Giải bài tập mạng máy tính Computer Networking A TopDown Approach 6th

Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 1
Computer Networking - A Top-Down Approach Featuring the Internet, 5
th
edition
Solutions to Review Questions and Problems (Vietnamese version)
Author : K55CC translate team.(K55CC-University of engineering and technology-Vietnam national university)
This document belong to K55CC.All copies or sharing must be allowed by K55CC.
Chapter1: Introduction-Review Question
1: S 

   thay th cho nhau.
End system gt ni internet
 v giao thc ngoi giao (diplomatic protocol)
Gi s Alice, m i s ca quc gia A mun mi Bob, m i s c B,  i. Alice  ch 
gi   cn gi Bob  n tho   n   ca    ". Thay  
 gi Bob  cho thy mt i gian. Bob  ng b  rng i 
s c th  n m Alice  Bob tip tc gi p" qua li cho
n khi h   i gian. Bob y ti s    tho thun,
hy vng  c khi hoc sau khi th thu c  cho
 hoc Alice hoc Bob lch s hy b s tham gia nu h   hp 
n
dch v t 
M    c ni vs
u vi
cn dch v t  server.
 truy cp.
1. Dial-up modem over telephone line: residential;
2. DSL over telephone line: residential or small office;
3. Cable to HFC: residential;

4. 100 Mbps switched Ethernet: company;
5. Wireless LAN: mobile;
6. Cellular mobile access (for example, WAP): mobile
 truyn ci 1 t truyn mi user trong m
truyc v 
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 2
 truys. VD vi X Mbps Ethernet (
X = 10, 100, 1,000 or 10,000), m truyn lien tc vi t X Mbps nu ch 
i d liu. Nu user ho truyc vi t X Mbps.
ng v  truy
 truyng trc mng xo truyn qua si
ng tr
t khong t truyn c  c
kiu chia s t?
Dial up modems: up to 56 Kbps, bandwidth is dedicated; ISDN: up to 128 kbps, bandwidth is
dedicated; ADSL: downstream channel is .5-8 Mbps, upstream channel is up to 1 Mbps, bandwidth is
dedicated; HFC, downstream channel is 10-30 Mbps and upstream channel is usually less than a few
Mbps, bandwidth is shared. FTTH: 2-10Mbps upload; 10-20 Mbps download; bandwidth is not shared.
  truy c bin hi
bit c
Hi truy c bin.
- M
n 1 tr m truy cm c ng
c kt ni Internet b
- Mng truy cn r thc truy h
t thn thoi, tr c qup
dch v vin tp s truy cc
kilomet t .

n li ca mng chuyn mn so vi chuyn m
Mng chuyn m m bng c a 2 m n c
gi. Hu hng chuyn mn nay (bao gm c o s m b
m ni.
 s c chuyn t host gn host nhn. T truyn gia host g
n l s switch s dng chuyn m  
chuyn ting thi gian delay gim n g  
tr khi truy 
Ti thm t
0
, host gi bu truyn. Ti thm t
1
= L/R1, host gc truy
 c nhn t khi truy i thm t
1

 truyn host nhn ti thm t
1
. Ti thim t
2
= t
1

c truy c nhn ti host nhy, tng thi gian tr 
Câu 15: Giả sử nhiều user chia sẻ 1 link 2Mbps. Và cũng giả sử rằng mỗi user truyền lien tục vs tốc độ
1Mbps khi truyền, nhưng mỗi user chỉ truyền 20% thời gian.
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

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a. Nếu dùng chuyển mạch điện thì có bao nhiêu user được sử dụng?

b. Giả sử dùng chuyển mạch gói. Tại sao nếu có ít hơn hoặc bằng 2 user cùng truyền thì không phải
đợi? và nếu nhiều hơn 2 user cùng truyền thì phải có hàng đợi?
c. Tính xác suất để mỗi user được truyền.
d. Giả sử có 3 user. Tính xác suất tại bất kì thời điểm nào, cả 3 user cùng truyền 1 lúc. Tính khoảng
thời gian để hình thành hàng đợi.

