Data Link Layer Ethernet, Collisions and Duplex/Auto-Negotiation

What does MAC stand for?

Media Access Control

What is MAC all about?

Broadcast networks, Multiple access protocols and n > 1 senders over one shared channel

How can collision domains be identified?

• Only half duplex

• All components see the same signals on the line

• If two or more stations transmit at the same time, a collision happens

What is the difference between a repeater/hub and a switch/bridge?

• Repeater/Hub: Layer 1, connects stations/segments in the same collision domain

• Switches/Bridges:
  

  • Connect different collision domains with each other

  • Do not propogate collisions

  • Do propogate broadcasts

What should be the minimum transmission delay in comparison to the propagation delay so that collisions can be detected?

transmission delay > 2 * propagation delay

Why can collision domains empose restrictions on the maximum cable length?

Due to the transmission delay -> propagation delay dilemma

What is the solution do this dilemma

Do not use technologies which have to deal with collisions:

• Full duplex and only two end-points

• Always use switches and never repeaters/hubs

What is required for full duplex ethernet?

• Only Bridges/Switches

• Matching cabling:
  

  

What happens in the scenario below, where the server with a 1 GBit/s port talks to a host with a 10 MBit/s port?

• Buffer overflow at the port to the host

• Probably some higher layer will notice this and send slower (TCP)

What is the basic principle of auto-negotation?

Two hosts can communicate via special packets that contain information about their transmission speed