CS413 Computer Networks ASN 4 Solutions
a network.
13. Does Ethernet provide connection-oriented or connectionless service? [2 marks]
Solution:
Ethernet provides connectionless transfer(2) service of information frames.
16. Suppose two Ethernet LANs are interconnected by a box that operates as follows. The box
has a table that tells it the physical addresses of the machines in each LAN. The box listens to
frame transmissions on each LAN. If a frame is destined to a station at the other LAN, the box
retransmits the frame onto the other LAN, otherwise the box does nothing.
Solutions follow questions:
a. Is the resulting network still a LAN? Does it belong in the data link layer or the network
layer? [2 marks]
The resulting network is a local area network(1) that has been extended. The extended LAN
transfers frames, and so it still belongs in the data link layer(1).
b. Can the approach be extended to connect more than two LANs? If so, what problems
arise as the number of LANs becomes large? [2 marks]
Yes, more than two LANs can be connected(1) using the above approach to form an
extended LAN. As the number of LANs becomes large, the number of physical addresses
stored in the bridge grows and becomes unmanageable(1). Each time a machine is added the
addresses in all the boxes need to be updated. Serious problems arise if boxes are connected
so that loops can occur.
17. Suppose all laptops in a large city are to communicate using radio transmissions from a high
antenna tower. Is the data link layer or network layer more appropriate for this situation?
[2 marks]
Solution:
The data link layer is concerned with the transfer of frames of information across a single
hop . The network layer involves the transfer of information across a network using multiple
hops per path in general. The connection from a radio antenna to the laptops is direct, and
thus a data link layer protocol is more suitable for this situation (2).
Now suppose the city is covered by a large number of small antennas covering smaller areas.
Which layer is more appropriate? [2 marks]
A number of areas each covered by small antennas can be interconnected using the
"bridging" approach of problem 16, which remains in the data link layer. However, the
network layer may be more appropriate(2) because it provides for the transfer of data in the
form of packets across the communication network. A key aspect of this transfer is the
routing of the packets from the source machine to the destination machine, typically
traversing a number of transmission link and network nodes where routing is carried out.
Leon-Garcia/Widjaja 2