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Unformatted text preview: for a des9na9on is the union of all shortest paths G towards the des9na9on – Similarly source tree F 2 4 E 3 10 3 2 4 A 4 B H 1 D 2 2 3 C 16 5 10/29/13 Sink Trees (2) F • Implica9ons: – Only need to use des9na9on 4 to follow shortest paths – Each node only need to send G 3 to the next hop • Forwarding table at a node A – Lists next hop for each des9na9on – Rou9ng table may know more 4 2 E 3 10 2 4 B 1 2 2 H D 3 C 17 Dijkstra’s Algorithm Algorithm: • Mark all nodes tenta9ve, set distances from source to 0 (zero) for source, and ∞ (inﬁnity) for all other nodes • While tenta9ve nodes remain: – Extract N, the one with lowest distance – Add link to N to the shortest path tree – Relax the distances of neighbors of N by lowering any beler distance es9mates 18 6 10/29/13 Dijkstra Comments • Dynamic programming algorithm; leverages op9mality property • Run9me depends on eﬃciency of extrac9ng min cost node • Gives us complete informa9on on the shortest paths to/from one node – But requires complete topology 28 Introduc9on to Computer Networks Distance Vector Rou9ng (§5.2.4) Computer Science & Engineering 7 10/29/13 Topic • How to compute shortest paths in a distributed network – The Distance Vector (DV) approach Here’s my vector! Here’s mine 30 Distance Vector Rou9ng • Simple, early rou9ng approach – Used in ARPANET, and “RIP” • One of two main approaches to rou9ng – Distributed version of Bellman Ford – Works, but very slow convergence aier some failures • Link state algorithms are now typically used in prac9ce – More involved, beler behavior 31 8 10/29/13 Distance Vector Se[ng Each node computes its forwarding table in a distributed se[ng: 1. ...
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This document was uploaded on 04/04/2014.
 Fall '09

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