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Unformatted text preview: CS536: Network Layer Charles Killian Transport Layer 1 Announcements ❒ MidTerm Grading Done! ❍ Pick yours up if you haven’t ❒ Homework Assignments ❍ #3 Ready (due 4/14) – Chapter 4 ❒ Final Project (due 4/30) ❍ Topic due Thursday by email, details online. ❍ ~7 Page survey paper ❍ No original research ❒ Final Exam Review (4/30) Network Layer 42 Network Layer 43 Distance Vector: link cost changes Link cost changes: ❒ node detects local link cost change ❒ updates routing info, recalculates distance vector ❒ if DV changes, notify neighbors “good news travels fast” x z 1 4 50 y 1 At time t , y detects the linkcost change, updates its DV, and informs its neighbors. At time t 1 , z receives the update from y and updates its table. It computes a new least cost to x and sends its neighbors its DV. At time t 2 , y receives z ’s update and updates its distance table. y ’s least costs do not change and hence y does not send any message to z . Network Layer 44 Distance Vector: link cost changes Link cost changes: ❒ good news travels fast ❒ bad news travels slow  “count to infinity” problem! ❒ 44 iterations before algorithm stabilizes: see text Poisoned reverse: ❒ If Z routes through Y to get to X : ❍ Z tells Y its (Z’s) distance to X is infinite (so Y won’t route to X via Z) ❒ will this completely solve count to infinity problem? x z 1 4 50 y 60 Network Layer 45 Comparison of LS and DV algorithms Message complexity ❒ LS: with n nodes, E links, O(nE) msgs sent ❒ DV: exchange between neighbors only ❍ convergence time varies Speed of Convergence ❒ LS: O(n 2 ) algorithm requires O(nE) msgs ❍ may have oscillations ❒ DV : convergence time varies ❍ may be routing loops ❍ counttoinfinity problem Robustness: what happens if router malfunctions? LS: ❍ node can advertise incorrect link cost ❍ each node computes only its own table DV: ❍ DV node can advertise incorrect path cost ❍ each node’s table used by others • error propagate thru network Network Layer 46 Chapter 4: Network Layer ❒ 4. 1 Introduction ❒ 4.2 Virtual circuit and datagram networks ❒ 4.3 What’s inside a router ❒ 4.4 IP: Internet Protocol ❍ Datagram format ❍ IPv4 addressing ❍ ICMP ❍ IPv6 ❒ 4.5 Routing algorithms ❍ Link state ❍ Distance Vector ❍ Hierarchical routing ❒ 4.6 Routing in the Internet ❍ RIP ❍ OSPF ❍ BGP ❒ 4.7 Broadcast and multicast routing Network Layer 47...
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This note was uploaded on 10/24/2009 for the course CS 536 taught by Professor Sonia,f during the Spring '08 term at Purdue.
 Spring '08
 Sonia,F

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