13 IMS related functions
27.0603GPPMobile Station (MS) supporting Packet Switched servicesPacket domainRelease 17TS
13.1 General
IP Multimedia Core Network Subsystem (IMS) related functions affects the way the MS sets up some Session Management information elements when activating or modifying PDP context(s).
IMS is based on IETF protocols with SIP as described in RFC 3261 [54] as the framework. Example signalling flows can be found in 3GPP TS 24.228 [50], while differences between standard SIP and IMS are specified in 3GPP TS 24.229 [51].
GPRS aspects within the MS when connected to IMS are specified in 3GPP TS 24.229 [51], while the corresponding functionality within the GGSN, PCF and P-CSCF is specified in 3GPP TS 29.061 [17] and 3GPP TS 29.207 [52]. Encoding of the session management information elements relevant for IMS are specified in 3GPP TS 24.008 [12].
Mapping of SDP to QoS attributes and authorisation of QoS attributes is specified in 3GPP TS 29.208 [53].
13.2 DNS Server Discovery
In the IMS the MS can request a DNS Server IPv6 address(es) via normal IETF DHCPv6 [55] request/response signalling or by using the Protocol Configuration Option information element when requesting PDP context activation. The corresponding procedure is specified in 3GPP TS 29.061 [17]
13.3 P-CSCF Server Discovery
In the IMS the MS can request a P-CSCF IPv6 address(es) for SIP signalling via normal IETF DHCPv6 request/response signalling in combination with normal IETF DNS request/response signalling or by using the Protocol Configuration Option information element when requesting PDP context activation. The P-CSCF discovery procedure is specified in 3GPP TS 24.229 [51].
13.4 PDP Context used for IMS Signalling
Before the MS can request IMS services, a PDP context is activated to carry the IMS signalling. This PDP context can be for IMS signalling only or a general-purpose PDP context (i.e. may also carry the media). The MS can request that a PDP context is for IMS signalling only by setting the IM CN subsystem signalling flag in the Protocol Configuration Option information element when activating a PDP context. Whether or not a PDP context is activated to be used for general purpose or for IMS signalling only, the MS can request that a PDP context will be prioritised by setting the QoS attribute Signalling Indication. The encoding of the IM CN subsystem signalling flag and the Signalling Indication information elements are specified in 3GPP TS 24.008 [12]. The corresponding procedures are specified in 3GPP TS 24.229 [51] and 3GPP TS 29.061 [17].
13.5 Binding Information
The MS supports the binding mechanism for service-based local policy control. When an authorization token is included in an IMS SIP message, the MS will include binding information in the Traffic Flow Template information element when activating or modifying a PDP context intended to carry certain IMS IP flow(s). The binding information consists of the authorization token and the flow identifier(s) of the IMS IP flow(s) the MS puts on the same PDP context, e.g. due to the same QoS requirements for those IMS IP flows. The authorization token and the flow identifier are specified in 3GPP TS 29.207 [52].
If the MS multiplexes media flows from different IMS sessions in the same PDP Context, the MS shall include the binding information of all multiplexed sessions, i.e. the media authorization tokens of all multiplexed IMS sessions and the flow identifiers of all multiplexed IP flows, in the PDP Context Activation/Modification request.
If the MS includes binding information, it shall populate the TFT filters with wildcard values.
13.6 Mapping of SDP to QoS Attributes
The type of application and the users choice of perceived quality are often fully enough information to set the requested QoS attributes when activating or modifying the PDP context(s) carrying the applications IMS IP flow(s). However, if the application receives SDP parameters, the MS can take guidance and map some of the SDP parameters, e.g. b=AS:<bandwidth-value>, to the corresponding requested QoS attributes, e.g. Maximum and Guaranteed Bitrate for uplink and downlink. The rules for mapping SDP parameters to QoS attributes are specified in 3GPP TS 29.208 [53].
13.7 Authorization of QoS Attributes
When the PDP context is activated or modified, for an IMS session where service-based local policy is applied, the MS can check that the values of some requested QoS attributes, e.g. Guaranteed or Maximum Bitrate uplink and downlink, do not exceed the values of the corresponding Maximum Authorized QoS attributes, e.g. Maximum Authorized Bandwidth uplink and downlink. The values of the Maximum Authorized QoS attributes are derived from the SDP parameters of the IMS media components identified. The rules for deriving the Maximum Authorized QoS attributes per flow identifier and per PDP context are specified in 3GPP TS 29.208 [53].
13.8 Support for forking
A MS originating a SIP session is able to handle several forked responses. Forking can occur in a downstream SIP proxy outside the 3GPP network. In case of service-based local policy, the same authorization token is received for all the forked responses for that session.
Detailed call control procedures for forking are specified in 3GPP TS 24.229 [51]. Specific procedures for setting the Maximum Authorized QoS attributes in relation to several forked responses are specified in 3GPP TS 29.207 [52] and 3GPP TS 29.208 [53].
