Introduction to Data Communications
Previous 37a. Service Access Ports (SAPs) Next

37a. Service Access Ports (SAPs)

SAPs are Service Access Ports. A SAP is a port (logical link) to the Network layer protocol. If we were operating a multiprotocol LAN, each Network Layer protocol would have its own SAP. This is the method that the LLC uses to identify which protocol is talking to which. For example, Unix's TCP/IP, Novell's SPX/IPX and IBM's Netbios would all have different SAPs to identify which was which.


	Address		Assignment



	00		Null LSAP

	02		Individual LLC Sublayer Management Function

	03		Group LLC Sublayer Management Function

	04		IBM SNA Path Control (individual)

	05		IBM SNA Path Control (group)

	06		ARPANET Internet Protocol (IP)

	08		SNA

	0C		SNA

	0E		PROWAY (IEC955) Network Management & Initialization

	18		Texas Instruments

	42		IEEE 802.1 Bridge Spannning Tree Protocol

	4E		EIA RS-511 Manufacturing Message Service

	7E		ISO 8208 (X.25 over IEEE 802.2 Type 2 LLC)

	80		Xerox Network Systems (XNS)

	86		Nestar

	8E		PROWAY (IEC 955) Active Station List Maintenance

	98		ARPANET Address Resolution Protocol (ARP)

	BC		Banyan VINES

	AA		SubNetwork Access Protocl (SNAP)

	E0		Novell NetWare

	F0		IBM NetBIOS

	F4		IBM LAN Management (individual)

	F5		IBM LAN Management (group)

	F8		IBM Remote Program Load (RPL)

	FA		Ungermann-Bass

	FE		ISO Network Layer Protocol

	FF		Global LSAP
DSAP stands for Destination Service Access Port and is the receiving station's logical link to the Network Layer protocol. SSAP stands for Source Service Access Port and is the transmitting station's logical link to the Network Layer Protocol.

SAPs ensure that the same Network Layer protocol at the Source talks to the same Network Layer protocol at the Destination. TCP/IP talks to TCP/IP, Netbios talks to Netbios and IPX/SPX talks to IPX/SPX.

Introduction to Data Communications
Previous Table of Contents Next