4 Mapping between TC transaction sublayer messages and layer 3 radio path messages

09.113GPPSignalling Interworking for supplementary servicesTS

This clause describes the mapping of TC transaction sublayer messages to layer 3 radio path messages over the external interfaces. The precise coding of these messages is given in other technical specifications.

4.1 D-interface to A-interface mapping

Table 4.1 shows the mapping of TC transaction sublayer messages to layer 3 messages on the radio path.

Table 4.1: Mapping of TC transaction sublayer messages to layer 3 radio path messages

TC transaction sublayer message

Layer 3 radio path message

BEGIN

REGISTER (note 1)

CONTINUE (note 2)

FACILITY/REGISTER (note 3)

END (note 2)

RELEASE COMPLETE/REGISTER (note 3)

ABORT (note 2)

RELEASE COMPLETE

NOTE 1: AC name is not mapped to a version indicator.

NOTE 2: The user information field if present is discarded.

NOTE 3: A CONTINUE or END is mapped to REGISTER if a new transaction has to be established.

4.2 A-interface to D-interface mapping

Table 4.2 shows the mapping of layer 3 radio path messages to TC transaction sublayer messages.

Table 4.2: Mapping of layer 3 radio path messages to TC transaction sublayer messages

Layer 3 radio path message

TC transaction sublayer message

REGISTER

BEGIN (note)

FACILITY

CONTINUE

RELEASE COMPLETE

END

NOTE: The right AC name shall be included, see clause 3.

4.3 Procedures

The mapping from TC Transaction Sublayer messages to Layer 3 radio path messages must include a replacement of the tag and length of the Component Portion in the Transaction Sublayer message with the Information element identifier and length of the Facility Information Element for the Layer 3 message. Similarly for the reverse mapping. However, if a version indicator is received an AC name will be provided in the BEGIN message, see clause 3.

All transaction sublayer messages, except the ABORT message, will normally contain one or more components. If components are included, the conversion algorithm described below applies. If a message does not contain a component, then the corresponding message is also sent without a component: messages shall not be withheld by the interworking function.

For call independent SS operations each message shall only contain a single component. If a message contains more than one component then a RELEASE COMPLETE message with the cause "Facility rejected" (see GSM 04.08) and without any component shall be sent on the radio path (see GSM 04.10).

TC Transaction sublayer messages can also contain a dialogue portion. If a user-information is received within this dialogue portion, it will not be conveyed in a Layer 3 radio path message.

If an ABORT message is received in TC, a RELEASE COMPLETE message is to be sent on the radio path. The RELEASE COMPLETE message shall not contain any component. If a cause is to be provided to the MS, one of the cause codes of GSM 04.08 shall be used.

If an ABORT message with a dialogue portion indicating "version fallback" (e.g. the cause "AC-not-supported") is received in TC then, if the MSC does not re-attempt the "dialogue" (e.g. by using a different AC name), it shall send a RELEASE COMPLETE to the MS with the cause "Facility rejected" (see GSM 04.08) and without any component.

If an END message with a dialogue portion indicating "dialogue refused" is received in TC then the MSC shall send a RELEASE COMPLETE to the MS with the cause "Facility rejected" (see GSM 04.08) and without any component.

If a layer 3 radio path message or a component in the layer 3 radio path message is rejected by the MSC, the MSC shall:

– return a RELEASE COMPLETE message to the MS. If the reject condition is not associated with a component, one of the cause codes of GSM 04.08 shall be inserted, as described below. If it is a component (except a REJECT component), a REJECT component with the appropriate problem code shall be inserted in the RELEASE COMPLETE message, as described below. If the reject condition concerns a REJECT component the RELEASE COMPLETE message may be empty;

– terminate the transaction with the VLR by use of an ABORT message.

If a dialogue cannot be established with the HLR because no common AC name is available then the MSC shall send a RELEASE COMPLETE to the MS with the cause "Facility rejected".