Digital Data Transmission: Transmission Techniques

Earlier articles on the topic: : Digital Data Transmission and Digital Data Transmission: Transmission Mode.

A communication network consists of a collection of devices (or nodes) that wish to communicate and interconnect together. The primary objective in any communication network is simply moving information from one source to one or more destination nodes. 

Based on the techniques used to transfer data, communication networks can be categorized into Broadcast and Switched networks.

Let's talk about the transmission techniques in detail.

Broadcast Networks

In Broadcast networks, data transmitted by one node is received by many, sometimes all, of the other nodes. This refers to a method of transferring a message to all recipients simultaneously.

For example – a corporation or other voluntary association, that provides live television or recorded content such as movies, newscasts, sports, public affairs programming, and other television programs for broadcast over a group of radio stations or television stations.

Switched Networks

In switched-communication networks, the data transferred from source to destination is routed through the switch nodes. The way in which the nodes switch data from one link to another, as it is transmitted from source to destination node, is referred to as a switching technique.

Three common switching techniques are Circuit Switching, Packet Switching, and Message Switching.

Circuit Switching

A Circuit Switching network is one that establishes a fixed bandwidth circuit (or channel) between nodes and terminals before the users may communicate, as if the nodes were physically connected with an electrical circuit. 

The route is dedicated and exclusive, and released only when the communication session terminates. Circuit switching is what most of us encounter on our home phones. A single circuit is used for the entire duration of the call. Applications which use circuit switching go through three phases: Establish a Circuit, Transfer of data and Disconnect the Circuit.

Packet Switching

It is a sophisticated means of maximizing transmission capacity of networks. Packet switching refers to protocols in which messages are broken up into small transmission units called packets, before they are sent. 

Each packet is transmitted individually across the net. The packets may even follow different routes to the destination. Since there is no fixed path, different packets can follow different path and thus they may reach to destination out of order.

Message Switching

In message switching, end-users communicate by sending each other a message, which contains the entire data being delivered from the source to destination node. As a message is routed from its source to its destination, each intermediate switch within the network stores the entire message, providing a very reliable service. 

The intermediary nodes (switches) have the responsibility of conveying the received message from one node to another in the network. Therefore, each intermediary node within the network must store all messages before retransmitting them one at a time as proper resources become available. This characteristic is often referred to as Store and- Forward. Electronic mail (e-mail) and voice mail are examples of message switching systems.

Well, that's it on techniques of transmission. We shall discuss The OSI model in the next article, stay tuned for that.

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