4 Service characteristics

04.053GPPData Link (DL) Layer General AspectsRelease 1999TS

4.1 General

The data link layer provides services to layer 3 and utilizes the services provided by the physical layer.

In the present document and 3GPP TS 04.06 the following general syntax is used for describing primitives.

XX ‑ Generic Name ‑ Type (Parameters).

where XX designates the layer providing the services. In the present document XX is DL and MDL for the data link layer and PH for the physical layer.

4.2 Services provided to layer 3

4.2.1 General

The specification of the interactions with layer 3 (primitives) provides a description of the services that the data link layer, plus the physical layer, offer to layer 3, as viewed from layer 3.

Two forms of information transfer services are associated with layer 3. The first is based on unacknowledged information transfer at the data link layer and the second service is based on acknowledged information transfer at the data link layer using multiple frame operation. Different information transfer services may co‑exist on the same data link subject to restrictions imposed by the type of channel being used (see subclause 3.4).

In addition, the data link layer will pass primitives between the physical layer and layer 3 for random access operation on the RACH.

4.2.2 Priority

The priority between data links shall be as follows:

On SDCCH:

Highest priority: SAPI = 0;

Lowest priority : SAPI = 3.

On SACCH:

The priority arrangement on the SACCH must ensure that if a SAPI = 3 frame is awaiting transmission, two SAPI = 0 frames are not sent in consecutive SACCH frames. In addition, for the mobile to network direction it must also be ensured that any SAPI = 3 frame is followed by at least one SAPI = 0 frame.

4.2.3 Segmentation

For the acknowledged mode of information transfer the data link layer offers segmentation at the transmitter of layer 3 message units if the message unit is longer than the information field of the data layer frames. At the receiver the segmented layer 3 message units are concatenated such that the integrity of the layer 3 message unit is restored.

For unacknowledged operation the data link layer does not offer segmentation services.

4.2.4 Unacknowledged information transfer service

NOTE: In this case the information transfer is not acknowledged at the data link layer. Acknowledgement procedures may be provided at higher layers.

The characteristics of the unacknowledged information transfer service are summarized in the following:

a) provision of a data link connection between layer 3 entities for unacknowledged information transfer of layer 3 message units;

b) identification of data link connection endpoints to permit a layer 3 entity to identify another layer 3 entity;

c) sending of frames in accordance with priority given to the message;

d) no verification of message arrival within the data link layer.

The primitives associated with the unacknowledged information transfer service are:

DL‑UNIT DATA‑REQUEST/INDICATION

The DL‑UNIT DATA‑REQUEST primitive is used to request that a message unit be sent using the procedures for unacknowledged information transfer service; DL‑UNIT DATA‑INDICATION indicates the arrival of a message unit received by means of unacknowledged information transfer. Parameters associated with these primitives are the message unit, priority and the type of channel being used (BCCH, PCH + AGCH or specific type of DCCH).

4.2.5 Acknowledged information transfer services

One mode of acknowledged operation is defined, i.e. multiple frame operation.

The characteristics of this service are summarized in the following:

a) provision of a data link connection between layer 3 entities for acknowledged information transfer of layer 3 message units;

b) identification of data link connection endpoints to permit a layer 3 entity to identify another layer 3 entity;

c) sequence integrity of data link layer message units in the absence of machine malfunctions;

d) notification to the peer entity in the case of errors, for example, loss of sequence;

e) notification to the layer 3 entity of unrecoverable errors detected by the data link layer;

f) flow control;

g) sending of frames in accordance with the indicated SAPI value (see also subclause 4.2.2);

h) segmentation and concatenation control functions;

i) suspension of the service during change of dedicated channels and resumption of service on the new channel without message loss (SAPI = 0 only); duplication of messages which may occur are treated on layer 3 (SAPI = 0 only).

  1. prioritization of messages by a layer 3 entity with preemption of low priority messages by high priority messages (SAPI = 0 only).

The following list gives an overview of the primitives associated with the multiple frame acknowledged information transfer services (for detailed specification, see 3GPP TS 04.06):

a) Data transfer using I frames:

DL‑DATA‑REQUEST/INDICATION

The DL‑DATA‑REQUEST primitive is used to request that a message unit be sent using the procedures for multiframe acknowledged information transfer. The DL‑DATA‑ INDICATION primitive indicates the arrival of a message unit received by means of acknowledged information transfer. The parameters associated with these primitives are the message unit, the type of channel being used and, for a DL-DATA-REQUEST primitive, the message priority.

b) Establishment of multiple frame operation using the SABM command:

DL‑ESTABLISH‑REQUEST/INDICATION/CONFIRM

These primitives are used to request, indicate and confirm the establishment of multiple frame operation between two data link layer entities. Possible parameters are the message unit, the establish mode and the type of channel being used.

c) Suspension of multiple frame operation:

