Switches are used in computer networks to allow more hosts to connect over a larger geographic area by forwarding packets between connected networks, similar to how telephone exchanges connect calls. Switches have multiple input and output ports, can transfer packets from any input to any output, and create the impression that hosts are directly connected even when on different networks. Key issues for switches are limited bandwidth of outputs, contention when more packets arrive than can be delivered, and congestion when buffers fill and packets are discarded.

1. Switching & Forwarding
By Md. Naseem Ashraf
BE/5504/09
A Presentation for Computer Networks
Birla Institute of Technology, Mesra, Extension Center - Patna

2. Where else have we seen this problem
before the advent of computer
networks?
• Limit on the Number of Hosts
• Limit on the size of Geographic Area a
network serves
What was the problem with Directly
Connected Networks?
Answer: Telephone Networks

3. Solution from the Telecommunication
Industries
• Use of a call exchange to switch your call
to the desired destination (Forwarding).
• Switches create an impression that
you’re connected to the receiver of the
call.

4. Caller
• Set on another
network of
cables
elsewhere
Telephone
Exchange
• Is a Switch
with all
networks
connected
Receiver
• Set on
another
network of
cables

5. Switches in Computer Networks
• Computer Networks use Packet Switches.
• No direct connection is required between
hosts.
• A Multi-input, multi-output device which
transfers packets from an input to outputs.
• They maybe servers, computers, satellites etc.
But, Still, What are Switches?

6. Summarizing Forwarding Features of
Switches
• Switches do have a fixed number of inputs &
outputs limiting the number of hosts. But,
why care? Just connect them, switches,
together.
• They can span larger geographic area.

7. Key problems to look at when using
Switches
• They have Finite bandwidth of its outputs.
• Contention:
Arrival Rate of Packets > Delivery Rate of Packets
• Buffering:
The use of storage buffers by switches to keep a certain
amount of input stored to balance contention.
• Congestion:
The loss of data packets when the buffer limit is
exceeded and contention is not controlled; The incoming
packets are discarded too frequently.

8. That’s all for Today, Folks!!
END GAME