Question

1. Describe CDM  and TDM and highlight the differences between them?

2. Explain the following switching operations:

a. circuit switching             b. packet switching

3. Show (Draw) the OSI model.

4. Explain the functions of the Presentation layer.

Answer 1

Time Division Multiplexing is a digital multiplexing technology that separate data stream based on time .In this technique a MUX collects and store the incoming data from the sending device through this slow speed communication channel connected to it.The connected data is received and separated by a DE-MUX. And then transmitted to the appropriate receiving device .The TDM can be applied only when the transmission speed of the high-speed communication channel is equal to the sum of all the slow speed channel connected to the MUX.It can be implemented by two ways:- 1) Synchronous TDM and 2) Asynchronous TDM

In code division multiplexing, every user can transmit over the entire frequency spectrum all the time. CDM used in parts of the cellular telephone system and for some satellite communication . The specific version of CDM used in cell phones is known as Code Division Multi-Access (CDMA). CDM is achieved through application of spread-spectrum techniques. Spread spectrum techniques can be classified into two categories:

1) Direct-Sequence

2) Frequency hopping techniques

DIFFERENCE:-  

TDM works by dividing the time into time slices so that it is possible to reuse the available time whereas CDM is a networking technique which combines multiple data signals for simultaneous transmission over a common frequency band.

Time-Division Multiplexing works primarily with digital signals (sometimes analog) and separates various data streams based on time and not frequency or space whereas  Code-Division Multiplexing makes use of several channels that share the same frequency spectrum at the same time

CIRCUIT SWITCHING':-

In this switching between the sending and receiving device this circuit may pass through a number of devices .Once the circuit has been set up, The dedicated path will continue to exist the circuit until the circuit is terminated.Thus in circuit switching and end to end path is set up before any data can be sent .It works like the similar to telephone box.

PACKET SWITCHING :-

It is similar to message switching , but here the message is split into packets off fixed size.A packet consists of a header path that stores the address of a receiver ,control information ,packet no,etc . And the data that has to be transferred and a tailer at the end that contain error checking information.The packet may take different routes to reach the receiver and may reach the receiver at different time.

OSI MODEL.:-

FUNCTION OF PRESENTATION LAYER :- It is also called the syntax layer which act as a transmitter between the application program and the network format.This layer is concerned with the syntax and semmentics of data to be transmitted.

Generally, user program do not exchange data in a binry format instead they exchange it as name,address,dates,messages,pictures and so on.Moreover different computer stores the data in a different formats but to enable communication between this computers.The Presentation layer translates the data into a standard format to be sent on the network.

The main function of this layer is data compression ,which is done to be reduced the number of bits.Another function is security which can be implemented by authentication, data encryption and decryption function unauthorized user from accessing and interpreting the data.