A network protocol is used to transport the data stream protocol over a network. It can be considered as the plumbing that supports the IPC mechanisms used by the data stream protocol, as well as supporting basic network operations such as file transfers and print sharing.
Back-end databases can reside on a local area network (LAN) that connects it with the client application, or it can reside at a remote site, connected via a wide area network (WAN) and/or gateway. In both cases, it is possible that the network protocols or physical network supported by the various back-end databases are different from those supported by the client or each other. In these cases, a client application must use different network protocols to communicate with various back-end databases.
The network transport protocols supported within SQL Server include NetBEUI, TCP/IP, SPX/IPX using NWLink, DECnet, AppleTalk, and VINES IP.