Sliding Window Protocol Simulator
(3-Column)

See the download page to obtain this program

Protocol Description

SWP (Sliding Window Protocol) a connection-less protocol. It allows data to be sent in one direction between a pair of protocol entities, subject to a maximum number of unacknowledged messages. SWP is described in Section 4.2.4 of the lecture notes, and in Section 3.4 of [Tanenbaum 1996]. If SWP is operated with a window size of 1, it is equivalent to the Alternating Bit Protocol. The simulation below does not include the users; see the five-column version for this.

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 DT(0), DT(1), etc. Once sequence numbers reach a maximum number (like 7), they wrap back round to 0. The content of messages is not explicitly identified. An acknowledgement AK(n) means that the DT message numbered n is the next one expected (i.e. all messages up to but not including this number have been received). Since sequence numbers wrap round, an acknowledgement with sequence number 1 refers to messages 0, 1, 7, 6, etc. Note that if a DT message is received again due to re-transmission, it is acknowledged but discarded.

The protocol has a maximum number of messages that can be sent without acknowledgement. If this window becomes full, the protocol is blocked until an acknowledgement is received for the earliest outstanding message. At this point the transmitter is clear to send more messages.

Protocol Parameters

Maximum Sequence Number
Window Size

Protocol Simulation

Up one level to Protocol Simulators

Web Ken Turner Home   Email    Search Search Web Pages

Last Update: 15th July 2006
URL: http://www.cs.stir.ac.uk/~kjt/software/comms/jasper/SWP3.html