Information Technology - Telecommunications and Information Exchange between Systems - Local and Metropolitan Area Networks - Specific Requirements - Part 2: Logical Link Control
|Publication Date:||7 May 1998|
|ICS Code (Networking):||35.110|
Scope and purpose
This International Standard is one of a set of international standards produced to facilitate the interconnection of computers and terminals on a Local Area Network (LAN). It is related to the other international standards by the Reference Model for Open Systems Interconnection (OSI).
NOTE-The exact relationship of the layers described in this Interactional Standard to the layers defined by the OS1 Reference Model is under study.
This International Standard describes the functions, features, protocol, and services of the Logical Link Control (LLC) sublayer in the ISO/IEC 8802 LAN Protocol. The LLC sublayer constitutes the top sublayer in the data link layer (see figure 1) and is common to the various medium access methods that are defined and supported by the ISO/IEC 8802 activity. Separate International Standards describe each medium access method individually and indicate the additional features and functions that are provided by the Medium Access Control (MAC) sublayer in each case to complete the functionality of the link layer as defined in the LAN architectural reference model.
This International Standard describes the LLC sublayer service specifications to the network (Layer 3), to the MAC sublayer, and to the LLC sublayer management function. The service specification to the network layer provides a description of the various services that the LLC sublayer, plus underlying layers and sublayers, offer to the network layer, as viewed from the network layer. The service specification to the MAC sublayer provides a description of the services that the LLC sublayer requires the MAC sublayer. These services are defined so as to be independent of the form of the medium access methodology, and of the nature of the medium itself. The service specification to the LLC sublayer management function provides a description of the management services that are provided to the LLC sublayer. All of the above service specifications are given in the form of primitives that represent in an abstract way the logical exchange of information and control between the LLC sublayer and the identified service function (network layer, MAC sublayer, or LLC sublayer management function). They do not specify or constrain the implementation of entities or interfaces.
This International Standard provides a description of the peer-to-peer protocol procedures that are defined for the transfer of information and control between any pair of data link layer service access points on a LAN. The LLC procedures are independent of the type of medium access method used in the particular LAN.
To satisfy abroad range of potential applications, three types
of data link control operation are included (see clause 4). The
first type of operation (see clause 6) provides a
This International Standard identifies four distinct "classes"
of LLC operation. Class I provides data-link-connection
The basic protocols described herein are peer protocols for use in multistation, multiaccess environments. Because of the multistation, multiaccess environment t shall be possible for a station to be involved in a multiplicity of peer protocol data exchanges with a multiplicity of different stations over a multiplicity of different logical data links and/or data link connections that are carried a single physical layer (PHY) over a single physical medium. Each unique to-from pairing at the data link layer shall define a separate logical data link or data link connection with separate logical parameters and variables. Except where noted, the procedures described shall relate to each data link layer logical data link or data link connection separately and independently from any other logical data link or data link connection that might exist at t the stations involved.
ISO/IEC 10038 : 1993, annex C, provides additional services to allow the MAC service user the ability to determine and use multiple routes through a bridged LAN. This International Standard specifies the provision for an optional Route Determination Entity (RDE) within the LLC sublayer. This is entity provides for the discovery and selection of a path (bridged route) for each required data link through the bridged LAN. It does not preclude the LLC service user from providing its own method of discovery and selection of routes.
To evaluate conformance of a particular implementation, it is necessary to have a statement of which capabilities and options have been implemented. Such a statement is called a Protocol Implementation Conformance Statement (PICS), as defined in ISO/IEC 9646-1 : 1994. This International Standard provides such a PICS proforma (Annex A) in compliance with the relevant requirements, and in accordance with the relevant guidance given in ISO/IEC 9646-2 : 1994.
1Information about references can be found in 1.3