Computer Networking: A Top-Down Approach,
8th Edition
Solutions To Review Questions And Problems
Version Date: May 2012
,This Document Contains The Solutions To Review Questions And Problems For The 5th
Edition Of Computer Networking: A Top-Down Approach By Jim Kurose And Keith
Ross. These Solutions Are Being Made Available To Instructors ONLY. Please Do NOT
Copy Or Distribute This Document To Others (Even Other Instructors). Please Do Not
Post Any Solutions On A Publicly-Available Web Site. We’ll Be Happy To Provide A
Copy (Up-To-Date) Of This Solution Manual Ourselves To Anyone Who Asks.
Acknowledgments: Over The Years, Several Students And Colleagues Have Helped Us
Prepare This Solutions Manual. Special Thanks Goes To Honggang Zhang, Rakesh
Kumar, Prithula Dhungel, And Vijay Annapureddy. Also Thanks To All The Readers
Who Have Made Suggestions And Corrected Errors.
All Material © Copyright 1996-2012 By J.F. Kurose And K.W. Ross. All Rights Reserved
,Chapter 1 Review Questions
1. There Is No Difference. Throughout This Text, The Words “Host” And “End
System” Are Used Interchangeably. End Systems Include Pcs, Workstations, Web
Servers, Mail Servers, Pdas, Internet-Connected Game Consoles, Etc.
2. From Wikipedia: Diplomatic Protocol Is Commonly Described As A Set Of
International Courtesy Rules. These Well-Established And Time-Honored Rules
Have Made It Easier For Nations And People To Live And Work Together. Part Of
Protocol Has Always Been The Acknowledgment Of The Hierarchical Standing Of
All Present. Protocol Rules Are Based On The Principles Of Civility.
3. Standards Are Important For Protocols So That People Can Create Networking
Systems And Products That Interoperate.
4. 1. Dial-Up Modem Over Telephone Line: Home; 2. DSL Over Telephone Line:
Home Or Small Office; 3. Cable To HFC: Home; 4. 100 Mbps Switched Ethernet:
Enterprise; 5. Wifi (802.11): Home And Enterprise: 6. 3G And 4G: Wide-Area
Wireless.
5. HFC Bandwidth Is Shared Among The Users. On The Downstream Channel, All
Packets Emanate From A Single Source, Namely, The Head End. Thus, There Are
No Collisions In The Downstream Channel.
6. In Most American Cities, The Current Possibilities Include: Dial-Up; DSL; Cable
Modem; Fiber-To-The-Home.
7. Ethernet Lans Have Transmission Rates Of 10 Mbps, 100 Mbps, 1 Gbps And 10 Gbps.
8. Today, Ethernet Most Commonly Runs Over Twisted-Pair Copper Wire. It Also Can
Run Over Fibers Optic Links.
9. Dial Up Modems: Up To 56 Kbps, Bandwidth Is Dedicated; ADSL: Up To 24 Mbps
Downstream And 2.5 Mbps Upstream, Bandwidth Is Dedicated; HFC, Rates Up To
42.8 Mbps And Upstream Rates Of Up To 30.7 Mbps, Bandwidth Is Shared. FTTH:
2-10Mbps Upload; 10-20 Mbps Download; Bandwidth Is Not Shared.
10. There Are Two Popular Wireless Internet Access Technologies Today:
a) Wifi (802.11) In A Wireless LAN, Wireless Users Transmit/Receive Packets
To/From An Base Station (I.E., Wireless Access Point) Within A Radius Of Few
Tens Of Meters. The Base Station Is Typically Connected To The Wired Internet And
Thus Serves To Connect Wireless Users To The Wired Network.
b) 3G And 4G Wide-Area Wireless Access Networks. In These Systems, Packets Are
Transmitted Over The Same Wireless Infrastructure Used For Cellular Telephony,
With The Base Station Thus Being Managed By A Telecommunications Provider.
This Provides Wireless Access To Users Within A Radius Of Tens Of Kilometers Of
The Base Station.
, 11. At Time T0 The Sending Host Begins To Transmit. At Time T1 = L/R1, The Sending
Host Completes Transmission And The Entire Packet Is Received At The Router (No
Propagation Delay). Because The Router Has The Entire Packet At Time T1, It Can
Begin To Transmit The Packet To The Receiving Host At Time T1. At Time T2 = T1
+ L/R2, The Router Completes Transmission And The Entire Packet Is Received At
The Receiving Host (Again, No Propagation Delay). Thus, The End-To-End Delay Is
L/R1 + L/R2.
12. A Circuit-Switched Network Can Guarantee A Certain Amount Of End-To-End
Bandwidth For The Duration Of A Call. Most Packet-Switched Networks Today
(Including The Internet) Cannot Make Any End-To-End Guarantees For Bandwidth.
