The same people who developed the first KaZaA file-sharing program took part. Unfortunately, Skype has inherited the worst features of its predecessor: the VoIP program works like a self-organizing distributed peer-to-peer (P2P) network. Skype is a kind of "black box" in which there is a multi-level encryption system. The system also uses anti-debugging techniques of the executable file, which, in turn, provides the ability to download confidential information from a computer and transfer it to the network using a proprietary protocol. The mentioned protocol has the ability to bypass firewalls, and also cleverly masks its traffic, which prevents it from being blocked. All these "super abilities" of Skype make it an excellent carrier of viruses, worms and drones that establish their own personal distributed networks inside the Skype network. In addition to this, Skype rather brazenly uses the resources of the user's host, straining the central processor and forming a powerful flow of traffic, which is rarely, and especially in Russia, is free. It turns out that calls are free of charge rather conditionally.
In the structure of the Skype network, you can find: regular nodes (SC - Skype Client) and super nodes (SN - Super Node). A node with a public IP address and a fairly wide channel automatically becomes a super-node and serves to pass the traffic of SC nodes, helping them to overcome protection (for example, bypassing firewalls or network address translators) and equally distributing the load between hosts . This self-organizing distributed decentralized peer-to-peer network has a centralized element - Skype -login -server, which is responsible for authorization of Skype clients and guarantees the uniqueness of call signs for this distributed network.
The problem that has arisen can be solved using the TURN protocol. This protocol increases the latency and the possibility of losing a large number of UDP packets, and this adversely affects the quality and stability of the connection.
In this case, administrators close UDP traffic. Skype, meanwhile, automatically connects to the new TCP. The administrator, of course, can close all unused ports, but that was not the case, because there are no such ports. When connecting to a remote host, the operating system assigns any free TCP/UDP port to the client, which will be used to receive . If you close all ports, it will be impossible to establish TCP / UDP connections.
There is only one way out of this situation - disable direct access to the Internet and force all users to log in through a proxy server. Although these measures will be useless: Skype will "get acquainted" with the browser configuration and will use the proxy server as its own.
Skype traffic blocking
Skype developers warn administrators that any attempts to identify and block its traffic will be unsuccessful, since Skype traffic recognition is a very complex process, and its blocking is possible only by encrypted content that does not contain any logical sequences. But, due to the fact that the Skype developers missed some points, there is also an unencrypted part of the traffic. The traffic analyzer can detect a UDP connection using an open protocol to obtain the public IP addresses of the supernodes, and the RC4 stream is used twice by the TCP connection, which makes it possible to decrypt part of the constant fields of the Skype protocol headers and calculate the first 10 bytes of the key by decrypting portions of the persistent header fields of the Skype protocol. Unfortunately, at the moment there is no completely ready-made Skype traffic blocker.
UDP traffic is much easier to recognize and easier to block. A two-byte identification number (ID) and a packet type (payload) go at the beginning of each frame. The UDP packet contains a 39-byte NACK packet, which is passed through the obfuscation program and contains the packet identifier data, the function number (func) that is passed through the obfuscator, the sender IP and the recipient IP.
It follows that in order to block UDP traffic, the following rule must be added to the firewall:
Blocking UDP traffic will not help, because Skype automatically switches to TCP, but in this case, you can do something. Incoming IP headers
Simson L. Garfinkel
Due to the increase in the rate of use of high-speed Internet access, an increasing number of companies and private users are beginning to use the Internet as a means to make phone calls. This technology is called Voice over Internet Protocol (VoIP).
All telephone systems in the world use a microphone to convert sound waves into electrical waves, and a loudspeaker to convert electrical signals back to sound at the other end of the wire. But this technology, used to link a microphone and a loudspeaker, has improved significantly over the past 125 years. Earlier systems connected the microphone directly to the loudspeaker via copper wire. In the 1970s, AT&T used the first systems that could send multiple phone calls over a single wire, converting each phone call into a stream of digital data. VoIP systems have continued this evolution by taking independent digital data, compressing it, splitting the streams into data packets, and sending those packets over the Internet. Naturally, upon receipt, this process went in the opposite direction.
