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 Comm Corner

Small Office, Home Office
Wireless Networks

John Woody is a net working communications consultant specializing in small office, home office networks, training setup, and internet connectivity.

Michael Espinoza is owner of Technology Coaching, a training and consulting firm that specializes in the PDA market. He co-chairs the PDA SIG with John Woody.

Wireless networks are becoming viable solutions for office and home computing by offering easy ways to link two or more computers together. The main advantage concerns not having to run cabling between the computers. The next advantage is that the computer does not have to remain at one location. Cabling for the network can be a real problem in that the network may have to run between rooms or floors and would carry an installation cost that makes the network prohibitive. Or, the cabling, if left uncovered, would be in the way, or would be unsightly. And, the convenience of being able to move that new laptop computer from room to room is really nice. The IEEE 802.11 series of standards are becoming known as the wireless Ethernet

And, as noted in my October 2002 column, wireless networking is main stream. One account noted that the wireless LAN market is slated to grow from $771 million dollars in 1999 to over $2.2 billion in 2004. (Wireless LAN Market Analysis, 2000). Wireless broadband routers and other components are now shelf purchase items. Belkin, Linksys, Intel, Buffalo, Cisco, Netgear, U.S. Robotics, Multitech, Grandtec, OriNOCO, D-Link, SMC, and 3Com all have wireless systems and components that meet the IEEE 802.11 series standards. All of the computer catalogs that I use, Data Comm Warehouse, Micro warehouse, Zones, and PC Connection, carry multiple vendors. The local sellers, Best Buy, CompUSA, and Altex all have components on the shelf. Whether all of the vendors meet all of the IEEE 802.11 series standards is another question. The standard is such that components from different vendors is suppose to work together.

IEEE 802.11 Series Standards
This IEEE standard is fairly new. It was approved in 1997. In its original form, the standard proposed three techniques, mutually incompatible, for the physical layer, i.e., the media.IR  (InfraRed) pulse position modulation, RF (Radio Frequency) signaling in the 2.4 GHz band using FHSS (Frequency Hopping Spread Speculum), or DSSS (Direct Sequence Spread Spectrum), as noted in the October 2002 column. The IR method never worked commercially. The RF methods worked, but had low transmission speeds (2Mbit/s). IEEE then set up two task groups to find alternative methods of 802.11. Task Group A would look at the 5 - GHz band to attempt to achieve throughput speed of up to 54 Mbit/s. Task Group B would continue to explore the 2.4 - GHz throughput speed band. 

The Task Group A exploration was to publish its 802.11a standard by 2002 or 2003. It is not completely out yet, though there are some components becoming available. The Task Group B standard published in 1999. Most wireless systems being sold today follow the 802.11b standard at the 11 Mbit/s speed rate.

The transmission medium is the most striking difference between wired Ethernet and wireless LANs. This medium is the RF method of sending the data from node to node in the LAN. Radio waves broadcast on a given band can be received by any receiver within the range tuned to that same frequency. Wireless NIC (Network Interface Cards) are equipped with antennae, radio transceiver, and circuitry to convert between the analog radio signal and the digital pulse used by computers. The range is governed by the signal power, distance, and interference from intervening objects (trees, walls, etc.), and other radio signals. The 802.11b range is approximately 300 feet unobstructed. Radio signals are governed by groups in the United States and other bodies internationally. The FCC (Federal Communications Commission) is the U. S. governing body. The 802.11b standard delivers its maximum performance within the FCC limits, current radio technology, and the laws of physics. Unobstructed, the standard delivers up to 11 Mbit/s. It is also designed to step down to a slower transmission rate when the signal is obstructed, i.e., walls, leaves, etc., get in the way. The step-down speed rates are 11, 5.5, 2, and 1 Mbit/s. My Lucent/OriNOCO equipped laptop shows this speed step-down when I move it down stairs to watch television as I surf the Net. My network connection, however, is fully compatible with all the functions that I need to do any work, i.e., search other computers, print, or save data files at these slower speeds.

