5 Handling of User-to-user signalling

23.0873GPPRelease 17Stage 2TSUser-to-User Signalling (UUS) supplementary service

5.1 Timers

UUS related timers are needed only for UUS service 3. Timers T1-UUS3, T3-UUS3 and T4-UUS3 are used only when UUS service 3 is requested during an active call.

Table 5.1: UUS Timers

Timer	Name	Value	Run at	Started	Stopped	Expiry
T1-UUS3	Remote network control	10s	MSC of the remote subscriber	UUS3 service request sent to the remote subscriber	Answer to UUS3 service request received from the remote subscriber	Rejection of UUS3 service is sent toward the requesting network
T2-UUS3	UUS3 flow control	10s	MSC of the served subscriber and MSC of the remote subscriber	The MSC receives service acceptance	When UUS3 service is deactivated	Flow control parameter is incremented. Timer is restarted. Note 1.
T3-UUS3	Served subscriber control	10s	MS of the served subscriber	UUS3 service request sent to the requesting network	Acceptance to UUS3 service received from requesting network	Consider UUS3 service as not activated
T4-UUS3	Serving network control	10s	MSC of the served subscriber	UUS3 service request sent to the remote network	Acceptance to UUS3 service received from remote network	Rejection of UUS3 service is sent toward the served subscriber

NOTE: If a user information message has been discarded due to flow control, a congestion control message shall be sent to the user.

5.2 Information flows of UUS services

5.2.1 Service 1 (UUS1)

5.2.1.1 Flow control

No specific flow control is needed to restrict the amount of messages sent for either implicit or explicit UUS service 1 as the user-to-user information is transferred in call control messages.

5.2.1.2 Information flows

Figure 5.2.1.2: MAF043

5.2.1.2.1 Implicit activation

Figure 5.2.1.2.1.1: Information flow for UUS1 implicit request (mobile to mobile call)

5.2.1.2.2 Explicit activation

Figure 5.2.1.2.2.1: Information flow for UUS 1 explicit request (mobile to mobile call)

5.2.2 Service 2 (UUS2)

5.2.2.1 Flow control

Up to two UUI messages can be sent in each direction. If either party tries to send more than two UUI messages, they are discarded.

5.2.2.2 Information flows

Figure 5.2.2.2: MAF044

Figure 5.2.2.2.1: Information flow for UUS2 explicit request (mobile to mobile call)

5.2.3 Service 3 (UUS3)

5.2.3.1 Flow control

Network flow control mechanisms shall exist after the connection has been established in order to restrict the amount of UUI sent in each direction. A burst capability of sending N messages shall immediately be available to each user, where N initially equals the value of the burst parameter X. The value of N shall be decremented by one for every message sent by the user and incremented by Y at regular intervals of T2-UUS3 (see table 5.1). The value of N shall be limited to a maximum of X.

The value of the burst parameter X shall be 16.

The value of the replenishment parameter Y shall be 8.

Network flow control shall be performed only by the sending user’s network.

If the MSC receives UUI messages from the MS at a rate which exceeds the flow control limit, it shall discard the UUI messages that cannot be handled and respond to the first discarded UUI message with a congestion control message.

When the flow control restrictions are removed, an indication that further UUI messages can be accepted shall be given. See the Processes Serving_MSC_Handle_UUS_In_Active_Call and Remote_ MSC_Handle_UUS_In_Active_Call.

5.2.3.2 Information flows

Figure 5.2.3.2: MAF045

Figure 5.2.3.2.1: Information flow for UUS3 explicit request during call establishment (mobile to mobile call)

Figure 5.2.3.2.2: Information flow for UUS3 explicit request during active call (mobile to mobile call)

5.3 Messages and their contents

This clause contains the detailed description of the information flows used by UUS.

