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?
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