1、INTERNATIONAL STANDARD ISO/IEC 15802-l First edition 1995-I l-01 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Common specifications - Part 1: Medium Access Control (MAC) service definition Technologies de /information -
2、 T.4l.kommunications et bchange dinformation entre syskmes - RBseaux locaux et mbtropolitains - Spkcifications communes - Partie 1: DBfinition du ContrUe dacc b) the parameters associated with each primitive action and event, and the form they take; and 4 the interrelationship between, and the valid
3、 sequences of, these actions and events. The principal objectives of this part of ISO/IEC 15802 are 4 to specify the characteristics of a conceptual Medium Access Control Service; b) guide the development of Medium Access Control Protocols; and 4 guide the development of OSI protocols which make use
4、 of the MAC Service. This part of ISO/IEC 15802 does not specify individual implementation or products, nor does it constrain the implementation of Medium Access Control entities and interfaces within an information processing system. There is no conformance of equipment to this part of ISO/IEC 1580
5、2. Instead, conformance is achieved through implementation of conforming Medium Access Control Protocols that fulfil the Medium Access Control Service defined in this part of ISO/IEC 15802. 2 Normative references The following International Standards contain provisions which, through reference in th
6、is text, constitute provisions of this part of ISO/IEC 15802. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO/IEC 15802 are encouraged to investigate the possibility of applying the most recent
7、editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. ISO/IEC 7498-l : 1994, Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model. IS0 7498-3 : 1989, Information processing systems -
8、Open Systems Interconnection - Basic Reference Model - Part 3: Naming and addressing. ISOIIEC 10731 :1994, Information technology - Open Systems Interconnection - Basic Reference Model - Conventions for the definition of 0.51 services. ISO/IEC 15802-l :1995(E) 0 ISO/IEC 3 Definitions For the purpose
9、s of this part of ISO/IEC 15802, the following definitions apply. 3.1 Basic reference model definitions Although the MAC Service is not identified or defined in the OSI Basic Reference Model, this part of ISO/IEC 15802 is based on the concepts developed in the Basic Reference Model and makes use of
10、the following terms defined in ISO/IEC 7498, as they might apply to the Medium Access Control Sublayer: 4 Entity b) Sublayer c) Service 4 Service-access-point e) Service-access-point-address f) Service-data-unit 0) Subnetwork address 3.2 Service conventions definitions Although the MAC Service is no
11、t identified or defined in the OSI Basic Reference Model, this part of ISOAEC 15802 makes use of the following terms defined in ISO/IEC 10731, as they might apply to the Medium Access Control Sublayer: a) Servlce user b) Service provider c) Primitive 4 Request 4 Indication 3.3 MAC Service definition
12、s 3.3.1 group-address; group-MSAP-address; group Medium Access Control Service-access- point address: A value, otherwise valid as a Medium Access Control Setvice-access- point address, identifying a set of Medium Access Control Service-access-points, the set of end systems on which the identified Se
13、rvice-access-points are located being any subset of all stations on a particular local area network. NOTE - By contrast, the general definition of an (N)-address restricts the identified Service-access-point to a single open system. 4 Abbreviations LAN MAC MSAP MSDU OSI QOS OUI Local Area Network Me
14、dium Access Control Medium Access Control Service-access-point Medium Access Control Service-data-unit Open Systems interconnection Quality of Service Organizationally Unique Identifier 0 ISOAEC ISO/IEC 15902-l :1995(E) 5 Conventions 5.1 General considerations This part of ISO/IEC 15802 uses the des
15、criptive conventions given in ISO/IEC 10731. The service model, service primitives, and time-sequence diagrams used are entirely abstract descriptions; they do not represent a specification for implementation. 5.2 Parameters Service primitives, used to represent service user/service provider interac
16、tions (ISO/IEC 10731) convey parameters which indicate information available in the user/provider interaction, and have a global significance. The parameters which apply to each group of MAC Service primitives are set out in table 1. Each “X” in the table indicates that the primitive labelling the c
17、olumn in which it falls shall carry the parameter labelling the row in which it falls. Some entries are further qualified by items in parentheses. These are a) A parameter specific constraint: (=) indicates that the value supplied in an indication primitive is always identical to that supplied in a
18、previous request primitive issued at the peer service-access-point. b) Indication that some note applies to the entry: (see note x) indicates that the referenced note contains additional information pertaining to the parameter and its use. In any particular interface, not all parameters need be expl
19、icitly stated. Some may be implicitly associated with the MSAP at which the primitive is issued, for example, an MA-UNITDATA.request need not include the source address parameter which may be associated with the MSAP at which the primitive is issued. 6 Overview of the MAC Service The MAC Service pro
20、vides for the transparent transfer of data between MAC Service users. lt makes invisible to these MAC Service users the way in which supporting communications resources are utilised to achieve this transfer, except when the MAC Service provider supports the MAC Service user specifying Routing Inform
21、ation. In particular, the MAC Service provides for the following: a) Independence of the underlying MAC Sublayer and Physical Layer -the MAC Service relieves MAC Service users from all concerns, with the exception of QoS considerations, regarding which MAC technology is available. b) Transparency of
22、 transferred information - the MAC Service provides for the transparent transfer of MAC Service user-data. lt does not restrict the content, format or coding of the information, nor does it ever need to interpret its structure or meaning. It may however restrict the maximum number of octets of MAC S
23、ervice user-data that can be supplied in a user/provider interaction. c) Priority selection - the MAC Service makes available to MAC Service users a means to request the transfer of data at a specified priority. d) Addressing - the MAC Service provides the means for the MAC Service user to identify
24、itself and to specify the MSAP to which data is to be transferred. e) Routing Information -the MAC Service allows the user optionally to specify the route to the destination MSAP. 3 ISO/IEC 15802-l :1995(E) 0 ISO/IEC 7 Types of MAC Service Currently there is one type of MAC Service defined; the conn
25、ectionless-mode MAC Service. 8 Features of the MAC Service The MAC Service provides the following features to the MAC Service user: a) A means by which MSDUs of limited length are delimited and transparently transmitted from one source MSAP to a destination MSAP in a single MAC Service access, witho
26、ut establishing or later releasing a connection. b) Associated with each instance of connectionless-mode transmission certain measures of QoS, which may be requested by the sending MAC Service user when the connectionless-mode transmission is initiated and may be modified by the MAC Service provider
27、 depending on the MAC technology. 9 Model of the MAC Service Although the MAC Service is not identified or defined in the OSI Basic Reference Model, this part of ISO/IEC 15802 uses the abstract model for a layer service defined in ISO/IEC 10731, clause 4 as it might apply to the MAC Sublayer. The mo
28、del defines the interactions between the MAC Service users and the MAC Service provider which take place at the two MSAPs. Information is passed between the MAC Service user and the MAC Service provider by service primitives, which may convey parameters. 9.1 Model of a MAC connectionless-mode transm
29、ission A defining characteristic of MAC connectionless-mode service - as provided between any two MSAPs - can be modelled in the abstract as an association between the two MSAPs. This association is permanent. I I L _ _ _ _ _ AssociationtHwaenAandB- _ _ _ _ 1 MAC Service Provider Figure 3 - Model fo
30、r a MAC Service Connectionless-mode Transmission Only one type of object, the unitdata object, can be handed over to the MAC Service provider via a MSAP. In figure 3, MAC Service user A represents the MAC Service user that passes objects to the MAC Service provider. MAC Service user B represents the MAC Service user that accepts objects from the MAC Service provider. 9.2 Service provided by the connectionless-mode MAC Service In general, the MAC Service provider may perform any or all of the following actions 4 discard objects; b) change the order of the objects.
