Service Access Poin

Service access point: referred to as SAP, is a hierarchical system of communication interface between the upper and lower layers, N SAP is N1 layer can access the N layer service place.

In short, the service access point is a logical interface between the adjacent layer entity. From the physical layer, each layer to the upper layer service access point. In connection to the Internet in the ordinary micro-computer, the data link layer service access point TYPE type description, (e.g. 0800 on behalf of the upper layer is a IP ), network layer service access point is the head of IP protocol field ( 17 upper is UDP, 6 is TCP, 89 OSPF, 88 EGIRP, 1 ICMP ), transport layer service access point is port number.