# Alternating Bit Protocol Simulator

## Protocol Description

ABP (Alternating Bit Protocol) is a connection-less protocol for transferring messages in one direction between a pair of protocol entities. It is a simple form of the Sliding Window Protocol with a window size of 1. The message sequence numbers simply alternate between 0 and 1. ABP is also known as Stop and Wait.

The protocol simulation shows a time-sequence diagram with transmitting and receiving protocol entities, and a communications medium that carries messages. The transmitter simply sends messages numbered DATA(0) or DATA(1); the content of messages is not identified. These are acknowledged with ACK(1) or ACK(0) respectively. The number in the ACK message identifies the next sequence number the protocol will accept. Note that if a DATA message is received again because of re-transmission, it will be acknowledged but discarded.

## Protocol Simulation

Either click on the potential next event listed at the bottom, or let the simulation run automatically by clicking the ``Run'' button. At any stage you can undo the last event using the ``Undo'' button.

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