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SEM 2 2015/2016

MTN3023Computer Networking

Exercise and Homework Chapter 1

Name : EMMA SAFWANAH BINTI SAHIIN

Matric N!m"er :#$%1&1%'($&)

*ect!re +ro!p: #

*ect!rer: Mr Na,re "in A"d!- ashid

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R12. What advantage does a circuit-switched network have over a packet-switched network?

What advantages does TDM have over FDM in a circuit-switched network?

 Answer: ircuit-switched networks have a huge overhead that is created to !ake sure that

!essage is de"ivered. #n contrast the packet-switched networks are ver$ %uick &ut do

not o''er the guarantee. TDM a""ows a"" the &andwidth to &e used 'or a short period o' 

ti!e. This is ver$ versati"e 'or &urst packet sending.

R1(. )ow "ong does it take a packet o' "ength 1*+++ &$tes to propagate over a "ink o' distance

2*,++ k!* propagation speed 2., 1+( !s* and trans!ission rate 2 M&ps? More genera""$* how

"ong does it take a packet o' "ength / to propagate over a "ink o' distance d* propagation speed

s* and trans!ission rate R &ps? Does this de"a$ depend on packet "ength? Does this de"a$

depend on trans!ission rate?

10 )ow "ong does it take a packet o' "ength 1*+++ &$tes to propagate over a "ink o' distance

2*,++ k!* propagation speed 2., 1+( !s* and trans!ission rate 2 M&ps?

 Answer: 2,++1+3402.,1+3(05+.+1s 5 1+!s

20 More genera""$* how "ong does it take a packet o' "ength / to propagate over a "ink o' 

distance d* propagation speed s* and trans!ission rate R &ps? Answer: ds

40 Does this de"a$ depend on packet "ength? Answer: 6o

70 Does this de"a$ depend on trans!ission rate? Answer: 6o

R18. 9uppose )ost A wants to send a "arge 'i"e to )ost . The path 'ro! )ost Ato )ost has

three "inks* o' rates R1 5 ,++ k&ps* R2 5 2 M&ps* and R4 5 1 M&ps.

a0 Assu!ing no other tra''ic in the network* what is the throughput 'or the 'i"e trans'er? Answer: ,++kp&s

&0 9uppose the 'i"e is 7 !i""ion &$tes. Dividing the 'i"e si;e &$ the throughput* rough"$

how "ong wi"" it take to trans'er the 'i"e to )ost ? Answer: 71+3

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=p"ore propagation de"a$ and trans!ission de"a$* two

centra" concepts in data networking. onsider two hosts* A and * connected &$ a sing"e "ink o' 

rate R &ps. 9uppose that the two hosts are separated &$ ! !eters* and suppose the

propagation speed a"ong the "ink is s !eterssec. )ost A is to send a packet o' si;e / &its to

)ost .

a. >press the propagation de"a$* dprop* in ter!s o' ! and s. Answer: dprop 5 !s seconds

&. Deter!ine the trans!ission ti!e o' the packet* dtrans* in ter!s o' / and R. Answer: dtrans 5 /R seconds

c. #gnoring processing and %ueuing de"a$s* o&tain an e>pression 'or the end to-end

de"a$. Answer: dend-to-end 5 !s @ /R0 second

d. 9uppose )ost A &egins to trans!it the packet at ti!e t 5 +. At ti!e t 5 d trans* where is

the "ast &it o' the packet? Answer: The &it is ust "eaving )ost A.

e. 9uppose dprop  is greater than d trans. At ti!e t 5 dtrans* where is the 'irst &it o' the

packet? Answer: The 'irst &it is in the "ink and has not reached )ost .

'. 9uppose dprop is "ess than dtrans. At ti!e t 5 dtrans* where is the 'irst &it o' the packet? Answer: The 'irst &it has reached )ost .

g. 9uppose s 5 2., 1+(* / 5 12+ &its* and R 5 ,< k&ps. Find the distance ! so that

dprop e%ua"s dtrans. Answer: Want

M 5 /R s 5 12+,1+42.,>1+(0 5,4< k!

=2,. 9uppose two hosts* A and * are separated &$ 2+*+++ ki"o!eters and are connected &$ a

direct "ink o' R 5 2 M&ps. 9uppose the propagation speed over the "ink is 2., 1+ ( !eterssec.

a. a"cu"ate the &andwidth-de"a$ product* R dprop. Answer: 1

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&. onsider sending a 'i"e o' (++*+++ &its 'ro! )ost A to )ost . 9uppose the 'i"e is

sent continuous"$ as one "arge !essage. What is the !a>i!u! nu!&er o' &its that

wi"" &e in the "ink at an$ given ti!e? Answer: 1a!p"e* an i!age or a !usic 'i"e0 into s!a""er packets

and sends the packets into the network. The receiver then reasse!&"es the packets &ack into

the origina" !essage. We re'er to this process as !essage seg!entation. Figure 1.2B i""ustrates

the end-to-end transport o' a !essage with and without !essage seg!entation. onsider a

!essage that is ( 1+< &its "ong that is to &e sent 'ro! source to destination in Figure 1.2B.

9uppose each "ink in the 'igure is 2 M&ps. #gnore propagation* %ueuing* and processing de"a$s.

a. onsider sending the !essage 'ro! source to destination without !essage

seg!entation. )ow "ong does it take to !ove the !essage 'ro! the source host to the

'irst packet switch? Ceeping in !ind that each switch uses store-and-'orward packet

switching* what is the tota" ti!e to !ove the !essage 'ro! source host to destination

host?

 Answer: #t wou"d take 7 seconds (M&7M&ps0 to reach the 'irst switch* and 12 seconds

to co!p"ete

&. 6ow suppose that the !essage is seg!ented into (++ packets* with each packet &eing

1+*+++ &its "ong. )ow "ong does it take to !ove the 'irst packet 'ro! source host to the

'irst switch? When the 'irst packet is &eing sent 'ro! the 'irst switch to the second

switch* the second packet is &eing sent 'ro! the source host to the 'irst switch. At what

ti!e wi"" the second packet &e 'u""$ received at the 'irst switch?

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 Answer: 1++++&its2++++++&ps 5 .++,sec or ,!s 'or the 'irst packet to reach the 'irst

switch* and 2+!s 'or the second switch to &e recieved

c. )ow "ong does it take to !ove the 'i"e 'ro! source host to destination host when

!essage seg!entation is used? o!pare this resu"t with $our answer in part a0 and

co!!ent.

 Answer: B88 .++, 5 4.88,sec* as opposed to 12 seconds* so it wou"d &e &etter to

seg!ent and save ti!e

d. #n addition to reducing de"a$* what are reasons to use !essage seg!entation?

 Answer: #t cause 'ree up space. Ma$&e to reduce packet "oss

e. Discuss the draw&acks o' !essage seg!entation.

 Answer: ou"d cause congestion with a"" o' the e>tra packets