TL:
a. c truyi user cn 1 nng truyn.
b. Theo gi thit, mi user cn 1Mbps khi truyn, n
cng truyi
.
c li, nn s 3Mbps, nhi
ng h ng truyn.
c. t = 0.2
d.  
3
. (1-p)
3-3
= (0.2)
3
i
t c ho tt c 
truy
  s     1 host ngu    ng c nh. Li 
khong tr i?
n tr gm: tr khi x  khi lan ta (propagation delay), tr khi truyn (transmission
 i. Tr tr i, tt c nhng khong tr  nh.
ng th truy ng truyn kho
truy chuy thu
ng tgian = d/s.

 thu  chuyn R.
 s host A mun gi 1 file ln  n B, t l

a. Gi s c nghn trong mng truyn file?
b. Gi s ng 4 tric file bi gian
xp x  truyn host B?
c. i R2 gi
TL:
a. 500 kbps. 
b. 4.000.000 byte = 4.000 KB = 32.000 Kbit. Tgian = 32000/500 = 64 s
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

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c. ng = 100 kbps. Tgian = 320 s.
m v  thc hi xng hp mt hay nhiu
nhim v c thc hin bi nhiu tc k?
5 nhim v u khin lui, dt kt
ni. C xng hp 1 hay nhiu nhim v c thc hin bi nhiu tng. VD: kii
c cung cp  nhiu tng.
  t message  tng ng d   t segment  tng giao vn? Mt datagram  tng
network? Mt frame  tt?
- 
- 
.
- a tng giao v.
- 
t router x  tt switch x  tt host x  t
  tng 1, 2, 3 tng v  t
2 tng v  c 5 tng.
Chapter1: : Introduction- Problem

P5: Gi s t ni vi nhau b c
 lan tn host B.
a. Biu di tr lan ta (d
prop

b. nh thi gian truyn c
trans

c. B  tr x i. Vit biu th tr gim k
d. Gi s Host A bu truyi thm t = 0. Ti thm t = d
trans
, bit cu
c 
e. Gi s d
prop
> d
trans
. Ti thm t = d
trans
 
f. Gi s d
prop
< d
trans
. Ti thm t = d
trans
 
g. Gi s s = 2,5.10
8
 d

prop
= d
trans

TL:
a. d
prop
= m/s (s)   tr lan ta (tht kho
b. d
trans
= L/R (s)   tr truyn (thi gian t n khi bit cui
i host).
c. d
A-B
= d
prop
+ d
trans
= m/s + L/R (s)
d. Ti t = d
trans
, bit cua ri khi host A.
e. Ti t = d
trans
, bit  ng truyc host B.
f. Ti t = d
trans
n host B.
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 5
g. d
prop
= d
trans
 m/s = L/R  m = Ls/R = 523158 (m)
c gi gii gian thc t n host B qua 1 mng chuyn m
A chuyn giu s 
bytes. Ch ng duy nht t n B t truy tr lan t
host A t n
i gian k t c to (t u gc
 n khi bit cuc gi host B)?
 c truyt c c to
y cn:
3
10.64
8.56
(s) = 7 (ms).
Thi gian c truy
6
10.2
8.56
(s) = 224

s
 tr lan t
 tr n khi gi

s + 10 ms = 17,224 ms
P12: Gi s ng truyn tc truyc phi

x t ng truy tr 
tin.
 tr  
 1)  
 tr c
(L/R + 2L/R + + (N-1).L/R) / N
= L/(RN) * (1 + 2 + + (N-1))
= L/(RN) * N(N-1)/2
= LN(N-1)/(2RN)
= (N-1)L/(2R)
P24: Gi s c ni trc tip vs nhau bng t R = 2
Mbps. Tc  lan tng truy
8
m/s.
a.  tr (R.d
prop
).
b. c g  n B. Gi s c truyc. S bit t
c truyng truyn ti b
c. Gi
prop
.
d.  rng cng truyn b
e. Vic t rng cng truyn. Cho bit t lan tc
 truy ng truy
TL:
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 6
a. R.d

prop
= R. m/s = 2. 20.10
6
/ (2,5.10
8
) = 160.000 bits.
b. S bit tc truyng truyn ti bm = R.d
prop
= 160.000 bits.
c.  gi tr(d
prop
) ca ng truy bit t  ng
truyn
d.  rng c ng truyn / (R.d
prop
) = 20.10
6
/ 160.000 = 125 m
e.  rng ca 1 bit = m / (R.d
prop
) = s/R.

