Chapter 5 Link Layer and LANs Computer Networking: A Top Down Approach Featuring the Internet , 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004.
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If someone else is talking – stop talking (collision detection)
CSMA collisions collisions can still occur: propagation delay means two nodes may not hear each other’s transmission collision: entire packet transmission time wasted spatial layout of nodes note: role of distance & propagation delay in determining collision probability
used to get datagram from one interface to another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses and ARP Each adapter on LAN has unique LAN address Broadcast address = FF-FF-FF-FF-FF-FF = adapter 1A-2F-BB-76-09-AD 58-23-D7-FA-20-B0 0C-C4-11-6F-E3-98 71-65-F7-2B-08-53 LAN (wired or wireless)
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 ?
forwards packets to outgoing interface based only on label value (don’t inspect IP address)
MPLS forwarding table distinct from IP forwarding tables
signaling protocol needed to set up forwarding
forwarding possible along paths that IP alone would not allow (e.g., source-specific routing) !!
use MPLS for traffic engineering
must co-exist with IP-only routers
MPLS forwarding tables R1 R2 D R3 R4 R5 0 1 0 0 A R6 in out out label label dest interface 10 A 0 12 D 0 1 0 8 A 1 in out out label label dest interface 6 - A 0 in out out label label dest interface 10 6 A 1 12 9 D 0 in out out label label dest interface 8 6 A 0