P-Persistent CSMA: (for slotted channels) retry immediately with probability p when channel becomes idle (may cause instability)
Non-persistent CSMA: (for nonslotted channels) retry after random interval
human analogy: don’t interrupt others!
CSMA collisions collisions can occur: propagation delay means two nodes may not hear each other’ transmission collision: entire packet transmission time wasted spatial layout of nodes along ethernet note: role of distance and propagation delay in determining collision prob.
look up net. address of B, find B on same net. as A
link layer send datagram to B inside link-layer frame
B’s MAC addr A’s MAC addr A’s IP addr B’s IP addr IP payload datagram frame frame source, dest address datagram source, dest address 184.108.40.206 220.127.116.11 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 22.214.171.124 A B E
Network Architecture Internet ATM ATM ATM ATM Service Model best effort CBR VBR ABR UBR Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no Congestion feedback no (inferred via loss) no congestion no congestion yes no Guarantees ?