Wireless LAN: An overview By Kimberly Hiller (Originally published Jan 4, 2001)

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1 Wireless LAN: An overview By Kimberly Hiller (Originally published Jan 4, 2001) Brought to you b Wireless LANs are the hot new enterprise technology that everyone is talking about and considering implementing in varying degrees. Wireless LANs are no longer a technology for vertical markets (medical, education, or manufacturing); applications for this technology are only limited to imagination and available products. But are wireless LANs appropriate from your environment now? Understanding the basics is key in proposing, purchasing, deploying, and managing wireless LANs. Technology basics How wireless LANs work The role of a wireless LAN in the enterprise is to extend network coverage to allow for in-building or campus communication for mobile users. There are four components to a wireless LAN: Access Points (AP) Wireless LAN Network Interface Cards (NIC) Wired LAN Mobile device/desktop PC Access points convert airwave data into wired data (i.e., Ethernet or Token Ring), essentially acting as a bridge between the wired LAN and wireless clients. Users (clients) are assigned a MAC address that is recognized by the access points. Wireless LANs use electromagnetic waves (radio and infrared) to transmit data without physical connection between access points. Users access the wireless LAN through wireless LAN NICs in notebook computers or through ISA or PCI adapters in desktop computers or handheld devices. It should be noted that a wireless LAN can exist without connection to the wired LAN, but users would only be able to communicate with other users within the same subnet. This type of configuration is highly secure and portable. Access points can support a small group of users in a range of several hundred feet; most access points are rated for 60 to 70 users simultaneously. The more access points, the higher the throughput; however, higher encryption levels will lower throughput. Access points can be positioned anywhere that they can receive radio waves, and higher is better. Access points are defined by Extended Service Set Identification (ESSID), which is part of the IEEE standard. Clients need to be configured with the access point's ESSID in order to communicate. Multiple access points on the same subnet should have the same ESSID and allow for roaming. Server access points with the same ESSID form an Extended Service Set (ESS). It is possible for clients to allow "wild card" ESSID. Wild cards search for the strongest signal access point, regardless of ESSID. This is a benefit for corporate environments with many offices. Wild cards allow employees to communicate in any office. However, wild cards can be a security breach if appropriate encryption measures are not taken. Anyone with a laptop and wireless PC card could tap the access points. How does the data travel? Understanding spread spectrum technology Wireless LANs transmit data radio waves; radio waves are transported by Spread-Spectrum Technology (SST). SST wireless LANs allow many users to share the same frequency band, a facility accomplished mainly by Code Division Multiple Access (CDMA). This enables the simultaneous transmission of SST signals on a single frequency. It works by allocating to each user a unique sequence for identification by the receiver. While Time Division Multiple Access (TDMA) multiplexing can also be used, it is CDMA that has found most favor for SST WLAN use. There are two approaches within SST: Frequency-Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). Modulation, familiar to all of us from radio audio, is the process in

2 which a lower frequency wave is superimposed on a wave of higher frequency that is fixed and constant (the carrier wave), thus modifying it to produce an information-bearing signal. DSSS "spreads" the signal across a broad band of radio frequencies and creates a redundant pattern called a "chip" to transmit. FHSS "hops" between frequencies as is encounters noise on the band. The type of modulation technique (DSSS or FHSS) used depends on the product. DSSS and FHSS are physical technologies and are not interoperable. Table 1 DSSS and FHSS Comparison FHSS Band 2.4GHz 2.4GHz Standard IEEE b IEEE Modulation Technique Amplitude Modulation (AM) Frequency Modulation (FM) Carrier Channel Fixed in 17MHz channel Sends data over 1MHz channel Services Supported Data Voice, data, video Maximum Number of Independent Channels 3 15 Industry Technology b HomeRF, Bluetooth Understanding 2.4 GHz and 5 GHz bands The band is the speed at which the radio waves travel. Today there are two bands of choice for wireless LANs: 2.4GHz and 5GHz. The 2.4GHz band is used worldwide; however, in much of the world this band is used for cellular phones, creating interference. The 2.4GHz frequency was chosen in the early 1990s to allow for global development of unlicensed wireless LANs. Wireless LANs do not require special site licenses where they meet the regulatory requirements that are set for unlicensed usage in the Industrial, Scientific, and Medical (ISM) frequency bands (915MHz and 2.4GHz). The 2.4GHz band has a power limit of one watt. Signals modulated at 2.4GHz tend to reflect off solid objects such as walls and buildings. Signal bouncing causes delays in delivery of data. While the 2.4GHz band does not cause harmful interference, it does accept any interference it receives. Bluetooth, microwave ovens, cordless telephones, wireless security cameras, and IEEE b devices all operate in this band, which increases the chance of interference. Being an unlicensed band means that anyone can transmit in it. Using the 2.4GHz band makes wireless LANs prone to interference but easy to install and use on a global scale. The 5GHz band is also globally available. (Europe has approved 5.2GHz for HiperLAN2.) Operating in the 5GHz band, wireless LANs will not incur interference from Bluetooth or HomeRF devices, microwave ovens, cordless telephones, or wireless security cameras, since these devices cannot operate in this band. The IEEE a committee has ratified the standard for use of wireless devices in the 5GHz band; no products are currently on the market. Wireless network management Management of a wireless network is no different then managing a wired LAN; fault, configuration, account, performance, and security management are all required. Wireless LAN management has a twist: wireless users are random; they can go on and off the network sporadically. Network managers need to be prepared for this type of user. Network managers need a single element manager, but the market is not there yet. Factors to be considered when managing a wireless LAN include seamless integration with the existing wired LAN, single element management, open systems architecture, and ease of use and maintenance. Operating requirements Typical Components: Access Points Wired LAN

