Exactly how Skype Works

Skype ip telefoni is a software application that allows you to create free phone calls to more than 75 million people worldwide, and shockingly cheap calls to practically all over the place else on Earth! As a result of that, Skype ip telefoni has become the fastest growing service in the history of the Internet. Recently, the company has been acquired by eBay, another step forward towards achieving the final goal of making Skype the world’s largest communication company.

Skype is easy to install and use. It allows its users to make crystal clear calls, regardless of their place, send instant messages, switch easily between text and voice communication, make video calls, conference calls, transfer files, call landlines plus cell phones for a fraction of the cost of a traditional call. Skype is truly making a revolution in the way we communicate.

But so how exactly does it actually work? This article targets describing the Skype network as well as the technology behind it.

Skype is a type of peer-to-peer Voice-Over-IP client, based on the Kazaa file sharing program. The designers of Skype claim that it provides better voice quality than similar applications like MSN and Yahoo Messenger. It also encrypts calls end-to-end.

You can find two types of machines in the Skype ip telefoni network – ordinary host (Skype Client) and Super Node (SN). An ordinary host is the computer of a regular user who has the application set up and connects to the network in order to communicate with other users. The Super Nodes are the end-point of ordinary offers in the network. In other words, ordinary website 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 an excellent node and must register itself with the Skype login server for any successful login. The Skype sign in server is the only central device in the whole network. For more information on psycholog online depresja take a look at the internet site.
It stores the usernames and respective security passwords of all Skype users. Nslookups have shown that this server is located in Denmark. All of Super Nodes connect to the sign in server in attempt to verify the username password of the client. It stores your Skype Name, your own e-mail address, and an encrypted representation of your password.

If you are a normal Skype user, then your computer is considered an ‘ordinary host’ that links to a Super Node. The Top Nodes are servers, located in different parts of the world. But your Skype client, must know to which SN it has to connect. Therefore , every Skype client (SC) keeps a local table that contains the IPs and corresponding ports of Super Nodes. This is called a host cache and it stored in the Windows Registry of the given SC. So essentially, every time you load up Skype, it reads the date from the web host cache, takes the first IP and port from there and tries to connect to this SN. If the connection neglects for some reason (the SN is off-line; it is no longer part of the network, etc) then it reads the next line in the table. In case it fails to connect to any of the IPs listed, the Skype ip telefoni returns a login error on start-up. Hence, the host cache must contain at least one valid entry in order for the application to connect to the system and work properly. Valid entrance means an IP address plus port number of an online Super Client. The path to the table in the Windows Registry is HKEY_CURRENT_USER / SOFTWARE / SKYPE / PHONE / LIB / CONNECTION / HOSTCACHE. You can verify that on your computer simply by opening the Start menu, then click Run and enter ‘regedit’, without the dashes. Of course , the exact path could be different in the next versions of the program.

As a concept, Super Nodes were introduced in the third-generation P2P systems. They allow improved search functionality, reduced file-transfer latency, network scalability, and the ability to resume interrupted downloading and simultaneously download segments of one file from multiple peers. Generally, they help ordinary hosts connect with each other and guide efficiently the particular encrypted network traffic.

Super Nodes are also responsible for the ‘Global Indexing’. This technology enables you to search for other users in the network. The company guarantees it will find an user if he has authorized and has logged in during the last seventy two hours.

A very interesting moment regarding the Skype network is that it ‘self-modifiable’. If you have the application installed, your computer may turn into a Super Node, without you even knowing it, because those abilities don’t have a noticeable impact on a computer’s performance. SNs basically keep addresses of up to several hundred Skype ip telefoni users, without carrying any voice, text or file-transfer data. Because manner, the more Skype users come online, the more supernodes become available to expand the capacity of the network.

Skype routes the traffic intelligently simply by choosing the optimum data transfer path. Since it uses either TCP or UDP protocol, it breaks the whole data stream into separate packets, which can take different paths towards the end destination. The final arrangement is performed at the receiving end.

As far as security and privacy are concerned, Skype utilizes Advanced Encryption Standard, known as Rijndel, used also by the U. S. Government organizations to protect sensitive information. Skype uses 256-bit encryption.

The particular programmers of Skype have implemented wideband codecs which allows it to maintain a good sound quality at a bandwidth of 32kb/s and allow frequencies among 5-8, 000Hz to pass trough.

Your list of contacts, the application stores in the Windows Registry. This is called the Friend list and once again, it is electronically encrypted. So , the list is regional for every machine, or in other words, it’s not downloaded from the central server.

Let’s take a briefly describe the tasks of the Skype ip telefoni client. First it connects to the network. It then listens on particular ports for incoming calls, refreshes the host cache table, utilizes wideband codecs, maintains the friend list, encrypts messages and determines if there is a firewall or not.

The login process:

The login procedure is the most important one and it consists of a number of phases. As mentioned, SC must connect with a valid SN in order to authenticate the username and password with the Central Server.

Skype ip telefoni gets the fist IP from the sponsor cache, sends it an UDP packet and waits for response. If there is no response after 5 seconds, it sends a TCP packet to the same IP. It tries to establish a TCP connection to the particular HC IP address and interface 80 (HTTP port). If nevertheless unsuccessful, it tried to connect to IP address and port 443 (HTTPS port). If this does not work either, it reads the next address in the HC. If Skype is unable to connect to the SN, it will report a sign in failure.

The application comes with several build-in addresses of different nodes, called bootstrap super nodes.

If the connection attempt is successful, the client must authenticate the user name and password with the Skype login server, which holds all user names and passwords and makes sure they are unique across the entire network. When the application connects for an SN, it receives an up-to-date listing of other active SNs, so it has got the most current information.

The Media Transfer process:

The video/voice communication through Skype is established through UDP. The secret here is that quite often, one of the users is behind a firewall or perhaps a router, hence it doesn’t have an actual IP address. But if both Skype clients are on real IPs, then the media traffic flows directly together over UDP. The size of the tone of voice packet is 67 bytes, that is actually the size of UDP payload. One second conversation results in roughly 140 voice packets being exchanged both ways, or 3-16 kilobytes/s.

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