Sequenced Packet Exchange

Sequenced Packet Exchange, abbreviated SPX, is a Transport Layer protocol (Layer 4 of the OSI Model) used in Novell Netware networks. The SPX layer sits on top of the IPX layer (Layer 3) and provides connection-oriented services between two nodes on the network. SPX is used primarily by client/server applications.
Whereas the IPX protocol is similar to IP, SPX is similar to TCP. Together, therefore, IPX/SPX provides connection services similar to TCP/IP.