tailieunhanh - Lecture Digital communication systems - Lecture 19

The following will be discussed in this chapter: Investigating mass communication effects, effects on knowledge and attitudes, media effects on behavior: a short history, the impact of televised violence, encouraging prosocial behavior, other behavior effects, research about the social effects of the internet, communication in the future: social impact. | 11 19 12 INTRODUCTION TO EECS n DIGITAL COMMUNICATION SBSTEMS Fall 2012 Lecture 19 addressing forwarding routing distance-vector routing link-state routing Today no failures Fall 2012 Lecture 19 Slide 1 The Problem Distributed Methods for Finding Paths in Networks Addressing how to name nodes - Unique identifier for global addressing - Link name for neighbors Forwarding how does a switch process a packet Routing building and updating data structures to ensure that forwarding works Functions of the network layer Fall 2012 Lecture 19 Slide 2 Forwarding Shortest Path Routing Switch Core function is conceptually simple - lookup dst_addr in routing table returns route . outgoing link for packet - enqueue packet link_queue - send packet along outgoing link And do some bookkeeping before enqueue - Decrement hop limit TTL if 0 discard packet - Recalculate checksum in IP header checksum Fall 2012 Lecture 19 Slide 3 Each node wants to find the path with minimum total cost to other nodes - We use the term shortest path even though we re interested in min cost and not min hops Several possible distributed approaches - Vector protocols esp. distance vector DV - Link-state protocols LS Fall 2012 Lecture 19 Slide 4 1 11 19 12 Distributed Routing A Common Plan Determining live neighbors - Common to both DV and LS protocols - HELLO protocol periodic Send HELLO packet to each neighbor to let them know who s at the end of their outgoing links Use received HELLO packets to build a list of neighbors containing an information tuple for each link timestamp neighbor addr link Repeat periodically. Don t hear anything for a while link is down so remove from neighbor list. Advertisement step periodic - Send some information to all neighbors - Used to determine connectivity costs to reachable nodes Integration step - Compute routing table using info from advertisements - Dealing with stale data Fall 2012 Lecture 19 Slide 6 Distance-Vector Routing DV .