Content for TS 23.228 Word version: 18.5.0

1… 3… 4… 4.2.4… 4.3… 4.4… 4.13… 4.16… 5… 5.2… 5.3… 5.4… 5.4.7… 5.4.8… 5.4a… 5.5… 5.5.3… 5.6… 5.6.3… 5.7… 5.7.3… 5.7.5… 5.7.8… 5.8… 5.10… 5.11… 5.11.3… 5.11.3.3 5.11.3.4 5.11.4… 5.11.5… 5.11.5.3… 5.11.6… 5.12… 5.16… 5.16.2… 5.19… 5.20… A… E… E.2.2… G… G.5… H I… J… K… L… M… M.3… N… P… Q… Q.2.5… R… S… T… U… U.2… V… W… X… Y… Z… AA… AA.3… AB… AC… AC.7… AC.7.2… AC.7.2.2 AC.7.2.3… AC.7.4… AC.9…

5.11.3.4 Sample MM session flow - addition of another media
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5.11.3.4 Sample MM session flow - addition of another media p. 169

For this end-to-end session flow, we assume the originator is a UE located within the service area of the network operator to whom the UE is subscribed. The UE has already established an IM CN session and is generating an invite to add another media (e.g. video to a voice call) to the already established session. Note that the invite to add media to an existing session could be originated by either end. The invite, and subsequent flows, are assumed to follow the path determined when the initial session was established. Any I-CSCFs that were included in the initial session would be included in this session.

The originating party addresses a destination that is a subscriber of the same network operator.

The destination party is a UE located within the service area of the network operator to which it is subscribed.

The flow presented here assumes that Policy and Charging Control is in use.

Reproduction of 3GPP TS 23.228, Fig. 5.33: Multimedia session flow - addition of another media

Figure 5.33: Multimedia session flow - addition of another media

Step-by-step processing of this end-to-end session flow is as follows:

Step 1.

UE#1 sends a SIP INVITE request, containing new SDP for the new media and including the original SDP, to P-CSCF#1, which was obtained from the CSCF discovery procedures.

Step 2.

P-CSCF#1 forwards the INVITE to the next hop name/address, as determined from the registration procedures. In this case the next hop is S-CSCF#1 within the same operator's network.

Step 3.

S-CSCF#1 validates the service profile, and invokes whatever service logic is appropriate for this session attempt.

Step 4.

S-CSCF#1 recognises that this invite applies to an existing session. It therefore forwards the INVITE along the existing path to S-CSCF#2.

Step 5.

S-CSCF#2 validates the service profile, and invokes whatever service logic is appropriate for this session attempt.

Step 6.

S-CSCF#2 remembers (from the registration procedure) the next hop CSCF for this UE. It forwards the INVITE to P-CSCF#2 in the home network.

Step 7.

P-CSCF#2 remembers (from the registration procedure) the address of UE#2 and forwards the INVITE to UE#2.

Step 8.

UE#2 returns the media stream capabilities of the destination to the session originator, along the signalling path established by the INVITE message.

Step 9.

P-CSCF#2 authorizes the QoS resources required for this additional media.

Step 10.

P-CSCF#2 forwards the SDP to S-CSCF#2.

Step 11.

S-CSCF#2 forwards the SDP to S-CSCF#1.

Step 12.

S-CSCF#1 forwards the SDP message to P-CSCF#1.

Step 13.

P-CSCF#1 authorizes the additional resources necessary for this new media.

Step 14.

P-CSCF#1 forwards the SDP message to the originating endpoint, UE#1.

Step 15-19.

The originator decides the offered set of media streams for this media addition, and sends the offered SDP to P-CSCF#1.

Step 20.

Depending on the bearer establishment mode selected for the IP-CAN session, resource reservation shall be initiated either by the UE or by the IP-CAN itself. UE#2 initiates the resource reservation procedures for the resources necessary for this additional media as shown in Figure 5.33. Otherwise, the IP-CAN initiates the reservation of required resources after step 9.

Step 21.

Depending on the bearer establishment mode selected for the IP-CAN session, resource reservation shall be initiated either by the UE or by the IP-CAN itself. After determining the offered set of media streams for this additional media, in step #15 above, UE#1 initiates the reservation procedures for the additional resources needed for this new media as shown in Figure 5.33. Otherwise, the IP-CAN#1 initiates the reservation of required resources after step 13.

Step 22-25.

When the terminating side has successfully reserved the needed resources, it sends the "reservation successful" message to UE#1 along the signalling path established by the INVITE message. The message is sent first to P-CSCF#1.

Step 25a.

P-CSCF#1 authorizes any additional media for the proposed SDP.

Step 26.

P-CSCF#1 forwards the message to UE#1.

Step 27-31.

UE#1 sends the final agreed SDP to UE#2 via the established path.

Step 32-35.

UE#2 responds to the offered final media.

Step 35a.

P-CSCF#1 authorizes the media agreed.

Step 36.

The response is forwarded to UE#1.

Step 37.

UE#2 may optionally delay the session establishment in order to alert the user to the incoming additional media.

Step 38.

If UE#2 performs alerting, it sends a ringing indication to the originator via the signalling path. The message is sent first to P-CSCF#2.

Step 39.

P-CSCF#2 forwards the ringing message to S-CSCF#2.S-CSCF#2 invokes whatever service logic is appropriate for this ringing flow.

Step 40.

S-CSCF#2 forwards the message to S-CSCF#1.

Step 41.

S-CSCF#1 forwards the message to P-CSCF#1.

Step 42.

P-CSCF#1 forwards the message to UE#1.

Step 43.

UE#1 indicates to the originator that the media addition is being delayed due to alerting. Typically this involves playing a ringback sequence.

Step 44.

When the destination party accepts the additional media, UE#2 sends a SIP 200-OK final response along the signalling path back to the originator. The message is sent first to P-CSCF#2.

Step 44a.

After sending the 200-OK, UE#2 may initiate the new media flow(s).

Step 45.

P-CSCF#2 enables the media flows authorized for this additional media.

Step 46.

P-CSCF#2 forwards the final response to S-CSCF#2.

Step 47.

S-CSCF#2 forwards the final response to S-CSCF#1.

Step 48.

S-CSCF#1 forwards the final response to P-CSCF#1.

Step 49.

P-CSCF#1 enables the media flows authorized for this additional media.

Step 50.

P-CSCF#1 forwards the final response to UE#1.

Step 51.

UE#1 starts the media flow(s) for this additional media.

Step 52.

UE#1 responds to the final response with a SIP ACK message, which is passed to the destination via the signalling path. The message is sent first to P-CSCF#1.

Step 53.

P-CSCF#1 forwards the ACK to S-CSCF#1

Step 54.

S-CSCF#1 forwards the ACK to S-CSCF#2.

Step 55.

S-CSCF#2 forwards the ACK to P-CSCF#2.

Step 56.

P-CSCF#2 forwards the ACK to UE#2.