Basic CS-Networks [TCS Placement]: Sample Questions 75 - 76 of 133

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Question 75


Write in Short

Short Answer▾

What do you meant by “triple X” in networks?


Triple X is a combination of:

  • The function of PAD (Packet Assembler Disassemble) described in a document known as X. 3. X. 3 specifies the parameters for terminal-handling functions such as line speed, flow control, character echo etc. for a connection to an X. 25 host.
  • Standard protocol between the terminal and the PAD called X. 28. X. 28 defines the DTE-C (asynchronous character mode) interface to a PAD, including the commands for making and clearing down connections, and manipulating the X. 3 parameters.
  • Protocol between the PAD and the network called X. 29. X. 29 defines the DTE-P (packet mode) interface to a PAD, i.e.. how the PAD encapsulates characters and control information in X. 25 packets.

Question 76


Describe in Detail


What is Stop-and-wait Automatic Repeat Request?


  • 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.
Given the Image is Define the Stop-And-Wait Automatic Repeat Request

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