standard UART port. The UART protocol can be as simple as the industry standard AT protocol, which allows the device to be configured to cable replacement mode. This means it now only takes a matter of hours (instead of weeks) to enable legacy wireless products that communicate via UART port.

Features by version

Bluetooth 1.0 and 1.0B
Versions 1.0 and 1.0B had numerous problems and the various manufacturers had great difficulties in making their products interoperable. 1.0 and 1.0B also had mandatory Bluetooth Hardware Device Address (BD_ADDR) transmission in the handshaking process, rendering anonymity impossible at a protocol level, which was a major set-back for services planned to be used in Bluetooth environments, such as Consumerium.

Bluetooth 1.1
In version 1.1 many errata found in the 1.0B specifications were fixed. There was added support for non-encrypted channels.

Bluetooth 1.2
This version is backwards compatible with 1.1 and the major enhancements include
Adaptive Frequency Hopping (AFH), which improves resistance to radio interference by avoiding using crowded frequencies in the hopping sequence Higher transmission speeds in practice extended Synchronous Connections (eSCO), which improves voice quality of audio links by allowing retransmissions of corrupted packets. Received Signal Strength Indicator (RSSI) Host Controller Interface (HCI) support for 3-wire UART HCI access to timing information for Bluetooth applications.

Bluetooth 2.0
This version is backwards compatible with 1.x and the major enhancements include
Non-hopping narrowband channel(s) introduced. These are faster but have been criticised as defeating a built-in security mechanism of earlier versions; however frequency hopping is hardly a reliable security mechanism by today's standards. Rather, Bluetooth security is based mostly on cryptography. Broadcast/multicast support. Non-hopping channels are used for advertising Bluetooth service profiles offered by various devices to high volumes of Bluetooth devices simultaneously, since there is no need to perform handshaking with every device. (In previous versions the handshaking process takes a bit over one second.) Enhanced Data Rate (EDR) of 2.1 Mbit/s. Built-in quality of service. Distributed media-access control protocols. Faster response times. Halved power consumption due to shorter duty cycles.

Future Bluetooth uses
One of the ways Bluetooth technology may become useful is in Voice over IP. When VOIP becomes more widespread, companies may find it unnecessary to employ telephones physically similar to today's analogue telephone hardware. Bluetooth may then end up being used for communication between a cordless phone and a computer listening for VOIP and with an infrared PCI card acting as a base for the cordless phone. The cordless phone would then just require a cradle for charging. Bluetooth would naturally be used here to allow the cordless phone to remain operational for a reasonably long period.

Security concerns
In November 2003, Ben and Adam Laurie from A.L. Digital Ltd. discovered that serious flaws in Bluetooth security lead to disclosure of personal data. It should be noted however that the reported security problems concerned some poor implementations of Bluetooth, rather than the protocol itself.

In a subsequent experiment, Martin Herfurt from the was able to do a field-trial at the CeBIT fairgrounds showing the importance of the problem to the world. A new attack called BlueBug was used for this experiment.

In April 2004, security consultants @Stake revealed a security flaw that makes it possible to crack into conversations on Bluetooth based wireless headsets by reverse engineering the PIN.
This is one of a number of concerns that have been raised over the security of Bluetooth communications. In 2004 the first purported virus using Bluetooth to spread itself among mobile phones appeared for the Symbian OS. The virus was first described by Kaspersky Labs and requires users to confirm the installation of unknown software before it can propagate. The virus was written as a proof-of-concept by a group of virus writers known as 29a and sent to anti-virus groups. Because of this, it should not be regarded as a security failure of either Bluetooth or the Symbian OS. It has not propagated 'in the wild'.
In August 2004, a world-record-setting experiment showed that with directional antennas the range of class 2 Bluetooth radios could be extended to one mile. This enables attackers to access vulnerable Bluetooth-devices from a distance beyond expectation.

