Maintaining FIFO property

Maintaining the first in first out (FIFO) property on the communication channels in another requirement for WARPED. When messages are sent from one process to another process, the ordering of the messages has to be preserved. The first message sent from a particular process should be the first message received by a destination process from that particular sender process. Some of common approaches to provide FIFO in the communication channels are as follows:

• In the first approach, the message passing layer gives a explicit ordering to the messages sent across the network. This can be done by adding a sequence number to the messages sent across the network. At the destination process, the message passing layer can find out whether the message received is out of order or not through this sequence field in the message sent across the network. This is usually done if the underlying protocol does not provide a ordered message delivery.
• In the second approach, the message passing layer can use an underlying protocol which provides the ordering of the messages. TCP/IP protocol is one such protocol that provides a reliable, ordered message delivery.

Since TCPMPL uses the TCP/IP protocol, the ordering of the messages are provided as part of the TCP/IP services.