Another difference between Ethernet and wireless LANs is the way that each controls access to the medium, the determination who may talk and when. Ethernet uses CSMA/CD (Carrier Sense Multiple Access with Collusion Detection) as Ethernet devices can send and listen to the cabling at the same time, detecting the pattern that shows a collision is taking place. A radio can not transmit and listen on the same channel at the same time as its own transmission drowns out all other signals. 802.11b LANs use CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) through a four-way handshake to gain access to the airwaves. A originating node sends a short RTS (Request To Send) packet on the air addressed to the destination. If that destination hears the transmission and is able to receive, it replies with a short CTS (Clear To Send) packet. The originating node then sends the data and the destination acknowledges all transmitted packets by returning a short ACK (Acknowledgment) packet for every transmitted packet received.

Wireless LAN topologies are also slightly different from the Ethernet Star configuration. The simplest topology is referred to as an ad hoc group of independent wireless nodes communicating as a peer-to-peer network. The 802.11b standard refers to this arrangement as an IBSS (Independent Basic Service Set). The standard provides a measure of coordination by electing one node as the proxy for controlling the LAN. Ad hoc networks are great for lone machine or hard to wire locations. Ad hoc networks also work for temporary networks such as a group of laptops in a conference room.

Complex topologies or infrastructure topologies include Access Points or base stations as part of the network. Access Points provide synchronization and coordination to the network. Access Points have a connection into the wired portion of the network and are able to receive and send to multiple wireless nodes. The 802.11b standard refers to a topology with a single Access Point as a BSS (Basic Service Set). Additional Access Points are installed in the network expands. Multiple Access Point networks are called ESS (Extended Service Sets). Each Access Point is assigned a different channel to minimize RF interference. Each mobile device will find the clearest signal and least amount of network traffic to allow seamless roaming from one Access Point to another.

The wireless network needs some tolerance of connections being dropped and reestablished to ensure minimum disruption of data delivery, including forwarding of distributed nodes. Higher level networking protocols such as TCP/IP may not be tolerant of this network jumping. The TCP/IP DHCP assignment of IP addresses may chase a node to lose its connection when it moves across cell boundaries in an ESS. This area of the standard is under review to make improvements.

Authentication and privacy issues restrict the ability to transmit in the wireless network. If authentication is open, i.e., no restrictions, then any 802.11b compliant device can be authenticated. When authentication is exercised, then each device logging onto the network must prove it belongs there via a shared authentication key by acknowledging that it knows that shared key. Privacy is the second half of the security formula and is supported in 802.11b as WAP (Wired Equivalent Privacy). WAP uses shared keys and a pseudorandom number (PN) as a technique to encrypt data packets that are transmitted. 802.11b WAP supports both 64-key and 128-key encryption.

Network Description
I have been using a wireless network node in my home LAN for over two years. I have a Lucent/OriNOCO wireless PC Card NIC mounted in one of the PCMCIA slots of my Toshiba laptop. It is 802.11b 11 Mbit/s compatible and works through an OriNOCO 2000 Access Point. The Access point connects into the ethernet wired network through a 10/100 100baseT HUB. As noted above, this node performs all network functions without problems. I have file and printer service at the 11 Mbit/s speed any time I am near the Access point. The speed falls off when I move the laptop downstairs and to the back of the house. The Access Point NIC has an antenna installed. The antenna connects to the PC Card NIC via a three (3) foot cable, giving me the flexibility to move the antenna for best reception. Downstairs and at the back of the house, I get 2 Mbit/s throughput speeds. This might be better if I had an antenna on the laptop NIC.
I have network access controlled by my NT 4.0 server. To access my network, the NT authentication and privacy codes must be known by outside wireless users. I do not have the privacy encryption mode turned on at this time, as the throughput speed is lower when the WAP encryption is turned on.

I am well satisfied with the long term performance of the OriNOCO components. I plan on installing a Multitech wireless router in the near future to test this unit against the current equipment. Wireless networks take away some of the installation problems of routing wiring and fixing the locations of computers. The components are available from multiple vendors and has become a shelf item in cost. The IEEE 802.11b standard has proven to be good and works. I am looking forward to the IEEE 802.11a standard of 54 Mbit/s speeds.

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