Computer Networks MCQ - Why does TCP retransmit the message

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Computer Networks MCQ - TCP and retransmission of data packets

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1. Which of the following communication protocols ensures the sender to resend the message, if the sender did not receive an acknowledgement for a sent message?

a) Only TCP

b) Only UDP

c) Both TCP and UDP

d) Neither TCP nor UDP

Answer: (a) Only TCP In Transmission Control Protocol (TCP), the sender will resend the message in case if the sender does not receive an acknowledgement for a sent message. Because of this TCP is referred as reliable communication protocol. Why do we say that the TCP connection is reliable? Transmission is made reliable via the use of sequence numbers and acknowledgments.  Conceptually, each octet of data is assigned a sequence number.  The sequence number of the first octet of data in a segment is transmitted with that segment and is called the segment sequence number.  Segments also carry an acknowledgment number which is the sequence number of the next expected data octet of transmissions in the reverse direction.  When the TCP transmits a segment containing data, it puts a copy on a retransmission queue and starts a timer; when the acknowledgment for that data is received, the segment is deleted from the queue.  If the acknowledgment is not received before the timer runs out, the segment is retransmitted. [Reference] TCP guarantees the delivery of data and packets in the same order as they were sent. When does TCP retransmission occur? / Why does TCP retransmit? TCP retransmission occurs if the sender TCP did not receive an acknowledgement for the segment it sent to the receiver. TCP will resend the corrupted packets whereas UDP not.

 

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Computer Networks MCQ - Handling of corrputed data packets by TCP and UDP

Multiple choices questions in Computer Networks, Computer Networks solved MCQ, How does TCP and UDP work?, handling of corrupted data packets by TCP, handling of corrupted data packets by UDP, Corrupted message will not be delivered to a receiving process by TCP. What is checksum

Computer Networks MCQ - TCP and UDP - Corrupted messages

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1. Suppose a message may be corrupted between the sending process and the receiving process and as a result the receiving process may receive a corrupted message. Which of the following protocols works this way?

a) Only TCP

b) Only UDP

c) Both TCP and UDP

d) Neither TCP nor UDP

Answer: (d) Neither TCP nor UDP          Neither protocol will allow a corrupted message to be delivered to a receiving process; both protocols use checksums to ensure that corrupted messages are not delivered to the receiving process. Checksum will be used at both the receiver and sender’s end. How checksum is used to handle corrupted messages (data packets)? Checksum is a simple error detection mechanism to determine the integrity of the data transmitted over a network. Communication protocols like TCP/IP/UDP implement this scheme in order to determine whether the received data is corrupted along the network. The sender of an IPv4 datagram would compute the checksum value based on the data and embed it in the frame. The receiver would also compute the checksum locally and based on the result ascertain the data integrity. Similarly the TCP/UDP data which forms the payload for the IP datagram would have its checksum computed and embedded as a part of the TCP/UDP frame. TCP will resend the corrupted packets whereas UDP not.

 

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