3 Wireless LAN Network Interface Cards Mobile device/desktop PC The number of access points needed depends on the area of mobility required and the number of mobile users. A wireless LAN can exist without connection to the wired LAN, but users will only be able to communicate with other users within the same subnet. This type of configuration is highly secure and portable. Technology analysis Business use Table 2 Types of Wireless Area Networks Area Network Acronym Market Wireless Personal/Peripheral Area Network Type of Information Communicated Applications WPAN Consumer/Residential Personal Bluetooth, HomeRF, IEEE Wireless Local-Area Network WLAN Enterprise/Campus Corporate or Internet IEEE b/a, HiperLAN2 Wireless Wide-Area Network WWAN Enterprise/Metropolitan Corporate or Internet HiperAccess, 3G, GPRS, IEEE a Benefits and risks Benefits It extends the network to remote sites. Wireless has portability. With either method of spread spectrum, DSSS or FHSS, the end result is a system that is extremely difficult to detect, does not interfere with other services, and still carries a large bandwidth of data. Wireless LAN adapter cards are becoming integrated in laptop and desktop computers as well as handheld devices, lowering the set-up cost of a wireless LAN. Wireless LANs are no longer a technology for vertical markets: medical, education, or manufacturing. Applications for the technology are only limited to imagination and available products. Risks Warring wireless industry camps are confusing, dividing, and scaring potential customers. Today WLANs only recognize these IP devices: palmtops, cell phones, laptops. In order for it to communicate with 3G products, there is a need for an automatic switching mechanism. Although SST is not as prone to interference as to preclude use in data transmissions, the signal can be obstructed by reinforced concrete. Because of the nature of their synchronization, DSSS products do not permit roaming between channels. Roaming communities must be all on the same channel, thus creating a limit of one channel for most DSSS installations. If DSSS Access Points are placed on the same channel, they will interfere with each other. If the new Access Point is placed on a different channel, users cannot roam to it. Today's wireless technologies are inoperable with each other. Bluetooth, HiperLAN2, MMAC, , b, and a products cannot communicate with each other. Work is being done by the IEEE towards interoperability between and Bluetooth. ETSI, IEEE, and MMAC are working together to settle interoperability and interference issues.

