Computer Networks Lecture 8: Principles of Reliable Data Transfer

Reliable Data Transfer (RDT)

• The primary goal of reliable data transfer is to ensure that data is delivered correctly and in the correct order over a communication channel.

Finite State Machines (FSM)

• Finite State Machines (FSM) play a crucial role in reliable data transfer by managing the sender's and receiver's states to ensure error-free data transfer.

RDT Acronym

• RDT stands for Reliable Data Transfer.

Factors Not Considered in Reliability

• Human factors are NOT considered part of reliability in data transfer.

Function of RDT in Network Protocols

• The function of reliable data transfer (RDT) in network protocols is to provide error-free data transfer between devices.

State Transitions in RDT

• State transitions in reliable data transfer are managed using Finite State Machines (FSM), which track the sender's and receiver's states.

Error Recovery in Reliable Channel

• In the context of reliable transfer over a reliable channel, the receiver plays a crucial role in recovering from errors by detecting and correcting errors.

Error Recovery Mechanism in RDT2.0

• In RDT2.0, the mechanism used to recover from bit errors in the channel is checksums.

New Mechanisms in RDT2.0

• The new mechanisms introduced in RDT2.0 beyond RDT1.0 are error detection and correction using checksums and acknowledgement packets (ACK/NAK).

Fatal Flaw in RDT2.0

• If ACK/NAK is not received in RDT2.0, it leads to a fatal flaw, resulting in the sender retransmitting the packet indefinitely.

Checksums in RDT2.0

• The role of checksums in RDT2.0 is to detect bit errors in the channel.

Sender's Action on Receiving NAK

• On receiving a NAK, the sender retransmits the packet.

Receiver's Action on Receiving Packet

• The receiver explicitly tells the sender that a packet was received OK by sending an ACK packet.

Purpose of Sequence Numbers

• The purpose of adding sequence numbers to each packet by the sender is to ensure that packets are delivered in the correct order.

Receiver's Action on Corrupt Packet

• In RDT2.0, the receiver discards the corrupt packet and sends a NAK to the sender.

Consequence of Not Receiving ACK/NAK

• The consequence of not receiving ACK/NAK, resulting in a fatal flaw in RDT2.0, is the sender retransmitting the packet indefinitely.

Action on Corrupt Packet

• When a corrupt packet is received in RDT2.0, the receiver discards the packet and sends a NAK to the sender.

Error Detection in RDT2.0

• Checksums are used to detect bit errors in RDT2.0.