Bluetooth uses the SAFER+ algorithm for authentication and key generation.
Bluetooth profilesIn order to use Bluetooth, a device must be able to interpret certain Bluetooth profiles. These define the possible applications. Following profiles are defined:

  • Generic Access Profile (GAP)
  • Service Discovery Application Profile (SDAP)
  • Cordless Telephony Profile (CTP)
  • Intercom Profile (IP)
  • Serial Port Profile (SPP)
  • Headset Profile (HSP)
  • Dial-up Networking Profile (DUNP)
  • Fax Profile LAN Access Profile (LAP)
  • Generic Object Exchange Profile (GOEP)
  • Object Push Profile (OPP)
  • File Transfer Profile (FTP)
  • Synchronisation Profile (SP) - This profile allows synchronisation of Personal Information Manager (PIM) items. As this profile originated as part of the infrared specifications but has been adopted by the Bluetooth SIG to form part of the main Bluetooth specification, it is also commonly referred to as IrMC Synchronization.
  • Hands-Free Profile (HFP)
  • Human Interface Device Profile (HID)
  • Hard Copy Replacement Profile (HCRP)
  • Basic Imaging Profile (BIP)
  • Personal Area Networking Profile (PAN)
  • Basic Printing Profile (BPP)
  • Advanced Audio Distribution Profile (A2DP)
  • Audio Video Remote Control Profile (AVRCP)
  • SIM Access Profile (SAP)

Compatibility of products with profiles can be verified on the Bluetooth Qualification website

Friday, March 11, 2005

IEEE 802.11

IEEE 802.11 or Wi-Fi denotes a set of Wireless LAN standards developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802). The term is also used to refer to the original 802.11, which is now sometimes called "802.11legacy".

A D-Link 802.11b Wireless router for SOHO use.The 802.11 family currently includes six over-the-air modulation techniques that all use the same protocol, the most popular (and prolific) techniques are those defined by the a, b, and g amendments to the original standard; security was originally included, and was later enhanced via the 802.11i amendment. Other standards in the family (c–f, h–j, n) are service enhancement and extensions, or corrections to previous specifications. 802.11b was the first widely accepted wireless networking standard, followed (somewhat counterintuitively) by 802.11a and 802.11g.

802.11b and 802.11g standards use the unlicensed 2.4 GigaHertz (GHz) band. The 802.11a standard uses the 5 GHz band. Operating in an unregulated frequency band, 802.11b and 802.11g equipment can incur interference from microwave ovens, cordless phones, and other appliances using the same 2.4 GHz band.

The original version of the standard IEEE 802.11 released in 1997 specifies two raw data rates of 1 and 2 Megabits per second (Mbit/s) to be transmitted via infrared (IR) signals or in the Industrial Scientific Medical frequency band at 2.4 GHz. IR remains a part of the standard but has no actual implementations.

The original standard also defines Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as the media access method. A significant percentage of the available raw channel capacity is sacrificed (via the CSMA/CA mechanisms) in order to improve the reliability of data transmissions under diverse and adverse environmental conditions.

At least five different, somewhat-interoperable, commercial products appeared using the original specification, from companies like Alvarion (PRO.11 and BreezeAccess-II), Netwave Technologies (AirSurfer Plus and AirSurfer Pro) and Proxim (OpenAir). A weakness of this original specification was that it offered so many choices that interoperability was sometimes challenging to realize. It is really more of a "meta-specification" than a rigid specification, allowing individual product vendors the flexibility to differentiate their products. Legacy 802.11 was rapidly supplemented (and popularized) by 802.11b.

The 802.11b amendment to the original standard was ratified in 1999. 802.11b has a maximum raw data rate of 11 Mbit/s and uses the same CSMA/CA media access method defined in the original standard. Due to the CSMA/CA protocol overhead, in practice the maximum 802.11b throughput that an application can achieve is about 5.9 Mbit/s over TCP and 7.1 Mbit/s over UDP.

802.11b operates in the 2.4 GHz RF spectrum. Hence, metal, water, and thick walls absorb 802.11b signals and decrease the range drastically.

