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84 Chapter 3: Switched/Campus LAN Solutions
Workgroup and Campus ATM Switches
Workgroup ATM switches can be used to deploy ATM to the desktop over low-cost ATM
desktop interfaces. Campus ATM switches are generally used to link ATM routers or LAN
switches. This use of ATM switches can minimize congestion while enabling the deployment
of such new services as VLANs. Campus switches need to support a wide variety of both local
backbone and WAN types while still commanding a respectable price/performance ratio for
local backbone functionality.
Enterprise ATM Switches
Enterprise ATM switches are multiservice devices that are designed to form the backbones of
large enterprise networks. They are intended to complement the role played by today's high-
end multiprotocol routers. Like campus ATM switches, enterprise ATM switches can be used
to interconnect workgroup ATM switches or other ATM-connected devices. Enterprise-class
switches can serve as the single point of integration for all the multiservice technologies that
can be found in enterprise backbones today. By integrating all of these services onto a common
platform and a common ATM transport infrastructure, network designers can gain greater
manageability while eliminating the need for multiple overlay networks.
Defining LAN Interconnection Methods
Network performance can be improved by dividing a segment into less-populated segments and
connecting them with a bridge, switch, or router. Segmentation reduces traffic on each segment.
The two methods of interconnecting a LAN segment are:
·
Bridging/switching
·
Routing
Bridging/Switching
A bridge is a device that connects one network to another. Bridges and switches are devices that
operate principally at Layer 2 of the OSI reference model. They are referred to as data-link
layer devices
. Bridges connect and enable packet forwarding between different network
segments.
A network bridge performs much the same function as a bridge that might be used in everyday
traffic. Network bridges decide whether data is going to the LAN on the east wing of the campus
or whether the data is crossing the bridge to the west wing. A bridge examines each message
on a LAN and forwards the data that is destined to the other network. In bridging networks,
addresses have no specific relationship to location. Therefore, messages are sent to every
address on the network and are accepted only by the intended destination node. Bridges learn
which addresses are on which network and develop a table so that future messages can be sent
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