Try not to think in terms of server and client being separate machines. Or thinking that a server needs to be complex or able to handle an unlimited number of

Try not to think in terms of server and client being separate machines. Or thinking that a server needs to be complex or able to handle an unlimited number of nodes. It's possible to be both a client and a server. And that is in fact what Skype was doing. Some clients were also functioning as supernodes.