SkypeOut and SkypeIn Gateways, Yet Again
I think I can milk this topic for one more post.
Looking again at James Enck's item on the Skype architecture, I realize I inferred "media gateways" where I read "gateways". That's not necessarily the correct interpretation. "Gateways" could mean IP-IP gateways, performing a Session Border Controller-type role. This would be the point at which the internal Skype protocol, whatever it is, is decrypted and translated to the version of SIP required by the particular carrier partner, and the media stream is decrypted (as well as little details like counting minutes are taken care of).
This makes more sense to me than Skype converting IP to TDM to handoff to their carrier partners. Still not as disruptive as simply building these capabilities into the client software and letting it run on an arbitrary supernode, but I guess sometimes architectural purity can take a backseat to pragmatism.