Connection-Less Network Protocol (CLNP)


Introduction

OSI CLNP is a standard protocol by ISO which provides the ability to send a datagram unit over to a destination system. Semantically it is similar to IP, in fact, it originally was derived from IP. One of the proposed uses for CLNP is in conjunction with IP in the network layer proposed by TUBA.


Datagram

Each datagram is an independent unit of transmission with no relationship to other datagram units that are sent over the same network service provider. In particular ,the order of delivery may not be preserved.

Transmission

CLNP operates by exchanging Network Protocol Data Units (NPDU). Since data units can exist in different sizes going from one subnetwork to another, one of the main functions CLNP provides is segmentation.

The sending end system forms its NPDU up to the maximum size of its originating network. Subsequent intermediate systems may need to divide the original up into a number of smaller segments. The reassembly of the segments takes place only at the destination system.

The fields in the NPDU can be classified as the following:

Lifetime control
This function requires that the NPDU be discarded by an intermediate network entity, if it has been circulating in the network for an overly long time.

Segmentation fields
These tell the receiving end, the ordering, completeness and correctness of the NPDUs, so that the exact PDU can be reassembled at the destination system.

Addressing
This includes both the source and destination NSAP addresses and the length of each address.

Options
Options provide services such as source routing, route recording, error reporting ,priority and some other QOS functions.

User data
Finally the actual user data from the data request primitive.

Progress

Work is progressing at this time on extensions to CLNP, including network layer multicast capabilities, arbitrary packet coloring for policy routing purposes and more flexible type of service selection.