B.1 Format of a flow identifier

29.2143GPPPolicy and charging control over Rx reference pointRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

B.1.1 General

A flow identifier is expressed as a 2-tuple as follows:

where both are numbered starting from 1. The encoding of the flow identifier is as indicated in 3GPP TS 24.008 [12].

If UE and AF share an algorithm for a given application, which guarantees that UE and AF assign the same ordinal number to each media component, the ordinal numbers of the IP Flows within a media component shall be assigned according to the following rules:

– All IP flow(s) or bidirectional combinations of two IP flow(s) within the media component, for which a downlink destination port number is available, shall be assigned ordinal numbers in the order of downlink destination port numbers.

– All IP flows, where no downlink destination port number is available, shall be assigned the next higher ordinal numbers in the order of uplink destination port numbers.

The ordinal number of a media component shall not be changed when the session description information is modified.

If no SDI with fixed and unique positions for media components is exchanged between UE and AF, the UE and AF may assign the ordinal numbers of the media components in another application-dependent algorithm which guarantees that UE and AF assign the same ordinal number to each media component.

If UE and AF do not share an algorithm for a given application, which guarantees that UE and AF assign the same ordinal number to each media component, the ordinal number of the media component shall be set to zero and the ordinal number of the IP flows shall be assigned according to the following rules:

1. If ordinal numbers for several IP flows are assigned at the same time, all uplink IP flows shall be assigned lower ordinal number than all downlink IP flows.

2. If ordinal numbers for several IP flows are assigned at the same time, all uplink and all downlink IP flows shall separately be assigned ordinal numbers according to increasing internet protocol number assigned by IANA (e.g. 6 for TCP and 17 for UDP)

3. If ordinal numbers for several IP flows are assigned at the same time, for each internet protocol with a port concept, all uplink and all downlink IP flows of this internet protocol shall separately be assigned ordinal numbers according to increasing port numbers.

4. If IP flows are removed from an existing session, the previously assigned binding info shall remain unmodified for the remaining IP flows.

5. If IP flows are added to an existing session, the previously assigned binding info shall remain unmodified and the new IP flows shall be assigned ordinal numbers following the rules 1. To 3., starting with the first previously unused ordinal number. The numbers freed in step 4. Shall not be reused.

If the IP flows correspond to AF signalling (e.g. SIP signalling IP Flows), and no IP flow information is provided both the ordinal number of the media component and the IP flows shall be set to zero. In the case when the IP flow information of the AF signalling is provided, the ordinal number of the media component will be set to zero, and the ordinal number(s) of the IP flows shall follow the rules set above for the case when the UE and AF do not share an algorithm for a given application.

B.1.2 Derivation of Flow Identifiers from SDP

B.1.2.1 Standard Procedure

The procedure in Table B.1.2.1.1 shall be applied for SDP of "session" disposition type within SIP and for all SDP outside SIP.

Table B.1.2.1.1: Standard Procedure to derive Flow Identifiers from SDP

The ordinal number of the position of the media component

The ordinal number of the IP flow(s) within the media component description

The ordinal number of the position of the "m=" line in the SDP

The ordinal number of the IP flow(s) within the "m=" line assigned in the order of increasing downlink destination port numbers, if downlink destination port numbers are available. For uplink or inactive unicast media IP flows, a downlink destination port number is nevertheless available, if SDP offer-answer according to RFC 3264 is used.

The ordinal number of the IP flow(s) within the "m=" line assigned in the order of increasing uplink destination port numbers, if no downlink destination port numbers are available.

B.1.2.2 SDP with "early session" disposition type

The procedure in Table B.1.2.2.1 shall be applied for SDP of "early session" disposition type within SIP. The "early session" disposition type is specified within IETF RFC 3959 [27].

Table B.1.2.2.1: Procedure to derive Flow Identifiers from "early session" disposition SDP

The ordinal number of the position of the media component

The ordinal number of the IP flow(s) within the media component description

If a single media component with one media type (e.g. "audio" or "video") is contained in "early session" disposition SDP and a single media component with the same media type is contained in the "session" disposition SDP of the same SIP dialogue, and if both SDP media components are described in a single Rx service information media component, that Rx service information media component shall obtain the media component number derived from "session" disposition SDP following the rules in table B.1.2.1.1.

Otherwise each media component shall obtain the ordinal number of the position of the "m=" line in the "early session" disposition SDP plus 1000 as media component ordinal number.

As in table B.1.2.1.1.