4 Common misconceptions Wireless LANS are less secure than wired LANS Wireless LANs are thought to be less secure because data travels through the air as opposed to the perceived more secure cabling of wired LANs. Wired and wireless LANs share the same security issues: vulnerability to hackers and eavesdroppers as well as authorized users. In order for a wireless LAN to be compromised, the DSSS spreading code or FHSS hopping pattern and modulation techniques, radio domains, channels, subchannels, security ID, and passwords must be known. IEEE certified wireless LAN products include Wireless Equivalent Privacy (WEP) that encrypts all data that passes between access points and wireless NICs. Wireless LANs also have the ability to lock out users down to the wireless station level. Users can be included or locked out to the wireless network at any time. No more wired LANS While it is true that a wireless LAN does not need a wired LAN to exist, advancements in wireless LAN technology are not signaling the end of the wired network. Standards While the wireless organizations have all set up their own camps and have a "not going to budge" attitude, they IEEE (U.S.), ETSI (Europe), and MMAC (Japan) are working together towards a global standard in the 5GHz band utilizing OFDM. The wireless industry will evolve as standards are released. Table 3 Wireless LAN Standards Organizations Organization Acronym Web Address Country Purpose European Telecommunications Standards Institute Institute of Electrical and Electronics Engineers Federal Communications Commission Multimedia Mobile Access Communications Promotion Council Alliances and Associations Wireless Ethernet Compatibility Alliance ETSI Europe Promote European telecommunications standards. IEEE Global Promote the engineering process of electrical and information technologies and sciences. FCC United States MMAC- PC Establish policies that govern interstate and international communications by TV, radio, wire, satellite, and cable. Japan Develop high-performance wireless systems. WECA Global To certify interoperability of IEEE b products. Products bearing the Wi-Fi symbol have passed independent testing for interoperability with other Wi- Fi certified products. Wireless LAN Association WLANA Global Education organization. Technology leaders Leaders Cisco Systems Aironet 340 Series Lucent Technologies ORiNOCO Significant players 3Com AirConnect Apple Computer AirPort

5 BreezeCOM BreezeACCESS, BreezeNET PRO 11, and BreezeNET DS.11 Enterasys RoamAbout Intermec Intermec 2101, 2100, and 2102 LXE 6200, 6400, and 6500 No Wires Needed Wireless LAN products Nokia A032 Nortel Networks e-mobility Proxim Harmony, RangeLAN-DS, RangeLAN2, Symphony, and Stratum Symbol Technologies Spectrum24 Technology alternatives Bluetooth Bluetooth was originally conceived as a way to connect laptops, PDAs, and cellular telephones wirelessly. It is the next generation of peer-to-peer computing. The first Bluetooth specification consisted of a common set of specifications for wireless voice and data transmission at short range. The release of Bluetooth 2.0 is highly anticipated. The slow speeds offered (officially 1 Mbps, but around 750 Kbps is actually achievable) will not be a viable alternative for daily use of the corporate LAN, but will enable occasional use. Bluetooth operates in the same 80 channels in the 2.4GHz band as the standard WLANs and has already been found to cause interference if used in the same environment. Once is ratified, Bluetooth and devices will be able to interoperate. Bluetooth should not be viewed as a competing wireless LAN technology, but rather as a companion. 1-Mbps voice/data Uses 2.4GHz frequency Can be used up to a distance of 10 meters Omnidirectional Point-to-multipoint Incompatible with b HiperLAN2 High Performance Radio LAN Type 2 (HiperLAN2) is a broadband wireless operating in the 5GHz band with data rates up to 54 Mbps. HiperLAN2 requires that a connection between the access point and wireless NIC be established before data is transmitted. Its QOS parameters, something that is working on, are capable of traffic prioritization that is required for 3G, ATM, and IP-based networks as well as for wireless LANs. HiperLAN2 is promoted by both the FCC and ETSI Broadband Radio Access Network (BRAN) and is mostly deployed throughout Europe. It is competes with b/a for market share and global acceptance. IEEE The IEEE standard specifies the physical and MAC layers for wireless LANs. There are six standards: a 5GHz band via Orthogonal Frequency Division Multiplex (OFDM) b 2.4GHz band, DSSS physical layer, and data transfer rates between 5.5 Mbps to 11 Mbps d Defines physical requirements (channelization, hopping, patterns, new values for current MIB attributes) to extend into new regulatory domains (countries) e Enhancements to support LAN applications with QOS, COS, security, and authentication requirements such as voice, media streams, videoconferencing f Recommended practices for Multi-Vendor Access Point Interoperability via Inter-Access Point Protocol (IAPP) Access Distribution Systems Support g Use of DSSS to 20 Mbps+ and orthogonal frequency division multiplexing (OFDM) to 54 Mbps. This will be backward-compatible with b and extend it to rates greater than 20 Mbps.

6 This will improve access to fixed LANs and internetwork infrastructure (including other WLANs) via access points as well as ad hoc networks. Including the standard itself, three have been ratified: a, and b. Insight What the industry and the world are witnessing and experiencing is the future of data communications. However, as the industry grows, the messages sent out to the end users are confusing. In order to keep up with the game, look for standard certified products, either IEEE b or HiperLAN2. Bluetooth is not a replacement technology of wireless LANs; it is a companion technology that will allow even greater mobility in the enterprise once standards and products are in place. Wireless LANs do not mean the death of the wired LAN; a wired infrastructure is vital to any network.