Release: Rel-5 Work Item: Source

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3GPP TSG-SA WG2 meeting #28 Tdoc S2-023491rev21

Bangkok, Thailand, 11th – 15th November 2002

Title: Draft Response to LS on Structure of IMS Charging Identifier (ICID)

Response to: S2-023252 (S5-024487)- LS on Structure of IMS Charging Identifier (ICID)

Release: Rel-5

Work Item: -

Source: SA2

To: SA5

Cc: CN1, CN3, CN4

Contact Person:

Name: Stephen Dutnall

Tel. Number: +33 618 415 778

E-mail Address:

Attachments: None

1. Overall Description:

SA2 thanks SA5 for the liaison statement (and associated attachment) on the Structure of the IMS Charging Identifier (ICID) tdoc number S2-023252 (S5-024487). On analysing the liaison statement and the attached information from TS 32.225v5.0.0 regarding the definition of the ICID, SA2 has a number of questions that need clarification

  1. According to the written text in the LS the ICID

“… is made up of a 32-bit running count, followed by the IP-address of the node that generates the ICID … “

however the text in TS 32.225v5.0.0 states the following:

The charging correlation vector contains an IMS part (ICID - a unique number plus an IP address) and an access part (GPRS Charging ID and GGSN address)”

Action point for SA5: SA2 asks if SA5 to confirm that the “32 bit part” of the ICID is a running count and not a unique number as currently stated in 32.225v5.0.0. If this is the correct understanding SA2 asks SA5 to update their specifications accordingly.

  1. According to the structure of the ICID SA5 allows the support of IPv4 and IPv6 addresses for the node generating the ICID.

    1. SA2 restates the fact that according to 23.228v5.6.0 it is assumed that all IMS nodes use only IPv6 addresses as specified by 3G TS 23.221: "The IM CN subsystem shall exclusively support IPv6."

Note IP version interworking handling for the IMS is currently a Release 6 work item. However to pave the way for the R6 work item on access independence that could allow use of IP v4 for IMS, it might be useful to keep the possibility to allow the support of IPv4 or IPv6 addresses for the node generating the ICID.

Action point for SA5: SA2 asks clarifications on the requirements that IMS nodes support IPv4 and IPv6 versions.

  1. According to SA2’s understanding the ICID is made unique by the combination of the IP address and the 32 bit running count. In the case that SA5 maintains its support for IPv4 address usage in the ICID, then the support of private IPv4 addresses in the IMS nodes would introduce a potential IP address overlap risk. Currently it is undefined whether the IPv4 address is public or private.

Action point for SA5: SA2 asks SA5 whether or not it agrees with the risk identified and if so to clarify its current specifications to quote that for IPv4 addresses a public IP v4 address will be used in order to ensure global uniqueness of the ICID.

  1. Finally if SA5 maintains that the ICID is to support IPv4 and IPv6 addresses in the ICID, then SA2 raises the question why two separate ICID layouts are defined (one for iPv4 address the other for IPv6 address) and not a single layout, which would permit both IPv4 and IPv6 address usage.

Action point for SA5: SA2 asks SA5 to explain why separate layouts are used for IPv4 and IPv6 ICID generation.
2. Actions:

See above

3. Date of Next SA2 Meeting:






xx January 2002

San Francisco, USA


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