Introduction

This Part defines a protocol fulfilling the role of a Subnetwork Dependent Convergence Protocol (SNDCP) as defined in Internal Organization of the Network Layer [ISO-8648].

Connectionless-mode network protocols are intended to be capable of operating over connectionless-mode services derived from a wide variety of subnetworks and data links. In order to simplify the specification of the protocol, their operation is defined with respect to an abstract underlying service, rather than any particular subnetwork service. This abstract underlying service consists of a single SN-UNITDATA primitive that conveys the source and destination subnetwork point of attachment addresses, a SUBNETWORK QUALITY-OF-SERVICE parameter, and a minimum number of octets of user data.

The Subnetwork Dependent Convergence functions providing this underlying service are constrained by the specific characteristics of a particular subnetwork service (e.g., CDPD Mobile Data Link Protocol) and by the assumptions made by the subnetwork-independent protocol providing Connectionless Network Service (e.g., IP or CLNP). Where the services assumed by the Network Layer do not map into the services provided by the Data Link Layer, an SNDCP is operated to provide the required functions.