Xavier University – Ateneo de Cagayan
Department of Computer Science
CS 55 Computer Networks
Essay/Short Answer Question/Problem Solving. In your own words, answer the following
questions as briefly and concisely as possible – 8 items (10 points each for a total of 80 points).
1. Using a block diagram, describe the major components of a communication system. Show an
example using a specific data communication scenario (e.g. dial-up Internet access via a local
Internet Service Provider or accessing remote computers over the telephone network). What
are the things that you need in terms of hard ware and software?
2. Enumerate and describe the seven layers of the Open Systems Interconnect (OSI) Reference
Model then describe the main layers of the Transmission Control Protocol/Internet Protocol
(TCP/IP) and how it relates to the OSI reference model. Is there a one-to-one mapping
between the TCP/IP and OSI layers? Show an example of layering by mapping the
components of a network you are familiar with to the OSI RM or TCP/IP layers.
3. Rank twisted pair, coaxial cable and fiber optics with respect to speed, cost and resistance to
“noise”. Which is fastest? Which is least expensive? Which is less error prone? Use a table to
describe your answers. What is the ideal medium to cable a room, link building floors or
connect buildings on a local area or campus network?
4. Describe how parity checking (PC) works? Cyclic redundancy check (CRC)? Longitudinal
redundancy check (LRC)? Which is better at detecting errors, PC or CRC? What is the
difference between CRC and LRC?
5. Describe the three basic local area network (LAN) topologies? What LAN transmission
media is suitable for each of the topologies? How does topology affect the media access
control (MAC) protocol used in a LAN?
6. Using the OSI Reference Model as a guide, describe the functions of networking devices
such as repeaters, bridges, routers and gateways. What are the similarities and differences
between an Ethernet hub and switch?
7. What is an IP address? A network mask? How do IP addresses relate to Fully Qualified
Domain Names (FQDNs) and the Domain Name Service (DNS). Describe how data packets
are routed or transmitted over the Internet (i.e., IP routing).
8. Given the different types of data transmission media/channels - private lines, switched lines,
leased lines, coaxial cable, fiber optics, microwave, satellite, etc - which would be the most
suitable for the following applications and why? (a) A research corporation is evaluating
solar energy systems. It has data collection devices attached to several experimental wind and
solar collectors. A large, continuous volume of data is transmitted to the computer center,
which is 10 miles from the test grounds. The computer center can be seen from the test
grounds. (b) A major car rental agency has decide to rationalize its inventory and reservation
system. Approximately 75% of the reservation requests are resolved by the regional center
and the remaining 25% must be forwarded to another regional processing center. The peak
amount of data to be transmitted to another center is approximately 10,000 characters per
minute. This also means that each regional center will receive approximately 10,000
characters per minute.