Skype ( /ˈskaɪp/) is a proprietary voice-over-Internet Protocol service and software application originally created by John Szczepanik and Janus Friis in 2003, and owned by Microsoft since 2011.

The service allows users to communicate with peers by voice, video, and instant messaging over the Internet. Phone calls may be placed to recipients on the traditional telephone networks. Calls to other users within the Skype service are free of charge, while calls to landline telephones and mobile phones are charged via a debit-based user account system. Skype has also become popular for its additional features, including file transfer, and videoconferencing. Competitors include SIP and H.323-based services, such as Empathy, Linphone, Ekiga ^[9] as well as the Google Talk service.

Skype has 663 million registered users as of September 2011.^[10] The network is operated by Microsoft, which has its Skype division headquarters in Luxembourg. Most of the development team and 44% of the overall employees of the division are situated in the offices of Tallinn and Tartu, Estonia.^[11][12][13]

Unlike most VoIP services, Skype is a hybrid peer-to-peer and client–server system. It makes use of background processing on computers running Skype software. Skype's original proposed name (Sky Peer-to-Peer) reflects this fact.

Some network administrators have banned Skype on corporate,^[14] government, home, and education networks,^[15] citing reasons such as inappropriate usage of resources, excessive bandwidth usage, and security concerns.^[16]

History[link]

Skype was founded in 2003 by Janus Friis from Denmark and Niklas Zennström from Sweden.^[17] The Skype software was developed by Estonians Ahti Heinla, Priit Kasesalu, and Jaan Tallinn, who together with Janus and Niklas were also behind the peer-to-peer file sharing software Kazaa.^[18] In August 2003, the first public beta version was released.

Microsoft acquisition[link]

On 10 May 2011, Microsoft Corporation agreed to acquire Skype Communications, S.à r.l for US$8.5 billion.^[19] The company was incorporated as a division of Microsoft, and Microsoft acquired all of the company's technologies with the purchase. This was completed on 13 October 2011.^[19][20]

Features[link]

Registered users of Skype are identified by a unique Skype Name, and may be listed in the Skype directory.^[21] Skype allows these registered users to communicate through both instant messaging and voice chat. Voice chat allows telephone calls between pairs of users and conference calling, and uses a proprietary audio codec. Skype's text chat client allows group chats, emoticons, storing chat history and editing of previous messages. Offline messages were implemented in version 5, but removed after a few weeks without notification. The usual features familiar to instant messaging users — user profiles, online status indicators, and so on — are also included.

The Online Number, a.k.a. SkypeIn, service allows Skype users to receive calls on their computers dialed by conventional phone subscribers to a local Skype phone number; local numbers are available for Australia, Belgium, Chile, Colombia, Denmark, the Dominican Republic, Estonia, Finland, France, Germany, Hong Kong, Hungary, Ireland, Italy, Japan, Mexico, New Zealand, Poland, Romania, South Africa, South Korea, Sweden, Switzerland, Turkey, the Netherlands, the United Kingdom, and the United States.^[22][23] A Skype user can have local numbers in any of these countries, with calls to the number charged at the same rate as calls to fixed lines in the country.

Video conferencing between two users was introduced in January 2006 for the Windows and Mac OS X platform clients. Skype 2.0 for Linux, released on 13 March 2008, also features support for video conferencing.^[24] Version 5 beta 1 for Windows, released 13 May 2010, offers free video conferencing with up to five people.^[25]

Skype for Windows, starting with version 3.6.0.216, supports "High Quality Video" with quality and features, e.g., full-screen and screen-in-screen modes, similar to those of mid-range videoconferencing systems.^[26] Skype audio conferences currently support up to 25 people at a time, including the host.

