Information Technology Reference
In-Depth Information
25
Networks
25.1 Introduction
Most computers in organisations connect to a network using a LAN. These networks nor-
mally consist of a backbone, which is the common link to all the networks within the organi-
zation. This backbone allows users on different network segments to communicate and al-
lows data into and out of the local network. Figure 25.1 shows a local area network which
contains various segments: LAN A, LAN B, LAN C, LAN D, LAN E and LAN F. These are
connected to the local network via the BACKBONE 1. Thus, if LAN A talks to LAN E then
the data must travel out of LAN A, onto BACKBONE 1, then into LAN C and through onto
LAN E.
Networks are partitioned from other networks with a bridge, a gateway or a router. A
bridge links a network of one type to an identical type, such as Ethernet to Ethernet, or To-
ken Ring to Token Ring. A gateway connects two dissimilar types of networks and routers
operate in a similar way to gateways and can either connect to two similar or dissimilar net-
works. The essential operation of a gateway, bridge or router is that they only allow data
traffic through that is intended for another network, which is outside the connected network.
BACKBONE 2
LAN B
BACKBONE 1
Bridge
Gateway
or Router
LAN A
LAN C
LAN D
Local network
LAN E
LAN F
Local network
Local network
Bridge
Gateway
or Router
Local network
Local network
BACKBONE3
Figure 25.1
Interconnection of local networks
