Sequenced Packet Exchange (SPX) is the OSI-model Transport layer protocol in the IPX/SPX protocol stack. It is a reliable, connection-oriented protocol, similar to the TCP protocol of the TCP/IP, but it is datagram rather than stream protocol.
SPX packet structure
Each SPX packet begins with a header with the following structure:
The Connection Control fields contains 4 single-bit flags:
The Datastream Type serves to close the SPX connection. For this purpose two values are used:
References
Sequenced Packet Exchange Wikipedia(Text) CC BY-SA