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Wireless Network - Facts and Future Part 1 of 2Will you hold my baby? She is going to be the President some day. Every child has the potential to do something great that will affect society and so it is with wireless networking. This technology is still very much in its infancy yet it has so much potential. Currently, wireless connectivity offers many obvious benefits like mobility, expedience, convenience and cost. And the future has so much more to offer, but don't let the marketing hype balloon your expectations for what present day systems can deliver because there are shortcomings. Additionally, there are several different wireless systems in-service and others soon planned to be in-service so it is important to pick a wireless network that best fits your needs. For many, when the word 'wireless' is mentioned it conjures up an image of a cell phone. Others may think of their cordless home phone. While others may think of the wireless TV device that broadcasts their satellite TV programming from the living room to their bedroom. These are all good examples of well established wireless technology. However, another technology that is starting to gain many people's attention is wireless networking. A wireless network should not be confused with the laptop dial-up modem network connection. Although this is a wireless connection that establishes a network connection, this technique uses the cellular phone system to connect to a specific phone number where a network connection can be established and most are limited to 14 Kb/s. On the other hand, a wireless network is where your computing device automatically connects to a wireless network when you are within the broadcast range of an Access Point (AP) and you can communicate at speeds 100 to 500 times faster than cellular dialup. IEEE 802 Committee The Institute of Electrical and Electronic Engineers (IEEE) 802 Local Area Network/Metropolitan Area Network (LAN/MAN) Standards Committee sets many (if not all) of the standards for network protocol. This work is broke down into several sub-committees and they are listed here to indicate how wireless network fits in to the overall structure. [1]
The IEEE 802 LAN/MAN Standards Committee has 4 groups working on standards for radio based systems; IEEE 802.11(WLAN), IEEE 802.15 (WPAN), IEEE 802.16 (WMAN) IEEE 802.20 (Wireless Mobile). Each will be addressed but we will focus most of our attention on IEEE 802.11 since it is currently in service and widely adopted. IEEE 802.11 The first proposal this subcommittee considered was the 802.11a which defined a physical transport layer and was based on Orthogonal Frequency Division Multiplex (OFDM) technology. Consequently, ratification of this proposal was delayed because of complexity in the OFDM technology and end user products based on this standard weren't seen until 2002. The second proposal 802.11b was based on Direct Sequence Spread Spectrum (DSSS) which is a relative simple technology and it was quickly ratified and end user products soon began to emerge 2 years earlier in 2000. This particular High-Frequency Wireless Local Area Network (WLAN) has also come to be known as Wireless Fidelity or Wi-Fi for short. [2] When this article was written, the latest proposal 802.11g was under consideration and was soon expected to be ratified. The following tables illustrate the key aspects of the 3 different 802.11 standards.
Performance What you see is not what you get. Reference [2] reports data throughput performance takes a significant hit for a couple of reasons. Let's use an 802.11b type of network just as an example. Please note that all wireless networks will suffer the same performance degradation as described in this example. The 802.11b specification indicates a maximum throughput of 11 Mb/s; however, the physical layer overhead cuts that rate by 40% which then yields an effective transfer rate of 6 Mb/s. Currently, wireless LANs use the Industrial Scientific and Medical (ISM) unlicensed spectrum. Consequently they are prone to interference and transmission errors which require retransmission. A 50% error rate will reduce the real throughput by 2/3s, thus further dropping the throughput to 2Mb/s, and this would be the effective rate shared by every device on the wireless LAN. Interference, congestion and transmission error could force the physical layer to step down its transmission speed to one of the lower rates detailed in Table 1, thus further reducing throughput. So don't expect the highest throughput rate unless you have an optimal environment. There is a toddler toy that is made from several brightly colored donut shape objects all of different sizes. These plastic donuts are placed on a plastic spindle with the largest one on the bottom and the smallest one on top. This is a good visual example of what the data throughput looks like when charted on a 3D graph. The highest data rate would be the smallest donut because it has the smallest radius (distance) from the spindle (antenna) and the lowest data rate would be the largest donut with the largest radius from the spindle (antenna) and each step up or down increases or decreases the throughput. Obviously, the best performance would be to park your wireless device close to the base station. Interference The Federal Communication Commission (FCC) has defined several ISM spectral bands for unlicensed use. The first band is commonly referred to as the 900MHz spectrum and it is defined by frequencies between 902 - 928 MHz. Many products were initially developed around this older frequency. The second band is commonly referred to as the 2.4 GHz spectrum and it is defined by frequencies between 2.4 - 2.4835 GHz. In recent years we have seen an upsurge in the products developed for this higher frequency band. The third band is commonly referred to as the 5.8 GHz spectrum and it is defined by frequencies between 5.725 - 5.825 GHz. Products are just now hitting the market that utilize this new band. The Uniden cordless phone is just one. The 2.4 GHz ISM band is highly congested with a number of products that will cause interference with a wireless network. The following lists many of the devices that will give you an indication as to the magnitude of the problem: microwaves, cordless phones, video transmitters like remote television transmitters, baby monitors, external wireless security cameras. Some wireless speakers and wireless headsets operate on the 2.4 GHz frequency and all of the Bluetooth devices like keyboards, mice, trackballs, digital cameras, printers and scanners. Some wireless smoke detectors and some of the PDA units use the 2.4 GHz band. The 2.4 GHz band has become so congested that IT Managers have taken action to clean it up in their realm of control. Many universities have installed or have begun work to install a wireless network campus-wide and to that end polices have been approved to totally eliminate or drastically restrict the use of any 2.4 GHz device. Many of the devices listed above can be