802.11b products appeared on the market very quickly, since 802.11b is a direct extension of the DSSS modulation technique defined in the original standard. Hence, chipsets and products were easily upgraded to support the 802.11b enhancements. The dramatic increase in throughput of 802.11b (compared to the original standard) along with substantial price reductions lead to the rapid acceptance of 802.11b as the definitive wireless LAN technology.
With high-gain external antennas, the protocol can also be used in fixed point-to-point arrangements, typically at ranges up to eight kilometers (km) although some report success at ranges up to 80–120 km where line of sight can be established. This is usually done in place of costly leased lines or very cumbersome microwave communications equipment. Current cards can operate at 11 Mbit/s, but will scale back to 5.5, then 2, then 1, if signal quality becomes an issue.

Extensions have been made to the 802.11b protocol (e.g., channel bonding and burst transmission techniques) in order to increase speed to 22, 33, and 44 Mbit/s, but the extensions are proprietary and have not been endorsed by the IEEE. Many companies call enhanced versions "802.11b+".

The first widespread commercial use of the 802.11b standard for networking was made by Apple Computer under the trademark AirPort. On the non-Apple market, Linksys could be considered the current leader.

Channels and international compatibility
802.11b and 802.11g divide the spectrum into 14 overlapping, staggered channels of 22 megahertz (MHz) each. Channels 1, 6 and 11 (and in some geographic areas channel 14) do not overlap and those channels (or other sets with similar gaps) can be used such that multiple networks can operate in close proximity without interfering with each other.

The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, and uses a 52-subcarrier OFDM (Orthogonal Frequency Division Multiplexing) with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s. The data rate is reduced to 48, 36, 34, 18, 12, 9 then 6 Mbit/s if required. 802.11a has 12 non-overlapping channels, 8 dedicated to indoor and 4 to point to point. Is not interoperable with 802.11b, except if equipment that implements both standards.

Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points; it also means that 802.11a cannot penetrate as far as 802.11b, since and it is also absorbed more readily, other things (such as power) being equal.

Different countries have different regulatory support, although a 2003 World Radiotelecommunciations Conference made it easier for use worldwide. 802.11a is now approved by regulations in the United States and Japan, but in other areas, such as the European Union, it had to wait longer for approval. European regulators were considering the use of the European HIPERLAN standard, but in mid-2002 cleared 802.11a for use in Europe. In the US, a mid-2003 FCC decision may open more spectrum to 802.11a channels.

Of the 52 OFDM subcarriers, 48 are for data and 4 are pilot subcarriers with a carrier separation of 0.3125 MHz (20 MHz/64). Each of these subcarriers can be a BPSK, QPSK, 16-QAM or 64-QAM. The total bandwidth is 20 MHz with an occupied bandwidth of 16.6 MHz. Symbol duration is 4 microseconds with a guard interval of 0.8 microseconds. The actual genration and decoding of orthogonal components is done in baseband using DSP which is then upconverted to 5 GHz at the transmitter. Each of the subcarriers could be represented as a complex number. The time domain signal is generated by taking an Inverse Fast Fourier Transform (IFFT). Correspondingly the receiver downconverts, samples at 20 MHz and does an FFT to retrieve the original coefficients. The advantages of using OFDM include reduced multipath effects in reception and increased spectral efficiency.

802.11a products started shipping in 2001, lagging 802.11b products due to the slow availability of the 5 GHz components needed to implement products. 802.11a was not widely adopted overall because 802.11b was already widely adoped, because of 802.11a's disadvantages, because of poor initial product implementations, making its range even shorter, and because of regulations. Manufacturers of 802.11a equipment responded to the lack of market success by improving the implementations (current-generation 802.11a technology has range characteristics much closer to those of 802.11b), and by making technology that can use more than one 802.11 standard. There are dual-band, or dual-mode or tri-mode cards that can automatically handle 802.11a and b, or a, b and g, as available. Similarly, there are mobile adapters and access points which can support all these standards simultaneously.

In June 2003, a third modulation standard was ratified: 802.11g. This flavor works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbit/s, or about 24.7 Mbit/s net throughput like 802.11a. It is fully backwards compatible with b and uses the same frequencies. Details of making b and g work well together occupied much of the lingering technical process. In older networks, however, the presence of an 802.11b participant significantly reduces the speed of an 802.11g network.

