A few days ago I wrote about the observations, by Christensen et al., on vertical integration – when it's valuable and when it becomes a disadvantage. Their point: when your task presses the limits of the available technology, optimization is essential and vertical integration is best, as the parts that must work together, i.e. be jointly optimized, are better controlled under the same roof.
As technology improves, you can afford the overhead and obtain the benefits of modularity. People working on separate modules don't need to coordinate details within their modules, separate companies can specialize, and really big systems (like the Internet) can emerge.
VoIP, i.e. telephony which is separate from the underlying transport, emerged once there was excess capacity in the underlying transport. VoIP's first major success was in international wholesale (iBasis and ITXC – later bought by Teleglobe) where the VoIP carriers connected directly to the Internet backbone thus getting adequate capacity. The second major success was IP-PBXs, running on enterprise networks that were over-provisioned and/or had simple QoS (typically 2 levels; gold bits & brown bits). The most recent success is the emerging consumer VoIP – Vonage, AT&T CallVantage and the like, and Skype! These services had to wait for deployment of residential broadband.
Compare this with mobile phone services, mobile Internet and other forms of wireless Internet. How close are we? Unfortunately we have a way to go.
Yes, I've used Skype over wireless and, yes, the much hyped IP Multimedia Subsystem (IMS) is based on IP and SIP. But it's not so simple.
WiFi networks have plenty of capacity if you are sitting in one place with only a few others sharing the same access point. The moment you roam to another access point you face a gap in connectivity of perhaps several seconds, at least if it's a layer 3 handoff (to an access point with a different SSID) requiring a DHCP request (for a new IP address). High traffic can cause even stationary web surfing to suffer. Henning Schulzrinne recently presented work done with Andrea Forte and Sangho Shin at the 65th IETF meeting in March. They measured hundreds of clients connecting with multiple 802.11 access points. Among other things, as congestion went up the rate of handoffs soared – less than one minute between handoffs for 22.8% of the clients and between 1 & 5 minutes for another 34%. The clients are continuously seeking stronger signals and end up thrashing between access points or even disconnecting and then reconnecting to the same access point. The good news is that most of the problems they found can be fixed with better algorithms using existing 802.11 protocols and some clients, e.g. Apple's, already perform quite well. But still it will take years to see new algorithms that are also widely deployed, i.e. a new generation of equipment.
With 3G mobile networks, we have different issues. Yes, IMS is "VoIP", but it's highly optimized and tightly controlled (by the mobile operator). Thus, neither Skype nor Vonage will use IMS without first partnering (i.e. paying) the mobile operator.
What about straight Internet access? The good news is 3G networks have been designed to support Internet access, at least asymmetric access for web surfing, and have been optimized for handoff of active IP sessions. Implementing handoffs has required protocol optimizations (network engineers call these layer violations) and throughput has been optimized via centralized management of client power and uplink scheduling (violating the end-to-end principal?). Luckily, these optimizations happen below layer 3 – there really is a modular boundary at the IP layer.
The immediate problems are too little capacity on the uplink, at least during busy periods, long latencies and walled garden policies (whether implemented with IMS or otherwise). With first generation W-CDMA equipment, users share 384 kbps (peak) on the uplink. That's fine at 2am, but less so when there are others on the air. Ubiquitous deployment of HSUPA will improve latency and provide adequate uplink capacity, e.g. enough headroom so explicit QoS is no longer an issue for 3rd party VoIP. I'm guessing HSUPA hype in 2007, urban deployments in 2008 and widespread availability in 2010 and beyond.
Walled gardens are a big issue today, but one that will fall to competition. Once there is widespread, broadband wireless Internet connectivity from competing mobile operators, WiFi hotspots, WiMAX and other approaches, it will be impossible to sustain a walled garden. Fixed-line Internet connectivity gives people access to myriad niche services that can't be offered under the walled garden business model.
Widespread use on 3rd-party VoIP on the mobile Internet may lag it's use on the fixed Internet by 5-10 years, but it's coming – IMS or not.