FDM Requires Sophisticated Analog Hardware To Shift Signal Into Appropriate
Frequency Bands.
13. A) 2 Users Can Be Supported Because Each User Requires Half Of The Link Bandwidth.
b) Since Each User Requires 1Mbps When Transmitting, If Two Or Fewer Users
Transmit Simultaneously, A Maximum Of 2Mbps Will Be Required. Since The
Available Bandwidth Of The Shared Link Is 2Mbps, There Will Be No Queuing
Delay Before The Link. Whereas, If Three Users Transmit Simultaneously, The
Bandwidth Required Will Be 3Mbps Which Is More Than The Available
Bandwidth Of The Shared Link. In This Case, There Will Be Queuing Delay
Before The Link.
c) Probability That A Given User Is Transmitting =
0.2
3 3 33
d) Probability That All Three Users Are Transmitting Simultaneously = 1 P
P 3
= (0.2)3 = 0.008. Since The Queue Grows When All The Users Are Transmitting,
The Fraction Of Time During Which The Queue Grows (Which Is Equal To The
Probability That All Three Users Are Transmitting Simultaneously) Is 0.008.
14. If The Two Isps Do Not Peer With Each Other, Then When They Send Traffic To
Each Other They Have To Send The Traffic Through A Provider ISP (Intermediary),
To Which They Have To Pay For Carrying The Traffic. By Peering With Each Other
Directly, The Two Isps Can Reduce Their Payments To Their Provider Isps. An
Internet Exchange Points (IXP) (Typically In A Standalone Building With Its Own
Switches) Is A Meeting Point Where Multiple Isps Can Connect And/Or Peer
Together. An ISP Earns Its Money By Charging Each Of The The Isps That Connect
To The IXP A Relatively Small Fee, Which May Depend On The Amount Of
Traffic Sent To Or Received From The IXP.
15. Google's Private Network Connects Together All Its Data Centers, Big And Small.
Traffic Between The Google Data Centers Passes Over Its Private Network Rather
Than Over The Public Internet. Many Of These Data Centers Are Located In, Or
Close To, Lower Tier Isps. Therefore, When Google Delivers Content To A User, It
Often Can Bypass Higher Tier Isps. What Motivates Content Providers To Create
These Networks? First, The Content Provider Has More Control Over The User
8th Edition
Solutions To Review Questions And Problems
Version Date: May 2012
,This Document Contains The Solutions To Review Questions And Problems For The 5th
Edition Of Computer Networking: A Top-Down Approach By Jim Kurose And Keith
Ross. These Solutions Are Being Made Available To Instructors ONLY. Please Do NOT
Copy Or Distribute This Document To Others (Even Other Instructors). Please Do Not
Post Any Solutions On A Publicly-Available Web Site. We’ll Be Happy To Provide A
Copy (Up-To-Date) Of This Solution Manual Ourselves To Anyone Who Asks.
Acknowledgments: Over The Years, Several Students And Colleagues Have Helped Us
Prepare This Solutions Manual. Special Thanks Goes To Honggang Zhang, Rakesh
Kumar, Prithula Dhungel, And Vijay Annapureddy. Also Thanks To All The Readers
Who Have Made Suggestions And Corrected Errors.
All Material © Copyright 1996-2012 By J.F. Kurose And K.W. Ross. All Rights Reserved
,Chapter 1 Review Questions
1. There Is No Difference. Throughout This Text, The Words “Host” And “End
System” Are Used Interchangeably. End Systems Include Pcs, Workstations, Web
Servers, Mail Servers, Pdas, Internet-Connected Game Consoles, Etc.
2. From Wikipedia: Diplomatic Protocol Is Commonly Described As A Set Of
International Courtesy Rules. These Well-Established And Time-Honored Rules
Have Made It Easier For Nations And People To Live And Work Together. Part Of
Protocol Has Always Been The Acknowledgment Of The Hierarchical Standing Of
All Present. Protocol Rules Are Based On The Principles Of Civility.
3. Standards Are Important For Protocols So That People Can Create Networking
Systems And Products That Interoperate.
4. 1. Dial-Up Modem Over Telephone Line: Home; 2. DSL Over Telephone Line:
Home Or Small Office; 3. Cable To HFC: Home; 4. 100 Mbps Switched Ethernet:
Enterprise; 5. Wifi (802.11): Home And Enterprise: 6. 3G And 4G: Wide-Area
Wireless.
5. HFC Bandwidth Is Shared Among The Users. On The Downstream Channel, All
Packets Emanate From A Single Source, Namely, The Head End. Thus, There Are
No Collisions In The Downstream Channel.
