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ISO CONP: Connection-Oriented Network Protocol

Connection-Oriented Network Protocol (CONP) is an OSI network layer protocol that carries upper-layer data and error indications over connection-oriented links. Two types of OSI network layer services are available to the OSI transport layer:

  • Connectionless Network Service (CLNS)- CLNS performs datagram transport and does not require a circuit to be established before data is transmitted.
  • Connection-Mode Network Service (CMNS)- CMNS requires explicit establishment of a path or circuit between communicating transport layer entities before transmitting data.

CONP, based on the X.25 Packet-Layer Protocol (PLP), provides the interface between CMNS and upper layers. It is a network layer service that acts as the interface between the transport layer and CMNS. Six services are provided to transport-layer entities: one for connection establishment, one for connection release, and four for data transfer. Services are invoked by some combination of four primitives: request, indication, response, and confirmation.

There are two types of addresses used in the network layer communication:

  • Network Service Access Point (NSAP) - NSAP addresses identify network layer services, one for each service running.
  • Network Entity Title (NET) - NET addresses identify network layer entities or processes instead of services.

Protocol Structure - ISO CONP: Connection-Oriented Network Protocol

The General Format of NSAP:  


1byte

2bytes

2-4bytes

0-13bytes

1-8bytes

1byte

IDP

DSP

AFI

IDI

CDP

CDSP

AFI

IDI

CFI

CDI

RDAA

ID

SEL

  • IDP - Initial Domain Part
  •   AFI - Authority and Format Identifier, two-decimal-digit, 38 for decimal abstract syntax of the DSP or 39 for binary abstract syntax of the DSP
  •   IDI - Initial Domain Identifier, a three-decimal-digit country code, as defined in ISO 3166
  •   DSP - Domain Specific Part
  •   CDP - Country Domain Part, 2..4 octets
  •   CFI - Country Format Identifier, one digit
  •   CDI - Country Domain Identifier, 3 to 7 digits, fills CDP to an octet boundary
  •   CDSP - Country Domain Specific Part
  •   RDAA - Routing Domain and Area Address
  •   ID - System Identifier (1..8 octet)
  •   SEL - NSAP Selector

 

While RDIs and RDCIs need not be related to the set of addresses within the domains they depict, RDIs and RDCIs are assigned based on the NSAP prefixes assigned to domains. A subscriber RD should use the NSAP prefix assigned to it as its RDI. A multihomed RD should use one of the NSAP prefixes assigned to it as its RDI.
Related Protocols
ES-IS , CLNP , IDRP ,IS-IS , CONP

Sponsor Source

CONP is defined in ISO (www.iso.org ) 8208, 8878 and ITU X.213 and X.223.



Reference

http://www.doc.ua.pt/arch/itu/rec/product/X.htm :

X.213: Information technology - Open Systems Interconnection ?Network service definition  

X.223: Use of X.25 to provide the OSI connection-mode Network service for ITU-T applications