GSM协议栈实体

Overview

This section offers a brief description of the different layers which constitute the mobile station Protocol Stack. It is also intended to offer an overview of the intersystem interface. The Protocol Stacks are used to define the functionality of the GSM protocols for interfaces. The GSM specifications are normative when used to describe the functionality of interfaces, but the stacks and the subdivision of protocol layers do not imply or restrict any implementation.

1 PL - Physical Layer

The base of the Protocol Stack rests on the physical layer.

2 DL - Data Link

The Data Link Layer (DL) is used to handle an acknowlowdged connection between mobile and base station. The LAPDm protocol is used.

3 RR - Radio Resource

Radio Resource (RR) manages the resources of the air-interface. That means configuration of physical layer, cell selection and cell reselection, data transfer, RR-Connection handling.

4 MM - Mobility Management

Mobility Management (MM) handles registration aspects for the mobile station. It detects changes of location areas and updates a mobile station in the new location area.

5 CC - Call Control
Call Control (CC) provides the call functionality. This includes call establishment, call maintenance

procedures like Hold, Retrieve or Modify, and call disconnection.

6 SS - Supplementary Services

Supplementary Services (SS) handles all call independent supplementary services like call forwarding or call barring.

7 SMS - Short Message Services

Short Message Services (SMS) is used for sending and receiving point-to-point short messages. Additionally the reception of cell broadcast short messages is included. Call Control (CC), Supplementary Services (SS) and Short Message Services (SMS) together are referred to as Connection Management (CM) sometimes.

8 MMI - Man Machine Interface

The man machine interface (MMI) is the interface to the user. Normally it is connected with a keypad as input device and a display as output device. In G23, there is a AT Command Interpreter (ACI), therefore, sometimes the MMI is also referred to as ACI in the present document if “the layer above layer 3″ is to be identified.

Between the several entities data interfaces are defined. These data interfaces are called Service

Access Points (SAPs), indicating that an upper layer uses the services of a lower layer.

The GSM specification do not set out any implementation of the Protocol Stack. The following diagrams show the implementation described in all these documents for the mobile station. All entities Technical Document GSM Protocol Stack Message Sequence Charts MM (6147.203.97.102), v0.3 Draft

except the Man Machine Interface and Physical Layer are implemented as part of the Protocol Stack - with ACI seen as an integral part of the stack in almost all cases.

For GPRS, there are more entities.

9 GRR (RLC/MAC) – Radio Link Control/Medium Access Control

This layer contains two functions: The Radio Link Control function provides a radio-solution-dependent reliable link. The Medium Access Control function controls the access signalling (request and grant) procedures for the radio channel, and the mapping of LLC frames onto the GSM physical channel.

10 LLC – Logical Link Control

The LLC entity provides multiple highly reliable logical links for asynchronous data transfer between the MS and the network. It supports variable-length information frames, acknowledged and unacknowledged data transfer, flow and sequence control,error detection and recovery, notification of unrecoverable errors, user identity confidentiality, and ciphering of user and signaling data.

11 GMM – GPRS Mobility Management

The GMM entity provides procedures for the mobility of the MS, such as informing the network of its present location, and user identity confidentiality. It manages the GMM context (attach, detach, routing area updating), supports security functions such as authentication of user and MS, controls ciphering of data, and initiates the response to paging messages.

12 SM – Session Management

The main function of the session management (SM) is to support PDP context handling of the user terminal. Session Management activates, modifies and deletes the contexts for packet data protocols (PDP). Session Management services are provided at the SMREG-SAP and the SNSM-SAP for anonymous and non-anonymous access. The non-anonymous and anonymous access procedures for PDP context activation and PDP context deactivation are available at the SMREG-SAP.In addition there exists a PDP context modification for non-anonymous PDP contexts.

13 SNDCP - Subnetwork Dependant Convergence Protocol

SNDCP carries out all functions related to transfer of Network layer Protocol Data Units (N-PDUs) over GPRS in a transparent way. SNDCP helps to improve channel efficiency by means of compression techniques. The set of protocol entities above SNDCP consists of commonly used network protocols. They all use the same SNDCP entity, which then performs multiplexing of data coming from different sources to be sent using the service provided by the LLC layer.

14 GACI – GPRS Application Control Interface

The GACI is the GPRS extension of the ACI. It is specified in GSM 07.07 and 07.60. It is responsible for processing of the GPRS related AT Commands to setup, activate and deactivate the PDP context parameter. It also provides functionality for the interworking between GMM/SM/SNDCP and a packet oriented protocol like PPP.

15 GSMS - GPRS Short Message Service

Like GACI, GSMS, the GPRS Short Message Service, is also not a new entity of its own, but it is the GSM SMS entity enhanced by GPRS functionality.