With VoIP, two people can talk to each other using headphones and microphones connected to their computers. Alternatively, a VoIP adapter can be used to translate standard analog phone tones into internet packets. VoIP gateways connect Internet systems to public telephone networks (PSTN). As a rule, the use of these gateways is paid. Companies such as Vonage sell customers a package that includes a VoIP adapter and the ability to use the company's VoIP gateway, which gives Vonage customers the illusion of using a regular phone, with the only difference being that you need to connect the Vonage adapter to a cable modem or home network, and not to a pair of wires going to the central office of the telephone company.
There are many different, generally incompatible technologies for sending voice over the Internet. The H.225 standard of the International Telecommunication Association provides voice and video teleconferencing; The Internet Engineering Task Force (IETF) uses an incompatible system called the Session Initiation Protocol (SIP). Cisco has developed a proprietary system called the Skinny Client Control Protocol (SCCP).
Skype is a proprietary VoIP system that was developed by Skype Technologies S.A., a corporation registered in Luxembourg. This company was founded by Janus Friis and Niklas Zennstrom, the same entrepreneurs who developed the popular file sharing system KaZaA. Like KaZaA, Skype is based on peer-to-peer LAN (peer-to-peer) technology, instead of passing all calls through a central server, as Vonage does, the Skype client searches and finds other Skype clients, it then builds a network from these links that can be used to find other users and send messages to them. But unlike the KaZaA program, which derives its revenue from advertising, Skype is currently free of add-ons and spyware (adware and spyware). Instead, the Skype system generates revenue by charging users for the use of terminal gateways that connect the Skype program network to the public telephone network.
Skype differs from other VoIP systems in several key ways:
Skype is very popular. During the first week of operation in August 2003, more than 60,000 people downloaded the Skype client. Today Skype is available for the following operating systems: MS Windows, MacOS, PocketPC and Linux. In October 2004, the creators of Skype revealed that more than a million people already use their program.
Use of Skype software and network is free; there are only nominal prices for calls made using the "Skype Out" and "SkypeIn" features, which allow you to make calls from Skype to public telephone networks.
Skype is much easier to use than any other VoIP system. The Skype client is fairly easy to install. Other than choosing a username, no other configuration is required. And unlike the SIP system used by Vonage, Skype clients work seamlessly behind firewalls (firewalls/firewalls) and network address translation (NAT) systems.
Skype offers an excellent sound compressor with a quality that is often superior to traditional phone systems, provided the Skype user has high speed Internet access.
In addition to voice telephony, Skype supports instant messaging, search and file transfer.
Skype uses encryption. Unlike traditional telephony and other VoIP systems, Skype claims that the transmission of all information is encrypted using 128-bit and higher cryptographic codes, which, according to them, makes it almost impossible to passively intercept Skype conversations, and the ability to decrypt and hear their content.
ISDN is another kind of digital telephone system that is popular in Europe and Asia. ISDN is similar to VoIP in that the audio is digitized and sent over the network, and also in that ISDN phone lines require special equipment to use.
All in all, Skype comes across as an extremely useful program for individuals and organizations that need high quality voice communications and have access to broadband internet.
Although Skype uses peer-to-peer communication to locate other Skype users and forward voice messages, there are many aspects in which Skype differs from other "pure" peer-to-peer systems:
KaZaA it is a popular file sharing program. Although the exchange of some files with this program takes place with the consent of the copyright holders, nevertheless it seems that the main use of KaZaA is the illegal exchange of unlicensed copies of music and film files.
KaZaA and Skype seem to be companies that have something in common. Both were founded by the same people, the technical team in both companies is almost the same, and most of the technology used by Skype was originally developed for the KaZaA program. Version 3.0 of the KaZaA Program also includes the Skype client; KaZaA 3.0 can transmit voice messages over the Skype network.
Two versions of the KaZaA program are distributed. The free version is ad-supported, while the paid version, which costs around $25, is ad-free. Promotional free versions of KaZaA are placed there using software developed by GAIN. Such software is often referred to as "spyware" because it crawls the websites users visit and places advertisements accordingly. KaZaA questions the claim that GAIN is a spyware: they claim that the program cannot catch keystrokes, analyze files on a hard drive, or disclose information about a given user to third parties. Moreover, this software can be easily removed using the standard Windows Add/Remove function.
