Reliable Data Transfer Part 1

The internet network layer provides only best effort service with no guarantee that packets arrive at their destination. Also, since each packet is routed individually it is possible that packets are received out of order. For connection-oriented service provided by TCP, it is necessary to have a reliable data transfer (RDT) protocol to ensure delivery of all packets and to enable the receiver to deliver the packets in order to its application layer.

A simple alternating bit RDT protocol can be designed using some basic tools. This protocol is also known as a stop-and-wait protocol: after sending each packet the sender stops and waits for feedback from the receiver indicating that the packet has been received.

Stop-and-wait RDT protocols have poor performance in a long-distance connection. At best, the sender can only transmit one packet per round-trip time. For a 1000 mile connection this amounts to approximately 1 packet (about 1500 bytes) every 20 ms. That results in a pathetic 75 KB per second rate.

To improve transmission rates, a realistic RDT protocol must use pipelining. This allows the sender to have a large number of packets "in the pipeline". This phrase refers to packets that have been sent but whose receipt has not yet verified by the receiver.

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reliable data transfer 2.1,
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[kempisabel]

Thank you so much! Your explanation is so clear! Please post more videos about networking!

[tomegavazov]

I finally figured out why we need the f***g sequence number :D
Thank you so much.

[dikakaidn]

I thought rat 2.0 is the one with bit error?

[haileabtesfamariam]

Great explanation but you have lagged the version functionalities by 1. E.g. NACK free is rdt 2.2 but you refered it as rdt 2.1. Nonetheless, Great video so far.

[suhailfsheikh]

How does sender know if the last ACK/NAK is received properly at receiver?