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Skype Technology



The only pre-requisite for using Skype is that the user must have Skype software running on the computer. This software can be downloaded for free and easily installed.

Skype scores over other VoIP clients as it operates on a P2P model, not the traditional client-server model. These decentralized P2P networksscale indefinitely without increasing the search time and without the need for costly centralized resources. And since the processing and networking power of the end users is utilized, each new node added to the network adds to the potential processing power and bandwidth of the network.

Another point on which Skype scores over other protocols like SIP and H.323 is its ability to permit calls to traverse symmetric NATs and firewalls . SIP and H.323 fail here because they employ User Datagram Protocol (UDP) and point-to-point networking making NAT traversal problematic.

Skype takes care of privacy matters as it automatically encrypts everything before sending it through the Internet. Since all calls are routed through public Internet, encryption is a real necessity. Then on arrival, the message is decrypted on the spot and turned back into high quality voice, plain text or regular file.

In spite of all these features, Skype does face criticism because it has a closed code and the protocol is proprietary. SIP and H.323 are open standard. The use of propreitary protocol makes it difficult for other providers to interact with Skype network.

What's similar and what's not between SIP and Skype:

SIP

Skype

SIP operates on a traditional server-client model

Skype operates on peer-to-peer model

SIP has costly centralized infrastructure

The user directory of Skype is decentralised and distributed among the network

NAT and firewall traversal is problematic

Skype allows calls to traverse NAT and firewall

"There are 3 million SIP phones." [www.sipphone.com]

Skype has millions of download but it is not necessary they translate into actual usage. Disclosure of actual calls made per day will be the actual indication of its usage

The open standards of SIP permit different vendors to build different pieces that will interoperate with others. There is a wide range of hardware like business or consumer phone, adapters, routers and they can be directly plugged to Internet

Skype has a proprietary protocol. It doesn't have enough hardware to brag about. It must build each piece or commercially motivate a company to do so

All companies can use SIP enabled system to avoid phone bills!

All private users can use Skype to avoid phone bills!