Ethernet Medium Access Control Protocol A B C

Ethernet (Medium Access Control Protocol) A B C D q A single shared comm. Line v Used by all (each check if “free” or “busy”) v Message is broadcasted to all q Message has v “destination address” and “message-body” Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 1

Ethernet Protocol (how it works) A B C D My message!! Process it… D message Not mine. Discard it… q Node A wants to send something to node D v Message’s “destination address” = D v Message is broadcasted to all… q Every Machine checks v If not mine, then discard; else process message; Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 2

Ethernet Protocol (Collision) A B C D q What if shared line is busy when node B wants to send? v Eg: If node A is currently sending…. v Node B waits… and send after node A is done. q What if many nodes are waiting… v And simultaneously send when node A is done! Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 3

LAN How to Resolve Collisions !! q Length of collision delay is randomly generated. q So, different delays for different waiting nodes…. Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 4

LAN (MACP – details from text) Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 5

LAN (MACP – details from text) Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 6

LAN (MACP) Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT

WAN Network…. q Paths from B to F? q What if node C is faulty? Leong. HW, So. C, NUS © Leong Hon Wai, 2003 -2008 (UIT 2201: Networks) Page 8