TAILIEUCHUNG - Lecture Digital communication systems - Lecture 20

The learning objectives for this chapter include: distinguish among the types of informal controls on the media, explain the most important ethical principles, explain what the standards departments and performance codes are, discuss the relationship between the media and their advertisers vis-à-vis ethical practices, understand the pros and cons of pressure groups. | 11 26 12 INTRODUCTION TO EECS n DIGITAL COMMUNICATION SBSTEMS Fall 2012 Lecture 20 Failure-resilient Routing Fall 2012 Lecture 20 Slide 1 Failures Problems Links and switches could fail - Advertisements could get lost - Routing loop A sequence of nodes on forwarding path that has a cycle so packets will never reach destination - Dead-end route does not actually reach destination - Loops and dead-ends lead to routes not being valid Solution - HELLO protocol to detect neighbor liveness - Periodic advertisements from nodes - Periodic integration at nodes - Leads to eventual convergence to correct state see Chapter 18 Fall 2012 Lecture 20 Slide 2 Routing Loop in Link-State Protocol B to D is via A. Link AD fails. A s LSA to B is lost. A now uses B to get to D. But B continues to use A. Routing loop Must wait for eventual arrival of correct LSAs to fix loop. Fall 2012 Lecture 20 Slide 3 Distance-Vector Pros Cons and Loops Simple protocol Works well for small networks - Works only on small networks Suppose link AC fails. When A discovers failure it sends E cost INFINITY to B. B advertises E cost 2 to A A sets E cost 3 in its table Now suppose link BD fails. B discovers it then sets But what if A had advertised to B before B advertised to A E cost INFINITY. Sends info to A A sets E cost INFINITY. Fall 2012 Lecture 20 Slide 4 1 11 26 12 Fixing Count to Infinity with Path Vector Routing In addition to or instead of reporting costs advertise the path discovered incrementally by the Bellman-Ford update rule Called path-vector Modify Bellman-Ford update with new rule a node should ignore any advertised route that contains itself in the advertisement Path Vector Routing Fall 2012 Lecture 20 Slide 5 l1 l2 -ĨÃĨE ACE CE l3 l2 bde l2 l1 BDE DE 13 11 To reach E come this way CEi Path E E V To reach E come this way l2 path E For each advertisement run integration step - . pick shortest cheapest quickest etc. Ignore advertisements with own address in .

• Kĩ thuật Viễn thông
• Communication systems
• Digital communication systems
• Digital communication
• Multiuser communication
• Multicarrier system
• Adaptive equalization
• Filter channel
• communication systems research
• communication applications
• electronic media
• communication solutions
• systems management