Knowledge Checks

Routing versus forwarding.

Choose one the following two definitions that makes the correct distinction between routing versus forwarding.

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.

Routing is the local action of moving arriving packets from router’s input link to appropriate router output link, while forwarding is the global action of determining the source-destination paths taken by packets.

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1/7

Packet switching versus circuit switching (1).

Which of the characteristics below are associated with the technique of packet switching? Select all correct answers. [Hint: more than one of the answers is correct].

Resources are used on demand, not reserved in advance.

Data may be queued before being transmitted due to other user’s data that’s also queueing for transmission.

This technique was the basis for the telephone call switching during the 20th century and into the beginning of this current century.

This technique is used in the Internet.

Reserves resources needed for a call from source to destination.

Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two approaches for implementing this technique.

Congestion loss and variable end-end delays are possible with this technique.

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2/7

Packet switching versus circuit switching (2).

Which of the characteristics below are associated with the technique of circuit switching? Select all correct answers. [Hint: more than one of the answers is correct].

Resources are used on demand, not reserved in advance.

This technique was the basis for the telephone call switching during the 20th century and into the beginning of this current century.

Data may be queued before being transmitted due to other user’s data that’s also queueing for transmission.

This technique is used in the Internet.

Congestion loss and variable end-end delays are possible with this technique.

Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) are two approaches for implementing this technique.

Reserves resources needed for a call from source to destination.

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3/7

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.

Question 1.3.4

What is the maximum number of connections that can be ongoing in the network at any one time?

[Note: you can find more questions like this one here.

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4/7

Trying out traceroute.

Perform a traceroute from your computer (on whatever network you happen to be on) to gaia.cs.umass.edu. Use traceroute (on Mac terminal) or tracert (on Windows command line) or tracepath (on a Linux command line). Enter the missing part of the name of the router just before the host gaia.cs.umass.edu is reached:

??.cs.umass.edu

Note: Routing may change, so the answer here may not be correct anymore. Also, if you are a Verizon user, there are known problems using traceroute with Verizon - if traceroute shows you two hops only to gaia.cs.umass.edu or any destination, skip this question.

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Not quite. Your answer isn't correct. Note that network configurations may change and so the earlier answer to this question in early 2020 may no longer be the right asnwer,. So your answer could be correct.

5/7

What is a network of networks?

When we say that the Internet is a “network of networks,” we mean? Check all that apply (hint: check two or more).

The Internet is the largest network ever built.

The Internet is the fastest network ever built.

The Internet is made up of a lot of different networks that are interconnected to each other.

The Internet is made up of access networks at the edge, tier-1 networks at the core, and interconnected regional and content provider networks as well.

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6/7

Packet switching or Circuit-switching?

Consider a scenario in which 5 users are being multiplexed over a channel of 10 Mbps. Under the various scenarios below, match the scenario to whether circuit switching or packet switching is better.

Question List:

Each user generates traffic at an average rate of 2.1 Mbps, generating traffic at a rate of 15 Mbps when transmitting

Each user generates traffic at an average rate of 2 Mbps, generating traffic at a rate of 2 Mbps when transmitting

Each user generates traffic at an average rate of 0.21 Mbps, generating traffic at a rate of 15 Mbps when transmitting

Answer List:

Packet switching
Neither works well in this overload scenario
Circuit switching

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7/7

Knowledge checks

Routing versus forwarding.

Packet switching versus circuit switching (1).

Packet switching versus circuit switching (2).

How many calls can be carried?

Trying out traceroute.

What is a network of networks?

Packet switching or Circuit-switching?

Question List:

Answer List: