Transport Layer – Sequenced Packet Exchange (SPX)

Sequenced Packet Exchange (SPX) is the reliable transport protocol used by IPX when connection-oriented communication is required. Much like TCP, SPX uses sequence numbers and acknowledgments to be sure that data is reliably passed between hosts. Beginning with NetWare 4.0, a new (and backwards-compatible) version of SPX called SPX II was released, providing a sliding window flow-control mechanism. You should be aware that not all IPX network communication requires the use of SPX. IPX is also capable of interacting with some of the other upper-layer protocols directly.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.