IMS-WIMAX Interworking - An Introduction The Need Levels of interworking

IMS-WIMAX Interworking - An Introduction

The Need

As WiMAX deployments grow, it offers an alternate access mechanism for subscribers for their communication needs. Converging this access into the 3G architecture is in interest of the carriers for two major reasons:

• WiMAX, like other emerging wireless standards has the potential of being disruptive, in that it can grow virally and side-step an existing 3G infrastructure by allowing voice/video/data connectivty over a high speed wireless bandwidth while also allowing mobility to subscribers. (Of course, this is only a technical probability - there are legal and financial ramifactions that need to be addressed before such a para-net can actually be deployed)

• WiMAX connectivity will provide 3G networks with an increased customer base to target. It is in their (3G oeprator's) interest to tap into as many such access networks as possible to ensure that the 'mainstream revenue' (i.e. voice telephony) continues to fuel their business while offering value added services via such hybrid networks to excite users to use this converged networks. As an example, if a Verizon were to provide 'service portability' to its users, where Joe, could avail of his VOD streaming service irrespective of the device and network he is using (using a multimedia phone while on the road over cellular, PC at home using DSL, a laptop at a coffee shop using WLAN or WiMax), then it is a good reason for Joe to pay for this converged service. If Verizon was to offer a service that promised a softphone call from his PC could transfer to his cell phone as he walks out of range without service disruption, then it would be a good reason for Joe to pay for this service as opposed to a free Skype that does not offer this continuity.

Levels of interworking

3GPP interworking for access networks [22.934] offers the following six levels of 'interworking'

• Common billing – this is not true integration. WiMax and 3G exist as separate networks but can be billed together from an operator. This doesn’t even require common billing infrastructure, just common mediation

• AAA is controlled by 3GPP core for both 3G and WiMax access. However, WiMax network is still separate from 3G network.

• All 3GPP services are accessible by WiMax subscribers. WiMax morphs into an access-network into the 3G subsystem. All control is performed by the 3G core, with any required interworking (such as AAA algorithm differences, QoS policy differences) happening at the edge of the network such that 3G Control is ‘master’ and WiMax translated controls act as the ‘slave’ local to the WiMax network, but under direction from 3G core. Note that in this evolution, the Wimax MS becomes an IMS compliant UE with a SIP client running in it.

• Service Continuity-. In this case, services provided by the ‘common network’ can work irrespective of whether the subscriber is in a WiMax NSP or a 3G network. This is for 3G packet network only (not CS)

• Service Continuity with no user-experience change – in this case, service continuity is optimzed to a degree where handovers are not visible to the user at all.

• 3GPP CS services – in this final scenario, CS services based in a 3G network will also be accessible to a WiMax network user.

Our goal is to study/investigate level 3, which is currently partially defined by standards and what it takes to reach level 6.

Do note that a lot of our discussions will not be specific only to WiMAX - they will apply to any 3rd party access network (W-lan, dsl, cable) but we will be using WiMAX as a realization for our discussions.

maintained by: arjun@hsc.com

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