DL‑SUSPEND‑REQUEST/CONFIRM

These primitives are used in a MS to request and confirm the suspension of multiple frame operation while changing a dedicated channel. A possible parameter is the type of channel to be affected.

d) Resumption of multiple frame operation:

DL‑RESUME‑REQUEST/CONFIRM

These primitives are used in a MS to request and confirm the resumption of multiple frame operation after it has been suspended (see paragraph c) above). Possible parameters are the message unit and the type of channel to be affected.

e) Restoration of multiple frame operation:

DL‑RECONNECT‑REQUEST/CONFIRM

These primitives are used in a MS to request and confirm the restoration of multiple frame operation on the old channel after failure of the channel change. Possible parameters are the message unit and the type of channel to be affected.

f) Termination of multiple frame operation:

DL‑RELEASE‑REQUEST/INDICATION/CONFIRM

These primitives are used to request, indicate and confirm an attempt to terminate multiple frame operation between two data link layer entities or an attempt to perform local end release. The parameters associated with this primitive are the type of channel and the release mode.

4.2.6 Random access procedure

The primitives associated with random access are:

DL‑RANDOM ACCESS‑REQUEST/INDICATION/CONFIRM

The DL‑RANDOM ACCESS‑REQUEST primitive is used in the MS to request the transmission of a random access burst. The DL‑ RANDOM ACCESS‑CONFIRM primitive is used to notify layer 3 that the random access burst has been sent. The DL‑RANDOM ACCESS‑INDICATION primitive is used in the network to indicate the arrival of a random access burst. The parameter associated with the REQUEST primitives is the random access message unit. The parameters associated with the INDICATION primitive are the random access message unit and the time slot in which the random access burst was received. The parameter associated with the CONFIRM primitive is a message unit containing the number of the time slot in which the random access burst was sent.

4.3 Services required from the physical layer

The services provided by the physical layer are described in detail in 3GPP TS 04.04. They are summarized in the following:

a) physical layer connection for transparent transmission of frames. The bits of a frame are to be delivered to the peer data link entity in the same order in which they were submitted to the physical layer by the sender;

b) indication of the physical status of the Dm channel;

c) transmission of data link layer message units in the same order as they were issued by the data link layer;

d) provision of frame synchronization;

e) provision of error protection to ensure a low residual bit error rate at the data link layer;

f) transmission (in the MS) and reception (in the network) of random access bursts.

The primitives between the data link layer and the physical layer are:

a) Data transfer:

PH‑DATA‑REQUEST/INDICATION

These primitives are used to request that a message unit be sent and to indicate the arrival of message unit. Parameters associated with these primitives are the data link layer message unit, the priority and the type of channel being used.

b) Random access:

PH‑RANDOM ACCESS‑REQUEST/INDICATION/CONFIRM

The REQUEST primitive is used to request (in the MS) that a random access frame be sent and the INDICATION primitive is used to indicate (in the network) the arrival of a random access frame. A parameter associated with these primitives is the random access message unit. The CONFIRM primitive is used (in the MS) to confirm in which time slot the random access burst was sent.

c) Connection establishment:

PH‑CONNECT‑INDICATION

This primitive is used to indicate that a specific physical resource has been established on the physical layer. The parameter associated with this primitive is the type of channel.

NOTE: Activation of a physical resource is usually initiated by the layer 3 entity without involving data link layer entities.

d) Transmission synchronization:

PH‑READY‑TO‑SEND‑INDICATION

This primitive is used to enable the data link layer to synchronize to the next instant of physical transmission. The parameter associated with this primitive is the type of channel.

PH‑EMPTY‑FRAME‑REQUEST

This primitive is used by the data link layer instead of the PH‑DATA‑REQUEST primitive when no frame has to be sent after receiving the PH‑READY‑TO‑SEND indication. The parameter associated with this primitive is the type of channel.

4.4 Administrative services

4.4.1 General description of administrative services

The data link layer entity supports several internal functions of the MS or the network not requiring layer 3 peer‑to‑peer information transfer. The functions provided by the data link layer are:

‑ error reporting between the data link layer and the layer 3 entity;

‑ abnormal release of the data link layer in case of protocol or other failures from which the data link layer cannot recover on its own.

The administrative functions and the interactions between the data link layer and the layer 3 entities are described in terms of service primitives.

4.4.2 Definition of primitives for administrative services

The primitives between the layer 3 entity and the data link layer for supporting administrative services are:

a) Error handling:

MDL‑ERROR‑INDICATION

This primitive is used by the data link layer to indicate that there is an error in the data link layer procedures that cannot be resolved by normal exception handling procedures. Parameters associated with this primitive are the reason for error reporting and the type of channel.

b) Release:

MDL‑RELEASE‑REQUEST

This primitive is used by the layer 3 entity to initiate abnormal local end release of a data link. Parameters associated with this primitive are indications of which data links are to be released and the reason for abnormal release.