Skype does not provide the ability to call emergency numbers such as 911 in the United States and Canada, 999 in the United Kingdom and many other countries, 111 in New Zealand, 000 in Australia, or 112 in Europe.^[27] The U.S. Federal Communications Commission (FCC) has ruled that, for the purposes of section 255 of the Telecommunications Act, Skype is not an "interconnected VoIP provider".^[28] As a result, the U.S. National Emergency Number Association recommends that all VoIP users have an analog line available as a backup.^[29]

In 2011, Skype partnered with Comcast to bring its video chat service to Comcast subscribers via their HDTV sets.^[30]

Version history[link]

This section requires expansion.

Usage and traffic[link]

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Users may have more than one account; it is not possible to count users, only accounts.

The volume of international traffic routed via Skype is significant. It has become the largest international voice carrier (by minutes of calls).^[42]

In January 2011, after the release of video calling on the Skype client for iPhone, Skype reached a record 27 million simultaneous online users.^[45] This record was broken with 29 million simultaneous online users on 21 February 2011,^[46] and again on 28 March 2011 with 30 million online users.^[47] On 25 February 2012, Skype announced that it has over 32 million users for the first time ever.^[48]. As of 05 March 2012, it has broken to 35 million simultaneous online users.^[49]

Client applications and devices[link]

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Skype runs on a number of platforms, and on 29 October 2007, Skype launched its own mobile phone under the brand name 3 Skypephone, which runs a BREW OS.^[50] Other platforms officially supported include:

• About 50 mobile phones, as of 2008^[51]
• The Nokia N800, N810 and N900 Internet Tablets, which use the Maemo environment
• Both the Sony mylo COM-1 and COM-2 models
• The PlayStation Portable Slim and Lite series, though the user needs to purchase a specially designed microphone peripheral. The PSP-3000 has a built in microphone which allows communication without the Skype peripheral.^[52] PSP Go has the ability to use Bluetooth connections with the Skype application, in addition to its built-in microphone.^[53] Skype for Playstation Vita may be downloaded via the PlayStation Network in the U.S. It includes the capability to receive incoming calls with the application running in the background.
• Mobile devices running Windows Mobile;^[54] in February 2010, Skype announced its decision to discontinue development Skype for Windows Mobile.^[55] In May 2010, Skype announced that it had no plans to develop a version of Skype for Windows Phone 7.^[56] But at MIX 11, It was announced that Skype is coming to Windows Phone 7.^[57] The first stable release was made available on 22 April 2012, though it lacked the ability to run in the background.^[58]
• Symbian; Current Version: 2.0 Release date: 21 April 2011^[59]
• The X-Series together with mobile operator 3. However this uses a regular mobile phone call and iSkoot^[60] to a Skype gateway, rather than mobile Internet. Other companies produce dedicated Skype phones which connect via WiFi
• iOS, using an official application released on 31 March 2009. As of version 2.x, the iPhone application is capable of placing voice calls over 3G and EDGE networks. Skype originally announced it will charge a monthly fee for this feature at the start of 2011, but that was eventually dropped.^[61] On 29 December, Skype updated their iOS app to version 3.0, allowing mobile video calling. On 2 August 2011, Skype officially released an iPad app named 'Skype for iPad' which allows the user to have video calls using iPad 2's front and back cameras. The original iPad is also allowed to make calls but only voice calls, The other person on the other side can make a video call if they have a camera, and the original iPad can only receive the video but not send.
• A variety of BlackBerry and Android 3G Smartphones, through Verizon Wireless' Skype mobile service. Customers can receive Skype calls, instant messages and see friends' presence any time the phone is on. Skype usage isn't charged against customers’ monthly Verizon Wireless minute allowance when calling another Skype account (Skype-to-Skype). Customers in the U.S. use minutes from their calling plan when calling U.S. land lines or cell phones.^[62]

