Download Integrated Telecommunication Networks I

Integrated Telecommunication Networks I
Electrical Engineering Department
Telecommunications Section
Integrated Master in Electrical Engineering and Computers
Luis Bernardo
February 3, 2010
2nd Exam
Odd Semester
Duration: three hours + 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 the distance-vector routing protocol with poison reverse is used on the
network depicted on the right to generate the routing tables. The network consists of
five routers (A to E) interconnected by the seven connections represented.
a) Calculate the content of the distance vectors sent by node B to its neighbors, after the
routing tables are stabilized. Justify your answer showing the routing table of node B,
and the method used to calculate the vectors presented.
b) Imagine now that the router B fails with a power failure and assume that the routers exchange vectors synchronized
periodically. After how many vector exchanges will the new routing tables stabilize? Or, will the routing tables
count to infinity. Justify your answer.
2. Assume now that the link state routing protocol is used to calculate the unicast and multicast routing tables for the
network shown in the previous question. What is the content of the multicast routing table on router B for the
address associated to group G, which includes all routers (A to E)? Justify your answer. NOTE: If you need to
calculate a spanning tree, you do not need to present the tree’s calculation.
3. Please list the main innovative features of AODV (Ad hoc On-demand Distance Vector) protocol over the original
distance-vector routing protocol.
4. A client is connected to the ISP (Internet Service Provider) through a traffic shapper. It consists of two modules: a
token bucket (TB) followed by a leaky bucket (LB). The bitrate of the connection link is 50 Mbit/s. It was
negotiated a service level agreement (SLA) with an average rate of 10Mbit/s, allowing peaks of traffic with a
bitrate of 25 Mbit/s and with a duration of 20ms. Define the value of the parameters of TB and LB in order to
satisfy the SLA negotiated. Justify your answer.
5. A weighted fair queue (WFQ) algorithm is used on a router with five input lines (A,
B, C, D and E) and an output line O. Assume that the weights used in WFQ
algorithm for each line is: : wA= 1, wB= 4, wC= 3, wD= 2 e wE= 1. The unit of
measurement for the WFQ algorithm is the Kilo byte. Assume that there are five
messages waiting to be transmitted, as depicted in the figure on the right. What will
be the order in which they will be transmitted on the line O? Justify your answer.
A
B
C
D
E
2K
5K
4K
3K
2K
O
6. Comment the sentence, indicating whether it is true or false: "In a network of networks (internet) a datagram-based
approach reduces the amount of RAM use in the multi-protocol routers compared to a virtual circuit based
approach." Justify your answer.
7. What is the ARP (Address Resolution Protocol)? Describe how it works, using an example.
8. Imagine that there are two users connected to two separate private networks, and the NAT (Network Address
Translation) routers used in these private networks are of the type Full Cone. Can you have an application running
on one network and sending an UDP packet to a server located in the other private network without this UDP
packet going through any server / proxy with a public IP? Justify your answer by describing what hinders
communication, or all the steps that are needed to allow the communication.
Please turn the page
9. If you want to receive IPv4 multicast traffic in an application, the application creates a multicast socket and
associates it to a multicast (class D) IP address. If the network has a multicast routing protocol enabled, how do the
multicast routers know which IP multicast addresses are associated to the applications running on a network?
Identify what is the protocol used for this purpose and describe its operation.
10. One solution commonly proposed to increase the throughput in an IP network is the use of MPLS (MultiProtocol
Label Switching). What is MPLS? Why can it improve the network
performance?
...
11. Assume that the sequence of segments represented on the right is consistent
with the TCP protocol and that A is sending a response segment for each data
segment received. The MTU (Maximum Transmission Unit) is 1kByte.
Answer these two questions: i) Do all four segments of data were correctly
received by A? ii) State when was a read operations (read (n)) invoked by the
application in A, representing the number of bytes read in each operation.
A
Data (1K), seq=6k, ack=2k, win=1k
ack=7k, win=4k
Data (1K), seq=7k, ack=2k, win=1k
ack=8k, win=5k
Data (1K), seq=8k, ack=2k, win=1k
ack=9k, win=4k
Data (1K), seq=9k, ack=2k, win=1k
ack=9k, win=5k
...
12. The aim is to use a TCP connection to send uncompressed audio (64Kbit/s)
through a wireless network with a high error rate and a propagation time also
high. Assuming that there are never congestion problems, which of the following changes could improve the
reception quality of the audio on the network: A) Turn off the slow-start algorithm? B) Turn off the Nagle
algorithm? or C) Increase the size of the TCP receive buffer? Justify your answer and identify the option that
further improves the data rate.
13. Please list what were the main improvements of the standard AAL 2 (ATM Adaptation Layer) from the previous
standard (AAL 1), which lead to the replacement of AAL 1 by the AAL 2.