In late August I wrote on the technology-driven transition from vertical integration to modular industry value chains and how it applied to telephony in general. A subsequent post on "layers violations" attempted to relate the concepts to mobile VoIP.
I have additional supporting links. First, my August post alluded to work by Henning Schulzrinne with Andrea Forte and Sangho Shin at the 65th IETF meeting in March. At that time, the only reference the abstract of a presentation at WitMeMo’06. The full paper is now on the web. It's 802.11 in the Large: Observations at an IETF meeting by Andrea Forte, Sangho Shin and Henning Schulzrinne. As discussed in the previous post, this work points out the extent of problems with current 802.11 implementations, i.e. problems in today's products.
The question for mobile VoIP is whether fast handoff can be achieved at layer 3 (the IP layer) without a tight integration with layer 2 (the radio link). Traditional mobile networks (GPRS, CDMA 2000 & UMTS) use vertical integration – what a network engineer would call a layers violation – in order to achieve high performance handoffs. Obviously, WiFi networks (and other general purpose wireless networks) don't do that today. We could just wait until wireless technology becomes much better – for example until dual radios cost no more than a single radio thus allowing IP session setup over a new radio link while existing IP traffic flows over the existing radio link. But it could be years before that approach becomes low cost.
Or we could attempt to modularize the "layers violations." The latter is what the IRTF (Internet Research Task Force - the research arm of the IETF) MobOpts Research Group is discussing.
As background there already are Mobile IP protocols defined for both IPv4 and IPv6, but these don't provide handoffs that are fast enough for seamless voice telephony. Quite a bit of work has been done on IP protocols for fast handoff of IP sessions. For example, RFC 4068 Fast Handovers for Mobile IPv6, describes what to do at the IP layer,
without depending on specific link-layer features while allowing link-specific customizations.
Unfortunately, to achieve seamless voice telephony handoffs, you will require either two radios or some link-specific customization. This is where the MobOpts Reseach Group (RG) proposal comes in.
MobOpts RG is discussing ways to standardize the needed link-specific customization – see IRTF draft Unified L2 Abstractions for L3-Driven Fast Handover. In effect they propose standardizing the layers violation. If adopted by radio link equipment vendors, this would modularized the value chain without waiting for extra technology to show up!
Of course this is a proposal, not an RFC much less a standard. So any implementation is at least a few years off. That's consistent with my view, expressed in my August 31st post, that widespread mobile VoIP will lag fixed line VoIP by at least five years, but it's coming!