Introduction

This Part defines the services, procedures and encoding required to provide the Medium Access Control (MAC) layer of the Airlink Interface between the Mobile Data Base Station (MDBS) and Mobile End Systems (M-ESs).

The MAC layer defines a protocol that operates within the Data Link Layer of the OSI reference architecture. In the specification of the CDPD Airlink Interface, the Data Link Layer is separated into two distinct sublayers defined by their functions:

• Logical link control functions

Logical link control provides services for information transfer over logical data link connections between the CDPD Network and M-ESs, including functions for addressing, sequence control, error recovery and flow control. It is provided by the Mobile Data Link Protocol (MDLP) defined in Part 403.

•Medium access control functions

Medium access control functions arbitrate access to the shared medium between M-ESs and an MDBS. The MAC layer also provides frame recognition, delimiting and error detection/correction. It is provided by the procedures and encoding defined in this Part.

The logical link control sublayer and MAC sublayer together encompass the functions of the Data Link Layer as defined in the OSI model.

In the remainder of this specification, the term Data Link Layer is used to refer to the MDLP protocol entity. It is understood that this term refers to the logical link control sublayer provided by MDLP, as distinct from the MAC sublayer defined in this Part.

The definition of the MAC layer takes into consideration the concepts and principles of the following:

a. [ISO-7498]—The reference model and layer service conventions for OSI

b. [IEEE-802]—Local area network—Overview and architecture

c. [ISO-8802-3]—Local area network—Carrier sense multiple access with collision detection

d. [ISO-10039]—Medium access control service definition.