Computer Network midterm Exam with
Answers Graded A
What is a protocol? Which of the following human scenarios involve a protocol (recall:
"Protocols define the format, order of messages sent and received among network entities,
and actions taken on message transmission, receipt")? - Ans --Two people
introducing themselves to each other.
-One person asking, and getting, the time to/from another person.
-A student raising her/his hand to ask a really insightful question, followed by the teaching
acknowledging the student, listening carefully to the question, and responding with a clear,
insightful answer. And then thanking the student for the question, since teachers love to get
questions.
Access network per-subscriber speeds. Match the access network with the approximate
speeds that a subscriber might experience. (Note: if you look these up, do so in the 8E
textbook, slides,or video -- not in the 7E or earlier versions, since link access speeds are
always increasing over the years). - Ans -1)Ethernet - Wired. Up to 100's Gbps per
link.
2)4G cellular LTE - Wireless. Up to 10's Mbps per device.
3)802.11 WiFi- Wireless. 10's to 100's of Mbps per device.
4)Cable access network- Wired. Up to 10's to 100's of Mbps downstream per user.
5)Digital Subscriber Line-Wired. Up to 10's of Mbps downstream per user.
Link Transmission Characteristics. Which of the following physical layer technologies has
the highest transmission rate and lowest bit error rate in practice? - Ans -Fiber optic
cable
1
Page
, Routing versus forwarding. Choose one the following two definitions that makes the correct
distinction between routing versus forwarding. - Ans -Forwarding is the local action of
moving arriving packets from router's input link to appropriate router output link, while
routing is the global action of determining the source-destination paths taken by packets.
Packet switching versus circuit switching (1). Which of the characteristics below are
associated with the technique of packet switching - Ans -1. Data may be queued
before being transmitted due to other user's data that's also queueing for transmission.
2.This technique is used in the Internet.
3.Resources are used on demand, not reserved in advance.
4. Congestion loss and variable end-end delays are possible with this technique.
Packet switching versus circuit switching (2). Which of the characteristics below are
associated with the technique of circuit switching? - Ans -1.Reserves resources
needed for a call from source to destination.
2.Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two
approaches for implementing this technique.
3. This technique was the basis for the telephone call switching during the 20th century
and into the beginning of this current century.
How many calls can be carried? Consider the circuit-switched network shown in the figure
below, with four circuit switches A, B, C, and D. Suppose there are 20 circuits between A
and B, 19 circuits between B and C, 15 circuits between C and D, and 16 circuits between D
and A. What is the maximum number of connections that can be ongoing in the network at
any one time? - Ans -70
Trying out traceroute. Perform a traceroute from your computer (on whatever network you
2
happen to be on) to gaia.cs.umass.edu. Use traceroute (on Mac terminal) or tracert (on
Page
Answers Graded A
What is a protocol? Which of the following human scenarios involve a protocol (recall:
"Protocols define the format, order of messages sent and received among network entities,
and actions taken on message transmission, receipt")? - Ans --Two people
introducing themselves to each other.
-One person asking, and getting, the time to/from another person.
-A student raising her/his hand to ask a really insightful question, followed by the teaching
acknowledging the student, listening carefully to the question, and responding with a clear,
insightful answer. And then thanking the student for the question, since teachers love to get
questions.
Access network per-subscriber speeds. Match the access network with the approximate
speeds that a subscriber might experience. (Note: if you look these up, do so in the 8E
textbook, slides,or video -- not in the 7E or earlier versions, since link access speeds are
always increasing over the years). - Ans -1)Ethernet - Wired. Up to 100's Gbps per
link.
2)4G cellular LTE - Wireless. Up to 10's Mbps per device.
3)802.11 WiFi- Wireless. 10's to 100's of Mbps per device.
4)Cable access network- Wired. Up to 10's to 100's of Mbps downstream per user.
5)Digital Subscriber Line-Wired. Up to 10's of Mbps downstream per user.
Link Transmission Characteristics. Which of the following physical layer technologies has
the highest transmission rate and lowest bit error rate in practice? - Ans -Fiber optic
cable
1
Page
, Routing versus forwarding. Choose one the following two definitions that makes the correct
distinction between routing versus forwarding. - Ans -Forwarding is the local action of
moving arriving packets from router's input link to appropriate router output link, while
routing is the global action of determining the source-destination paths taken by packets.
Packet switching versus circuit switching (1). Which of the characteristics below are
associated with the technique of packet switching - Ans -1. Data may be queued
before being transmitted due to other user's data that's also queueing for transmission.
2.This technique is used in the Internet.
3.Resources are used on demand, not reserved in advance.
4. Congestion loss and variable end-end delays are possible with this technique.
Packet switching versus circuit switching (2). Which of the characteristics below are
associated with the technique of circuit switching? - Ans -1.Reserves resources
needed for a call from source to destination.
2.Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two
approaches for implementing this technique.
3. This technique was the basis for the telephone call switching during the 20th century
and into the beginning of this current century.
How many calls can be carried? Consider the circuit-switched network shown in the figure
below, with four circuit switches A, B, C, and D. Suppose there are 20 circuits between A
and B, 19 circuits between B and C, 15 circuits between C and D, and 16 circuits between D
and A. What is the maximum number of connections that can be ongoing in the network at
any one time? - Ans -70
Trying out traceroute. Perform a traceroute from your computer (on whatever network you
2
happen to be on) to gaia.cs.umass.edu. Use traceroute (on Mac terminal) or tracert (on
Page