Chapter2: Application Layer -Review Question
 1: 
- The Web - HTTP;
- File transfer (bittorrent) - FTP;
- Remote login - Telnet;
- Network News - NNTP;
- E-mail - SMTP;

 t gi
- Network architecture t h thp v
- Application architecture c hin ng d
u khin hong c
ng dng chia s file P2P. Bi nh
server trong 1 giao tip gii sao?
i giao dng dng chia s file P2P
 g
 s bn mut giao dch gii t cao, bn
UDP hay TCP?
N dn thit lng chuyn ch mt 1 RTT
u tu s dng TCP bn mt  cho vic thit
lp kt n
u khi-of-band?
FTP s dng 2 kt ni TCP song song. Mt kt n king hu
chuyn giao 1 tp tint kt n chuyp tin . Bm
c g kt ni vi t ng FTP 
"out-of-band" .
 t gia download-and-delete mode and the download-and-keep mode in POP3?
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 7
- Vi download-and-delete y tin nhn t m n s
b t ra mt v cn gi quyn t
nhi)
- Trong download-and-keep, tin nhn s  i s dng ln.
 t tii li s dng ln, tt c 
 c chuy
     mt  M       (alias) cho 1
hostname   host name of the mail server?

c s d  a mail server va ch IP.
Cverlay network N The edgesc
c t 
- t h thng g tt gi
- a router.
- The edges c.
-  i   thn bia ch IP ca 1 hay nhiu
node ca h th gode h
s tr n ca h thng.
 P2P cho 2 giao thc quan tr

ng dng quan trp vi ki
a) File Distribution
b) Instant Messaging
c) Video Streaming
d) Distributed Computing
Chapter2: Application Layer -Problem

a. Mu t nh, client s gi 1 tin nhn 4
tin nhn phn hi? - Sai: gi 4 nhn 4
b.  gt n- 
c. Vi mt kt n  c hin 2 request
- Sai
d. u ca giao th rng.
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 8
: 

- Application layer protocols: DNS and HTTP

- Transport layer protocols: UDP for DNS; TCP for HTTP
Gi s t web ba 1 trang web. Bn cn la ch IP
cn phi l
DNS bn mt RTT thi gian l
1
, RTT
2
 RTT
n
ng text.
Bn mt RTT
0
  host ti server chi gian t n khi nhc
ng.

Tng th la ch 
1

n
;
a ch IP bn mt RTT
0
 kt n
0
n gi
ng.
ng thi gian cn thi
0
+ RTT
1


n
;


a. :
Kng ta cn 8 ln thit ln gt
th
0
= 16 RTT
0

ng th
0
+ RTT
1

n
+ 16 RTT
0

b. t ni song song:
1 ln kt ni gi nhng cn 2 ln kt nt th
0

ng th
0
+ RTT
1


n
+ 4 RTT
0
c. 


0

ng th
0
+ RTT
1

n
+ RTT
0
= 3 RTT
0
+ RTT
1

n


  s dc ging
 k
- SMTP kng m cha du chm.
- HTTP qu 
-  s dc ging SMTP    d
   dng ASCII

 s truy cp mail ca bn bng POP3
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 9
a. Gi s bnh da bc  ch  
i:
C: dele 1
C: retr 2


S: .
C: dele 2
C: quit
S: +OK POP3 server signing of
b. Ch  down xong gi
C: retr 2


S: .
C: quit
S: +OK POP3 server signing off
u  ch  down xong gi ng
hp 
C: list
S: 1 498
S: 2 912
S: .
C: retr 1



S: .
C: retr 2


S: .
C: quit
S: +OK POP3 server signing off

: Suppose you can access the caches in the local DNS servers of your depart ment. Can you
propose a way to roughly determine the Web servers (outside your department) that are most popular
among the users in your department?
  n ca DNS caches trong nh 
Web server xut hi bin nh
bi nu nhic gi
 t hin trong DNS caches nhilocal DNS cache,
y thi gian truy vn s ng hi gian truy vn l

Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 10
22: Consider distributing a file of F = 15 Gbits to N peers. The server has an upload rate of us = 30
Mbps, and each peer has a download rate of d i = 2 Mbps and an upload rate of u. For N = 10, 100, and
1,000 and u = 300 Kbps, 700 Kbps, and 2 Mbps, prepare a chart giving the minimum distribution time
for each of the combinations of Nand u for both client-server distribution and P2P distribution.