It is unlikely that the GAIN program has any effect on the privacy or reliability of phone calls made by Skype users to KaZaA 3.0 users; there is no viable way to analyze the content of conversations for targeted advertising without the conversations being listened to by a human, but the costs of such monitoring would be prohibitively high compared to the potential advertising revenue.
However, Civil Society Organizations should try to avoid using a program like KaZaA. Since KaZaA is primarily used for file sharing against the wishes of copyright holders, it is highly likely that KaZaA users will keep illegal copies of music and movies on their computers. Organizations are discouraged from storing such files on their computers because possession of such a counterfeit collection may result in legal liability.
The use of Skype has been tested in the conditions of Dial-Up dialing to the Internet provider when connected via an analog telephone line at a speed of 26 Kbps. The sound quality at this speed deteriorates significantly. However, Skype provides acceptable sound quality for an intelligible two-way conversation.
In order to use dial-up telephone lines, it is advisable to download all programs that also use the Internet. For example, all Internet browsers and email programs must be turned off. Skype will also work better if callers avoid talking at the same time, as this minimizes bandwidth requirements.
By using Skype in this way on low speed dial-up lines, Skype gives sound quality that is noticeably inferior to analog phone lines. However, the advantage of Skype is its low cost and security resulting from the use of encryption. In situations where international calls are prohibitively expensive, or where government or telecom wiretapping is a concern, the use of Skype should be encouraged.
Is Skype reliable? Is it safe to use? Is a Skype call much more secure than analog or ISDN phone calls? How reliable is Skype compared to other VoIP systems?
Answering these questions is not so easy. Reliability is a very abstract thing that is difficult to analyze in isolation: in order to assess the reliability of Skype, it is necessary to consider certain types of threats and then decide whether the principle of operation of this program is able to withstand these threats?
In addition, Skype security analysis is complicated for several reasons: firstly, the reliability of Skype conversations depends on many factors, including the reliability of the computer on which Skype is installed and the network used for conversations. Secondly, since the Skype protocol is proprietary and closed, the only source of information is the company's own claims about the reliability of the program, and the information that can be obtained from the technical analysis of this software. Third, since Skype is a peer-to-peer system, its overall reliability depends on the third parties that are on the network (but unknown to those that communicate directly on Skype). After all, since the Skype program may update itself every time it is restarted, the security of the entire system may change without notice or change that can be clearly noticed.
The following hallmarks of system reliability are of key importance to a civil society organization using Skype:
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Confidentiality |
Does the Skype system allow eavesdropping on conversations by unauthorized persons? |
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Identification |
If you called another user to a Skype conversation, are you sure that you got through to the exact user whose name you used when dialing? |
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Availability |
Does Skype always work if both users have Internet access, or are there times when you can't see the user even if both of you have downloaded the program? Can the current conversation be interrupted? |
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fault tolerance |
If Skype's network or infrastructure is broken or damaged in any way, can Skype users borrow chat while the network is down? |
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Sustainability |
If Skype's network or infrastructure is disrupted or damaged such that Skype can no longer function, can Skype users quickly reconnect with each other? |
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Integrity (of conversation) |
Are some of the conversations lost when sending them over Skype? Do the transferred files arrive undamaged? |
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Compatibility |
How can the use of Skype affect the use of other applications on the user's computer or network? Other peer-to-peer programs come with "spyware" spyware; what about Skype? |
To answer these questions, I corresponded with Kat James, who is Skype's US PR and media representative, Toivo Annus Skype developer Kelly Larabee another press Skype attache. I also spoke briefly on the matter with Kelly Larabee on the phone. In addition, I did a preliminary analysis of the Skype packets transmitted over the network, capturing all information packets before and after Skype calls that come in and out of the computer on which the Skype software is used.
As the creators of Skype say, this program encrypts or otherwise compresses information that is transmitted over the Internet. That is, when analyzing information packets, I could not easily see the unencrypted, plain text of my messages. But while I can confidently say that Skype is reliable in terms of casual eavesdropping, I can't say if it can protect against a more sophisticated attack.
