TRANSMISSIONA. SIMPLEX TRANSMISSION THIS METHOD ALLOWS FOR TR...

3. Transmission

a. Simplex transmission

This method allows for transmission in one direction only

b. Half duplex transmission

This method means that’s data can be transmitted in both directions, but is only on direction at a

time

c. Full duplex trasmission

This method of transimission allows for transmission in both directions simultaneously

* Two modes of transmission are used when transmitting data over communication lines.

They are

 asynchrorous

 synchronous

Asynchronous:

- One character at a time is transmitted or received

- Each character is preceded by a start bit and a stop bit

 The start bit is used to indicate or character is being sent

 The stop bit is used to indicate the end of the character

- Asynchronous transmission is used for low speed devices

Direction of transmission

S S S S

T T T T

A 11000001 O 1111111 A 11000010 O

R P R P

T T

Synchronous:

- The speed of transmission is much faster

- Transmission groups of character can be send down the line without the start and

stop bits

000111000001011100000011

Question 3. LAN_Local Area Networks?

• Def: A LAN is a communication network in that connects office equipment to

provide a variety of data communication service which features high transmission

rates and low error rates

• Characteristics:

- Utilisation of some type of switching topology

- Locality restricted to a few miles or in the same bulding

- Proprietorship by a single organisation

• Features:

- LAN is after used in offices & it connects of fire equipment to provide a variety of

data communication. Service with light transmission rate and low errors rate

- The majorities of LANs are connected by coxial cable, and the protocol(rule for

communication) is very simple

• Three other important aspects of LANs:

- Acess method (protocol)

Central control

CSMA_CD

Empty slot access

Token access/token passing

• LAN transmission modes:

There are 2 main types of LAN transmission modes

a. Baseband transmission: is essentially & binary method, each bit being

represented by one of two states of an electric pulse passing through the network.

Baseband is nevertheless suitable for most LANs, and is the mode employed by

Ethernet and Cambridge Ring network

b. Broadband transmission: the data is modulates into a carrier wave. Broadband

transmission has a much greater band width than baseband, it can transmit sth

like ten times as much in a given time

• LAN is one of the distributed processing designs

- LAN are considered loosely coupled system processors are located in separate

machines and communicate at relatively low speeds

- LAN is the means by which distribution takes places, regardless of what are

distributed

Chapter 10: DATA COMMUNICATIONS.

Question 1. Write a short note of?