Doesn't this therefore suggest we'll continue to see competing fully integrated yet isloated communications systems, with limited interoperability -- rather than an open, seamless one with no owner? There will thus not be a voice equivalent of the Web within the forseeable future.

Maybe using the PSTN for interop isn't such a bad idea after all. At least it works. Shame that there's no presence and availabilty features.

Hi Aswath,

There is a conference -- used to be called the Feature Interaction Workshop, and now it's called something else. The last one was in 2005, so they're about due for another.

Regarding the situation I described, why is that not a feature interaction? There are two features I see -- the simulring, and the call forward busy feature.

I think the POV I have on feature interactions is that most are easily solved. It is the esoteric cases that are frequently cited that are hard to solve, but perhaps not common problems. For instance, what would the world look like if my telephone was programmed to phone yours at exactly the instant it detected you were present, and your phone was programmed to do the same... we'd have a collision. Both would go to voice mail. Is this likely to happen? I think the timing alone is unlikely.

A

Martin:

Precisely. But the industry is promising independent feature development braking the mold of the “intelligent network”. But I am not sure why this implies we need to use PSTN for interop. We could just as easily use IP connectivity for media transport and a very basic subset of SIP in place of SS7. This way we do not have to lose presence and availability features. I think the problem is not technical, but business - the VoIP service providers are artificially creating a barrier.

Alec:

I had not realized from your description that you are including CFB. I said it is not a feature interaction because that problem is there even with out CFB.

It is true that feature interactions are solved. If nothing else, they are solved by definition. But it is a tedious work. When a new feature is proposed, one has to enumerate interaction with every other existing feature and develop resolution rules. If two features are being developed in isolation, the potential interaction will be discovered only after deployment. These two points suggest that even in IP domain, introducing new features is just as cumbersome as in PSTN. That was the point Carl and I had talked.

I don’t think I will call the call collision scenario to be an instance of feature interaction. But that is just me. In any event, this will not happen in VoIP :-) . After all both the end points are intelligent. They will recognize that they are talking to each other; they will do “enie meanie minie mo” and one session will survive. Sorry, I forgot. VoIP terminals haven’t become intelligent yet.

A lot of very bright people have worked on formal methods for the verification of services in the Intelligent Network, with little to show for it. The problem is fundamental to the services themselves, not with whether the INAP or SIP transport protocol is used to carry signalling.