 u phi ti thiu phi client-server, ta s
dc:
Dcs = max {NF/us, F/dmin}
 u phi ti thiu phi P2P, ta s dc:

  F = 15 Gbits = 15 * 1024 Mbits
u
s
= 30 Mbps
d
min
= di = 2 Mbps
Note, 300Kbps = 300/1024 Mbps


23. Consider distributing a file of F bits to N peers using a client-server architecture. Assume a fluid
model where the server can simultaneously transmit to multiple peers, transmitting to each peer at
different rates, as long as the combined rate does not exceed us
a. Suppose that us/N <= dmin . Specify a distribution scheme that has a distribution time of NF/us.
b. Suppose that us/ N ~ dmin . Specify a distribution scheme that has a distribution time of F/dmin .
c. Conclude that the minimum distribution lime is in general given by max{NF/us, F/ dmin ).

u phi file ti tng client, song song, v mt t 
t   download ca t thit us/N <= dmin. 
 nhc file vi mt t  i client nhn t us/N, th mi client
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nht c u nhnh file trong thi gian NF/us,
ng thi gian u ph

a. Gi s bn m c khi m  
 c gng kt ni v=> kt ni li.
b. Bn chc khi chy UDP server?
 go to kt ni ti server.

c. S d
 c gng kt ni TCP vi 1 ti i

Chapter3: Transport Layer -Review Question
 1. t kt ni TCP t n B.Gi s  A -
y port ngu B -
Source Port: y, Dest Port: x
Question 2
Gin ng dng li ch
Solution :
n ng dng ch n ng dng ca h phi s d kic
ngh u tit t truyn d liu ca ng d tc ngh  m tc
 truy ng ti ng dng,nhng ng dng chat voice hay hi tho trc
tuyn).Nhng ng d tin cy ca d lii gian.
Question 3. Ling d kh n d liy ngay c 
giao thc UDP?
Solution :
 n ng d c truyn d lic ca lp ng
dng.T i m cho vin li.
Question 4 True or False
a. Gi s host A truyn mt tp tin ln t li gi
ti host A. Host B s i ACK t  li
unlogical )
b. a ca s t ni.
c. Gi s host A truyn mt tp tin ln tc TCP,s byte d li t
 nh m cn.
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d. Gi s host A truyn mt tp tin ln tc TCP,S th t ca segment cho ln gi

 th t cho segment tip theo ph  l
phi gi l
e.  cho ca s n.
f. Gi s thi gian RTT gn nht trong kt ny pht thi gian timeout >=1 cho ln
truyn sd nhi ch k sd RTT gn nht).
g. Gi s host A gi 1 segment t-bytes d liu.V

Solution : a. F b. F c.T d. F e.T f. F g. F


Question 5
Gi s A gn nhau ti B.Segment th nh segment th 

b. Gi s  mth 2 v Vy stt ci t B v A

Solution :
a. 110-90 = 20 bytes.
b. 
Question 7: Hin tt ni TCP v   C 2 kt nn
cn gng   Vic truyn d liu bu  t thm. Vy
t truy i kt n
ng ca giao thc TCP ta bi  nu N kt n m
truyn tc nghi kt ni s nh (Tng nhau).
Solution :


Question 8
 kic nghn trong TCP. Nu xy ra timeout   t bng
mt na c 
 u xy ra mng threshold s t bng mt na ca Congwin (Congrestion

window)
Note : T truyn b gii hn bi ca s tc nghn Congwin. ng gia 2 pha
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Question 9 (P1 trong sách) Giả sử Network Layercung cấp dịch vụ sau. Network layer ở host nguồn chấp
nhận gửi 1 segment có max size là 1200 bytes và địa chỉ đích từ transport layer.Network layer đảm bảo gửi
thành công segment tới transport layer tại host đích.
Giả sử có nhiều tiến trình cùng chạy tại host đích.
a.Thiết kế một giao thức đơn giản cho transport layer để nhận được dữ liệu phù hợp cho mỗi tiến trình tại
host đích.Giả sử HĐH ở host đích có thể cấp 4 bytes port number cho mỗi tiến trình đang chạy.
b.Điều chỉnh giao thức đó để nó có thể trả về địa chỉ (“return address”) cho host đích.
c.Trong giao thức của bạn liệu transport layer có phải làm j trong lõi của mạng máy tính?

