TCS Papers: Sample Questions 352 - 352 of 502

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Question number: 352

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Describe in Detail

What is Stop-and-wait Automatic Repeat Request?

Explanation

  • Stop-and-Wait Automatic Repeat Request (Stop-and Wait ARQ), adds simple error control mechanism to the Stop-and-Wait Protocol which detects and corrects corrupted frames.

  • Typically detection of errors is done by the silence of the receiver but lost frames are difficult to handle, as repeated frame could be the correct, duplicate, or out of order. Solution is to number the frames, than a data frame out of order means that frames were either lost or duplicated. This allows corrupted and lost frames to now be resent.

  • Sender keeps a copy of the sent frame and starts a timer. If the timer expires and there is no ACK for the sent frame, the frame is resent, the copy is held, and the timer is restarted.

  • Since the protocol uses the stop-and-wait mechanism, there is only one specific frame that needs an ACK even though several copies of the same frame can be in the network.

  • Since an ACK frame can also be corrupted and lost, it too needs redundancy bits and a sequence number.

  • The ACK frame for this protocol has a sequence number field. The sender simply discards a corrupted ACK frame or ignores an out-of-order one.

Automatic repeat request

Automatic Repeat Request

Given the image is define the stop-and-wait Automatic repeat request