SkypeOut and SkypeIn Gateways, Part 2
Aswath provides an alternative conjecture on how Skype clients signal to Skype's carrier partners' media gateways. The two main differences between our theories (if I'm interpreting him correctly) are (1) he thinks that Skype is running dedicated servers as supernodes for SkypeIn and SkypeOut calls, where my theory is that they're using "any old supernode"; (2) he thinks the clients are talking the internal Skype protocol to supernodes, which translate to SIP, where my theory is that the clients are talking SIP with a supernode acting as a SIP proxy.
Given the dearth of actual data this is all built upon, it's hard to argue either conjecture. But there are some differing implications depending on which way it may work.
If Skype is in fact running dedicated servers as supernodes for SkypeIn and SkypeOut, growth in these services will require investment on Skype's part to meet the capacity demand. Given that Skype is collecting revenue for these services - and the revenue is prepaid - that's not a killer; however, it makes the business model less compelling. If they're using "any old supernode", growth is cheaper since they're making use of arbitrary users' computing resources.
Aswath's point about dedicated servers providing a few well-known interconnection points is a good one, though.
The other distinction, whether Skype clients are running "native SIP" with a supernode SIP proxy server, or whether a supernode translates for "Skype-ese" to SIP, I think is more of academic interest.