The 802.11g standard swept the consumer world of early adopters starting in January 2003, well before ratification. The corporate users held back and Cisco and other big equipment makers waited until ratification. By summer 2003, announcements were flourishing. Most of the dual-band 802.11a/b products became dual-band/tri-mode, supporting a, b, and g in a single mobile adaptor card or access point.

While 802.11g held the promise of higher throughput, actual results were mitigated by a number of factors: conflict with 802.11b-only devices (see above), exposure to the same interference sources as 802.11b, limited channelization (only 3 fully non-overlapping channels like 802.11b) and the fact that the higher data rates of 802.11g are often more susceptible to interference that 802.11b, causing the 802.11g device to reduce the data rate to effectively the same rates used by 802.11b. The move to dual-mode/tri-mode products also carries with it economies of scale (e.g. single chip manufacturing). The use of dual-band/tri-mode products ensures the best possible throughput in any given environment.

A new proprietary feature called Super G is now integrated in certain access points. These can boost network speeds up to 108 Mbit/s by using channel bonding. This feature may interfere with other networks and may not support all b and g client cards. In addition, packet bursting techniques are also available in some chipsets and products which will also considerably increase speeds. Again, they may not be compatible with some equipment.

The first major manufacturer to use 802.11g was Apple, under the trademark AirPort Extreme. Cisco joined the game by buying up Linksys, an early adopter, and also offers its own wireless mobile adaptors under the name Aironet.

In January 2004 IEEE announced that it had formed a new 802.11 Task Group (TGn) to develop a new amendment to the 802.11 standard for local-area wireless networks. The real data throughput will be at least 100 Mbit/s (which may require an even higher raw data rate at the physical layer), and so up to 4–5 times faster than 802.11a or 802.11g, and perhaps 20 times faster than 802.11b. It is projected that 802.11n will also offer a better operating distance than current networks. There are two competing variants of the 802.11n standard; WWiSE (backed by companies including Broadcom) and TGn Sync (backed by Intel and Philips). The standardization process is expected to be completed by the end of 2006.

802.11n builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). The additional transmitter and receiver antennas allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, perhaps through coding schemes like Alamouti coding.

Because the IEEE only sets specifications but does not test equipment for compliance with them, a trade group called the Wi-Fi Alliance runs a certification program that members pay to participate in. Virtually all companies selling 802.11 equipment are members. The Wi-Fi trademark, owned by the group and usable only on compliant equipment, is intended to guarantee interoperability. Currently, "Wi-Fi" can mean any of 802.11a, b, or g. As of fall 2003, Wi-Fi also includes the security standard Wi-Fi Protected Access or WPA. Eventually "Wi-Fi" will also mean equipment which implements the 802.11i security standard (aka WPA2). Products that say they are Wi-Fi are supposed to also indicate the frequency band in which they operate, 2.4 or 5 GHz.

The following standards and task groups exist within the working group:

  • IEEE 802.11 - The original 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and IR standard
  • IEEE 802.11a - 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001)
  • IEEE 802.11b - Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999)
  • IEEE 802.11d - international (country-to-country) roaming extensionsNew countries
  • IEEE 802.11e - Enhancements: QoS, including packet bursting
  • IEEE 802.11F - Inter-Access Point Protocol (IAPP)
  • IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)
  • IEEE 802.11h - 5 GHz spectrum, Dynamic Channel/Frequency Selection (DCS/DFS) and Transmit Power Control (TPC) for European compatibility
  • IEEE 802.11i (ratified 24 June 2004) - Enhanced security
  • IEEE 802.11j - Extensions for Japan
  • IEEE 802.11k - Radio resource measurements
  • IEEE 802.11n - Higher throughput improvements
  • IEEE 802.11p - WAVE - Wireless Access for the Vehicular Environment (such as ambulances and passenger cars)
  • IEEE 802.11r - Fast roaming
  • IEEE 802.11s - Wireless mesh networking
  • IEEE 802.11T - Wireless Performance Prediction (WPP) - test methods and metrics
  • IEEE 802.11u - Interworking with non-802 networks (e.g., cellular)
  • IEEE 802.11v - Wireless network management

Community Networks

With the proliferation of cable modems and DSL, there is an ever-increasing market of people who wish to establish small networks in their homes to share their high speed Internet connection.

