Page 147 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 9: Wireless MAN Systems

9.1 Metropolitan Area Network (MAN) Notes

Authors Kenneth C. Laudan and Jane P. Laudon (2001) of Management Information Systems:
Managing the Digital Firm 10th ed. define a metropolitan area network as:
A Metropolitan Area Network (MAN) is a large computer network that spans a metropolitan
area or campus. Its geographic scope falls between a WAN and LAN. MANs provide Internet
connectivity for LANs in a metropolitan region, and connect them to wider area networks like
the Internet.

9.1.1 Types of MAN Technologies

Some technologies used for this purpose are Asynchronous Transfer Mode (ATM), FDDI,
and SMDS. These technologies are in the process of being displaced by Ethernet-based connections
(e.g., Metro Ethernet) in most areas. MAN links between local area networks have been built
without cables using either microwave, radio, or infra-red laser links. Most companies rent or
lease circuits from common carriers because laying long stretches of cable can be expensive.

DQDB, Distributed-queue dual-bus, is the metropolitan area network standard for data
communication. It is specified in the IEEE 802.6 standard. Using DQDB, networks can be up to 20
miles (30 km) long and operate at speeds of 34 to 155 Mbit/s.
z z Asynchronous Transfer Mode (ATM): Asynchronous Transfer Mode (ATM) is, according
to the ATM Forum, “a telecommunications concept defined by ANSIand ITU (formerly
CCITT) standards for carriage of a complete range of user traffic, including voice, data,
and video signals,” and is designed to unify telecommunication and computer networks.
It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-
sized cells. This differs from approaches such as the Internet Protocol or Ethernet that use
variable sized packets or frames. ATM provides data link layer services that run over a
wide range of OSI physical layer links. ATM has functional similarity with both circuit
switched networking and small packet switched networking. It was designed for a network
that must handle both traditional high-throughput data traffic (e.g., file transfers), and real-
time, low-latency content such as voice and video. ATM uses a connection-oriented model
in which a virtual circuit must be established between two endpoints before the actual data
exchange begins. ATM is a core protocol used over the SONET/SDH backbone of thepublic
switched telephone network (PSTN) and Integrated Services Digital Network (ISDN), but
its use is declining in favour of all IP.
ATM was developed to meet the needs of the Broadband Integrated Services Digital
Network, as defined in the late 1980s.
z z Fibre Distributed Data Interface (FDDI) : Fibre Distributed Data Interface (FDDI) provides
a 100 Mbit/s optical standard for data transmission in local area network that can extend in
range up to 200 kilometers (120 mi). Although FDDI logical topology is a ring-based token
network, it does not use the IEEE 802.5 token ring protocol as its basis; instead, its protocol
is derived from the IEEE 802.4 token bus timed token protocol. In addition to covering
large geographical areas, FDDI local area networks can support thousands of users. As
a standard underlying medium it uses optical fiber, although it can use copper cable, in
which case it may be referred to as CDDI(Copper Distributed Data Interface), standardized
by ANSI as TP-PMD (Twisted-Pair Physical Medium-Dependent), also referred to as TP-
DDI (Twisted-Pair Distributed Data Interface). FDDI offers both a Dual-Attached Station
(DAS), counter-rotating token ring topology and a Single-Attached Station (SAS), token
bus passing ring topology.

z FDDI was considered an attractive campus backbone technology in the early to mid 1990s
since existing Ethernet networks only offered 10 Mbit/s transfer speeds and Token Ring

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