6 Elementary procedures for PDSS1

04.633GPPPacket Data on Signalling channels Service (PDS) Service Description, Stage 3TS

6.1 Overview

The elementary procedures for PDSS1 may be grouped into the following classes:

– PDSS1 establishment procedures.

– PDSS1 termination procedures.

– PDSS1 information phase procedures.

6.2 Procedures for establishment of a PDSS1 connection

The PDSS1 protocol entity in the mobile station or network in the idle phase shall on request of higher layers to establish a connection, analyse the request: the request contains all information necessary for the SETUP message and an indication whether the main or slow associated data link is to be used. The PDSS1 protocol entity shall then verify whether:

1) use of the indicated link for PDSS1 is possible and allowed;

and ask the MM sublayer whether:

2) establishment of a PDSS1 connection is possible and allowed.

– If one of these conditions is not fulfilled, the request is rejected.

– If the MM connection establishment is possible and allowed and the use of the indicated link is possible and allowed, the PDSS1 protocol entity asks the MM sublayer to establish an MM connection. The request contains a SETUP message to be transferred to the peer entity. The request from higher layers may already contain data to be transferred which does not exceed a maximum allowed length. In this case the data is included in the SETUP message.

– If the MM connection establishment fails or is rejected, the PDSS1 protocol entity aborts the establishment and gives an appropriate information to higher layers; it then returns to the idle phase.

An idle PDSS1 protocol entity shall on receipt of a SETUP message inform higher layers. If the SETUP message contained a data part, it passes the data part to higher layers and then continues as follows:

– If higher layers accept the establishment, the PDSS1 protocol entity shall send a SETUP ACKNOWLEDGE message to its peer entity and enter the PDSS1 information transfer phase. The acceptance from higher layers may already contain data to be transferred which does not exceed a maximum allowed length. In this case the data is included in the SETUP ACKNOWLEDGE message.

– If higher layers reject the establishment, the PDSS1 protocol entity shall send a RELEASE COMPLETE message with appropriate cause to its peer entity.

When a PDSS1 has transferred a SETUP message to its peer entity and receives as an answer a SETUP ACKNOWLEDGE message, it informs higher layers and enters the PDSS1 information transfer phase.

Abnormal cases

1) If during the establishment of a PDSS1 connection higher layers decide to abort the establishment, the PDSS1 protocol entity shall react as specified in subclause 6.3.

2) If during the establishment of a PDSS1 connection a lower layer failure occurs, the PDSS1 protocol entity shall abort the establishment and inform higher layers.

3) If the request from higher layers to establish a connection contained data with more than the maximum allowed length, the protocol entity shall reject the request with appropriate cause.

4) If the response from higher layers to accept a connection contained data with more than the maximum allowed length, the protocol entity shall reject the response with appropriate cause and then wait for further action from higher layers.

5) If after having informed higher layers that a SETUP has been received, no valid response was received from higher layers within 5 seconds, the protocol entity shall send a RELEASE COMPLETE message to its peer entity and inform higher layers that the connection establishment has been aborted.

6) If after having sent the SETUP message, no valid response was received from the peer entity within 10 + 10·T200·(N DIV N201) seconds (where N is the number of octets the SETUP message consisted of and T200 and N201 are as defined in GSM 04.06 for the used channel), the protocol entity shall send a RELEASE COMPLETE message to its peer entity and inform higher layers that and why the connection establishment has been aborted.

6.3 Procedures for release and termination of a PDSS1 connection

If during the establishment or information phase of a PDSS1 connection higher layers request to abort the establishment or to terminate the connection, the PDSS1 protocol entity:

– if it has sent or received the SETUP message, shall send a RELEASE COMPLETE message and then ask MM to release the MM connection; the request from higher layers may contain data to be transferred which does not exceed a maximum allowed length; in this case the data shall be included in the RELEASE COMPLETE message;

– otherwise shall ask MM to release the MM connection.

If during the establishment or information phase of a PDSS1 connection a PDSS1 protocol entity receives a RELEASE COMPLETE message from its peer entity, it shall inform higher layers and ask MM to release the MM connection. If the RELEASE COMPLETE message contains a data part, the data part is passed to higher layers.

Abnormal cases:

If the request from higher layers to abort or terminate the connection contained data with more than the maximum allowed length, the protocol entity shall send a RELEASE COMPLETE message without data part to its peer entity, and inform higher layers about the situation.

6.4 Procedures for the information phase of a PDSS1 connection

During the information phase of a PDSS1 connection, higher layers may request the transfer of data which does not exceed a maximum allowed length. The PDSS1 protocol entity then sends the data to its peer entity in a DATA message.

NOTE: Higher layers may apply activity supervision and, e.g., release a PDSS1 connection when it has been idle for a longer period.

Abnormal cases:

1) If during the information phase of a PDSS1 connection, a lower layer failure occurs, the PDSS1 protocol entity informs higher layers that the data transfer is suspended; if possible and allowed, the PDSS1 protocol entity asks MM to re-establish the MM connection. If the re-establishment is successful, the PDSS1 protocol entity proceeds as defined in subclause 6.4.1. If the re-establishment is unsuccessful, higher layers are informed that the connection is aborted.

2) If during the information phase of a PDSS1 connection, the PDSS1 protocol entity becomes aware that too much data is waiting for transmission ("congestion condition"), it informs higher layers that the data transfer is suspended. If the PDSS1 protocol entity later becomes aware that the congestion condition no more exists, it informs higher layers that data transfer can be resumed.

3) If the request from higher layers to transfer data contained data with more than the maximum allowed length, the protocol entity shall reject the request with appropriate cause.

6.4.1 Resumption of a connection

During a connection, after a radio link failure the MS shall try to initiate CM re-establishment. If a cell supporting re-establishment has been found and the CM re-establishment has been accepted by MM, the MS shall try to resume the PDSS1 connection:

– When the MS receives a message with the transaction identifier of the PDSS1 connection, it shall:

– if it is a PDSS1 DATA message, implicitly resume that connection;

– if it is a PDSS1 SETUP message, release that connection and treat the SETUP as the first message of a new transaction;

– if it is a PDSS1 RELEASE COMPLETE message, release that connection;

– if it did not yet perform such a release or implicit resumption, send a PDSS1 RESUME REQUEST which may be:

– explicitly acknowledged by the network with a PDSS1 RESUME ACK, or

– implicitly accepted by the network with transmission of a DATA message, or

– implicitly rejected by the network with the transmission of a PDSS1 SETUP, or

– explicitly rejected by the network with the transmission of a PDSS1 RELEASE COMPLETE message;

(all these messages with the same transaction identification).