Question

Could i please have assistance with the following.

A) TCP/IP protocol stack, how does a switch differ from a hub?

B) How does a switch/bridge know what station is on a given port?

C) What does a switch/bridge do if it does not know the out-going port of a destination MAC address?

D) How is a token ring similar to a Master-and-slave or polling channel access protocol?

Answer 1

a)
Hubs operates at layer-1(physical layer) while switch operates at layer-2(data link layer) or layer-3(network layer) of OSI model. Hubs transfers data to all the ports which are connected to it while switch is an intelligent device which transfers data only to the required destination and decreases traffic. As hub transfers data to all the ports, there is so much of traffic. Hubs work in half duplex mode whereas switch in full duplex mode.

b)
A Switch/Bridge does an operation which is called "learning". In this operation, it observes the headers of received Ethernet frames. By examining the MAC source address of each received frame it records the port on which it was received, In this way it learns which addresses belong to the computers connected via each port. That is why it is called intelligent devices.

The learned addresses are stored in a table with each port number. Once this table has been setup, the Switch/Bridge examines the destination address of all received frames, it then looks in the table to see if a packet with a source address matching the current destination address is present or not.
In this process we can come accross with 2 scenarios.
1.If the address is not found
2.If the address is found. Even after the address is found. There are 2 cases. i)port number is already associated. ii)port number is not associated.

1.If the address is not found:
It means that such frame has not been received from the source at all or this information has been deleted from the table due to restart of the device or shortage of memory. So, in this scenario as the Switch/Bridge does not know the port number. It sends the frame to all receivers. This process is called as flooding. By this it finds out the port number.

2.If the address is found.
i)port number is already associated: There will be no problem in this case. It directly uses the information.
ii)port number is not associated: The frame is forwarded to the address and gets the port number.

c)
In master-slave polling, slave always renders the services from the master but in token ring, a node get rendered only when it holds the token.