Solution :
a. Gi giao thi,STP chp nhn cho tii 1
chunk  liu ,ma ch t cng nh
a m a ti
layer s chuyi transport layer cSTP s gim tra
segment nhng vi tii gn nhn.
b. i segment s  (header).Mt trg cho port ngu
gi chp nhn ga ch t port ngu
m
STP to mt segment bao gm d liu ca application,port ngu chuyn
a ch  gi sang 
segment,STP s chuyn ti ng dng d liu cn nh port ngun.
c.  nt b u cui.

Question 10.(P2) Giả sử có 1 hành tinh có dịch vụ gửi thư.Mỗi gia đình có 1 địa chỉ(1 hòm thư riêng).Mỗi
thành viên trong gia đình đều có một tên riêng.Dịch vụ gửi thư có thể gửi từ nhà này sang nhà khác.Nó yêu
cầu phải cho bức thư và địa chỉ của nhà cần gửi vào trong phong bì.Mỗi gia đình đều có 1ng đại diện,ng
này sẽ nhận thư và phân phát thư cho các thành viên khác trong gia đình.
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a.Sử dụng giao thức ở Question 9 để gửi thư.Mô tả cách ng đại diện nhận và phân phát thư.
b.Trong giao thức này,liệu mail server có phải mở phong bì để kiểm tra bức thư bên trong hay không?

Solution :
a) Ng gi s i din c ba ch c
i din s viu ba ch ca
ch v gc
i din nh ly b
(Gi s i di or m 
b) Mail server k cn m  kia ch 

Question 11(P5) Tại sao bây h các ứng dụng chat voice hay video lại dùng TCP hơn UPD,trong khi TCP có
cơ chế kiểm soát tắc nghẽn gây trễ đường truyền?
 firewall hay chng truyn ti data ca UDP.Tronth 

Question 12.(P7) Giả sử một tiến trình ở host C có một UDP socket với port là 6789.Giả sử cả 2 host A và B
đều có thể gửi segment tới C với cùng một port đích là 6789.Liệu cả 2 segment đều cùng hướng đến cùng
một socket đích ở host C hay không?Nếu có thì làm sao để host C có thể biết đc sự khác nhau giữa 2
segment đó(nó có nguồn gốc từ đâu)?

i segment nh  cung cp 1 tia ch  nh
ngun gc c

Question 13.(P8) Giả sử Web server chạy trên host C tại port 80 và dùng kết nối kiên trì.Nó nhận đc 2 yêu
cầu từ host A và B.Liệu cả hai yêu cầu đc đc gửi trên cùng một socket của C.Nếu 2 yêu cầu đc trả lời qua 2
socket khác nhau thì liệu cả 2 socket đều có port là 80?

Solution : Trong kt n Web server to ra tng kt nt . Mi socket kt n
nh vi mt b ba ch IP ngun, port ngua ch c IP
m tra  i truy
cu t  c nhn
dia ch IP nguhi lp transport gi mt segment TCP
 tng ng d a ch IP ngunh bnh danh
socket.

Question 14(P9) Trong giao thức rdt,tại sao chúng ta cần sử dụng STT(sequence number)?

Solution :  d liu nh 

Question 15(P10) Trong rdt protocol,tại sao phải sử dụng bộ đếm thời gian(timer)?
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 15

Solution : Ni ch nh ca b i
kt lu b m truyn l

Question 16 (P11) Giả sử roundtrip delay (độ trễ phản hồi) giữa bên nhận và bên gửi là hằng số,và bên gửi
bik độ trễ này.Vậy ta có cần timer cho rdt 3.0 nữa hay không?Giả sử gói tin có thể bị mất.

Solution : Timer vn cn thii gian t n
m duy nh b m
hung c th,nu ACK k m n tri vn c bi.

