Download 1. Assume that for the network represented on the right the routing

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 When the Chord protocol is used in an unstable network, the finger table may become temporarily out of
date with nodes entering and leaving the Chord’s ring.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 What might be the consequences of outdated entries in the finger table?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.