by August 11, 2003 0 comments



Wi-Fi and 802.11 are often used interchangeably. The name 802.1 comes from the IEEE committee that standardized it. Wi-Fi or Wireless Fidelity is an interoperability certification program promoted by the Wi-Fi alliance, an association of wireless equipment manufacturers. The idea is that a consumer should look for the Wi-Fi logo and feel safe that this 802.11 product will work with other Wi-Fi certified products. 

802.11 comes in several flavors. 802.11b is the ‘vanilla’ wireless networking standard, operating over the 2.4 GHz band, and offers baseline wireless functionality. It’s the most widely deployed standard and is currently the only standard that can be used freely indoors in India. There is a limitation on the number of Wi-Fi networks that can simultaneously co-exist in an area. This is because there is limited spectrum availability in each band, and each Wi-Fi network uses a part of it. For example a total of 80 MHz is available in the 2.4 GHz band and each Wi-Fi network uses around 25 MHz of it. This implies that no more than three Wi-Fi networks can co-exist at a time in this band. This has nothing to do with the number of users using a 
single AP. 

The IEEE has only recently approved the 802.11g platform, which works at the 802.11b’s 2.4 GHz band and delivers five times its data rate, at about 54 Mbps. It’s also backward compatible with b, that is, g APs and clients will work with b, albeit at data transfer rates of b. The 802.11a is another Wi-Fi platform popular worldwide for enterprise deployment. The most important advantage it offers over g is that it it allows up to 8 networks to co-exist, much more than 3 permitted by ‘b’ and ‘g’. It operates on the relatively noisefree 5 GHz band. This, however, hasn’t been freed for use in India. 802.11e is another one to be standardized, and is meant to ensure Quality of Service support for LAN applications, which will be critical for delay-sensitive applications such as Voice over Wireless IP. In Wi-Fi, real data rates obtained are about 50-60% of these theoretical rates, for example real throughputs in 802.11b seldom exceed 6 Mbps.

IEEE 802.11b defines the physical layer and media access control (MAC) sub layer for communications across a shared, wireless local area network (WLAN). At the physical layer, IEEE 802.11b follows DSSS (Direct Sequence Spread Spectrum) modulation, which works by dividing the stream of information to be transmitted in small pieces, each of which is allocated across to a frequency channel across the spectrum. A data signal at the point of transmission is combined with a chipping code (also called higher data-bit rate) that divides the data according to a spreading ratio. The higher data-rate bit sequence works by converting every binary ‘1’ bit that’s transmitted to a sequence of ones and zeros. Every binary ‘0’ transmitted uses the inverse sequence of this ‘1’ bit.

802.11a and 802.11g don’t use DSSS, and instead the employ OFDM or Orthogonal Frequency Division Multiplexing that allows them to give higher data rates, albeit at higher power consumption.

Now lets look at the MAC or the Media Access Control sub-layer of the Data Link network layer. If you’re familiar with how Ethernet works, you’ll know that it uses the CSMA/CD technology (Collision Sense Multiple Access with Collision Detection) to transmit data, which happens at the MAC layer. This technology allows a transmitting node to detect a collision and retransmit.

It is difficult for a wireless client to be able to detect collisions. 802.11b instead uses the Carrier Sense Multiple Access with Collision Avoidance or CSMA/CA at the MAC sub-layer. A wireless station that wants to transmit data first listens on the wireless medium to determine if another station is currently transmitting. If the medium is being used, the wireless station calculates a random backoff delay after which it again listens for a free transmitting station. The base station acknowledges successful receipt.

SECURITY ISSUES
A security breach can take place as the client communicates with the AP. A hacker could ‘listen-in’ on the data transfers and could also gain access to your network. Security concerns continue to dog enterprise level Wi-Fi deployments. Unlike a wired network where controlled access to network jacks provides the first line of defense, a wireless network is inherently uncontainable by the walls of your office. To address this, IEEE developed the WEP (Wireless Equivalent Privacy) protocol. While WEP would fend off a casual eavesdropper, it will be ineffective against a committed hacker. We managed to break into a 64-bit WEP setup in four days of computing time. 