The security of information that is sent in encrypted or compressed form depends on many factors, including the use of special encryption and compression algorithms, how the encryption keys are chosen and how these keys are exchanged (known as key management), the implementation of these algorithms, and the protocol using these algorithms. , as well as the execution of these algorithms and protocols in this software.
Analysis of information packets sent between Skype users shows that a combination of these protocols is used to register on the network, find other users and make phone calls. It appears that the program is using the HTTP version of the protocol to communicate with the Skype server ui.skype.com (which is apparently located in Amsterdam) to perform user and password authentication and log in directly to the Skype server. A modified version of the HTTP protocol is used to send information to other Skype clients. As a result, the encoded protocol is used to transmit voice and text messages, as well as files.
Using Skype on a Macintosh computer, I made a call from Boston (Massachusetts, USA) to Budapest (Hungary), during which I exchanged instant messages, and also forwarded the file. All information packages were recorded by me. After analyzing them, I found that my Skype client in Boston first contacted the computer in the UK, apparently to check if I was using the latest version of the Skype client, and then search the Skype network in order to find the right one. me a respondent.
(The technology used by Skype for search and directory management is similar to that used by a system called Joltid's PeerEnabler, "whose original leaders and developers are from KaZaA and the FastTrack peer-to-peer network." Skype Press Officer insist that Skype does not use either the PeerEnabler or FastTrack network, but another program with similar characteristics.)
After the search was completed, a series of information packets were exchanged with a computer in Hungary, which continued throughout the conversation. All these packets did not succumb to my decryption. Perhaps because they were encoded, or compressed by an undocumented compression system.
Based on the analysis of captured information packets, I can conclude that while the current exchange of information between Skype clients can be encrypted, searches on behalf of Skype users, including searches necessary to initiate Skype calls, are amenable to observation by the Skype network. This means that even unprivileged network members can analyze traffic and determine that one user is calling another. It is not known whether the Skype network principle allows some nodes to view all search queries and call logs, or instead each node can see only a part of the total traffic.
What if Skype actually uses encryption?
Skype claims that its systems use the RSA encryption algorithm for key exchange and 256-bit AES for bulk encryption. However, Skype does not publish either its key exchange algorithms or its network protocol, and, despite constant requests, refuses to reveal the principle underlying the identity system of its certificates, or the implementation of encryption. Therefore, it is impossible to confirm the statements of the company itself regarding the encryption process. It is possible that the data, although encoded, is not secure enough.
Even if Skype is private and provides encryption, it is possible that the Skype system transmits encryption keys over voice channels (which may be encrypted with a different set of keys), or otherwise archives the keys on the user's hard drive. Access to these keys would enable third parties to decipher the recorded Skype dialects. A similar shareware key feature could be built into Skype, either for testing purposes or at the request of the police or intelligence agencies. Even if Skype does not currently have such monitoring features, they may be added in the future, and the modified client will then be distributed over the Skype network, either to all users or to those who meet certain selected criteria.
Skype uses encryption, but not at a high enough level. Even if Skype uses RSA, inefficient use of the algorithm cannot provide good protection. Due to the fact that at the moment Skype has not yet published its protocol, it is impossible to say whether the protocol using RSA is reliable enough or not.
The situation described above must be taken into account. A Skype conversation is much more private than a traditional analog or ISDN phone conversation. Anyone who has physical access to the telephone line at any point between any of the speaking parties can listen in on these conversations.
The strength of Skype encryption in general
Skype is also more reliable than today's VoIP systems, as encryption is not part of most VoIP offerings. However, it is possible to secure a VoIP conversation by routing VoIP traffic through a virtual private network (VPN). A system using VoIP over VPN is probably more reliable than Skype, provided the VPN is properly configured.
It is important to understand that the reliability of Skype can be undermined by the presence of spyware or other types of tracking programs that are running on the user's computer. For example, programs such as Netbus and Back Orifice allow third parties to turn on the computer's microphone and send sound recordings over the Internet to someone else's computer. Such a program can eavesdrop not only on Skype dialects, but also on any other conversations that take place in the office where the computer with the downloaded Skype program is located.