Wireless office networks are often unsecured or secured with WEP, which is said to be easily broken, although a substantial amount of data has to be collected before it can be cracked successfully. These networks frequently allow "people on the street" to connect to the Internet. There are also efforts by volunteer groups to establish wireless community networks to provide free wireless connectivity to the public.


In 2001, a group from the University of California at Berkeley presented a paper describing weaknesses in the 802.11 WEP (wired equivalent privacy) security mechanism defined in the original standard; they were followed by Fluhrer, Mantin, and Shamir's paper entitled "Weaknesses in the Key Scheduling Algorithm of RC4". Not long after, Adam Stubblefield and AT&T publicly announcing the first verification of the attack. In the attack they were able to intercept transmissions and gain unauthorized access to wireless networks.

The IEEE set up a dedicated task group to create a replacement security solution, 802.11i (previously this work was handled as part of a broader 802.11e effort to enhance the MAC layer). The Wi-Fi Alliance announced an interim specification called Wi-Fi Protected Access (WPA) based on a subset of the then current IEEE 802.11i draft. These started to appear in products in mid-2003. 802.11i (aka WPA2) itself was ratified in June 2004, and uses the Advanced Encryption Standard, instead of RC4, which was used in WEP and WPA.

Institute of Electrical and Electronics Engineers

The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization for the advancement of technology related to electricity. It is the largest technical professional organization in the world (in number of members), with more than 360,000 members in 150 countries (as of 2004).

IEEE's Constitution defines the purposes of the organization as "scientific and educational, directed toward the advancement of the theory and practice of electrical, electronics, communications and computer engineering, as well as computer science, the allied branches of engineering and the related arts and sciences." In pursuing these goals, the IEEE serves as a major publisher of scientific journals and a conferences organizer. It is also a leading developer of industrial standards in a broad range of disciplines, including electric power and energy, biomedical technology and healthcare, information technology, information assurance, telecommunications, consumer electronics, transportation, aerospace, and nanotechnology. IEEE develops and participates in educational activities such as accreditation of electrical engineering programs in institutes of higher learning.

IEEE produces 30 percent of the world's literature in the electrical and electronics engineering and computer science fields, and has developed more than 900 active industry standards. It also sponsors or cosponsors more than 300 international technical conferences each year.
Most IEEE members are electrical engineers, computer engineers, and computer scientists, but the organization's wide scope of interests has attracted engineers in other disciplines (e.g., mechanical and civil,) as well as biologists, physicists, and mathematicians.

The IEEE is incorporated in the State of New York, United States. It was formed in 1963 by the merger of the Institute of Radio Engineers (IRE, founded 1912) and the American Institute of Electrical Engineers (AIEE, founded 1884). It has a dual complementary regional and technical structure - with organizational units based on geography (e.g., the IEEE Philadelphia Section) and technical focus (e.g., the IEEE Computer Society). It manages a separate organizational unit (IEEE-USA) which recommends policies and implements programs specifically intended to benefit the members, the profession and the public in the United States.

Notable Presidents of IEEE and its founding organizations include Elihu Thomson (AIEE, 1889-1890), Alexander Graham Bell (AIEE, 1891-1892), Charles Proteus Steinmetz (AIEE, 1901-1902), Lee De Forest (IRE, 1930), Frederick E. Terman (IRE, 1941), William R. Hewlett (IRE, 1954), Ernst Weber (IRE, 1959; IEEE, 1963), and Ivan Getting (IEEE, 1978).

