Content for  TS 23.228  Word version:  19.0.0

This clause gives information flows for the procedures for placing sessions on hold that were previously established by the mechanisms of clause 5.4, clause 5.5, clause 5.6, and clause 5.7, and resuming the session afterwards. Two cases are presented: mobile-to-mobile (UE-UE), and a UE-initiated hold of a UE-PSTN session. For a multi-media session, it shall be possible to place a subset of the media streams on hold while maintaining the others. These procedures do not show the use of optional I-CSCFs. If an I-CSCF was included in the signalling path during the session establishment procedure, it would continue to be used in any subsequent flows such as the ones described in this clause.

An IMS session was previously established between an initiating UE and a terminating UE. Each of these UEs has an associated P-CSCF, and a S-CSCF assigned in their home network. The procedures are independent of whether the P-CSCFs are located in the home or visited networks. Therefore there is no distinction in this clause of home network vs. visited network. The hold and resume procedures are identical whether the UE that initiated the session also initiates the session-hold, or whether the UE that terminated the session initiates the session-hold. When a media stream has been placed on hold, it shall not be resumed by any endpoint other than the one that placed it on hold. The procedures for placing a media stream on hold, and later resuming the media stream, are as shown in the following information flow:

Information flow procedures are as follows:

An IMS session was previously established between an initiating UE and a MGCF acting as a gateway for a session terminating on the PSTN, or between an initiating MGCF acting as a gateway for a session originating on the PSTN to a terminating UE. The UE has an associated P-CSCF, an S-CSCF assigned in its home network, and a BGCF that chooses the MGCF. The procedures are independent of whether the P-CSCF is located in the subscriber's home or visited network. Therefore there is no distinction in this clause of home network vs. visited network. The session hold and resume procedure is similar whether the UE initiated the session to the PSTN, or if the PSTN initiated the session to the UE. The only difference is the optional presence of the BGCF in the case of a session initiated by the UE. Note that the BGCF might or might not be present in the signalling path after the first INVITE is routed. The procedures for placing a media stream on hold, and later resuming the media stream, are as shown in the following information flow:

Information flow procedures are as follows:

An IMS session was previously established between an initiating UE and a MGCF acting as a gateway for a session terminating on the PSTN, or between an initiating MGCF acting as a gateway for a session originating on the PSTN to a terminating UE. The UE has an associated P-CSCF, an S-CSCF assigned in its home network, and a BGCF that chooses the MGCF. The procedures are independent of whether the P-CSCF is located in the subscriber's home or visited network. Therefore there is no distinction in this clause of home network vs. visited network. The session hold and resume procedure is similar whether the UE initiated the session to the PSTN, or if the PSTN initiated the session to the UE. The only difference is the optional presence of the BGCF in the case of a session initiated by the UE. Note that the BGCF might or might not be present in the signalling path after the first INVITE is routed. The following information flow shows the procedures, where the session is set on hold from the PSTN side:

Information flow procedures are as follows:

This clause gives information flows for the procedures for an anonymous session. However, sessions are not intended to be anonymous to the originating or terminating network operators. The purpose of the mechanism is to give an IMS user the possibility to withhold certain identity information as specified in RFC 3323 and RFC 3325. The privacy mechanism for IMS networks shall not create states in the CSCFs other than the normal SIP states. IMS entities shall determine whether they are communicating with an element of the same Trust Domain for Asserted Identity or not as described in RFC 3325.

The user shall be able to request that her identity information is not revealed to the terminating party. If the originating user requests the session to be anonymous, the terminating side must not reveal any identity or signalling routing information to the destination endpoint. The terminating network should distinguish at least two cases, first where the originator intended the session to be anonymous, and second where the originator's identity was deleted by a transit network.

Procedures for establishment of an anonymous bearer path are not standardised in this release.