scope:

Introduction

This document specifies the Medium Access Control (MAC) Entity for data transmission over a TIA 136 communications Packet Data Channel (PDCH). A PDCH may be full rate, double rate or triple rate. The MAC, Radio Resource Management Entity (RRME) [4] and Broadcast Management Entity (BME) comprise the Radio Resource (RR) sublayer in the General Packet Radio System-136 (GPRS-136) protocol stack. The MAC entity supports two multiplexed MAC Logical Links (MLL) of different priorities. The first MLL is assigned higher priority and provides the higher layer and various management entities with expedited data delivery services. The other MLL is used for normal data transfer.

The MAC Entity is responsible for in-sequence delivery of normal data and expedited data provided to it by the higher layer. Both unacknowledged and acknowledged modes are supported on the downlink. Acknowledged mode is supported on the uplink. In acknowledged mode, error recovery is handled using a sliding window ARQ protocol.

The MAC entity at the base station is responsible for active mobile identity management (i.e., assignment and release of temporary local identifiers for mobiles engaged in data transmission or reception). These identifiers are used to carry out acknowledgment and assignment functions for uplink transmissions and to identify the recipient of data on the downlink. The base station MAC entity also controls phase assignments (i.e., it can order mobiles to look for uplink assignments and listen for downlink transmissions on specific time slots).

On the uplink, both contention and reservation based access are supported. Active Mobile Identity (AMI) values are used to provide acknowledgments to contending users and to identify time slots as contention slots or slots reserved for a specific mobile station.

Each ARQ mode transaction starts with the transmission of a BEGIN Protocol Data Unit (PDU) and proceeds with the transmission of CONTINUE PDUs. The BEGIN handshake establishes the AMI for the transaction and the mode of operation (i.e., fixed coding or incremental redundancy) for the transfer of subsequent CONTINUE PDUs. A variable number of blocks may be packed into each CONTINUE PDU depending on the modulation. ARQ Status PDUs are used to provide the peer transmission controller with knowledge about the receiver state.