Chapter 18 Questions

List four types of delays in a packet-switched network.

1. Transmission Delay 2. Propagation Delay 3. Queuing Delay 4. Processing Delay

If a label in a connection-oriented service is 8 bits, how many virtual circuits can be established at the same time?

2^8

In classless addressing, we know the first address and the number of addresses in the block. Can we find the prefix length? If the answer is yes, show the process.

Yes, N is given, use n = 32 - logBASE(2)N

In classless addressing, we know the first and the last address in the block. Can we find the prefix length? If the answer is yes, show the process.

Yes, given the address range you can find N using n = 32 - logBASE(2)N

In classless addressing, can two different blocks have the same prefix length? Explain.

Yes, prefix length defines number of addresses, no the block itself

What is the piece of information in a packet upon which the forwarding decision is made in each of the following approaches to switching? a.) Datagram b.) Virtual-Circuit

a.) Destination Address b.) label

Do we have any of the following services at the network layer of TCP/IP? If not, why? a.) Flow Control b.) Error Control c.) Congestion Control

a.) No, done at transport layer b.) Only for the header c.) No, done at transport layer

Why does the network-layer protocol need to provide packetizing service to the transport layer? Why can't the transport layer send out the segments without encapsulating them in datagrams?

The transport layer concerns itself with the logical link, but the network layer concerns itself with how the segments reach the other host and as such it chooses how to packetize the information.

Why is routing the responsibility of the network layer? In other words, why can't the routing be done at the transport layer or the data-link layer?

This is the whole purpose of the network layer

In Figure 18.10, assume that the link between R1 and R2 is upgraded to 170 kbps and the link between the source host and R1 is now downgraded to 140 kbps. What is the throughput between the source and destination after these changes? Which link is the bottleneck now?

Throughput = 140 Kbps, Source to R1 is bottleneck

Distinguish between the process of routing a packet from the source to the destination and the process of forwarding a packet at each router.

Routing finds the best path along which to send data. Forwarding simply moves data along a pre-defined path

List the three phases in the virtual-circuit approach to switching.

Setup, Data Transfer, Teardown