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Data Communication and Networks. INSTRUCTIONS TO CANDIDATES. •. This is a SIX (6) hour examination ... The exam paper is 5 pages including this cover page.
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Final Examination
Data Communication and Networks
In answering the following questions use the following network conguration Each no de in the network represents a router and the weights of the arcs represent the values of a cost metric used by a distance vector routing scheme
a Construct and write down the routing vector for no de C
b Write out the contents of the routing vectors sent to router F Show how these vectors are used to computer a new set of entries for Fs routing vector
c If the link b etween A and B fails show the eects on the routing vectors of the no des A B and F in the up date cycle that immediately follows the failure
d List three common routing metrics used in distance vector routing
Discuss using appropriate diagrams the op eration of the standard TCP way hand shake used to setup a connection b etween two Transp ort level entities
If the underlying network is not reliable packets can b e lost during connection setup For each of the p ossible situations listed b elow draw a picture that shows the situation describ e the problem that arises and discuss the techniques that can b e used to prevent proto col failure
a The connection request is lost
b The ACK packet from the receiver is lost
c A connection request stored in the network is suddenly delivered to a destination host after the connection to which it refers has b een used and terminated
Consider the problem of managing trac in a TCP connection that consist of a wireless and optical bre section Discuss how the characteristics of the dierent sections of the network aect the interpretation of metrics that are used to measure congestion Describ e two approaches to resolving the issues that arise in this situation and comment on their elegance and eciency
Explain what framing is and describ e two framing metho ds Give the advantages and disadvantages of these metho ds
Framing is used in conjunction with payload stung What is stung Give an example of character and bit stung and comment on their relative eciencies in terms of data transmission overhead
Dene RTT An estimate of RTT is used to set packet timeout counters in the sender side of a connection Explain how estimates of RTT can b e misleading and describ e a metho d used to resolve this problem
Explain the gobackn metho d for managing the retransmission of lost or corrupt PDUs Describ e another technique that can b e used to solve this problem Contrast the eciency of the techniques in terms of buer utilisation when transmitting data over a high bandwidth and high latency connection
Describ e the theoretical basis of CRC error detection Show how the CRC is computed given the following parameters Give the bit pattern for the nal transmitted frame including the CRC
G x x^ x^ x F r ame
Describ e the physical characteristics of an optical bre and explain how it can b e used to transmit data
Comment on the jointing techniques that are used to connect bres and the p ossible loss of signal that results
Describ e how data trac can b e multiplexed onto an optical bre and discuss any problems that may arise What issues need to b e considered
Optical bre networks are replacing copp er networks at a rapid rate Why is this happ ening and what are the b enets to telecommunications companies of doing this