13.9 Multiplexing of IMS media components to PDP contexts
The IMS network may use the SDP attribute "a=group:SRF" to order the MS to multiplex certain IMS media components within the same session on the same PDP context. If this attribute is not present then multiplexing the media components on PDP contexts is entirely MS specific. The rules for multiplexing IMS media components to PDP contexts are specified in 3GPP TS 24.229 [51].
13.10 Policy control rejection of PDP context
The GGSN rejects a PDP context activation or modification if service-based local policy cannot be exercised, e.g. erroneous binding information, or will not be exercised, e.g. binding information available although the current APN is not subject for policy control. The GGSN puts the actual Policy Control rejection code in the Protocol Configuration Option information element in the rejection message. An MS receiving a rejection message shall check the Protocol Configuration Option information element and take proper action.
The rejection cases as well as the Policy Control rejection codes are specified in 3GPP TS 29.207 [52]. Rules for the MS when receiving policy control rejections of a PDP context activation or modification are specified in 3GPP TS 24.229 [51].
Annex A (informative):
Summary of AT commands for the Packet Domain
This informative annex lists the AT commands for the Packet Domain that are fully described in 3GPP TS 27.007.
Table A.1: Summary of AT commands for the packet domain
|
Command |
Description |
|
+CGACT |
PDP context activate or deactivate |
|
+CGANS |
Manual response to a network request for PDP context activation |
|
+CGATT |
PS attach or detach |
|
+CGAUTO |
Automatic response to a network request for PDP context activation |
|
+CGCLASS |
PS mobile station class |
|
+CGCLOSP |
<VOID> |
|
+CGCLPAD |
<VOID> |
|
+CGDATA |
Enter data state |
|
+CGDCONT |
Define PDP context |
|
+CGEREP |
Control unsolicited PS event reporting |
|
+CGPADDR |
Show PDP address |
|
+CGREG |
Packet Domain network registration status |
|
+CGQMIN |
Quality of service profile (minimum acceptable) |
|
+CGQREQ |
Quality of service profile (requested) |
|
+CGSMS |
Select service for MO SMS messages |
Table A.2: Summary of Packet Domain Extensions to existing A/Gb mode AT commands
|
Command |
Description |
|
+CEER |
Extended error report (refer to 27.007) |
|
+CMEE |
Report mobile equipment error (refer to 27.007) |
|
+CR |
Service reporting control (refer to 27.007) |
|
+CRC |
Cellular result codes (refer to 27.007) |
Table A.3: Summary of AT commands for Packet Domain modem compatibility mode
|
Command |
Description |
|
A |
Answer – manual acceptance of a network request for PDP context activation |
|
D |
Dial – request Packet Domain service |
|
H |
On-hook – manual rejection of a network request for PDP context activation |
|
S0 |
Automatic answering control – automatic acceptance of a network request for PDP context activation |
Annex B (informative):
Octet Stream Protocol (OSP) PDP type
Void
Annex C (informative):
Change history
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Change history |
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Date |
TSG # |
TSG Doc. |
CR |
Rev |
Subject/Comment |
Old |
New |
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06-2004 |
TSG#24 |
NP-040247 |
089 |
2 |
Multiple IMS sessions using the same PDP context |
5.6.0 |
6.0.0 |
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06-2007 |
TSG#36 |
Upgraded to v7.0.0 |
6.0.0 |
7.0.0 |
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12-2008 |
TSG#42 |
Upgraded to v8.0.0 due to simple upgrade without no technical change |
7.0.0 |
8.0.0 |
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12-2009 |
TSG#46 |
Automatic upgrade from previous Release |
8.0.0 |
9.0.0 |
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12-2010 |
TSG#50 |
CP-100779 |
91 |
1 |
Correcting non-specific external references |
9.0.0 |
9.1.0 |
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03-2011 |
TSG#51 |
Automatic upgrade from previous Release version 9.0.0 |
9.0.0 |
10.0.0 |
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03-2011 |
TSG#51 |
Correction of heading and numbering made by MCC |
10.0.0 |
10.0.1 |
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09-2012 |
TSG#57 |
Automatic upgrade from previous Release version 10.0.1 |
10.0.1 |
11.0.0 |
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10-2014 |
Automatic upgrade from previous Release |
11.0.0 |
12.0.0 |
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12-2015 |
Automatic upgrade from previous Release |
12.0.0 |
13.0.0 |
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Change history |
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Date |
TSG # |
TSG Doc. |
CR |
Rev |
Cat |
Subject/Comment |
New |
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2017-03 |
CT#75 |
Automatic upgrade from previous Release |
14.0.0 |
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2018-06 |
CT#80 |
Automatic upgrade from previous Release |
15.0.0 |
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2020-06 |
CT#88e |
– |
– |
– |
Update to Rel-16 version (MCC) |
16.0.0 |
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2022-03 |
SA#95e |
– |
– |
– |
Update to Rel-17 version (MCC) |
17.0.0 |
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