Wireless LANs

Wireless LANs

LANs are important in two areas: in wireless office telecommunication systems (which are essentially cordless telephony as adjuncts to the on-premise PBXs) and in the use of wireless LANs (which employ either spread-spectrum or infrared technology).

The idea behind wireless LANs is augmentation, not replacement, of wired LANs and telephone systems. So, there may be issues with asbestos walls, or oak paneling, or ancient marble that's a pity to break into, that require some alternative to wire. Wireless LANs operate over a small range, about 1 to 330 feet (0.3 to 100 meters), so it's a microcellular architecture. Wireless LANs typically support what we'd call medium speeds today, ranging from 1Mbps to 11Mbps, although emerging standards, such as 802.11a, promise to increase those data rates to 40Mbps. The architecture of a wireless LAN in shown in Figure 14.15.

Figure 14.15. Wireless LAN architecture

graphics/14fig15.gif

Primary benefits of wireless LANs are that they reduce costs, particularly from the standpoint of moves, adds, and changes, in situations in which you need to dynamically reorganize where people and their devices reside. Wireless LANs also simplify the installation process, speed deployment, and enable mobility, so they facilitate low-cost installations, temporary arrangements, the working around environmental hazards or preserving historic buildings, and disaster recovery. All these applications are well suited for the consideration of a wireless LAN.

Wireless LANs can be implemented as infrared systems or as unlicensed narrowband microwave and spread spectrum that operate in the Industrial, Scientific, and Medical (ISM) band (900MHz and 2400MHz), as specified in ETSI 300.328.

IEEE 802.11 represents the first standard for wireless LAN products from an internationally recognized, independent organization, the IEEE. The 802.11 standard provides MAC (Media Access Control) and PHY (Physical Layer) functionality for wireless connectivity of fixed, portable, and moving stations moving at pedestrian and vehicular speeds within a local area. Specific features of 802.11 include support of asynchronous and time-bounded delivery service, accommodation of transmission rates of 1Mbps and 2Mbps, support of most market applications, multicast (including broadcast) services, network management services, and registration and authentication services. The target environments for use of 802.11 include inside buildings such as offices, banks, shops, malls, hospitals, manufacturing plants, and residences and outdoor areas such as parking lots, campuses, building complexes, and outdoor plants. New high-speed extensions include 802.11a, which will support up to 40Mbps in the 5GHz band, and 802.11b, which will support 11Mbps in the 2.4GHz band, by using DSSS.

HIPERLAN is the European Community's standard for wireless LANs. A committee set up by the ETSI designed it. The designed standard was aimed to be as close as possible in performance to wireline LANs such as Ethernet. A bit rate of 23.529Mbps was provided for each channel, and the five existing channels occupy 150MHz of bandwidth, in either the 5.15MHz to 5.30GHz range or the 17.1MHz to 17.2GHz range. At the lower frequencies, it has power up to 1 watt, and at the higher frequency band, it has power up to 100 milliwatts. It offers a range of three channels to five channels, with a little over 23Mbps for each channel. At 150 feet (46 meters) it can support 20Mbps. At 2,500 feet (762 meters), the data rates drop to 1Mbps. In the 17GHz band, 100Mbps to 150Mbps is possible. Time-bounded, or isochronous, services are defined for HIPERLAN and use distributed control, which is essentially a physical- and data-link-layer definition.

The Unlicensed National Information Infrastructure (UNII) band, originally called SUPERNet (Shared Unlicensed Personal Radio Networks), was originally proposed by WINForum and Apple. It's an allocation of some 300MHz, largely in the 5GHz to 6GHz bands, and it somewhat overlaps with the HIPERLAN standard.

A number of 10 Mbps+wireless LAN products are in development, including RadioLAN, Clarion, Aironet, the 802.11 high-speed extensions, and HIPERLAN 2, 3, and 4. There's also exploration at the 60GHz ISM band.

 



Telecommunications Essentials
Telecommunications Essentials: The Complete Global Source for Communications Fundamentals, Data Networking and the Internet, and Next-Generation Networks
ISBN: 0201760320
EAN: 2147483647
Year: 2005
Pages: 84

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