Computer Networks, LAN Switches

Ubiquitessly used in modern ethernet.

Hosts connected by twisted cables to a box called a switch in a closet.

—–Hub repeater is physical layer, all ports are wired together.

—–link layer is a switch. Switch look at sources and destination addresses. host on port 1 to output port 4, at same time port 2 sends to port 3. Two messages at same time, hub does only one message to all ports.

## so what if two hosts send message through switch fabric to same port?! Need buffer to temporarily store frames until they can be sent on inport to outport. Thank you Moorse law

##Also buffers can only hold so many packets so that is how loss occurs.

## full duplex means wire goes out and has input at same time.

Switches need to find the right output port for the destination address in the Ethernet frame. How?

Algorithm Backward Learning. Maps addresses and ports. Ethernet frames contain source address and destination address.

1)Algorithm look at source address.

2)Algorithm Forward to all ports

example A port 1 sends packets to D port 4, D sees a is sourced from port 1 so D now knows A is on port 1. in a situation where there are Multiple Switches B on port 2 and C on port 3 knows A is sending to port 4. So if switch knows source address will send directly to, otherwise switch station will broadcast to all ports. So loops in this topology will get to in next post.

 

 

—-link layer/ Network