Chapter3: Transport Layer - Problem
1. 

a. 
b. 
c. 
d. 
e. 

f. 
Answer:

source port numbers
destination port numbers
a) 
467
23
b) 
513
23
c) 
23
467
d) 
23
513
e) Yes
f) No

2. 


  i 1 bit s  n? L
Answer:
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

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0 1 0 1 0 0 1 1
+ 0 1 0 1 0 1 0 0

1 0 1 0 0 1 1 1

1 0 1 0 0 1 1 1
+ 0 1 1 1 0 1 0 0

0 0 0 1 1 1 0 0
 
- 

- 
- 




3. n thy r
truyn ti nhc ch
x
Answer:

i nh c chn ly ra
1, 1
 nhau
4. 
Answer:
timeouts.
timeouts
 
 

5. 
 
 
-- 
 ?
Answer:

-



Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 17



 
6. 



a. 
b. 

Answer:
a. =3.
-
-1].

--N, k-1]

-N, k]
b. --


7. 
a. selective repeat
windows 
b. windows 

Answer:
a. g.

0
.

1
(t
1
>t

0


2
(t
2
> t
1
timeouts 

3


4

1


5

3
. windows
b. 
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 18
8. 
a. T
b.  




Answer:

32
= 4294967296 sequence number
a. 


32 =
4.19 Gbytes
b. 




segment




  = 66 * 8012999 = 

32
+



  = 4,824*10
9

bytes

9. 
back-to-back. 


a. 

b. 

c. 

d. 


Answer:
a. 
- 
- 
- 
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 19
b. 
- acknowledgement 
- 
- 
c. 
- 
d.

10. 



Answer:


RcvWindow = 0. 
RcvWindow > 0. 

11. 

a. acknowledgments 

EstimatedRTT
b. c cho n SampleRTTs
c. 
Answer:
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC

 Page 20
a. 
(n)

EstimatedRTT
(1)
= SampleRTT
1
EstimatedRTT

(2)
.SampleRTT
1
+ (1-.SampleRTT
2
EstimatedRTT
(3)
.SampleRTT
1
+ (1-.SampleRTT
2
+ (1-.SampleRTT
3
]
= .SampleRTT
1
+ (1-..SampleRTT
2
+ (1-
2
.SampleRTT
3

EstimatedRTT
(4)
= .SampleRTT
1
+ (1-..SampleRTT
2
+ (1-

2
..SampleRTT
3
+ (1-
3
.SampleRTT
3

b. EstimatedRTT
(n)
. 

  




.SampleRTT
j
+   




c.

12.  






Answer:
Trong v  nhn t m nhn
 gi  ti tr c khi
timeout, TCP kia g  c
chuyn d lim gi sm gi tr 
 chuyn d liu  t l c R << S.
13.  
a.  

 
b. 
Answer:
a. 
cwnd 
cwnd 
cwnd 
cwnd 
cwnd 
cwnd 

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 Page 21
b.  
 
Trong RTT  
 
 
 





 
14. 


Answer




rdt3.0
15. Suppose an application uses rdt3.0 as its transport layer protocol. As the stop-and-wait protocol has very
low channel utilization (shown in the cross-country example), the designers of this application let the
receiver keep sending back a number (more than two) of alternating ACK 0 and ACK 1 even if the
corresponding data have not arrived at the receiver. Would this application design increase the channel
utilization? Why? Are there any potential problems with this approach? Explain
Answer
Yes. This actually causes the sender to send a number of pipelined data into the channel.
Yes. Here is one potential problem. If data segments are lost in the channel, then the sender of rdt 
re-send those segments, unless there are some additional mechanism in the application to recover from loss

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 Page 22
Chapter4: Network Layer  Review Question
t ng c s dng trong cui packet ca tng transport l
i ca ta t c g
n c layer switches?

Tr li:
Packet tc gt router mun chuyn packet phi da ch IP ca packet
(tng 3). A link-layer switch mun chuyn packet phi da ch MAC (tng 2).

R2: Hai chng ca tng network trong chuyn mng ca
tng network trong mt chuyn mch o?

Tr li:
Hai chng ca tng network trong datagram  network: chuynh tuyn.
Ba chng ca tng network trong virtual  circuit: chuynh tuyt lp tuyng.

R3: S a routing 

Tr li:
n mt packet t ma mt router, ra mu ra ca 
p.
nh  router ngu

R4: Routers trong chuyn mn mc s dng trong bnh tuyn? Nu vy,
 bnh tuy

Tr li:
c s dng cho c hai.

