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Network transmission methods
Network transmission method is the methodology by which the data travels on a network. It is the protocol followed by two nodes on a network to send and data from each other. There are various techniques for sending data that depends upon the type of connection between the two nodes. Two nodes might be separated by a huge distance, i.e. they might be a part of WAN (wide area network) or they could be present in the same room and at the same network. Network transmission method also depends upon the type of channel between the two nodes. A network would use the transmission method depending upon the speed and reliability of the channel between the nodes. In general in one local area network, the methodology would be uniform, but a node connecting two or more networks may use several methodologies at once. With the advance in technology several transmission techniques have evolved. We study a few of them in detail.
- Frame relay method: - The frame relay method is composed of frames. Frames are packets of data that have variable sizes but they have an upper limit on the amount of data they can carry. In a frame relay system the frames are relayed from one node to another. Just as a relay race, the first runner gives the stick to the second, second gives to the third and so on, similarly in a frame relay method the source relays the packet to one intermediate node and then that node forwards it to destination by relaying the node to other intermediate nodes. One single packet could be transmitted from many sources at a single point of time, i.e. more than one intermediate node has received the relay message and all are forwarding the packet. Therefore there is more than one path in a frame relay method that a packet can use to reach the destination. If the destination receives the frames from one or more destinations then it keeps the first successfully received packet and drops other packets. Frame relay method leaves the error correction to the end points; this makes it faster as the protocol itself does not involve any error correction. Following are the characteristics of a frame relay system:-
- It uses encapsulation of voice and data that allows same telephone line to be used as a voice as well as data line.
- It provides a permanent virtual circuit to a user and hence a reliable channel. An enterprise can also select the level of service quality, prioritizing certain packets over other.
- Its cheapness and ease of configuring the devices has made it very popular and is the most used method in rural and small cities.
- ISDN (Integrated Services Distributed Network):- The integrated services distributed network extends the concept of integrating voice and data over one line. With ISDN we can send video, voice, data, internet facilities and other digital network services over the same telephone lines. ISDN is basically a circuit switched system but it also allows packet switched transmission over the network. The ISDN service comes with various interfaces that vary in the data bit rates. These are
- Basic rate interface:- basic rate interface has a channel bandwidth of 144kbps. It contains three channels, two are 64kbps bearer channels (B' channels) and one is the 16 kbps signal channel also referred to as delta channel (D' channel). So the basic rate interface is referred to as 2B+D interface.
- Primary rate interface:- primary rate interface is much faster than the basic rate interface. It has a total bandwidth capacity of 2048 bits. There are two primary interfaces E1 and T1, E1 uses 30 B channels, 1 D channel and 1 timing and alarm channel of 64kbps, while T1 uses 23 B channels and 1 D channel, a total of 24 channels and a total bandwidth of 1544 kbps.
- Broadband ISDN (B-ISDN):- this is the fastest interface providing a bandwidth that can extend to hundreds of Mbps. This provides fast transmission of digital images and videos and other content.
- Cable modem: - a cable modem is referred to a connecting device that can transmit signals over a cable using radio frequency; it acts as a network bridge. The cable mentioned here is just not any cable but the television cable that is found in every house these days. They are mostly use to provide internet access along with the television using the high bandwidth of a television cable. Cable modems nowadays are also being used for telephonic services. This uses a protocol named VoIP (Voice over Internet protocol). It called a modem because it modulates the data and sends over a cable and then it demodulates on the receiver end.
- Digital subscriber line (DSL):- digital subscriber line provides voice and data transfer over the common telephone line. It uses a separate frequency for both type of transfers. It uses a 25khz for band for data and a 4khz band for voice. The typical download speeds are 386 kbps to 20 Mbps.
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