| reply to zaldy
Re: [Skype] Skype Network Usage said by zaldy:so what happen if more and more users set their Skype so it will not go on supernodes? Will Skype call quality suffers? Supernodes have three purposes within the Skype network:
1) They cache the database of all users to off-load sign-in authentication from the central Skype user database. The first time a Skype client signs on to the network, it contacts one of several predefined central servers operated by Skype. From then on, it will contact a list of locally cached supernodes obtained from the central server, instead. This is what allows Skype to work from many countries like the UAE, which block Skype's central servers, so long as a Skype client has previously signed on to the network from elsewhere and been able to build its own local cache of available supernodes. It's easy to block a limited set of known servers, but an entirely different thing to try to keep track of a dynamically changing set of supernodes to try to block. Each supernode only caches a very small portion of the database.
2) They maintain the distributed database of all users currently signed in to the network, so that other users can locate them. This is akin to SIP's registration. Each supernode only maintains a very small portion of the distributed database. It is sort of like a node in a binary tree.
3) They provide audio proxying for calls that cannot be connected directly P2P. Skype can make direct P2P connections in the overwhelming majority of cases, so proxying is only done in a very small percentage of cases--when BOTH parties are behind restrictive firewalls (symmetric NAT routers and proxied corporate firewalls that do not offer NAT). If either party is behind a full-cone or any type of restricted-cone NAT router, the call will be connected directly and NOT be proxied. Supernodes are NEVER involved in proxying audio for Skype-in/out calls.
Only computers directly connected to the Internet or behind full-cone NAT routers (typically gaming routers or other routers set to gaming mode) can become supernodes. Clients behind any other types of NAT routers CANNOT and DO NOT become supernodes. It is unclear, however, whether non-supernode clients do participate as nodes in the distributed user location database (purpose item 2 above). If they do, they have to be contacted by other database querying clients indirectly via supernodes, which may explain the somewhat large number of connections (to various supernodes) that many users observe.
When more and more users disable the ability to become supernodes, it puts a larger proportional load on those that are supernodes. The effect of this is to increase the time it takes to sign-on to the Skype network, and to make calls (or search for other users). In the extreme case where there were no supernodes, it would become impossible to sign-on to the network and make any calls. It also affects the quality of calls for those whose audio is proxied, if the increased load on the proxying supernode leads to its available bandwidth or computing capacity being saturated. It DOES NOT in any way, shape or form, affect the audio quality of calls that are not proxied by supernodes. The overwhelming majority of Skype calls (and all Skype-in/out calls) are not proxied, and thus are unaffected. |
