lec-29 - What's Next. Network Layer Network layer service...

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18 Oct 2008  BITS C481 (Computer Networks) 1 What’s Next… Network Layer Network layer service models (Done!!!) Forwarding versus routing (Done!!!) How a router works (Done!!!) Internet protocol (Done!!!) Routing (path selection) Algorithms Dijkstra’s algorithm Distance Vector (Today!!!) Hierarchical Routing Routing Protocols RIP BGP OSPF Multicast Routing

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18 Oct 2008  BITS C481 (Computer Networks) 2 Distance Vector Algorithm  Bellman-Ford Equation (dynamic programming) Define d x (y) := cost of least-cost path from x to y Then d x (y) = min {c v (x,v) + d v (y) } where min is taken over all neighbors v of x
18 Oct 2008  BITS C481 (Computer Networks) 3 Bellman-Ford example  u y x w v z 2 2 1 3 1 1 2 5 3 5 Clearly, d v (z) = 5, d x (z) = 3, d w (z) = 3 d u (z) = min {  c(u,v) + d v (z),   c(u,x) + d x (z),  c(u,w) + d w (z) }          = min { 2 + 5 1 + 3,  5 + 3}  = 4 Node that achieves minimum is next hop in shortest path  forwarding  table B-F equation says:

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18 Oct 2008  BITS C481 (Computer Networks) 4 Distance Vector Algorithm  D x (y) = estimate of least cost from x to y Node x knows cost to each neighbor v: c(x,v) Node x maintains distance vector D x = [D x (y): y є N ] Node x also maintains its neighbors’ distance vectors For each neighbor v, x maintains D v = [D v (y): y є N ]
18 Oct 2008  BITS C481 (Computer Networks) 5 Distance vector algorithm (4)

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This note was uploaded on 07/20/2009 for the course CONPUTER S BITS C481 taught by Professor Prof.virendersinghshekhawat during the Fall '08 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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lec-29 - What's Next. Network Layer Network layer service...

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