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Transcript
Integrated Telecommunication Networks I Departamento de Engenharia Electrotécnica Telecommunications Section Integrated Master in Electrical Engineering and Computers Luis Bernardo November 7, 2009 1st Test Odd Semester Duration: 90 minutes + tolerance (30 minutes) Answer the questions individually and briefly. First limit the responses to the key points, and then at the end, complete them. 1. Assume that for the network represented on the right the routing tables are generated using the link-state algorithm. The network consists of four routers (A-D) and three passive networks (U1-U3). a) Calculate the routing table for node A using the Dijkstra's algorithm. Justify your answer showing all intermediate steps. b) Now imagine that this network represented part of a network of networks (internet), where any node may communicate with any other node. The router A also runs link state protocol at the internet level, having as neighbors (at the internet) the routers R1 and R2. How many entries has the LSA (link state advertisement) packet flooded in the internet, and what are the destination in the LSA packet? How does the router B can get to know the routes received by A from the routing protocol on the internet? 2. Comment the sentence, indicating whether it is true or false: “The broadcast routing algorithm reverse path forwarding can be used to flood packets in a network when the unicast routing table is created using the AODV (Ad-hoc On-demand Distance Vector) protocol.” Justify your answer. 3. When the Chord protocol is used in an unstable network, the finger table may become temporarily out of date with nodes entering and leaving the Chord’s ring. What maintenance procedures are used to update the finger table? What might be the consequences of outdated entries in the finger table? Can it provoke failed resolutions of “successor(key)”? Justify your answer. 4. The congestion is one of the most serious problems that may occur in a packet network. In what kind of network do you think is easier to prevent a congestion situation from occurring: in datagram subnets or in a virtual-circuit subnet? Justify your answer. 5. Differentiated services are one of the most relevant mechanisms used today to ensure quality of service in an IP network. Imagine now that someone decided to implement the service without putting in the ingress routers a traffic shaper/dropper, and letting each network client mark packets freely. Is it possible to provide quality of service guarantees in this network? Justify your answer. 6. In a network of networks (internet), when a packet crosses a network with a very low packet’s maximum length, the multi-protocol router has to fragment the packet. There are two possible approaches to gather the fragments into the original packet: 1) the fragments are recombined at the network’s exit-gateway, 2) the fragments are recombined only on the destination host. Which of the two approaches has the lowest propagation delay end-to-end (takes less time to reach the destination host)? Justify the answer.