Each Information Element, IE is marked as (M) Mandatory, (C) Conditional, or (O) Optional. A mandatory information element shall always be present. A conditional information element shall be present if certain conditions are fulfilled; if those conditions are not fulfilled it shall be absent. An optional information element may be present or absent, at the discretion of the application at the sending entity. This categorisation is a functional classification, i.e. stage 2 information and not a stage 3 classification to be used for the protocol.

The stage 2 and stage 3 message and information element names are not necessarily identical.

5.3.1 Information elements used in the messages

The following UUS specific constructed information elements are used in the messages.

Table 5.3.1.1: UUS specific information elements

Parent Information Element	Child Information Element name	Information element Required	Information element description
UUS options	UUS1 UUS2 UUS3	C C C	The information element is present if UUS1 service is requested; otherwise it shall be absent. It may contain the following values: – Required – Not Required The information element is present if UUS2 service is requested; otherwise it shall be absent. It may contain the following values: – Required – Not Required The information element is present if UUS3 service is requested; otherwise it shall be absent. It may contain the following values: – Required – Not Required
UUS provision	UUS1 UUS2 UUS3	C C C	If UUS1 services is requested and provisioned the information element is present, otherwise it shall be absent. If UUS2 services is requested and provisioned the information element is present, otherwise it shall be absent. If UUS3 services is requested and provisioned the information element is present, otherwise it shall be absent.

5.3.2 Messages between MS and MSC

Call control messages (Setup, Alert, Connect, Disconnect, Release and Release Complete, refer to GSM 04.08) may carry UUS service activation request and response. They can carry also UUI for UUS1.

Facility message, refer to GSM 04.08, can carry UUS service 3 activation request and response.

Dedicated User-To-User message, refer to GSM 04.08, carries UUI for UUS service 2 and 3.

These messages are used both in serving and remote networks.

5.3.3 Messages between MSC and VLR (B interface)

These messages are used in the serving network.

Table 5.3.3.1: Messages between MSC and VLR

Message	Message sender	Information element name	Information element Required	Information element description
Send Info For Outgoing Call	MSC	– UUS options	– C	Refer to GSM 03.18. In addition: The information element is present if MS A requested UUS service; otherwise it shall be absent. The structure of UUS options is defined in table 5.3.1.1
Send Info For Outgoing Call negative response	VLR	– UUS reject	– C	Refer to GSM 03.18 In addition: The information element is present, if required UUS service was requested by MS A and service is not provided, otherwise it shall be absent.
Complete Call	VLR	– UUS provision	– C	Refer to GSM 03.18 In addition: The information element is present if MS A requested UUS service(s); otherwise it shall be absent. The structure of UUS Provision is defined in table 5.3.1.1
Send Info For UUS3	MSC	–	–	The message is sent when UUS3 service is requested during active call. NOTE: This message is used in serving and remote MSCs.
Send Info For UUS3 Ack	VLR	UUS provision	C	The information element is present if UUS3 service is provisioned; otherwise it shall be absent

5.3.4 Messages between MSC – MSC (E interface)

These messages are used in the remote network when UUS is supported in remote MSC in conjunction of SOR, refer to GSM 03.79.

Table 5.3.4.1: Messages between MSC – MSC

Message	Message sender	Information element name	Information element Required	Information element description
Resume Call Handling	MSCB	– UUS1 Service request UUS2 Service request UUS3 Service request UUS1 UUI UUS CF interaction	– C C C C C	Refer to GSM 03.79. In addition: The information element is present if UUS1 Service was requested in the original call and remote MSC supports UUS service; otherwise it shall be absent. The information element is present if UUS2 Service was requested in the original call and remote MSC supports UUS service; otherwise it shall be absent The information element is present if UUS3 Service was requested in the original call and remote MSC supports UUS service; otherwise it shall be absent. The information element is present if UUS1 UUI was present in the original call and remote MSC supports UUS service; otherwise it shall be absent. The information element is present if the remote subscriber has accepted UUS1 service request and call forwarding or call deflection has been activated after that; otherwise it shall be absent.