Day 8: Switching, ISDN, Multiplexing

Hello Dear Students,
     Hope you all are doing good..

Today's our topic is Switching, Multiplexing and ISDN.

Let's get started...

SWITCHING - Switching means the technique which can determine the connections between 2 or more devices and handles the movement of the data. A switched network has various interlinked nodes known as switches. Switches are the hardware or software devices that creates connections between 2 or more devices. 
Types of Switching -

  • CIRCUIT SWITCHING - Circuit Switching is used in the telephone lines where when we place telephone call, then the switching equipment within the system seeks out the physical path from your telephone to the receiver's telephone. It takes place at the physical level. There is no addressing in data transfer. In this, a set of switches are connected by physical links and each link is divided into n channels. The data is transmitted without any delay, once the circuit establishes. It requires more bandwidth for transmission.
Basically 3 phases are there- 
  1. Setup Phase
  2. Data Transfer Phase
  3. Tear Down Phase
The end terminals in circuit switching are- Telephone, Modem. It transmits the analog and digital data. It is bi-directional and used as real time transfer of voice signals. The routing is done during it's setup is done. 

  • MESSAGE SWITCHING - In message switching, there is no physical path in advance between the sender and the receiver. Message is send from source node to the intermediate node(i.e. IMP). The IMP stores the message temporarily, detect and remove errors and then the message is send to the receiver node. And that is why it is also known as store and forward network. The end terminals of message switching are telegraph, teletype. It transmits the digital data and the routing is manual. It also adds the destination address to the messages. 
IMP- IMP stands for Interface Message Processor. It was basically the 1st generation gateways in the late 1960s to 1989, but now it is known as the Routers.

  • PACKET SWITCHING - The entire message is broken into smaller pieces which are known as Packets. Packets has a header which contains the source address, destination address, other information, and it sends the packets data from node to node. However, the size of the packets depends upon the type of network used. The end terminal is Computers and it transmits the digital data and the binary information. It is routed independently and the application is the internet for datagram. It is of 2 types basically- 
  1. DATAGRAM - Each data packets are separately addressed and the packets are known as the data grams. Unique ID to data for transfer. It is done at network layer and is a connection-less network. 
  2. VIRTUAL CIRCUIT - In this, all the data packets follows same path and is done at the data link layer. It is a logical connection between the sender and the receiver before the data transfers. 
It increases the bandwidth of the network and is very fast for the real time operating system. However, its protocols are complex. 


ISDN - ISDN stands for Integrated Service Digital Network. It was developed by International Telecommunication Union in 1976. It is a high speed network service which can transmit voice data, text data, graphics, music, videos and any type of data over the telephone lines. It is basically a set of protocols which combines the digital telephone and data transport. 

ISDN Features-
  1. It supports the voice and non-voice applications.
  2. 64Kbps connection(higher speed at that time)
  3. Support switch and non-switch applications(supports both packet and circuit switching)
  4. Requires complicated setup from which connection can establish.
  5. OSI and TCP/IP models
Devices Used in ISDN Networking
  • TE1 and TE2 - Terminals in which we can create the connection in digital telephone lines. Basically it is a 4 wire twisted-pair digital link. 
  • TA - Terminal Adopter which is a device used as an inter-mediator device for non ISDN terminals.
  • NT 1 - This device provides line monitoring, error statics, proper timings.
  • NT 2 - This device provides switching, multiplexing, distribution of the information. This can be LAN server, multiplexer, or PBX(Private Branch eXchange).
CHANNELS OF ISDN
  • B CHANNEL - It is defined at 64Kbps data rate and is used to carry data, digital voice and other low data rate information.
  • D CHANNEL - It can either 60 or 64Kbps depending upon user's needs. It does not carry data.
  • H CHANNEL - It is the Hybrid channel. It starts from 384Kbps and goes to 1920Kbps. Provides the information at higher bit rates. Mostly used for Video Conferencing.


MULTIPLEXING - It is the process of sending the signals from 2 or more different sources simultaneously(at the same time). Multiplexing is done by a device known as Multiplexer(MUX). The multiplexer combines n different input lines to generate one output line. It is a many to one process. At the receiving end, the device is known as D-multiplexer(D-MUX) which separates the signals into one competent signal. 
Basically divided into 2 categories-
  • FDM - FDM stands for Frequency Division Multiplexing an analog technique which divides the frequency spectrum into logical channels, each user has its frequency band.
  • TDM - TDM stands for Time Division Multiplexing in which the user takes turn(in a round robin), periodically getting entire bandwidth for little burst of time.


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