Student ID Department/Year. Final Examination. Introduction to Computer Networks Class#: 901 E31110 Fall :30-11:10 Tuesday January 12, 2010

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1 Nam Stunt ID Dpartmnt/Yar Final Examination Introution to Computr Ntworks Class#: 901 E31110 Fall :30-11:10 Tusay January 12, 2010 Prohiit 1. You ar not allow to writ own th answrs using pnils. Us only lak- or lu-ink pns. 2. You ar not allow to ra ooks or any rfrns not on th qustion shts. 3. You ar not allow to us alulators or ltroni vis in any form. 4. You ar not allow to us xtra shts of paprs. 5. You ar not allow to hav any oral, visual, gstur xhang aout th xam qustions or answrs uring th xam. Cautions 1. Chk if you gt 10 pags (inluing this titl pag), 41 qustions. 2. Writ your nam in Chins, stunt ID, an partmnt/yar own on top of th first pag. 3. Thr ar in total 100 points to arn. You hav 100 minuts to answr th qustions. Skim through all qustions an start from th qustions you ar mor onfint with. 4. Us only English to answr th qustions. Missplling an grammar rrors will tolrat, ut you want to mak sur with thos rrors your answrs will still mak sns. 5. If you hav any xtra-xam mrgny or prolm rgaring th xam qustions, rais your han quitly. Th xam aministrator will approah you an al with th prolm. Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 1

2 a a 1. What os AIMD, TCP s ongstion ontrol mhanism, stans for? (2%) (a) Aitiv Inras Multipliativ Dras () Aggrssiv Inras Morat Dras () Aitiv Inras Morat Dras () Aggrssiv Inras Multipliativ Dras 2. Assum that th pakt siz is always 1 yt, th slow start thrshol is 20, thr is no loss, an transmission lay is ngligil. Whih of th following winow siz squn rsmls th havior of TCP in th slow start stat? (2%) (a) () () () () Assum that th pakt siz is always 1 yt, th slow start thrshol is 10, thr is no loss, an transmission lay is ngligil. Whih of th following winow siz squn rsmls th havior of TCP in th ongstion avoian stat? (2%) (a) () () () () Givn th TCP throughput mol riv from on of th homwork xriss, slt from low th onntion with th highst throughput. (2%) (a) RTT=100ms, Loss Rat=3% () RTT=50ms, Loss Rat=3% () RTT=50ms, Loss Rat=1% () RTT=200ms, Loss Rat=3% () RTT=200ms, Loss Rat=1% 5. Whih of th following is a vali IP arss? (2%) (a) /28 () /28 () /28 () /28 6. How many IP arsss an a mahin hav simultanously? (2%) (a) 1 () 2 Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 2

3 a () 3 () 4 7. How many IP arsss an a ntwork intrfa onfigur with simultanously? (2%) (a) 1 () 2 () 3 () 4 8. Whih of th following os not a lay to th transmission of pakts ovr a ntwork routr? (2%) (a) Input quu () Output quu () HOL loking () Buffr ovrflow () Swithing 9. Whih of th following os not xist in th ntwork har of an IPv4 pakt? (2%) (a) Sour arss () Dstination arss () Port numr () Chksum () IP protool vrsion numr 10. Whih of th following os xist in th ntwork har of an IPv6 pakt? (2%) (a) Option () Har lngth () Port numr () Chksum () IP protool vrsion numr 11. Whih of th following is not a nfit of using NAT? (2%) (a) Allowing multipl mahins in a loal ara ntwork givn only 1 IP arss to ass th Intrnt () Allowing th loal aministrator to assign th IP arsss for loal mahins frly () Prvnting th loal aministrator from rassigning th IP arsss whn th IP arss alloat y th ISP hangs () Allowing th loal aministrator to host W srvr frly () Ruing th han of th loal mahins ing pro y th hakrs 12. Whih of th following is th institut having th authority to assign IP arsss? (2%) (a) DNS Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 3

4 a () DHCP () NAT () ICANN () TCP/IP 13. Whih of th following is not a ntwork layr protool? (2%) (a) NAT () IPv6 () PIM () BGP () ICMP 14. Whih of th following routing algorithms rquirs th information of ntir topology? (2%) (a) DV () LS () Flooing () DVMRP 15. Whih of th following routing mhanisms omputs th shortst path? (2%) (a) RIP () OSPF () DV () LS 16. Whih of th following routing algorithms omputs th shortst path tr? (2%) (a) Stinr tr () Dijkstra () Flooing () RPF 17. Count to infinity is a prolm spifi to whih of th following mhanism? (2%) (a) RIP () DVMRP () DV () LS 18. Whih of th following is not haratristi of BGP? (2%) (a) Using TCP for onntions twn gatway routrs () Loop-fr routing Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 4