There are other points regarding the security of the Skype program that users should be aware of:
Ultimately, you need to remember that the reliability of the Skype system also depends entirely on the conscience of the Skype programmers and the organization of the Skype servers. It is possible that there are loopholes in the system that allow Skype or other companies to eavesdrop or record Skype conversations. Theoretically, the developers of Skype could even build a "loophole" into the system that could use a special program to turn on the microphone on the computer to either record all the sounds in the room on the hard drive or send this data over the Internet to another computer. Similar loopholes and pitfalls can also be introduced into any Skype program, or these features can be added later to individual users' Skype programs.
Each Skype user has a username and password. Each username is registered to a specific email address. In order to log in, the user must enter their username and password. If the password is lost, Skype will change the password and send a new one to the user's registered email address. This approach is called Email Based Authentication and Authorization The Skype client also has the ability to "remember" usernames and passwords and automatically log you in.
An additional complexity of the Skype system is its network. It looks like the Skype network is used to authenticate usernames and passwords, but it's not entirely clear how this is done. For example, Skype hosts can send an encrypted combination of usernames and passwords back to the Skype servers for authorization. They can also send back an unencrypted combination of usernames and passwords. The Skype network may not be involved at all, and all communication between Skype clients may serve other purposes. However, if the Skype network is still involved in this, then several types of attacks are possible:
Since Skype is a voice communication system, its users can identify the people with whom they communicate by voice. That is, the voice has biometric qualities. However, this does not work when communication is only through the exchange of written messages and files.
Under normal circumstances, the Skype authentication system seems to provide the same level of authentication as other username and password based systems such as AOL or HotMail. That is, most people can control their mailboxes, but sometimes attackers can find out someone else's password using guesswork, social engineering, using keyloggers, or using an intercepted message used to recover a password. Also, computer administrators can issue passwords, set new ones, or in some other way allow attackers to impersonate a registered user. At the same time, it can be assumed that the person with whom you communicate on Skype is in fact the one whose name you see, but you have no absolute guarantee of this.
One of the great engineering achievements of the 20th century was widespread access to the public telephone network. In many countries, users experience minor downtime of as little as 5 minutes per user per year or even less, which is equivalent to 99.99905% availability.
Although the original design of the Internet assumed that the network would survive the loss of some critical links (see the chapter on "fail-safety" below), this has only recently become the goal of developers and manufacturers of Internet equipment. The quality of Internet service as a whole still loses to the telephone one. Thus, it is possible that telephone calls over the Internet are less accessible than calls over public telephone networks. (Some commentators have noted that the availability of telephone networks is declining due to deregulation, and that the availability of a single system is less important given the prevalence of multiple, overlapping mobile networks.)
Additional factors may undermine the potential availability of Skype. Since the Skype client is dependent on username and password authentication, it is possible that the entire Skype network will fail if the Skype authentication servers fail or are otherwise unavailable. Existing VoIP systems do not have this problem, although those systems that rely on the service of a single gateway will experience a general breakdown if that gateway fails. (For example, all Vonage users will not be able to use phone service if the Vonage gateway fails.)
It is often said that the Internet was invented in order to resist nuclear war. The truth is that packet-switched networks were designed so that the exchange of information between nodes in the network could continue even if the direct link between those nodes was destroyed. The ability of a system to continue operating even after such damage is called fault tolerance.
The Internet device allows ISPs to choose how resilient they want their systems to be. If an organization connects to the Internet through its mail server using a single DSL line, and that line goes down, mail won't work. On the other hand, if an organization has two DSL lines, email will continue to function if one of those lines fails. Fault-tolerant systems are usually more expensive than systems with a single point of failure. In addition, fail-safe systems can rarely provide better day-to-day performance than non-fail-safe systems. As a result, most Internet users and Internet service providers do not use systems that can withstand the accidental failure of one or more of its components.
It is not known if the Skype identity servers can withstand network outages or attacks.
