# Alternating Bit Protocol

# 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.

## Protocol Parameters

The following settings are adequate for a simple simulation. For a more advanced exploration, choose different options and click Change Settings. This will cause the simulation to restart.

Optionally set the level of control that the simulator user needs over the medium:

Automatic:
  Messages are delivered immediately without loss. This is suitable for initial experimentation, but limits what can be explored. For example, message are never lost and never have to be timed out and resent.
Delivery:
  Alternatively, message delivery may be controlled - though messages will still never be lost. Choose this option to allow messages to be delivered in different orders and to be resent.
Delivery/Loss:
  Finally, delivery and loss of messages may be completely controlled. This is the most comprehensive option, but also the most complex one to manage.

Medium Control: | Automatic | Delivery | Delivery/Loss

## Protocol Simulation

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. Note that if a DATA message is received again due to re-transmission, it is acknowledged but discarded.

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