Introduction Assumption Reference Diagram 3GPP IP-CAN and IMS Go Reference Point Gm Reference Point Gq Reference Point Gi refernece point WiMAX Network Deployment WiMAX and IMS : Alternative 1 WiMAX and IMS : Alternative 2 List of use-cases

Introduction

This section describes the various use-cases that are envisioned which the interworking will need to support. Current focus is on 3GPP R7 and current release (?) of Wimax specifications. There are several assumptions and questions raised, which require further validations. In order to facilitate understanding and
comparisons, both 3GPP IP CAN and WiMAX interworking scenario have been studied. We plan to remove the 3GPP IP CAN scenarion in the end of the study.

You can contribute to this page by validating the assumptions, refining/answering questions, altering the use cases, or adding new use case.

Assumption

1. Vendors are claiming that R7 IMS will be available for deployment in late 2007. This also the time farme for the commercial deployment of Wimax. Due to this we have focused on studying interworking for 3GPP R7 and current WiMAX.
2. PCC (Policy and Charging Conmtrol) architecure is under study stage and will take some more time to be in a implementation stage. (3GPP TS 23.303, 23.882)

Reference Diagram

3GPP IP-CAN and IMS

The diagram above illustrates the primary interfaces which the IMS layer uses to interface with the IP-CAN layer. We assume that WiMAX will interconnect with a 3GPP network as a 3GPP compliant access network and will therefore have to provide the same interfaces to the IMS layer as a 3GPP IP-CAN layer provides. In other words, this reference diagram brings out the primary interfaces that a WiMAX access network will be required to provide to the IMS layer.

Go Reference Point

Go reference point is defined in 3GPP TS 29.207, 29.208. This reference interface is COPS (RFC 2748, 3084) based. This reference point is used for configuring the PEP (Policy Enforcement Point) which in 3GPP located inside GGSN by PDF (Policy Decesion Function). Following are the major functions performed at this interface:

1. Media Session Autherization at the time of media session setup (secondary PDP session setup) UE provides autherization token, Flow identifier and FQDN of PDF. Which is used by the GGSN for autherization. PDF on the bassis of autehrization token and flow identifers configuers the authorized QoS and packet classifier (Gate Fuction).
2. Exchange of GCID (GPRS Charging ID) and ICID (IMS Charging ID).
3. Approval of QoS Commit, Removal of QoS Commit and Revoke Authorisation.
4. Release of Media session when signalling session is released, no more credit in case of on line charging or any abnormal condition detected by IMS components.
5. GGSN comunicates the release of media session conditions undetectable by UE, in order to take appropriate signaling actions.

PEP implements PIB (Policy Information Base) which is manupulated by PDF using COPS.

Gm Reference Point

Gm reference point is defined in 3GPP TS 23.228.

Gq Reference Point

Gq reference point is defined in 3GPP TS 29.209. It is internal to IMS domain and is not of interest for this study.

Gi refernece point

Gi reference point is defined in 3GPP TS 23.060, TS 29.061. At this interface interworking with PDN is provided. We understand this interface in the context of interworking with IMS.

UE establishes a default PDP context for signalling. IMS domain name is used as APN name for creating the default PDP context. There are no policies enforced or default policies (TFT : Traffic Flow Template) as available from HSS or localy confiured are used. For every SIP session, a new secondary PDP context is created. SBLP are exchanged as through Go interface. All media session being controlled by a SIP session, share the secondary PDP context. Flow identifier exchanged as part of PDP context modification (?) process is used as discriminator. Following are the important points.

1. Default PDP context and secondary PDP context shares the same APN name. Since UE IP address is bound to a PDP context, for media sessions (secondary PDP context) same IP address is used. However, for signaling routing may be based on APN name. For media, normal L3 routing should be used (?).
2. P-CSCF and PDF are located in the same PLMN as of UE, that is VPLMN (always). This precludes the possibility of HPLMN GGSN being used either for signaling IMS controlled traffic (signaling, media).
3. Above two points also leads to a interesting conclusion that the IP address allocated to the UE shall be controlled by VPLMN (always) (?). Support of Mobile IP and VPN need to be investigated further. At this point of discussion, we do not differentiate between IPv4 and IPv6. But need to be understood.

These points are depicted in the following figure.

WiMAX Network Deployment

How would WiMAX network deployment look like? Let use first understand with IMS.

WiMAX and IMS : Alternative 1

WiMAX and IMS : Alternative 2

List of use-cases

1. IMS Registration
1. Non Emergency
2. Emergency
1. MS with Identity (With IMSIM)
2. Identity Less MS (No IMSIM)
3. User Authentication
2. SIP Signaling
1. Non Emergency Session
2. Emergency Session
3. SIP Forking
1. Parallel
2. Sequential
4. Authentication
3. Bearer Setup
1. QoS Autherization (Per MS, Per Session, Per Service)
2. QoS Re-Autherization
3. QoS Revoke
4. Upgrade/Downgrade of Session QoS
1. Codec Re-negotiation
5. Un-Authorized Emergence Bearer, i.e. exceeds the authorization
6. Policy un-enforced interface
7. Policy enforcement at NAP
4. Bearer Loss/Recovery
5. Session Release
6. Bearer Release
1. Explicit Release by MS
2. Network enforced release
3. Network detected release
7. Charging
1. UDR(Usage Data Record) generation : NAP, IMS
2. Charging Correlation
3. Online and offline charging

maintained by: Anil Kumar (anil.rajput@hsc.com)
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