Data communication - Question and answer - 7

31. Write about Error Control ?
Error control in the data link layer is based on ARQ (automatic repeat request), which is the re transmission of data. The term error control refers to methods of error detection and re transmission. Every time an error is detected in an exchange, specified frames are re-transmitted. This process is called ARQ.

32. What is ARPANET ?
The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switching network with distributed control and the first network to implement the TCP/IP protocol suite. The ARPANET was established by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense.

33. What is a gateway ?
A gateway is a piece of networking hardware used in telecommunications for telecommunications networks that allows data to flow from one discrete network to another.

34. What is NSFNet ?
The National Science Foundation Network (NSFNet) is a wide area network that was developed by the National Science Foundation to replace ARPANET as the main network linking government and research facilities. NSFNet was a major force in the development of computing infrastructure and enhanced network services.

35. What is Unguided medium?
Unguided medium transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them.

36. What is Block Coding ?
Block coding refers to the technique of adding extra bits to a digital word in order to improve the reliability of transmission. The word consists of the message bits (often called information, or data) plus code bits. It may also, as in the present case, contain a frame synchronization bit. A block code adds bits to existing message bits, or blocks, independently of adjacent blocks.

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