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Unformatted text preview: CS536: Network Layer Charles Killian Transport Layer 1 Announcements MidTerm Grading Done! Pick yours up if you havent 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 (Zs) distance to X is infinite (so Y wont 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 nodes 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 Whats 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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 Spring '08
 Sonia,F

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