Skype and NAT tunnelling
_A discussion of Voice-over-IP and a good explanation of why folks needs something that penetrates firewalls_
Skype Firewall and NAT (Network Address Translation) traversal:
Non-firewalled clients and clients on publicly routable IP addresses are able to help NAT’ed nodes to communicate by routing calls. This allows two clients who otherwise would not be able to communicate to speak with each other. Because the calls are encrypted end-to-end, proxies present no security or privacy risk.
Likewise, only proxies with available spare resources are chosen so that the performance for these users is not affected.
Several new techniques were also developed in order to avoid end-user configuration of gateways and firewalls, whose non-intuitive configuration settings typically prohibit the majority of users from communicating successfully. In short, Skype works behind the majority of firewalls and gateways with no special configuration.
Global decentralized user directory:
Most instant message or communication software requires some form of centralized directory for the purposes of establishing a connection between end users in order to associate a static username and identity with an IP number that is likely to change. This change can occur when a user relocates or reconnects to a network with a dynamic IP address. Most Internet-based communication tools track users with a central directory which logs each username and IP number and keeps track of whether users are online or not. Central directories%