R7: Ti sao mi c c cao
(Discuss why each input port in a high-speed router stores a shadow copy of the forwarding table)

With the shadow copy, the forwarding decision is made locally, at each input port, without invoking the
centralized routing processor. Such decentralized forwarding avoids creating a forwarding processing bottleneck at
a single point within the router

 vic m xy ra ti c vic mi c
th b loi b. (tr ng hp s dng b nh m)

Tr li:
My ra n i ti c forwarding chm  nh
router s b  b loi tr nu t forwarding ti thin, 
s c

 vic m xy ra ti cng ra.

Tr li:
Vic m xy ra n i ti cng ra
router) trong khi t ra ca 
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC
 Page 23

R11: HOL blocking  xy ra trong cc c

Tr li:
HOL blocking   datagram xp hang ti c hang i   cho  chuyn tip
xy ra ti c

a ch  

Tr li:
a ch IP cho mi interface.

R13: Chuyn sang h  nh a ch 223.1.3.27

Tr li:
11011111 00000001 00000011 00011100

R15: Gi s a host ngu nh, mt IP datagram gi t host ngun
 ng   chuy ngu

Tr li:
8 interfaces; 3 forwarding tables

R16: Gi s mt ng dng to ra 40bytes d liu trong khong thi d li
 ca mi datagram s  l
d liu ng d

Tr li:
Overhead: 20 byte ca TCP header, 20 byte ca IP header = 40 byte
 50% overhead

R17: Gi s host A gi host B mn
ng network trong host B s   bit TCP t
UDP hay m

Tr li:
ng giao thc ca IP datagram bao g giao thc tng transport 


nh rng ng qua IPv4, IPv6 nng t giao
thc t
Tr li:
 

 a hai thu
Thun nht t ngun t dng nhng kin
thnh, tng.
nh tuyn theo distance vector: : Vic thc hin lp li
c. M bii chuyn tip m n theo
 
Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC
 Page 24
R22, Tho lum th ch i
dung?
c tng h thng t u khit c y
nh tuyn trong ni b c bic
nh tuy thng t u khing dnh tuyn gi
V cc gii quyt khi mt router trong AS ch cn bit v ter
trong AS c
 cn thit vic mi h thng t tr (AS) s dnh tuyn intra- AS 
n t ch trong qunh tuyn trong AS.

Rng sau: RIP advertisements typically announce the number of hops to various
destinations. BGP updates, on the other hand, announce the _____ to the various destinations.
 -  ng.

Rt ng 

t phn ca mi la 1 router. Ranh gi cnh bi
giao din c
Pt phn ca ch c vii dng abcd/x. M gm 1 hay nhiu subnet.
Khi mt router qut prefix qua mm mt s thu
Trong thut ng BGP , mt tuyng BGP (hoc ch 
mttuyng).

Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition – Translate by K55CC
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Chapter4: Network Layer  Problem
m ca virtual-
a. Gi s ng chu ki l
vii cho kii sao
b. Gi s ru c n t
ng dn t nguc s dc quyn ca ngu
dng VC hay kii sao?
c. Gi s  lnh tuyn gia tt c 
nguu
khin lu? Ti sao

a. Vi 1 mi kt ni mng, mi router b li s n phnh tuyn ca kt n mc ti
thi  router tht bng dn mn node
i tt c u hing dn ma, tt c 
ng du t node sai phng kt ni sai, vi tt c du hin

Vi 1 mng ko kt nu hiu thit lp set up cho c ng dn mng
ng d thnh tuy cn update l 
distance vector ho  thy vs
tt distance vector, bnh tuy i thi thong bn
router tht b n thit k trong
 s du kinc
la chn cho t 
b.    t c ng dn gia node ngu
cn bip t tt c u
 i ko kt ny 1 kt

ni mng VC s 
c.  
n thi nh tuyt c 
c thit l  v 
 circuit netwok, gi s s ng 8 bits.
a. S t mang trong1 link?
b. Gi s node ging d thit lp kt ni. gi d 
ging vc s dng trong m  n
nh VC number  thit l  tnh?
c. Gi s s i link dng dn c
thit lp kt nng dn end  to    
chn VC number c ph thu
?

a. S t mang trong 1 link = 2^8 = 256