6. In Most American Cities, The Current Possibilities Include: Dial-Up; DSL; Cable
Modem; Fiber-To-The-Home.
7. Ethernet Lans Have Transmission Rates Of 10 Mbps, 100 Mbps, 1 Gbps And 10 Gbps.
8. Today, Ethernet Most Commonly Runs Over Twisted-Pair Copper Wire. It Also Can
Run Over Fibers Optic Links.
9. Dial Up Modems: Up To 56 Kbps, Bandwidth Is Dedicated; ADSL: Up To 24 Mbps
Downstream And 2.5 Mbps Upstream, Bandwidth Is Dedicated; HFC, Rates Up To
42.8 Mbps And Upstream Rates Of Up To 30.7 Mbps, Bandwidth Is Shared. FTTH:
2-10Mbps Upload; 10-20 Mbps Download; Bandwidth Is Not Shared.
10. There Are Two Popular Wireless Internet Access Technologies Today:
a) Wifi (802.11) In A Wireless LAN, Wireless Users Transmit/Receive Packets
To/From An Base Station (I.E., Wireless Access Point) Within A Radius Of Few
Tens Of Meters. The Base Station Is Typically Connected To The Wired Internet And
Thus Serves To Connect Wireless Users To The Wired Network.
b) 3G And 4G Wide-Area Wireless Access Networks. In These Systems, Packets Are
Transmitted Over The Same Wireless Infrastructure Used For Cellular Telephony,
With The Base Station Thus Being Managed By A Telecommunications Provider.
This Provides Wireless Access To Users Within A Radius Of Tens Of Kilometers Of
The Base Station.
, 11. At Time T0 The Sending Host Begins To Transmit. At Time T1 = L/R1, The Sending
Host Completes Transmission And The Entire Packet Is Received At The Router (No
Propagation Delay). Because The Router Has The Entire Packet At Time T1, It Can
Begin To Transmit The Packet To The Receiving Host At Time T1. At Time T2 = T1
+ L/R2, The Router Completes Transmission And The Entire Packet Is Received At
The Receiving Host (Again, No Propagation Delay). Thus, The End-To-End Delay Is
L/R1 + L/R2.
12. A Circuit-Switched Network Can Guarantee A Certain Amount Of End-To-End
Bandwidth For The Duration Of A Call. Most Packet-Switched Networks Today
(Including The Internet) Cannot Make Any End-To-End Guarantees For Bandwidth.
FDM Requires Sophisticated Analog Hardware To Shift Signal Into Appropriate
Frequency Bands.
13. A) 2 Users Can Be Supported Because Each User Requires Half Of The Link Bandwidth.
b) Since Each User Requires 1Mbps When Transmitting, If Two Or Fewer Users
Transmit Simultaneously, A Maximum Of 2Mbps Will Be Required. Since The
Available Bandwidth Of The Shared Link Is 2Mbps, There Will Be No Queuing
Delay Before The Link. Whereas, If Three Users Transmit Simultaneously, The
Bandwidth Required Will Be 3Mbps Which Is More Than The Available
Bandwidth Of The Shared Link. In This Case, There Will Be Queuing Delay
Before The Link.
c) Probability That A Given User Is Transmitting =
0.2
3 3 33
d) Probability That All Three Users Are Transmitting Simultaneously = 1 P
P 3
= (0.2)3 = 0.008. Since The Queue Grows When All The Users Are Transmitting,
The Fraction Of Time During Which The Queue Grows (Which Is Equal To The
Probability That All Three Users Are Transmitting Simultaneously) Is 0.008.
14. If The Two Isps Do Not Peer With Each Other, Then When They Send Traffic To
Each Other They Have To Send The Traffic Through A Provider ISP (Intermediary),
To Which They Have To Pay For Carrying The Traffic. By Peering With Each Other
Directly, The Two Isps Can Reduce Their Payments To Their Provider Isps. An
Internet Exchange Points (IXP) (Typically In A Standalone Building With Its Own
Switches) Is A Meeting Point Where Multiple Isps Can Connect And/Or Peer
Together. An ISP Earns Its Money By Charging Each Of The The Isps That Connect
To The IXP A Relatively Small Fee, Which May Depend On The Amount Of
Traffic Sent To Or Received From The IXP.
15. Google's Private Network Connects Together All Its Data Centers, Big And Small.
Traffic Between The Google Data Centers Passes Over Its Private Network Rather
Than Over The Public Internet. Many Of These Data Centers Are Located In, Or
Close To, Lower Tier Isps. Therefore, When Google Delivers Content To A User, It
Often Can Bypass Higher Tier Isps. What Motivates Content Providers To Create
These Networks? First, The Content Provider Has More Control Over The User
