1) Physical Layer

Define each of the following terms: signal, symbol, medium, carrier, full duplex and half duplex, bit rate and baud rate, circuit (in data communications).

This is an electromagnetic field that is used to transmit data from one point to the next (Andrew, 2004). Signal can either be in the form of DC which can be switched on and off to prevent and allow the flow of current.

Symbol is a digital pulse which is transmitted through the modem. It represents the availability of a signal during communication.

It is a communication channel through which information are conveyed from the sender to the receiver.

This is broadcasted electromagnetic wave at a balanced frequency through which information is imposed.

Simplex is a channel through which data is transmitted in one way and it is a channel which usually is not used because it does not allow for the transmission of control signals at the end.

Half Duplex

This is a channel which is able to send and receive transmitted data through a network at different times. It allows for the transmission and reception of data at different times. In this case the data transmitted cannot travel in both directions at the same time.

Full Duplex

This is a channel through which data can be transmitted in both directions at the same time. It therefore allows the user not to switch channels in order to receive data instead of receiving and transmitting data without changing data transmission channels.

Baud Rate

This is a very important measure of the number of line changes per second. It is the same as symbol rate and it is represented by binary encoded signal. It can also be referred as the rate at which signals are used on a circuit.

Bits rate

This is the number of data bits per second that pass through a line. It is the same as bound rate when binary signal is used to transmit data from one node to the next (Eugene, 2015). It can also be referred as the rate through which information is transferred through a channel.

This is the channel through which data is transmitted from one point to another or it is a complete line along which electromagnetic signals pass through to convey information.

2) Link Layer

a) Using flag byte framing, what will be the actual transmitted sequence for the following data stream:

Hello STX there DLEDLE everyone ETXCRLF

Start of text STX beginning of text, ETX end of text

Frames: STX frame data ETX frame data ETX

Byte stuff the character ETX

An escape character is introduced: DLE: Data link escape

There are some characters that needs to be stuffed is STXDLEETX

b) Using the flag bit sequence of 01111110 shows how the following bit string will be transmitted:


Suggestion: highlight inserted characters and bits in bold.

The sender will always add 00 after five 1’s and the receiver will always delete 0 after five 1’s.


3) Link Layer

What does Medium Access Control do? What are the different schemes used? Briefly explain how each scheme works. Which algorithms are centralized and which are distributed?

MAC is used to generate data link layer of Ethernet LAN system. It is therefore essential for transmitting data packets across network –interface card or across a remote shared channel. MAC usually generates address mechanism and channel access to allow available node within the network can communicate with other nodes in a different network (Glenn, 2012). MAC uses different schemes to ensure that it transmit data to and fro different nodes of the same network or other networks. The centralized algorithm that MAC uses is OSI model while Ethernet is used for distributed algorithm.


Andrew S. (2004). Computer Networks, ISBN: 0-13066102-3

Glenn B (2012) “Computer Science An Overview”, ISBN: 0-321-54428-5

Eugene B (2015) “Introduction to Networking and Data Communications