Skype is a software application that lets you make free phone calls to more than 75 million people worldwide, and calls to virtually anywhere incredibly cheap on earth! As a result, Skype has become the fastest growing service in Internet history. Recently, the company was acquired by eBay, another step forward to achieve the ultimate goal of making Skype the world's largest communications company.
Skype is easy to install and use. It allows its users to make crystal clear calls, regardless of their location, send instant messages, switch seamlessly between text and voice communication, make video calls, conference calls, transfer files, call landlines and mobile cell for a fraction of the cost of a traditional call. Skype is truly making a revolution in the way we communicate.
But how does it actually work? This article focuses on describing the Skype network and the technology behind it.
Skype is a type of Voice-Over-IP peer-to-peer client, based on the file sharing program Kazaa. The developers of Skype claim that it provides better voice quality than similar applications like MSN and Yahoo Messenger. Encrypt also end-to-end call.
There are two types of machines in the Skype network - ordinary host (Skype Client) and Super Node (SN). An ordinary host is a normal computer user that installed the application and connects to the network to communicate with other users. The Super Nodes are the end point of ordinary hosts on the network. In other words, ordinary hosts connect to the Super Nodes. Any computer with a public IP and proper hardware configuration can be a SN. An ordinary host must connect to a super node and must register with the Skype login server for a successful login. The Skype login server is the only center of all the network drives. Stores the user names and passwords of all Skype users. Nslookups have shown that this server is located in Denmark. All Super Nodes connect to the login server in attempt to verify the password of the client user name. Stores the Skype name, your e-mail address, and an encrypted representation of the password.
If you are a regular Skype user, then your computer is considered a 'regular visitor' that connects to a Super Node. The Super Nodes are servers, located in different parts of the world. But your Skype client, must know to which SN has to connect. Therefore, every Skype client (SC) maintains a local table that contains the IP addresses and corresponding ports of Super Nodes. This is called a host cache and stored in the Windows Registry data SC. So basically, every time you load up Skype, it reads the date from the host cache, takes the first IP and port from there and tries to connect to this SN. If the connection fails for some reason (the SN is online, but is no longer part of the network, etc.) then you read the next line from the table. In case you can not connect to any of the IP addresses listed, the Skype returns a login error upon start-up. Hence, the host cache must contain at least one valid entry for the application to connect to the network and functioning properly. voice means a number of valid IP address and port of an online Super Node. The path to the table in the Windows registry HKEY_CURRENT_USER / Software / SKYPE / PHONE / lib / CONNECTION / HOSTCACHE. You can verify that your computer by opening the Start menu, then Run and type 'regedit', without the dashes. Of course, the exact path could be different in the next versions of the application.
As a concept, Super Nodes were introduced in the third generation P2P. They allow improved search performance, reduced latency file transfer, network scalability, and the ability to resume interrupted downloads and simultaneously download segments of one file from multiple peers. Basically, they help ordinary hosts connect to each other and to effectively guide the encrypted network traffic.
The Super nodes are also responsible for the 'Global Indexing'. This technology allows you to search for other network users. The company guarantees that you will find a user if he has registered and has logged in during the last 72 hours.
A very interesting moment about the Skype network is that 'self-modifiable'. If you have installed the application, your computer may turn into a Super Node, without even knowing it, because these skills do not have a significant impact on the performance of a computer. SN basically store the addresses of up to several hundred Skype users, without in any given voice, text or file-transfer. In this way, more Skype users are online, the more supernodes become available to expand the network capacity.
Skype routes the traffic intelligently by choosing the optimal data transfer path. Since it uses TCP or UDP, it breaks the flow of data around in separate packages, which may take different paths to the final destination. The final provision is made at the receiving end.
With regard to the security and privacy are concerned, Skype uses Advanced Encryption Standard, known as Rijndel, also used by the US Government organizations to protect sensitive data. Skype uses 256-bit encryption.
The developers of Skype have implemented wideband codecs, allowing you to maintain good sound quality at a bandwidth of 32kb / s and allow frequencies between 5-8,000Hz to go through.
Your list of contacts, the application stores in the Windows registry. This is called the friends list and once again, is encoded digitally. Thus, the list is local for each machine, or in other words, is not downloaded from the central server.
we try to briefly describe the tasks of the Skype client. Before you connect to the network. He then listens on particular ports for incoming calls, refreshes the host cache table, uses wideband codecs, maintains contact list, encrypts messages and determines if a firewall is present or not.
The login process:
The login process is the most important and consists of several stages. As mentioned, SC must connect to a valid SN in order to authenticate the user name and password to the central server.
Skype gets the fist IP from the host cache, sends a UDP packet and waits for the answer. If there is no response after five seconds, it sends a TCP packet to the same IP. It tries to establish a TCP connection to the HC IP address and port 80 (HTTP port). If still unsuccessful, he tried to connect to the IP address and port 443 (HTTPS port). If this does not work, it reads the next address in the HC. If Skype is able to connect to a SN, it will report an access error.
The application comes with several build-in different nodes, called bootstrap super nodes addresses.
If the connection attempt is successful, the client must authenticate the user name and password with the Skype login server, which holds all the user names and passwords and makes sure they are unique in the entire network. When the application connects to an SN, it receives an updated list of other active SN, so it has the latest information.
The average transfer process:
The video / voice communication through Skype is established through UDP. The trick is that very often, one of the users is behind a firewall or a router, and therefore does not have a real IP address. But if both Skype clients are on real IPs, then the media traffic flows directly between them over UDP. The size of the voice packet is 67 bytes, which is actually the size of UDP payload. A second of the conversation results in approximately 140 voice packets to be exchanged in both directions, or 3-16 kilobytes / s.
If one of the called party or both do not have a public IP, then send voice traffic to another online Skype node over UDP or TCP. The developers of Skype have preferred to use UDP for voice transmission as much as possible.
An interesting fact is that even if both parties do not speak, voice packets will still be flowing between them. The aim of these so-called 'silent packages' is to keep the connection alive.
Conclusion:
There are several factors responsible for the success of Skype. First of all, the voice quality is better than other applications. it works without problems on computers with firewall. it is very easy to install and use. Skype's security is also a big plus. All that is transferred over the network is encrypted to ensure privacy. as a result Thus, even if hackers intercept the data being transferred, they will not be able to decode it.
the Skype application does not include any adware or spyware. But, there are cases in which third parties have been able to add these features (not only for Skype), so it is very important that you download from the right place. therefore, do one from the official site, or from respected sites color: as Http://www.freesecuredownloads.com/skype/index .html .
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