Page 68 - DCAP406_DCAP_207_Computer Networks

Unit 5: Networking Devices

Consider a case for data transmission from Computer 1 to Computer 5 on the network shown in Notes
Figure 5.3. When Computer 1 starts sending the data, it compares its IP address with Computer
5 i.e. destination computer addresses to know whether Computer 5 lies on its own network or
not. When Computer 1 finds that it is not on its network it transmits a data packet containing the
MAC address R of router in this case. When router receives this packet it sets the MAC address
of Computer 5 and sends the packet to the port which has the same IP destination address as
given in data packet. In this manner Computer 5 receives the data packet.

Figure 5.3: Communication via Router

Data Destination MAC Data Destination MAC

IP Address 5 Address IP Address 5 Address
of port X of 5

1 2 R S 4 6

Router

X Y

3 5

Routing Table

Network Port
Address
240.0.0.0 X
241.0.0.0 Y

5.1.1 Characteristics of Routers

1. Routers are multiport devices with high-speed backbones.
2. Routers also support filtering and encapsulation like bridges.
3. Like bridges routers are also self-learning, as they can communicate their existence to
other devices and can learn of the existence of new routers, nodes and LAN segments.
4. Routers route traffic by considering the network as a whole. It shows that they use a high
level of intelligence to accomplish this task. This characteristic makes them superior than
hubs and bridges because they simply view the network on a link-by-link basis.
5. The packet handled by router may include destination address, packet priority level,
least-cost route, minimum route delay, minimum route distance, and route congestion
level.

6. Routers constantly monitor the condition of the network, as a whole to dynamically adapt
to changes in the condition of the network.
7. They typically provide some level of redundancy in order that they are less susceptible to
catastrophic failure.

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