CSCI 278 : COMPUTER NETWORKS

Instructor : Seung Bae Im

MIDTERM EXAM ----- Spring 2002

Closed book, closed notes. Write neatly.

Name : _____________________________

1.(30 points) For the OSI 7 layers, describe the following terms:

(a) Peer-to-peer virtual communications

(b) n^th layer protocol

(c)  Multiplexing/demultiplexing.

(d) In what way OSI Model is important to us?

2.(10 points) State the reasons why TCP/IP protocol suite is dominant(used almost everywhere, used on  almost every machine) over all other protocols including OSI protocols.

3.(10 points) Describe

(a) Describe how Ethernets achieve the synchronizations; (1) Bit synchronization (2) Frame synchronization.

(b) What is a “collision domain” in Ethernets? What are the 2 devices that can separate a collision domain into more than one collision domain?

4.(20 Points) Answer the questions.

(a) Describe how “multibit modulation” works.

(b) What are 1) Bandwidth of a signal  2) Bandwidth of a channel ?

(c) State why 4B/5B code is more efficient than Manchester code.

(d) Describe differences between regular Ethernet hub and Ethernet Switch.

5.(10 points) Compare the “Connection-Oriented Service” and “Connectionless Service”.

6.(20 points) Discuss/describe

(a) Draw the protocol diagram(showing layers) for the LAN protocols—Show IEEE 802.2, 802.3, 802.5.  Also clearly show the Physical, MAC and LLC layers on the diagram.

(b) Ethernets have two frame formats(Ethernet II & IEEE802.3). The main difference is on their 2 byte fields: On Ethernet II, these 2 byte field is called “Type” field. On IEEE802.3, they are called as “Length” field. Describe how those two different frame formats can co-exist on a LAN.