Radio Frequency

Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. Such frequencies account for the following parts of the spectrum:

  • Extremely low frequency ELF 1 3–30 Hz 100,000 km – 10,000 km
  • Super low frequency SLF 2 30–300 Hz 10,000 km – 1000 km
  • Ultra low frequency ULF 3 300–3000 Hz 1000 km – 100 km
  • Very low frequency VLF 4 3–30 kHz 100 km – 10 km
  • Low frequency LF 5 30–300 kHz 10 km – 1 km
  • Medium frequency MF 6 300–3000 kHz 1 km – 100 m
  • High frequency HF 7 3–30 MHz 100 m – 10 m
  • Very high frequency VHF 8 30–300 MHz 10 m – 1 m
  • Ultra high frequency UHF 9 300–3000 MHz 1 m – 100 mm
  • Super high frequency SHF 10 3–30 GHz 100 mm – 10 mm
  • Extremely high frequency EHF 11 30–300 GHz 10 mm – 1 mm

Note: above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

The ELF, SLF, ULF, and VLF bands overlap the AF (audio frequency) spectrum, which is approximately 20–20,000 Hz. However, sounds are transmitted by atmospheric compression and expansion, and not by electromagnetic energy.

Electrical connectors designed to work at radio frequencies are known as RF connectors. RF is also the name of a standard audio/video connector, also called BNC (Bayonet Neill-Concelman).

Thursday, March 10, 2005

Wireless (WiFi) Networking

A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier: the last link with the users is wireless, to give a network connection to all users in a building or campus. The backbone network usually uses cables.

WLAN is expected to continue to be an important form of connection in many business areas. The market is expected to grow as the benefits of WLAN are recognized. Frost and Sullivan estimate the WLAN market to have been 0.3 billion US dollars in 1998 and 1.6 billion dollars in 2005. So far WLANs have been installed in universities, airports, and other major public places. Decreasing costs of WLAN equipment has also brought it to many homes. However, in the UK the exhorbitant cost of using such connections has so far limited use to airports' Business Class lounges, etc. Large future markets are estimated to be in health care, corporate offices and the downtown area of major cities. New York City has even begun a pilot progam to cover all five burroughs of the city with wireless internet.

Originally WLAN hardware was so expensive that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Such places could be old protected buildings or classrooms, although the restricted range of the 802.11b (typically 30ft.) limits its use to smaller buildings. WLAN components are now cheap enough to be used in the home, with many being set-up so that one PC (eg parents) can be used to share an Internet connection with the whole family (whilst retaining access control at the parents' PC).

Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards, primarily the various versions of IEEE 802.11 (Wi-Fi) (see separate articles) and HomeRF (2 Mb/s, intended for home use, unknown in the UK). An alternative ATM-like 5 GHz standardized technology, HIPERLAN, has so far not succeeded in the market and with the release of the faster 54Mb/s 802.11a standard, almost certainly never will.

The lack of default security of Wireless connections is fast becoming an issue, especially in the UK, where many Broadband (ADSL) connections are now offered together with a Wireless Basestation/ADSL Modem/firewall/Router access point. Further, many laptop PCs now have Wireless Networking built in (cf. Intel 'Centrino' campaign) thus eliminating the need for an additional plug-in (PCMCIA) card. This might even be enabled, by default, without the owner ever realising it, thus 'broadcasting' the laptop's accessibility to any computer nearby.

The use of Windows XP as the 'standard' in home PCs makes it very easy to setup a PC as a Wireless LAN 'basestation' and (using XP built in Internet Connection Sharing mode) allows all the PCs in the home to access the Internet via the 'base' PC. However lack of expertise in setting up such systems often means that your nextdoor neighbour also shares your Internet connection, sometimes without you (or they) ever realising it.

The frequency which 802.11b operates at is 2.4Ghz, which can lead to interference with many cordless phones.

There are two possible types of infrastructure: Peer-to-peer or ad-hoc mode and the so called infrastructure mode.

Peer-to-peer: This mode is a method for wireless devices to directly communicate with each other. Operating in ad-hoc mode allows wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points. Typically used by two PCs to connect to one another, so that one can share the other's Internet connection for example.

Infrastructure mode: This mode of wireless networking bridges a wireless network to a wired Ethernet network. Infrastructure mode wireless also supports central connection points for WLAN clients. A wireless access point is required for infrastructure mode wireless networking, which serves as the central WLAN communication station. Typically used by a stand-alone base-station (such as a Broadband/ADSL connection box).