Skype

Skype is a P2P Voice over IP service that can be used to make calls from computer to computer or computer to telephone. In addition to the common functions of instant messaging (IM) software such as text-based chat, file transfer, chat history etc, Skype mainly offers voice talk/telephone calling, and Skype's cheap price and easy manipulation has gained it popularity among a large number of people. As of 2007, Skype had over 50 million users and was valued at $2.6 billion.

Design

The Skype protocol is proprietary (closed) protocol, with encrypted content and control messages. However, through reverse engineering studies, many design features are known:

• Skype has a flat, unstructured network between index servers
• Skype has a two tier hierarchy, Super Nodes and Ordinary Nodes
  • Super Nodes connect to one another, building a flat, unstructured overlay
  • Ordinary Nodes connect to Super Nodes, that act as a directory server (similar to Napster)
• The Skype login server, where accounts are handled, is the only centralized component. It stores usernames, passwords, and buddy lists

Pros and Cons

• Pros:
  • free to other people on Skype and cheap to landliness and cell phones around the world.
  • Imports contacts from email-based applications which have been installed on the computer.
  • Finds people on MySpace using MySpaceIM with Skype.
  • Uses the Business Control Panel to manage multiple Skype Credit expenditure.
  • Sends faxes, implements conference call, connects to Official website to browse news, do shopping, listen to music etc.
  • Sets up a phone number in another country, which will rings on the computer.

• Cons:
  • Cannot replace the ordinary telephone for emergency calling.
  • Synchronization of sound largely depends on the speed of internet connection.
  • Doesn't use standard signalling protocols and is incompatible with other software.
  • Cannot guarantee end-to-end service quality, especially when the service crosses continents.