5. ims to gsm-umts roaming

5. ims to gsm-umts roaming - Roaming Between GSM/UMTS and...

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Roaming Between GSM/UMTS and IMS Networks Vikas Bajaj System Engineering and Emerging Technologies Aricent Bangalore, India Vikas.Bajaj@aricent.com Abstract —Operators around the world are planning deployment of IMS Networks. It is therefore expected that GSM, UMTS and IMS Networks will co-exist for several years before full transition to IMS networks happens. There is a need therefore to support roaming of users from the legacy GSM/UMTS to IMS networks if the user device hosts IMS client software. This paper analyzes the problem and identifies the need for a VLR functional entity in the IMS network. It evaluates architectural alternatives for VLR placement and recommends use of one alternative. Finally, it captures the call flows for Registration, Call origination and Call termination to validate the recommended architectural alternative. Keywords-component; Roaming; IMS; VLR; S-CSCF I. INTRODUCTION The IMSization (IP Multimedia Subsystem) of wireless and wireline networks has begun in right earnest given the solid benefits that the IP Multimedia Subsystem (IMS) offers in the long run to operators. However, as has been in the past, transformation of networks is always a humongous task and never happens overnight. This means that, for a significant time, legacy and next generation networks always have to co- exist and during the period of co-existence need to provide inter-working for seamless delivery of services to the end-user. This shall also be the case with IMS, and maybe carrying the legacy baggage may be even tougher given its convergent characteristics. It will need to share space with GSM, 3G UMTS, CDMA, Wireline VoIP, Triple Play and PSTN networks. 3GPP, the entity responsible for defining IMS, is aware of this need for co-existence and is working on addressing inter-working issues arising out of this co-existence. A recent example includes the Voice Call Continuity definition which addresses seamless transition of voice call from IMS to 3G Circuit Switched domain and vice versa. This paper analyzes solutions for one such issue arising out of co-existence of GSM/UMTS networks and IMS. It evaluates a use case in which a user, subscribed to a conventional GSM/UMTS service provider, roams into an area which only has an IMS network deployed. The user’s mobile device has the capability to use either networks i.e. in addition to being equipped with GSM/UMTS CS and PS protocol stacks, it is also equipped with an IMS client. The UE however is equipped with a SIM/USIM module and not an ISIM module that would be used in IMS clients. Assuming existence of a roaming arrangement between the home GSM/UMTS network provider (referred to as the GSM/UMTS partner in this paper) and visited IMS network (referred to as the IMS partner in this paper), this paper considers architectural alternatives for the IMS network to provide service to the roaming subscriber. II.
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5. ims to gsm-umts roaming - Roaming Between GSM/UMTS and...

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