Chapter 3 • Telecommunications and Networking 7710-mbps Ethernet16-mbps
Token Ring
LANLAN
RouterGatewayGatewayTo the InternetSwitch
HubHubBridge10-mbps
Ethernet
LAN
(hub contains
internal bus)10-mbps
Ethernet LAN10-mbps
Ethernet LAN10-mbps
Ethernet LANWireless Access Point100-mbps Fast Ethernet
backbone networkKey:
indicates microcomputer
or other network deviceFIGURE 3.8 Sample Backbone Networkswitchconnects more than two LANs, or LAN segments,
that use the same protocols. Switches are very useful to
connect several low-speed LANs (e.g., a dozen Ethernet
LANs running at 10 mbps) into a single 100-mbps back-
bone network (running Fast Ethernet). In this case, the
switch operates very much like a multiplexer. The top
vendors of these hardware devices include Cisco
Systems, Juniper Networks, 3Com (now owned by
Hewlett-Packard), and Alcatel-Lucent (France).
WIDE AREA NETWORKS Today’s more complex, more
widely dispersed organizations need wide area networks
(WANs), also called long-haul networks, to communicate
both voice and data across their far-flung operations. A
WAN differs from a LAN in that a WAN spans much greater
distances (often entire countries or even the globe) and is
usually owned by several organizations (including both
common carriers and the user organization). In addition, a
WAN employs point-to-point transmission (except for satel-
lites), whereas a LAN uses a multiaccess channel (e.g., the
bus and ring). We will note some exceptions, but for the
most part WANs rely on the public telephone network.DDD and WATS. The easiest way to set up a WAN is
to rely on ordinary public telephone service. Direct
Distance Dialing(DDD) is available through a telephone
company such as AT&T, Sprint Nextel, or Verizon and can
be used for voice and data communications between any
two spots served by the telephone network. Of course, the
speed for data transmission is quite limited (up to 56 kbps),
data error rates are relatively high, and the cost per hour is
very expensive. Wide Area Telephone Service(WAT S) is