Question $3[25]$

a$.$ What is the typical size of the header for an IPv$4$ datagram? $[1]$

b$.$ How is the $16-$bit IP checksum field calculated? $[2]$

c$.$ How is the TTL field used on the Internet? What purpose does it serve? $[2]$

d$.$ Which field is used for IP congestion control? How does it work? $[2]$

e$.$ Why is datagram fragmentation not an issue in IPV$6?$ How is this achieved? $[2]$

f$.$ A message of $2300$ bytes is to be transmitted over $2$ IP networks. The first has an MTU of $2300$ bytes and the second network has an MTU of $1500$ bytes. How many fragments are expected at the destination? Show the values of the following IP header fields and flags for each fragment on the two networks: Packet length, MF$,$ Fragment Offset and Identification. $[7]$

Page $3$ of $5$

Degree and Diploma Examinations: June $2018$ Introduction to Data Communication and Networking: CSI $21$M$2$

g$.$ What does ICMP stand for? Briefly explain the key areas of functionality for ICMP giving an example. $[3]$

h$.$ Convert the MAC address CC$-12-$DE$-4$A$-$BD$-88$ into the corresponding binary digits. $[3]$

i$.$ Given the following subnet masks determine the number of a$)$ host bits available and b$)$ the number hosts available. $[3]$

i$.,255\mathrm{.}255\mathrm{.}240\mathrm{.}0$

ii$.,255\mathrm{.}255\mathrm{.}255\mathrm{.}0$

iii. $,255\mathrm{.}255\mathrm{.}255\mathrm{.}128$

Question $4[25]$

a$.$ What is the role of the transport layer in the TCP$/$IP protocol stack? $[2]$

b$.$ Describe the functionality provided by the Transmission Control Protocol $($TCP$)[2]$

Consider the TCP connection mechanism.

c$.$ What mechanism is used to set up a TCP connection? $[1]$

d$.$ Why is the mechanism needed? $[2]$

e$.$ Outline how the mechanism works. $[3]$

For each of the following pair of terms, define each term, and clarify the key difference$($s$)$ between the two terms. Be clear and concise.

f$.$ Flow Control and Congestion Control $[4]$

g$.$ What is the role of a window in TCP$?[1]$

The output on the next page shows a tcpdump trace $($similar to Wireshark$)$ of the network packets exchanged between two computers on a network. Use your knowledge of TCP and IP to answer the following questions.

h$.$ What application$-$layer protocol is $($likely$)$ being used for this conversation? $[1]$

i$.$ What is the IP address of the client? $[1]$

j$.$ What is the Round$-$Trip Time $($RTT$)$ between the client and the server? $[1]$

k$.$ How much application$-$layer payload is in the client's first data packet? $[1]$

I. What is the TCP Initial Sequence Number $($ISN$)$ proposed by the server? $[1]$

m$.$ What is the Maximum Transmission Unit $($MTU$)$ size on this network? $[1]$

$n.$ What is the Maximum Segment Size $($MSS$)$ used by the server's TCP$?[1]$

o$.$ In total, how many bytes of application$-$layer data does the server send? $[1]$

p$.$ Which end initiates the closing of this TCP connection: client or server? $[1]$

q$.$ In total, how long did this conversation last? $[1]$

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Degree and Diploma Examinations: June $2018$

Introduction to Data Communication and Networking: CSI $21$M$2$

Time$($s$)$ SourceIP DestinationIP Size TCP SPort DPort SeqNum AckNum Window Flags

$29\mathrm{.}884192\mathrm{.}168\mathrm{.}1\mathrm{.}9,136\mathrm{.}159\mathrm{.}5\mathrm{.}1744$ TCP $1035,80133227,0$ win: $32768S$

$29\mathrm{.}886,136\mathrm{.}159\mathrm{.}5\mathrm{.}17,192\mathrm{.}168\mathrm{.}1\mathrm{.}9,44$ TCP $80,1035,3310607972,133228$ win: $24820$ SA

$29\mathrm{.}888192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $1035,80133228,3310607973$ win: $32768A$

$29\mathrm{.}948192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}17418$ TCP $1035,80133228,3310607973$ win: $32768$ PA

$29\mathrm{.}952136\mathrm{.}159\mathrm{.}5\mathrm{.}17192\mathrm{.}168\mathrm{.}1\mathrm{.}940$ TCP $80,1035,3310607973,133606$ win: $24820$ A

$29\mathrm{.}955136\mathrm{.}159\mathrm{.}5\mathrm{.}17192\mathrm{.}168\mathrm{.}1\mathrm{.}9329$ TCP $8010353310607973,133606$ win: $24820$ PA

$29\mathrm{.}959136\mathrm{.}159\mathrm{.}5\mathrm{.}17192\mathrm{.}168\mathrm{.}1\mathrm{.}91500$ TCP $8010353310608262133606$ win: $24820$ A

$29\mathrm{.}960136\mathrm{.}159\mathrm{.}5\mathrm{.}17192\mathrm{.}168\mathrm{.}1\mathrm{.}91500$ TCP $8010353310609722133606$ win: $24820$ PA

$29\mathrm{.}962192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $1035801336063310609722$ win: $31019$ A

$29\mathrm{.}970136\mathrm{.}159\mathrm{.}5\mathrm{.}17192\mathrm{.}168\mathrm{.}1\mathrm{.}9,1500$ TCP $80,10353310611182133606$ win: $24820$ A

$29\mathrm{.}972136\mathrm{.}159\mathrm{.}5\mathrm{.}17192\mathrm{.}168\mathrm{.}1\mathrm{.}91500$ TCP $801035,3310612642133606$ win: $24820$ A

$29\mathrm{.}972192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $1035,801336063310612642$ win: $28099$ A

$29\mathrm{.}973136\mathrm{.}159\mathrm{.}5\mathrm{.}17,192\mathrm{.}168\mathrm{.}1\mathrm{.}9,429$ TCP $80,1035,3310614102133606$ win: $24820$ FA

$29\mathrm{.}974192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $103580133606,3310614492$ win: $26250A$

$30\mathrm{.}072192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $1035801336063310614492$ win: $26250$ A

$30\mathrm{.}136192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $103580133606,3310614492$ win: $31370$ A

$30\mathrm{.}141192\mathrm{.}168\mathrm{.}1\mathrm{.}9136\mathrm{.}159\mathrm{.}5\mathrm{.}1740$ TCP $1035801336063310614492$ win: $0$ F

End