Peer-to-Peer Computing

P2P Applications 15

Skyp e is robust not only in the aspect of its ability to route traffic around

NATs or firewalls, but also in its lean requirements on bandwidths. Specifi-

cally, for voice traffic flows, typically the total uplink a nd downlink bandwidth

required is only around 40 kbps.

One key aspect about the protocol a nd architecture of Skype is that users

cannot possibly (as of this w riting) refuse to be a super-node. Indeed, when the

Skyp e client program discovers that the client’s machine is p owerful enough

in terms of machine architecture, bandwidth available, whether it is behind a

firewall or NAT, etc., the client machine could be “promoted” to be a supe r-

node. This enforce ment of super-node role could be a potential problem for

the robustness ...