Packet-switched networks are remarkably resilient. In most cases, Internet connectivity can be restored faster than traditional telephone networks by deploying wireless networking technologies. An additional advantage of Skype's other VoIP systems is that these systems were designed with mobile users in mind. They do not depend on changing the IP addresses of users.
As a result, Skype and other VoIP systems are generally more resilient to network outages. If the network fails in the building, you can simply take computers or VoIP phones, move them to another location and reconnect. Once your computer is registered with the Skype network, you will be able to make and receive calls regardless of your new location.
On the other hand, Skype clients would almost certainly not work if the Skype Reverse Identity Network became unavailable. This can happen as a result of a network breach, some type of hacker attack, a hostile intrusion, or the closure of the parent company. In such a case, the Skype network may become inaccessible to some or even all Skype users.
The integrity of the conversation provided by Skype has not been fully explored. It is possible that a conversation made using the Skype system may be cut off or distorted before reaching your interlocutor. Therefore, Skype does not guarantee that text messages and files will be delivered as sent.
However, in practice, Skype transmits voice well, and text messages and files are also transmitted without distortion. But when using Skype on 802.11 wireless networks, voice quality suffers significantly.
It is understandable that network administrators are concerned about the software that users download.
software, the use of which can have unpredictable consequences. Many universities, for example, complain that students using file-sharing systems like KaZaA consume large amounts of traffic and potentially expose their institutions to legal action by owners whose copyrights could be infringed. KaZaA users can also share the contents of their computers without even being aware of it.
Since communication via Skype is limited to voice only, the total network load created by the "supernode" must be doubled, due to the function of this node as an authorized node and duplication of communication. It is not known how this can be avoided.
Skype can also serve as a source of spyware. Although the creators of the program say that their program does not contain spyware or adware, it is possible that they are not telling the truth or their policy will change in the future. Skype may have vulnerabilities in its system that may be exploited by third parties.
It should be noted that most of the risks that arise in connection with the use of the Skype program are no different from the risks of e-mail or other personal means of information transmission. Indeed, the use of Skype is perhaps less risky for the overall integrity of the system, simply because Skype was originally designed for voice communications. However, you need to be careful when Skype is used to transfer files. Compared to KaZaA and other file sharing programs, Skype poses less risk because the exchange is always between certain people than when files are located through a search and they are downloaded from a potentially unknown source. Skype, on the other hand, is a more risky program because programs like KaZaA have built-in anti-virus protection that scans programs as they are downloaded; and Skype does not seem to have such protection.
Overall, Skype comes across as more reliable than traditional analog or ISDN telephony, but no more reliable than VoIP systems using virtual private networks (VPNs). There is a possibility that the Skype system will be hacked by an experienced person or a targeted attacker.
When using Skype, the following tips may be helpful:
skype url protocol: allows you to create paired calls (that is, one-on-one calls), as well as conference calls, video calls and chats.
By default, before making a call, the local Skype program displays a call confirmation dialog box. This dialog box also has the ability to disable its output later when making a call.
If the list of interlocutors specified (using phone numbers or Skype logins) is more than one, then the numbers or names of Skype accounts (logins) are separated by a semicolon (for example, interlocutor1; interlocutor2;...; interlocutorN).
Audio calls are divided into explicit And not explicit. Implicit audio calls imply an indication in the protocol of only the list of interlocutors.
skype:interlocutor1;interlocutor2;...;interlocutorN.
Explicit audio calls imply an indication in the “skype:” protocol not only of the list of participants, but also of the “call” argument.
Call Indicates an explicit audio call. This also allows you to set additional arguments, such as the video argument and the theme argument:
skype:interlocutor1;+1234567890;...;interlocutorN?call&topic=Topic line%20
In order to specifically specify an audio call without a video, you must set the "video" argument to "false" (video=false).
skype:interlocutor1;+1234567890;...;interlocutorN?call&video=true
Note: Participants using mobile devices can only join a group video call via voice communication.
Creates paired dialogues and group chats.
