Basic concepts of CLNP connectionless network protocols

There are a variety of Internet protocols. Today we will mainly introduce the ConnectionLess Network Protocol (CLNP. CLNP (ConnectionLess Network Protocol) is an ISO Network layer datagram Protocol that works at the Network layer of the Open System Interconnection Reference Model ISO 7498. CLNP is similar to an IP address in a TCP/IP environment and is used to provide services to the transport layer. therefore, CLNP is also called ISO-IP. another OSI protocol in the network layer is connection-oriented network protocol CONP. It mainly provides connection-oriented services at the network layer.

CLNP can be used between Network entities of the terminal system or in Network Layer relay systems of the Network Layer relay system of the Network Layer. CLNP mainly provides connectionless network services. CLNP is designed to act as an independent subnet convergence protocol (SNICP). Its function is to establish OSI network services on a defined set of underlying services, it also supports the uniformity of OSI connectionless network services on a group of identical or different interconnect subnets. when the subnet independent convergence protocol and/or subnet Access Protocol do not provide the functions required to connect a network service to another NSAP in all or part of the path, CLNP can be used for adjustment. in addition to SNICP, CLNP can also implement the functions of other protocols, so it is also applicable to environments in other subnet interconnection modes.

CLNP uses the NSAP address and title to identify network devices. The source address and target address parameters are the network service access point address (NSAP address), and the network entity title is used as the terminal system or intermediate system) the identifier of the network object in. the Network entity title and the NSAP address are allocated in the same namespace. whether the address is an NSAP address or a network entity title depends on the address resolution environment.

CLNP has the maximum datagram size that is the same as the IP address. When a datagram needs to pass through a network with the maximum datagram value less than the CLNP connectionless network protocol, CLNP provides the Group fragmentation) mechanism for data unit identification, grouping/total length and offset ). like an IP address, the checksum in the CLNP protocol header provides an authentication to check whether the CLNP datagram has been correctly transmitted and whether the lifecycle "Time to Live" is provided ") control mechanism, which limits the time when the datagram stays in the Internet system.

Protocol Structure

The PDU structure in CLNP is as follows:

Header Part Address Part Segmentation Part Option Part Data

The structure of the CLNP unconnected network protocol PDU header is as follows:

8 16 24 32 35 40 56 72 bit

Nlp id Length ID Version Lifetime Flags Type Seg. Length Checksum

Nlp id-Network Layer Protocol identifier. when this field is set to a binary value of 1000 0001, it is used to identify the ISO 8473 protocol that supports the connectionless network service in the network layer protocol. when this field is set to a binary value of 0000 0000, it is used to identify the interactive network layer sub-protocol.

Length ID-Length indicator indicates the head size octet ).

Version-Version/Protocol ID Extension identifies ISO 8473.

Lifetime-PDU Lifetime indicates the remaining Lifetime of the PDU, in units of 500 milliseconds.

Flags-three tags: License Segmentation Permitted), More Segments), Error Report ).

The Type-Type code field identifies the protocol data unit Type, which may be: Data PDU or error report PDU.

Seg. Length-the Segment Length field specifies the Length of the entire PDU octet), including the header and data section.

The Checksum-Checksum field is used to calculate the entire PDU header.

Address Part, including the target Address and Source Address, can be variable in OSI 8348/ad2.

Segmentation Part-if the egmentation Permitted Flag field of the PDU head is set to 1, the header structure must contain the Segmentation Part; if the Segmentation Permitted Flag value is 0, it indicates that no sub-protocol is used currently.

The Option Part-Options Part field is used to transmit optional parameters.

Data Part-the Data Part field in the pdu is an octal group of rules.

Protocols: IS-IS, CLNP, IDRP, CONP, ES-IS, ISO-TP

Organization Source: CLNP connectionless network protocol defined in ISO www.iso.com) Document 8473 and ITU http://www.itu.org/) Document X.213 and X.233.