Question

computer network
Please, Use your own words .
sorry No handwriting.
thanks

TCP is a very reliable transport layer protocol! This means that TCP uses error control mechanisms (or tools) to identify corrupted segments, lost segments, out-of-order segments, and copied segments. TCP error control mechanisms include checksum, acknowledgment, Time-out, and fast retransmission. Define each one of these four mechanisms in your own words.

Answer 1

TCP is very reliable transport layer protocol.

Error handling in TCP:

• TCP includes mechanism for detecting corrupted segments, lost segments,out-of-order segment and duplicate segments.
• TCP error control mechanism includes checksum, acknowledgement, timeout,fast retransmission.

Checksum:

• Each segment contains checksum field. TCP detects corrupted segement by using checksum field.
• Corrupted segment is discarded by destination and considered lost.

Acknowledgement:

• ​​​​​​​TCP sends acknowledgement when receiver receives data packet. It confirms receiving of data segments.
• The segments which consume a sequence number without data are also acknowledged.
• ACK segments never acknowledged.

Timeout:

• In timeout situation the segment is retransmitted when timer expires.
• Retransmission is the main task in error control. When a segment is corrupted, lost or delayed.
• TCP maintains RTO(retransmission time out) timer for segment which are sent but not acknowledged.
• When timer expires the outstanding(sent,but not acknowledged) segment is retransmitted.

Fast retransmission:

• RTO mechanism is works when RTO value is small. If it is large, it requires more time to confirm the segment is delivered or not.
• Sometimes one segment is lost and receiver receives so many out of order segements.
• To reslove this, 3 duplicate acknowledgement method is used. Missing segment is retransmitted immediately instead of retransmitting already delivered packet
• It is fast retransmission because it makes quicky retransmitted lost segement instead of waiting for timer to end.