Page 67 - DCAP406_DCAP_207_Computer Networks

Computer Networks/Networks

Notes Introduction

Network devices are components used to connect computers or other electronic devices together
so that they can share files or resources like printers or fax machines. Devices used to setup a
Local Area Network (LAN) are the most common type of network devices used by the public. A
LAN requires a hub, router, cabling or radio technology, network cards, and if online access is
desired, a high-speed modem.

5.1 Routers

Routers are used to connect both similar and dissimilar LANs, as shown in Figure 5.1. Router
operates on the network layer of OSI model using the physical layer, data link layer and network
layer to provide connectivity, addressing and switching as shown in Figure 5.2. These are highly
intelligent devices. In case of TCP/IP network, Internet Protocol (IP) is used as addresses for
network; this is the router who interprets the IP address and delivers the packet reliably. Now
we may say that router transmits the network layer data and therefore provides transmission of
data between LANs that use different data link protocols but using the same network layer
protocol. Because of this Ethernet can be connected with token ring network using routers.
Additionally, routers provide connectivity to MAN (SMDS) and WAN (X.25, Frame Relay and
ATM). Routers are protocol sensitive, typically supporting multiple protocols and large and
varying packet sizes such as might be involved in supporting both Ethernet and Token Ring.
A network consisting of routers can have multiple paths unlike bridges. Normally the shortest
of all paths in the network is used to transfer packets.

Figure 5.1: Router Network

Network Network
1 2 Network
R R
3
Router Router

Figure 5.2: OSI Correspondence in Case of Routers

Application Layer Application Layer
Presentation Layer Presentation Layer
Session Layer Session Layer
Transport Layer Transport Layer
Network Layer Network Layer
Data Link Layer Data Link Layer
Router
Physical Layer Physical Layer

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