If a conversation is made with a participant or participants with whom there are already conversations in the history, then the Skype application opens an existing conversation, and if such a conversation does not exist in the Skype history, a new conversation is created. If this opens an already existing conversation (having a specific topic) and the topic is also specified using the “ topic ” argument, then the Skype application changes the topic of the conversation to a new value.
skype:interlocutor1;+1234567890;...;interlocutorN?chat&topic=Topic line%20
Briefly: SIP is an open standard, and Skype- closed. But Skype better adapted to real conditions, SIP focused on near-ideal conditions.
SIP protocol, Session Interaction Protocol (RFC 3621) is completely open to developers. It is quite well thought out, and is currently the most popular, since it is quite simple for hardware implementation and, in addition to organizing voice communication sessions, provides a number of additional features. To protocol tasks SIP it is only necessary to establish and agree on a connection, and it is not necessary that this connection be voice - it can be any real-time data stream - video, multimedia data, interactive service.
The protocol commands are similar to HTTP, right down to the details.
A key feature of SIP is client-server orientation. It is assumed here that in any SIP telephony network there is a server ( GateKeeper).
Protocol SIP well oriented to work in local networks and on good Internet channels. But what happens when the ISP for some reason does not want users to be able to make calls via SIP? To achieve his goal, it will be enough for him to "cut" UDP packets with a port value of 5060, so that SIP stopped working properly. There are ways to avoid such arbitrariness, but these require interfering with the operation of the protocol, forcing you to forget about compatibility with standard equipment.
Protocol used Skype has always been and continues to be closed from third-party developers. It has a number of features that distinguish it from SIP.
First, the protocol Skype focused on p2p network (Peer-to-Peer). Skype works on the principle self-organizing distributed peer-to-peer network, in which there are no permanent servers. The role of the servers is performed by the network participants themselves, who have a direct IP address and a wide channel for connecting to the Internet.
Secondly, in the protocol Skype encryption is mandatory. This is a forced measure due to the p2p network structure Skype: Traffic passes through hosts that should not be trusted.
Third, Skype has a high resourcefulness, allowing it to work even on limited Internet connections. Skype is focused on a wide range of users from different countries and interference in the network in order to ban VoIP is less scary for him, because he is prepared for this. It is known that the protocol Skype has the ability to find ways to transmit voice information. For example, if the required range of UDP protocol ports is closed (typically, the Skype protocol uses the port UDP 40150), Skype switches to using free TCP ports, up to the known open port 80 (HTTP), and, if necessary, will use the connection through an HTTP proxy. It means that Skype will work practically everywhere where the Internet sites "open".
There is reason to believe that Skype uses a modified version of the standard SIP protocol. In other words, SIP was taken as the basis of the protocol Skype and improved, thanks to which Skype has a competitive advantage over operators SIP telephony- low cost of servicing the subscriber network and willingness to work almost everywhere and in any conditions.
The popular Skype program is one of the most innovative and at the same time popular social services all over the world. This is easily explained due to the mass of various advantages and unique opportunities that consist in unlimited communication with any Skype subscribers, regardless of their location or social status. In addition, there is no obligatory subscription fee in the program, and the principle of its management will be easily understood even by a beginner. However, each user should definitely familiarize himself with the main program documents and the principles of its work.
If you are interested in what the skype protocol is, then simple explanations from professional programmers will easily and easily help you understand this term. The Skype program protocol is one of the most important elements of the interactive network, which is built specifically for the Skype program to work.
Important: for maximum security, all the technical characteristics of this cipher are actually inaccessible to a wide range of users, have a special source code and are completely classified.
The main features of the Skype program cipher are the following characteristics:
Many Skype users are probably interested in the question: what protocol does skype use, to which there is a clear answer. For security purposes, software developers keep secret all the codes and data that underlie its well-established work, however, such facts are known:
Important: Many individual and corporate Skype users claim to have been able to declassify Skype's unique cipher, but this is not possible.
The protocol of the program allows its users to receive such special interactive services:
This protocol is implemented in the process of connecting an individual account of each user of the program. The connection occurs via a special NAT path, after which firewalls and individual hosts are searched for by the public IP addresses of users. Then the authenticity of each connection is necessarily checked by an individual password.
Thus, the developers of the program took care of creating a unique Skype protocol, which has a unique secret code, and also provides full security and the ability to use all the advantages of this program.
