Features
The basic computer-to-computer service allows users to speak, to send instant messages or to send files to one another from their computers via the Internet at no cost. Conferences of up to five users are supported.
SkypeOut is a paid feature of the Skype internet telephony service, which allows Skype users to call virtually any non-computer-based landline or mobile phone in the world.
Unlike international long-distance calls made from conventional phones, which are rated according to the relative distance between countries, SkypeOut bills all calls according to the relative prosperity of the country, the volume of calls made from and to a given country, access charges such as those to mobile (cell) phones. This rating method is used due to the fact that calls are rated the same regardless of place of origin.
This way, a SkypeOut user will be billed the same for a call placed to a phone number in London, whether the user is calling from his/her computer in London itself, from an internet cafe in Sydney, or from Honduras. The Global Rate which is the one used for many countries, and all First World countries, is currently 1.7 Euro Cents per minute. Credit, which is necessary to use SkypeOut, is usually purchased via credit card or online services such as PayPal or Moneybookers. The current deposit is either 10 or 25 Euros but if the service is not used for 180 days this expires automatically. In europe there is a 15% VAT charge which makes SkypeOut rates seem artificially cheap. Actual prices are closer to 2 cents per minute.
SkypeIn allows Skype users to receive calls on their computers dialed by regular phone subscribers to regular phone numbers. Beta released on March 10, 2005, SkypeIn permits users to subscribe to numbers in UK, USA, France, Hong Kong, Denmark, Finland, Norway and Sweden. Cost is €30 for a 12-month subscription, or €10 for a three-month subscription.
Voicemail was also released on March 10, 2005. This service allows callers to leave voice-mail messages for Skype users who are not online, on another call or otherwise indisposed. This can be purchased separately and is automatically bundled in with SkypeIn.
Skype Version 1.2 for Windows was released in March 23, 2005. Its most significant new feature is the provision of centrally-stored contact lists so that a user's contact information is available from any computer that is connected to Skype (in other previous versions, contact information was stored on the local computer).
Versions now exist for Microsoft Windows (Windows 2000, Windows XP and Windows CE (Pocket PC)), Mac OS X and GNU/Linux.
Technology
Each Skype user must have the Skype software running on his/her computer. This software is available for free and can be downloaded from the company website.
The main difference between Skype and other VoIP clients is that it operates on a peer-to-peer model rather than the more traditional server-client model. The Skype user directory is entirely decentralised and distributed among the nodes in the network, which means the network can scale very easily to large sizes (currently just over forty million users) without a complex and costly centralised infrastructure.
Skype also routes calls through other peers on the network, which allows it to traverse Symmetric NATs and firewalls, unlike most other VoIP programs (The two most common protocols, SIP and H323 are usually UDP and point-to-point, making NAT traversal problematic - see article). This, however, puts extra burden on those who connect to the Internet without NAT, as their computers and network bandwidth may be used to route the calls of other users. The selection of intermediary computers is fully automatic, with individual users having no option to disable such use of their resources. This fact is not clearly communicated, however, and seems to contradict the license agreement which would limit Skype's utilisation of the user's “processor and bandwidth [to the] purpose of facilitating the communication between [the user] and other Skype Software users” (section 4.1).
The Skype code is closed and the protocol is proprietary. However the Skype client's application programming interface (API) exposes the network to software developers. The Skype API allows other programs to use the Skype network to get "white pages" information and manage calls.
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(go to external website) - Skype is a free and easy way to make phone calls to any other PC user in the world, and now there's a way to make cheap calls to technophobe friends, too. |