Cordless Telephones

Skype is a software program that lets you make free calls to over 75 million people around the world, and amazingly cheap calls to almost anywhere on earth! For this reason, Skype has become the fastest growing service in the history of the Internet. Recently the company was acquired by eBay, take a step forward towards achieving the ultimate goal of making Skype the world's largest communications company.

Skype is easy to install and use. Makescrystal-users to make calls, regardless of their location, send messages, switch easily between text and voice communication, make video calls, conference calls, files, call landlines and mobile phones at a fraction of cost of a nice tradition. Skype is truly making a revolution in the way we communicate.

But how does this work? This article focuses on the description of the Skype network and the technology behind it.

Skype is a form of peer-to-peer –Voice over IP client, based on the Kazaa file-sharing program. The developers of Skype claim that this is a better sound quality of similar programs, like MSN and Yahoo Messenger. It 'also encrypts calls end-to-end.

There are two types of machines in the Skype network – ordinary host (client Skype) and Super Node (SN). An ordinary host is the computer is a normal user does not have the program installed and connected to the network to communicate with other users. SuperNodes are the point of arrival in regularly hosts on the network. In other words, ordinary hosts connected to the Super Node. Any computer with a public IP and the proper hardware configuration can be an SN. An ordinary host must connect to a super node and must register with the Skype login server for access to success. Skype login server is the only central unit in the entire network. Memorize the names of their respective username and password for all Skype users. Nslookup showed that this server isLocated in Denmark. All Super Nodes connect to login server in an attempt to verify the user name, password from the client. You save your Skype name, your e-mail, and a representation of the encrypted password.

If you are a regular Skype user, then the computer will be considered as a host "normal", connected to a Super Node. Super server nodes are in different parts of the world. But your clients should know that SN Skype to connect. Therefore, every SkypeClient (SC) maintains a local table that IP and corresponding ports of Super Nodes contain. This is called a closet full, and is stored in the Windows registry for the given SC. So basically, every time you load Skype, it reads the date of the host cache, takes the first IP and port from there and try to connect to this SN. If the connection is not any reason (the SN is signed, is no longer a part of the network, etc.) so that it reads the next row of the table. If notcommit to any of the IP addresses in the list, Skype returns a login failure to start-up. Therefore, the cache host at least one valid entry for the program includes a network connection and working properly. Valid, an IP address and port number for an online Super Node. The path to the table in the registry of Windows is HKEY_CURRENT_USER / SOFTWARE / Skype / Phone / lib / Associate / HOST CACHE. You can verify that the computer, open the Start menu and then click Run, andEnter "regedit" without hyphens. Of course, the exact path may be different in the following versions of the program.

As a concept, is introduced Super Node in the third generation of P2P networks. Can improve the search, the reduced latency of file transfer, network scalability and the ability to continue interrupted downloads, and simultaneously retrieve parts of a file from multiple peers. Basically, they help ordinary hosts connect to each other and guide efficientlynetwork traffic encrypted.

Super nodes are also responsible for the "Global Index". This technology allows you to search for other network users. The company guarantees that they will find when a user is registered and recorded in the last 72 hours.

A very interesting time on the Skype network is that it is "self-availability". If you installed the program, you can turn your PC into a Super Node, without even knowing it, becauseability not to have a substantial impact on the performance of a computer. SNS Fundamental save the addresses of some hundreds of Skype users without a voice, text, or the transfer of data files. In this way, the greatest number of Skype users online, more super nodes are available to expand the network capacity.

Skype routes the traffic intelligently by choosing the optimal route of transmission. Because it uses both TCP and UDP, as all data streamsseparate packages, which may take different paths to their final destination. The final agreement was made at the end of reception.

Regarding the security and privacy, Skype uses Advanced Encryption Standard, known as Rijndel, also used by U.S. government organizations to protect confidential information. Skype uses 256-bit encryption.

The developers of Skype have implemented wide-band codec, which maintain a good quality sound at a bandwidth of 32KB / s frequencybetween 5-8,000 Hz to pass through.

The list of contacts, the application stores the registry in Windows. This is known as the Buddy List and again, is digitally encoded. Yes, the list is local to each machine, or in other words, it is downloaded from the central server.

Let us see briefly the functions of the Skype client to describe. First, it connects to the network. Then listens on particular ports for incoming calls, working for the host cache table, the use of broadband codecKeep your contact list, encrypts messages and determines if a firewall or not.

The notification process:

The login process is the key, and consists of several stages. As mentioned, SC must connect with a valid SN for a user name and password for the central server for authentication.

Skype will be fist IP from the cache host sends a UDP packet and waits for response. If no response after 5 seconds, it sends a TCP packet to the same IP. Ittrying to create a TCP connection to HK IP address and port 80 (HTTP port). If still unsuccessful, attempts to connect the IP address and port 443 (HTTPS port). If it works or not, read the address in Hong Kong. If Skype is unable to access a SN will report an access error.

The application is built with different addresses in different nodes, called bootstrap super nodes.

If the connection attempt fails, the client must authenticate the username and password with the Skype login server that contains the usernames and passwords, and make sure that they are unique throughout the network. When the program connects to an SN, you will get an up-to-date list of other SNS active, so this is the most current information.

Process Media Transfer:

Video / voice communication through Skype was founded by UDP. The trick is that it is often one of the users are behind a firewall or a router, and is therefore not areal IP address. But if the two Skype clients are on a real IP address, so that the traffic of means of direct communication with each other over UDP. The size of voice packet is 67 bytes, which is actually the size of UDP payload. A second call will result in approximately 140 voice packets are exchanged in both directions, or 3-16 kilobytes / s.

As one of you called or both have a public IP, then they should send voice traffic to another online Skype node over UDP or TCP. The developers of Skype have preferredUses UDP for voice transmission, as possible.

An interesting fact is that, although both sides do not talk, voice packets still flow between them. The purpose of this so-called "packets of silence" is on the connection.

Conclusion

There are several factors responsible for the success of Skype. First, that the sound quality is better than other programs. It works without problems on computers with a firewall. It 'very easy to installand use. The security of Skype is also a great advantage. Everything transferred over the network is encrypted to ensure privacy. As a consequence of the fact that even if hackers intercept your data is transferred, will not be able to decode.

Skype does not contain adware or spyware does not. But there are cases in which third parties have succeeded in these functions (not only for Skype), so it's really important that you download from the right place.Just do it or the official site, or from reputable sites like http://www.freesecuredownloads.com/skype/index.html.

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