Switches and Bridges

Switches and bridges are concerned with connecting Homogeneous network(think Ethernet and 802.11)
They connect links together.

They have two approaches to user the packet header to forward. datagram connectionless and **virtual circuit **(connection orineted).


Every packet contains complete address of the host and just use the forward table. Given a forward table, datagram model’s host can send a packet
anywhere at anytime. It doesn’t need to establish a session.(Unlike virtual circuit).

Virtual circuit

Connection oriented just like TCP. Need to first get state info from the other host. Then transfer.

We need to use virtual circuit identifier VCI to identify a unique at each switch. It will be in the header package.
We also need a incoming interface for this VCI and an outgoing interface for this VCI.
**A potentially different VCI will be used for the outgoing
VCI is unique at the given link(ethernet).

VCI example:
For switch 1 S
incoming interface | incoming VCI | outgoing interface | outgoing VCI|

1 | 5 | 4 | 11 |

For switch 2

incoming interface | incoming VCI | outgoing interface | outgoing VCI|

5 | 11 | 9 | 2 |

Note the outgoing VCI at 1 switch == incoming VCI at another switch.

To send packet, we will use interface + VCI to determine where to switch.


Need to do a round trips to insert VCI entries for each switch along the way.
To do this we need to use global address of the end host.
But after the setup, we only need to use the VCI and the interface.

Learning forward table via spanning tree algo

Used to handle loop situation.

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