5 () Shortst path routing () Hot potato routing () Path vtor routing 19. Whih of th following annot an intra-as routing mhanism? (2%) (a) Hirarhial routing () DV () LS () Ranom walk () BGP 20. Whih of th following is not a funtion of a link layr protool? (2%) (a) MAC () Flow ontrol () Congstion ontrol () Error ttion () Error orrtion 21. Whih of th following omponnt of a omputr systm an t possily ontain implmntations of a link layr protool? (2%) (a) Ntwork ar harwar () Ntwork ar firmwar () Ntwork ar rivr () Oprating systm 22. Whih of th following an tt rrors in ommuniation? (2%) (a) Intrnt Chksum () CRC () Singl Parity Bit Chk () CDMA 23. Whih of th following an orrt rrors in ommuniation? (2%) (a) Intrnt Chksum () CRC () Singl Parity Bit Chk () CDMA 24. Whih of th following is a MAC protool? (2%) (a) CSMA/CD () Ethrnt () CDMA Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 5

6 a () WiFi 25. Whih of th following is not a ranom ass MAC protool? (2%) (a) CSMA/CD () Ethrnt () CDMA () WiFi () CSMA/CA 26. Whih of th following MAC protool rquirs tim synhronization? (2%) (a) Aloha () Slott Aloha () CSMA () Blutooth 27. How long is th Ethrnt arss? (2%) (a) 32 its () 36 its () 40 its () 44 its () 48 its 28. Whih of th following is th mhanism us to translat IP arss to MAC arss? (2%) (a) NAT () ARP () DNS () Manhstr Coing 29. Whih of th following ntwork topology is th on rat y a ntwork hu? (2%) (a) Star () Bus () Ring () Msh () Swith 30. Whih of th following ntwork topology is th on rat y a ntwork swith? (2%) (a) Star () Bus () Ring () Msh Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 6

7 a () Swith 31. Whih of th following is a haratristi of Ethrnt? (2%) (a) Carrir sns () Exponntial akoff () Collision ttion () Unrlial 32. Whih of th following is not a squn of K in th Exponntial Bakoff mhanism of Ethrnt? (2%) (a) () () () () Whih of th following os not xist in an Ethrnt pakt har? (2%) (a) CRC () Sour arss () Dstination arss () Praml () Manhstr o 34. Whih of th following is a wirlss link? (2%) (a) Satllit () WiFi () 3G () WiMAX 35. Whih of th following is not a wirlss link s haratristi? (2%) (a) Riv wirlss signal strngth rass as th istan twn th snr an rivr inrass. () Data ar moulat on ltromagnti wavs. () Data travling a wirlss link might intrfr y othr raio sours. () Wirlss signals might lok y ostals in th spa. () Wirlss signals might attnuat uring propagation. 36. Whih of th following is th MAC protool running on IEEE ? (2%) (a) CSMA () CSMA/CD () CDMA () CSMA/CA Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 7

8 37. Whih part of th IEEE s mhanism hlps avoi ollisions? (2%) (a) Exhang of RTS an CTS () Ranom DIFS an SIFS () Channl sltion () Ranom akoff 38. How many arss fils ar thr in an IEEE pakt har? (2%) (a) 1 () 2 () 3 () 4 () Whih of th following is th mhanism us to hanl moility in IP ntwork? (2%) (a) BGP () Roaming () Dirt routing () Inirt routing 40. Making an intrnational roaming all toay is quivalnt of making whih omination of alls? (2%) (a) 1 loal llular phon all + 1 intrnational (PSTN) all () 1 loal llular phon all + 2 intrnational (PSTN) alls () 2 loal llular phon alls + 1 intrnational (PSTN) all () 2 loal llular phon alls + 2 intrnational (PSTN) alls Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 8

9 41. Assss th futur of th wirlss Intrnt ass. Thr ar multipl ways to ass th Intrnt wirlssly. WiFi an 3G ar urrntly ominating th markt. WiMAX is athing up having a numr of as stations uilt an xprimntal oprations running. (1) Compar WiFi, 3G an WiMAX y th transmission rang. (5%) (2) Compar WiFi, 3G an WiMAX y th transmission throughput. (5%) (3) Among WiFi, 3G, an WiMAX, isuss whih srvi a usy salsman who maks voi alls an ra/sn mails taking th Taipi ity MRT a lot will hoos. (5%) (4) Follow (3). WiFly osts aout 400 NTD/month. 3G osts aout 850 NTD/month. If WiMAX is going to ost 400 NTD/month, o you think th usy salsman will prfr to swith to WiMAX? If WiMAX is going to ost 950 NTD/month, what woul th usy salsman hoos? Justify your answrs. (5%) Sampl Solution: (1) WiFi 10s mtrs 3G kilomtrs WiMAX kilomtrs (2) WiFi 100s Mps 3G 100s Kps WiMAX 10s Mps (3) On an isuss th as from iffrnt viwpoints. On xampl: In as of raing/sning mails, thr is not muh iffrn using WiFi at th hotspots vs. 3G. Howvr, to al to kp all on th mov, 3G, having a wir transmission rang is mor sustaining. (4) Again, tak your stan an justify. Provi hr is just an xampl: If WiMAX osts 400 NTD/month, th salsman is finitly going to swith. Th anwith an rang rquirmnts ar oth satisfi an yt it is hapr than 3G. If it s 950 NTD/month, th salsman only ns to mak 10s Kps alls at a tim. Thr s no ovious n to swith an spning mor for srvis that ar not nssary isn t quit what a usinssman woul o. Copyright 2010 Polly Huang Dpartmnt of Eltrial Enginring, National Taiwan Univrsity 9

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