1. LeongHW, SoC, NUS (UIT2201: Networks) Page 1© Leong Hon Wai, 2003-2008 (MACP) Medium Access Control Protocol

2. LeongHW, SoC, NUS (UIT2201: Networks) Page 2© Leong Hon Wai, 2003-2008 (MACP) Medium Access Control Protocol

3. LeongHW, SoC, NUS (UIT2201: Networks) Page 3© Leong Hon Wai, 2003-2008 Ethernet (Medium Access Control Protocol)  A single shared comm. Line  Used by all (each check if “free” or “busy”)  Message is broadcasted to all  Message has  “destination address” and “message-body” ABCD

4. LeongHW, SoC, NUS (UIT2201: Networks) Page 4© Leong Hon Wai, 2003-2008 Ethernet Protocol (how it works)  Node A wants to send something to node D  Message’s “destination address” = D  Message is broadcasted to all…  Every Machine checks  If not mine, then discard; else process message; ABCD My message!! Process it… Not mine. Discard it… Dmessage

5. LeongHW, SoC, NUS (UIT2201: Networks) Page 5© Leong Hon Wai, 2003-2008 Ethernet Protocol (Collision)  What if shared line is busy when node B wants to send?  Eg: If node A is currently sending….  Node B waits… and send after node A is done.  What if many nodes are waiting…  And simultaneously send when node A is done! ABCD

6. LeongHW, SoC, NUS (UIT2201: Networks) Page 6© Leong Hon Wai, 2003-2008 Collision Resolution  Length of collision delay is randomly generated.  So, different delays for different waiting nodes…. How to Resolve Collisions !!

7. LeongHW, SoC, NUS (UIT2201: Networks) Page 7© Leong Hon Wai, 2003-2008 [SG] Notes

8. LeongHW, SoC, NUS (UIT2201: Networks) Page 8© Leong Hon Wai, 2003-2008 WAN Network….  Paths from B to F?  What if node C is faulty?

9. LeongHW, SoC, NUS (UIT2201: Networks) Page 9© Leong Hon Wai, 2003-2008 WAN, LAN, Router combination (1)

10. LeongHW, SoC, NUS (UIT2201: Networks) Page 10© Leong Hon Wai, 2003-2008 WAN, LAN, Router combination (2)