replaced with wired devices; however, the microwave may be the greatest threat to clean wireless communication. From first hand experience, the following example may illustrate the severity of microwave interference. One night while watching television in the bedroom (via a 2.4 GHz broadcast unit), a neighbor next door turned on their microwave to heat up something and the consequence was a complete disruption of the television broadcast. Both houses were separated by a 16' yard and the neighbor's kitchen was located in the central part of their home. It would seem the power of the electro magnetic interference (EMI) emanating from the microwave was quite significant and if it can completely disrupt a video broadcast signal, then the same will affect the transmission quality of a wireless network. Perhaps newer microwaves have tighter constraints for EMI emission, but in either event microwave usage should be something to consider when planning a wireless network. Another form of interference called Multi-Path Collision occurs when the broadcast waves take 2 or more paths from the transmitter to the receiver. When the signals arrive at the receiver, they may be out of phase where their wave forms interfere to the decrement of the signal strength and loss of data. To help get around some of this congestion, the FCC has also defined several bands for the Unlicensed National Information Infrastructure (U-NII). The FCC has also designated the U-NII bands for high speed digital communications only, like wireless networking. The first band having a frequency range of 5.15 - 5.25 GHz is defined for indoor use only. The second band with a frequency of 5.25 - 5.35 GHz is defined for indoor/outdoor use. The third band with a frequency of 5.725 - 5.825 GHz is also defined for indoor/outdoor use. [3] It is interesting to note that the FCC has defined the ISM 5.8 band to be the same as the U-NII high band. It is unclear how these two bands will work together without congestion. Listed below is a summary of the various unlicensed bands. Security Security over the wireless network has been a great concern with administrators since the University of California Berkeley January 2001 publication of the Wired Equivalent Privacy (WEP) security flaws. WEP was the highly crackable security protocol, and at the time, it suffered from weak encryption, static encryption keys, keys limited to a maximum length of 40 bits and no key distribution method available. Since then the WI-FI Alliance standards group has introduced an interim standard, Wi-Fi Protected Access (WPA) to replace WEP. WPA implemented Temporal Key Integration Protocol (TKIP) and IEEE 802.1x which is a mechanism for enhanced mutual authentication and dynamic key distribution. However, WPA was only a stop-gap measure until the full blown 802.11i protocol was approved and implemented. It should be noted that IEEE 802.11i will fold in the Advanced Encryption Standard (AES) and IEEE 802.11i will be an extension of 802.11 ESN (Enhanced Security Network). [4] Other personal security considerations would be the Lightweight Extensible Authentication Protocol (LEAP) developed by Cisco. This is a proprietary system; however, Cisco has freely permitted licenses of this security technology. Protected Extensible Authentication Protocol (PEAP) was also developed by Cisco and is a proprietary system requiring licensing. A third consideration would be to establish ones own Virtual Personal Network (VPN), although there have been some reported weakness in this area are well. Other Networks Bluetooth The Bluetooth Special Interest Group is a collection of several cell phone and computer companies developing a wireless technology. Bluetooth is a specification for short range low cost link between mobile computers, mobile phones and other hand held devices that allows secure transmission of both voice and data. Bluetooth utilizes Frequency Hopping Spread Spectrum (FHSS) which is targeted for low cost, low power, low range and low data rate applications and reportedly only supporting 8 nodes. HomeRF The HomeRF Working Group is a consortium of major consumer electronics and computer companies and Home RF is their specification for wireless communication in the home. HomeRF permits PC, peripherals, cordless phones and other devices to communicate voice and data over their wireless network. The system can operate as an ad-hoc network where control is distributed between each data-only device. The system can also operate as an infrastructure network under the control of a control point that also provides a gateway to the telephone network for voice handling. HomeRF also utilizes FHSS and its maximum data throughput is 60% faster than Bluetooth. No further enhancements appear to be forthcoming in that the HomeRF Working Group disbanded January, 2003; however, HomeRF 2.0 products still appear to be available. ZigBee ZigBee technology is well suited for remote monitoring and control and sensory network applications. A few examples are wireless home security, remote A/C thermostats, remote lighting and drape control, call button for elderly and disabled, universal remote controller to TV and radio, wireless keyboard, mouse and game pads, wireless smoke and CO detectors. ZigBee operates in the 2.4GHz band globally at 250 Kb/s and an additional device operating on the 915Mhz band in the Unites States at 40 Kb/s. The network will work in both a 'star' and 'mesh' type of topologies. ZigBee's addressing scheme supports 255 active nodes per 'network coordinator', and multiple network coordinators can be linked together to support 4,000 unique nodes. Listed below is a summary of most wireless networks that are in-service or network specifications that are currently under consideration: In Closing Next month, in part two of this series, we will look at which networks and which specifications are under development and what they may have to offer. Also, we will take a look at what the future might hold for wireless networking. References There have been a couple of good 'How To' articles written about wireless networking: Cutting the Cord and Going Wireless, by Brent Ozar published in the January 2003 HAL PC Magazine; Wireless Security with VPN, by Brent Ozar published in the April 2003 HAL PC Magazine; How to Hookup, by Paul Boutin, published in the May 2003 Wired. And here are a couple of Internet sites that make available a database of registered Hotspots: www.WiFinder.com/index.php, 80211hotspots.com, NetStumbler.com. [1] Portfolio to IEEE 802 [2] Emerging Technology: Wirless LAN Standards [3] National Science Foundation Diary 42 [4] WPA: Is Wi-Fi Security bandage Going to Win Over Network Admins? |
2003 Ron Fenley worked as an engineer/analyst and retired in 1999. Ron moved to the country and now pursues his interest in computers, basic science and technology. Ron has been a computer enthusiast for 20 years and has been a HAL-PC member for about half that time. Ron can be reached at future@hal-pc.org
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