Reliable Data Transfer Protocols: RDT 2.2, 3.0, GBN, and Pipelining

What is RDT 2.2?

A stop-and-wait protocol that works over a channel with bit errors and requires only ACKs (not NAKs).

What additional requirements arise when a channel is lossy?

The protocol must detect packet loss and recover from it.

What techniques can be used to recover from packet loss?

Checksum, sequence numbers, ACK packets, and retransmissions.

How does the sender determine when to declare a packet lost?

By waiting for a specified period of time, known as a timeout.

What factors should be considered when setting a timeout period?

At least the round-trip time (RTT) including queuing and processing delays.

What is RDT 3.0?

An alternating-bit protocol where the sender starts a timer when sending a packet.

What happens in RDT 3.0 when no packets or ACKs are lost?

It behaves similarly to RDT 2.2: send packet, wait for ACK, repeat.

What occurs when a data packet is lost in RDT 3.0?

The receiver never sends an ACK, prompting the sender to resend the lost packet after a timeout.

What happens if an ACK packet is lost in RDT 3.0?

The sender resends the last packet after a timeout, and the receiver uses sequence numbers to discard duplicates.

What is a premature timeout in RDT 3.0?

When a timeout occurs but the data packet is eventually delivered, resulting in duplicate packets and ACKs.

What is the issue with the stop-and-wait protocol?

It wastes bandwidth by leaving the channel idle while waiting for an ACK.

What is pipelining in reliable data transfer?

Sending multiple packets without waiting for an ACK before sending another.

What is the window size in pipelined reliable data transfer?

The number of packets that can be sent before needing an ACK.

What is the Go-Back-N (GBN) protocol?

A protocol where the sender can transmit up to N packets without waiting for an ACK.

How does the GBN sender respond to an ACK receipt?

It uses cumulative acknowledgments; an ACK for packet n implies packets 0 through n have been received.

What happens when a timeout occurs in GBN?

All unacknowledged packets in the window are resent.

What does the GBN receiver do with a correct packet?

It passes the packet's data to the upper layer and sends an ACK for that packet.

What does the GBN receiver do with an incorrect or out-of-order packet?

It discards the packet and sends an ACK for the last correctly received packet.

What is a performance issue with GBN?

Large window sizes can lead to congestion due to many packets being retransmitted on a timeout.

What is the next topic to be discussed after GBN?

Another approach called selective repeat (SR) for pipelined reliable data transfer.