IEEE 802.11b

The 802.11b group within IEEE was driven largely by Lucent Technologies and Intersil Corp., and was designed to operate in the 2.4GHz ISM (Industrial, Scientific and Medical) band. The key contribution of the 802.11b addition to the wireless LAN standard was to standardise the physical layer support of two new speeds, 5.5Mbit/s and 11Mbit/s. To accomplish this, Direct Sequence Spread Spectrum (DSSS) had to be selected as the sole physical layer technique for the standard – since frequency hopping could not support the higher speeds without violating current FCC regulations – and a more efficient coding scheme known as complimentary code keying (CCK) was incorporated into the standard to attain a top-end data rate of 11 Mbit/s. The implication is that 802.11b systems will interoperate with 1Mbit/s and 2Mbit/s 802.11 DSSS systems, but will not work with 1Mbit/s and 2Mbit/s 802.11 FHSS systems.

However, early wireless adapters and access points were significantly more expensive than wired NICs and switches and wireless networks comprising components from different vendors often didn’t work well. Fortunately, both of these concerns had been largely addressed by the end of 2000. Market forces – both in terms of vastly increased volumes and competition – drove down the costs of 802.11b wireless solutions to much nearer those of their wired counterparts and interoperability problems were effectively eradicated following the setting up of the Wireless Ethernet Compatibility Alliance (WECA). Their certification programme – in which products are submitted for interoperability testing – played a hugely important role in making wireless technology more pervasive by assuring would-be adopters that they wouldn’t be stuck with proprietary, dead-end solutions. Any device that displays the Wi-Fi logo is guaranteed to have undergone WECA’s strict set of performance and compatibility tests.

As a consequence, 802.11b wireless networking enjoyed a rapid increase in deployment in enterprise settings and in educational and institutional networks and – as adapter and access point prices continued to fall – 802.11b wireless network products began to make inroads into home and SOHO applications. Initially, the demand for 802.11b in the home was driven by people who used a wireless-equipped notebook computer at work, and then took it home and wanted the same freedom from wired connection there too. However, more recently networking to share broadband Internet connections has become an increasingly important driver of 802.11b adoption in the home.

However, 802.11b isn’t perfect. One of its more significant disadvantages is its crowded frequency band. Numerous consumer devices use the same 2.4GHz radio spectrum as 802.11b and therefore represent a potential source of interference. These include microwave ovens, cordless phones, legacy wireless systems and home control devices that use the X-10 standard. The biggest threat, however, is from increasingly widely available Bluetooth devices. The problem is exacerbated by the fact that beyond its 15 to 45m range inside buildings – where it has to travel through walls and ceilings – 802.11b can also extend to up to 300m in line-of-sight outdoors.

Limited bandwidth is perhaps an even greater problem. Nominally 802.11b performs at an equivalent speed to that of 10Mbit/s wired Ethernet. However, overhead, configuration and security factors can reduce actual throughput to a typical 5Mbit/s. Whilst that is sufficient for web browsing, it’s inadequate for more demanding applications such as video streaming. Problems at the physical layer are one of a number of reasons for performance degradation. For example, the Physical Layer Convergence Protocol (PLCP) preamble included in each packet to determine transmission speed and assure synchronisation consists of 24 bytes; by contrast it is only 8 bytes for wired Ethernet. Obstacles in the path of signals can result in nodes dropping to lower speeds in an effort to maintain contact and the very nature of 802.11b’s collision avoidance methods impose significant bandwidth overheads.

Security is another important issue. Whilst Wired Equivalent Privacy (WEP) is an integral part of the wider 802.11 standard, it has been shown to have vulnerabilities making it relatively simple to decrypt the 40-bit security keys. A form of hacking known as war driving enables hackers to ride in a car with a wirelessly equipped laptop until they spot a vulnerable wireless network, park outside the building and access the network. Vendors are responding by creating defences like security keys that shift dynamically rather than remain static. However, it’s not foolproof and subject to the usual problem with proprietary fixes – they may not work with 802.11b equipment from other vendors. The industry is working on a couple of standardised fixes, including a new 128-bit encryption algorithm known as Advanced Encryption Standard (AES) that will require hardware or firmware upgrades, and a Temporal Key Integrity Protocol (TKIP) that will be compatible with WEP.

Despite its drawbacks, WEP is better than nothing. The bigger problem is the fact that many wireless networks are installed without even enabling it. In addition to taking care to ensure that WEP is enabled, there are a number of other simple measures users can take to increase their level of protection. These include changing all network names and passwords, using MAC (Media Access Control) address blocking and setting up the network as a closed system. Beyond that security can be tightened even further by implementing a Virtual Private Network (VPN) or RADIUS authentication server.

802.11b’s lack of interoperability with voice devices and absence of any Quality of Service (QoS) provisions for multimedia content are other, albeit, less serious problems.

While both the 802.11b and 802.11a specifications were approved in 1999, the former succeeded in making it to market ahead of its rival. That head start was to pay dividends when the combination of wider availability and greater affordability led to a big increase in the take up of broadband Internet connections in the early 2000s. This in turn gave a massive boost to home networking as more and more users sought to share their broadband connection across multiple home PCs. IEEE 802.11b was in the right place at the right time to reap the benefit.

So, whilst the 802.11a specification wasn’t written to directly address 802.11b’s perceived deficiencies and remained significantly behind its rival in terms of market penetration, the fact is that it does solve some of 802.11b’s more significant problems!