Skype and ENUM

Richard Stastny proposes extending ENUM to support Skype. He suggests a NAPTR of the following form:

IN NAPTR 100 100 “u” “E2U+x-skype:callto” “!^.*$!callto://detlev!” .

This solution would at least allow all ENUM clients running on the end-users device to use this feature.

Well, I’m sure Richard knows this, but it’s not clear to the average reader that the “end-user device” noted above must in this case be something running Skype’s software, and in particular, I believe for the moment it means a Windows PC running Skype (not sure if the callto hack works from a Mac). This is because Skype is a closed protocol and only the actual Skype software can make Skype calls. So your average brand-X VoIP phone cannot make use of the proposed skype callto address.

I’ve got nothing against the proposed ENUM hack, but it’s important to understand that it is not a cure for seamless Skype and SIP interoperability and integration, in contrast to the views of a few posts I’ve seen floating around referencing Richard’s post.

One particular question I have on this idea is that if I have to be running Skype on Windows to make use of the ENUM data in the first place, why wouldn’t I just call them directly via Skype? What’s the value of ENUM in this case? I guess the theory is that I’m more likely to know their phone number, or prefer to use their phone number, rather than their skype handle.

3 comments for “Skype and ENUM

  1. Hi David,
    1. it works on the Mac too ;-)
    2.It is true that your average brand VOIP phone cannot use it, but these also cannot use ENUM either (beside the SNOM or the IX66). These VoIP phones require the ENUM query to be done by the SIP server and here a SIP-Skype gateway is needed, not out of imagination ;-)
    3. This is not really a "hack", it is experimental and according to RFC 3761 ;-)
    4. Why not call directly on skype? Why not use the SIP URI for calling a SIP user? Same reason. In addition, if you enter a phone number and the called party is also on Skype, you get a short-cut ;-) We will see how bellheadish Niklas will be on this by-pass to Skype-Out ;-)
    5. One additional idea is of course to HAVE SIP-Skype gateways, especially for the PSTN-SIP-ENUM gateways.

  2. Hi Richard,

    Yep. I agree.

    My understanding is that (so far) Skype has taken the position that interop, and specifically SIP gateways, offer no value to Skype. Unless there are a lot of users on SIP, that are also using ENUM and have pure IP interop, Skype will see no pressure to interop with SIP. And their closed system makes deployment of a gateway by third parties challenging. So it doesn’t look like we’ll see SIP to Skype or Skype to SIP gateways any tme soon, if ever.

    SIP is reminding me of UNIX in the early days, where vendors all did things their own ways and there was very little network effect. SIP is happenign the same way. Very few services offer direct IP-based interconnect, especially at the phone number level, dialing ordinary numbers (who wants to hit a "*xxx select code" for every call). In fact, is there *any* ENUM-based phone number SIP IP peering between providers today?

  3. There’s a skype api, so i suspect niklas is cool with variations on callto:. btw, callto preceded skype; it was used by other systems first.

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