To overcome WEP’s limitation, a new breed of security procedures known as IEEE 802.1x, are there. When a device
requests access to the AP, the AP demands a set of credentials, some of which are authenticated by the AP itself and others are forwarded to a RADIUS (Remote Authentication Dial in server) server for authentication. This RADIUS server is actually a part of the wired network and also used to authenticate clients on the wired network. Having the same authentication authority makes network management considerably simple. The method of supplying credentials is defined in the 802.1X standard EAP (Extensible Authentication Protocol). There are four commonly used EAP methods: EAP-MD5, EAP-Cisco Wireless (also known as LEAP or Lightweight EAP), EAP-TLS, and
EAP-TTLS.

IEEE has bundled security enhancements into the soon to be released IEEE 802.11i platform. Two encryption methods replace the discredited WEP (Wired Equivalent Privacy) protocol. Temporal Key Integrity Protocol (TKIP) is an interim method. It will support older 802.11b-based clients and APs through software updates, but cryptographers say TKIP will be broken eventually. The other scheme, based on the Advanced Encryption Standard, will offer the best security but will likely require new hardware. While the specification won’t be final until the end of this year, the Wi-Fi alliance has already picked up a subset of these security features and they call them Wi-Fi Protected Access. A roadblock to WPA acceptance is its lack of compatibility with WEP cards. The availability of a security platform depends on your choice of APs and Wi-Fi cards.

Firmware and driver upgrades are often made available for APs to support a select security platform. 

WI-FI IN INDIA
The Indian Government’s Wireless Planning and Coordination Wing has de-licensed the indoor use of WLAN equipment using IEEE 802.11b. However there are a number of riders attached like limiting the maximum radiated power output to 100mW and not allowing use in open areas. The 802.11g also operates at the same band, it’s likely to be approved. For more, see
www.dotindia.com/wpcc/indoor_
delicense.htm
.

WHERE IS IT HEADED
With the June 12th ratification of the IEEE 802.11g standard for wireless LANs, the sector has received a boost in terms of both speed and bandwidth. But there’s a lot more action happening in the Wi-Fi world than that. On July 11, the Bluetooth 1.2 specification was released and the first devices supporting this are expected as early as September 2003. The new specification includes something called Adaptive Frequency Hopping, using which frequencies will be automatically re-negotiated so that multiple devices using the same band spectrum can co-exist. UK-based chip manufacturers like Cambridge Silicon Radio have already released their chips (BlueCore3) based on the 1.2 standards in anticipation.

Incidentally, this specification also aims at the 2.4 GHz pie that 802.11b and ‘g’ target!

The higher bandwidth of g will allow access to more users simultaneously. An amendment finalized on the 12 June allows g products to gracefully degrade to other standards (like a) to enable co-existence. However, the a standard has the advantage of offering more channels over b and g. 

Wireless video streaming. Though not quite up to the standards of sci-fi flicks where you see the protagonists walking around watching live-speed crystal clear audio/video on their handhelds, wireless video streaming seems to be possible now. But, it might go the video-conferencing way. What we are looking at to make this an acceptable success is to put this into the wide variety of portables (mobile phones, PDAs
and so forth). 

Ultra-wide Band. As we were going to press, the IEEE 802.15.3a (UWB) taskforce was to meet in San Francisco to select one out of the 30 odd proposals before it. Two of these are of particular interest, having been submitted in the last couple of weeks and backed by a big lineup of major players. It is hoped that after the finalization, the earliest products could hit markets by late 2005. UWB (Ultrawideband)is a low-cost interface that provides a whopping 110 Mb/sec and up to a distance of 11 meters! UWB uses the 3.7—4.2 MHz frequency range (C-band) that is also used to transmit TV broadcasts.

Already, even before standards have been approved, UWB is causing ripples and controversies. But no doubt when it comes, it would bring
speed and a large range of applications with it.

ZigBee. Forget high-speed and huge bandwidths, if you need low-powered, short distance, and low-speed (just 250 Kb/sec) connections, think of the ubiquitous bee. No, we are not talking about the honeybee or the bumblebee but the Motorola invention of “ZigBee”. The ZigBee also uses the 2.4 GHz free to use radio band and is eminently suited to menial tasks where other transceivers would quickly fizzle out. The company did demo the products a couple of months ago and it has caused a stir. The aim is to create a nest of ZigBees that will form their own peer-to-peer “meshes”.

No Comments so far

Jump into a conversation

No Comments Yet!

You can be the one to start a conversation.

Your data will be safe!Your e-mail address will not be published. Also other data will not be shared with third person.