Basic CS-Networks [TCS Placement]: Sample Questions 10 - 11 of 133

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Question 10

Networks
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Describe in Detail

Essay▾

What is usage of sequence number in reliable transmission?

Explanation

  • Frames are numbered using sequence numbers field in data frame.
  • To minimize the frame size, sequence numbers have smallest range to provide unambiguous communication and hence can wrap around.
  • TCP uses a 32-bit sequence number that counts bytes in the data stream.
  • Each TCP packet contains the starting sequence number of the data in that packet, and the sequence number (called the acknowledgment number) of the last byte received from the remote peer.
  • Each TCP peer must track both its own sequence and that of remote peer.

What is the use of flags in networking?

  • TCP uses a number of control flags to manage the connection- some pertain to single packet, but two flags (SYN and FIN) , require reliable delivery as they mark the beginning and end of the data stream. To insure their reliable delivery they are assigned spots in the sequence number space.
  • Each flag occupies a single byte.

Question 11

Networks
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Describe in Detail

Essay▾

What are the key elements of protocols?

Explanation

The key elements of a protocol are syntax, semantics and timing.

  • Syntax:
    • Syntax refers to the structure of data, meaning the order in which they are presented.
    • For example, a simple protocol might expect the first 8 bits of data to be the address of the sender, the second 8 bits to be the address of the receiver and the rest of the stream to be the message itself.
  • Semantics
    • Semantics refers to the meaning of each section of bits.
    • For example, how are a particular pattern to be interpreted? What action is to be taken based on the interpretation? Does an address identify the route to be taken or the final destination of the message?
  • Timing
    • The term timing refers to two characteristics:
      • When data should be sent?
      • How fast they can be sent?
    • For example, if a sender produces data at 100 mbps but the receiver can process data at only 1 mbps, the transmission will overload the receiver and some data will be lost. Timing would prevent this loss.

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