ARQ Protocols (Automatic Repeat ReQuest)
ARQ protocols are used for error control.
Lost packets are automatically retransmitted after a timeout.
The receiver has to return acknowledgements when packets are received correctly.
Types of ARQ protocols are:
As noted above, a timer is used to recover from lost data. If a timeout
occurs the sender resends all packets that have been sent, but not yet
been acknowledged. If a packet is received correctly and in order, it
is delivered to the user and an acknowledge is sent. In all other cases
the receiver discards the packet.
The Animation shows how Go-Back-N and Selective Repeat work. Click onto
any packet that should get lost. Additionally you have to provide the correct
acknowledgement number at the receiver.
Selective-repeat protocols avoid unnecessary retransmissions by having the
sender retransmit only those packets that it suspects were lost.
This individual retransmissions require that the receiver individually
acknowledges correctly received packets.