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Switching

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A hub simulates a shared medium meanwhile a switch simulates a bridged LAN while each segment contains 1 computer only.

When a hub is used, only 1 pair of computers can talk at a time.
When a switch is used, any number of pairs of computers can talk at the same time.

Combining Switches and Hubs

To reduce the cost, a number of computers can be connected to distributed hubs which later can be connected to a switch.

Bridging and Switching with other Technologies

These devices are also available for other technologies like: - FDDI - Token Ring

WAN Technologies and Routing

The LAN cannot be arbitrarily expanded.
We need other technologies to overcome the distances.

Characterization of Networks

There are 3 characteristics of a network:

Local Area Network

It is used in single building.

Metropolitan Area Network

it is used in single city

Wide Area Network

It is used over country or even continental levels.

Packet Switches

A packet switch consists of: 1. Network Interfaces 2. Memory 3. Program dedicated for function switching

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Packet Switches can connect to other Packet Switches or computers.
The speed between the switches is faster as compared to connections between a packet switch and a computer.

Packet Switches as a Building Blocks

Many packet switches can be connected together to form a WAN.
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Store and Forward

The packet switch contains memory which holds data on queue in case there is traffic.
After the traffic is low, it then forwards data to other packet switches or computers.

Physical Addressing in a WAN

  1. The data is transmitted in packets equivalent to frames.
  2. Each packet has a format with header.
  3. The packet header includes destination and source addresses.
  4. Many WANs use hierarchical addressing for efficiency. One part of address identifies destination switch. Other part of address identifies port on switch.
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Next Hop Forwarding

  1. If the destination is local computer, packet switch delivers computer port.
  2. If the destination is attached to another switch, this packet switch forwards to next hop through connection to another switch.
  3. The choice of another switch is based on destination address in packet.