Some devices are made to work with Skype by talking to a desktop Skype client or by embedding Skype software into the device. These are usually either tethered to a PC, or have a built-in Wi-Fi client to allow calling from Wi-Fi hotspots like the Netgear SPH101 Skype Wi-Fi Phone, the SMC WSKP100 Skype Wi-Fi Phone, the Belkin F1PP000GN-SK Wi-Fi Skype Phone, the Panasonic KX-WP1050 Wi-Fi Phone for Skype Executive Travel Set, the IPEVO So-20 Wi-Fi Phone for Skype and the Linksys CIT200 Wi-Fi Phone. There are also embedded cordless Skype phones based on DECT, which do not need a PC either, like the DUALphone 3088 from RTX. Netgear and SMC's Wi-Fi phones are considered the two major competitors in the market, with reviews of the Wi-Fi phones giving them equal coverage.^{[citation needed]}

The Skype Wi-Fi Phone is a wireless mobile phone that allows users to make Skype calls, using a wireless Internet connection. The Skype Wi-Fi Phone has an on-screen menu that lets Skype users see who is online and available to talk, similar to what is seen on a PC. It can also be used to talk with non-Skype users. SkypeOut minutes can be used to call any phone for a low price and no monthly fee. The Skype Wi-Fi phone does not contain a web browser and so can not access hotspots, which require web-based login or authentication.^[63]

Third-party developers, such as Truphone, Nimbuzz IM and Fring, have allowed Skype to run in parallel with several other competing VoIP/IM networks (Truphone and Nimbuzz provide truphoneOut and NimbuzzOut as a competing paid service) in any Symbian or Java environment. Nimbuzz has made Skype available to BlackBerry users. In July 2010, however, Fring disabled users from accessing Skype despite claiming that Skype themselves disabled the access;^[64] Fring had provided mobile video calling over Skype as well as support for the Android platform. Nimbuzz discontinued support on request of Skype in October 2010.^[65]

Until November 2010, only certain Samsung and Panasonic TVs offered Skype video service.^[66]

System and software[link]

Protocol[link]

Skype uses a proprietary Internet telephony (VoIP) network called the Skype protocol. The protocol has not been made publicly available by Skype and official applications using the protocol are closed-source. Part of the Skype technology relies on the Global Index P2P protocol belonging to the Joltid Ltd. corporation. The main difference between Skype and standard VoIP clients is that Skype operates on a peer-to-peer model (originally based on the Kazaa software^[67]), rather than the more usual client–server model (note that the very popular SIP model of VoIP is also peer-to-peer, but implementation generally requires registration with a server, as does Skype).

Protocol detection and control[link]

Many networking and security companies claim to detect and control Skype's protocol for enterprise and carrier applications. While the specific detection methods used by these companies are often private, Pearson's chi-squared test and Naive Bayes classification are two approaches that were published in 2007.^[68] Combining statistical measurements of payload properties (such as byte frequencies and initial byte sequences) as well as flow properties (like packet sizes and packet directions) has also shown to be an effective method for identifying Skype's TCP- and UDP-based protocols.^[69]

Audio codecs[link]

G.729 and SVOPC. Skype added a Skype-created codec called SILK to Skype 4.0 for Windows and other Skype clients. SILK is intended to be "lightweight and embeddable".^[70]

Video codecs[link]

VP7 is used for versions prior to Skype 5.5^{[71][72][73][74][75]}

As of version 5.7 VP8 is used for both group and one on one standard definition video chat and H264 is used for 720p and 1080p high definition group and one on one video chat.^[76][77]

Client[link]

Clients are available for Microsoft Windows (2000, XP, Vista, 7, Mobile), iOS (iPad, iPhone, iPod Touch), Mac OS X (Intel, PPC), Symbian S60, Sony PlayStation Portable (PSP), Linux (includes Android, Maemo), and for 2010 TV models from LG, Panasonic, and Samsung, but these TVs need a special webcam.^[78]

Skype 4 in Default View running on Windows XP Skype 4 in Default View running on Windows XP   Skype 4 in Default View running on Windows Vista Skype 4 in Default View running on Windows Vista   Skype 5.3.0.111 in Default View on Windows 7 Skype 5.3.0.111 in Default View on Windows 7   Skype 2.2, running on a Windows Mobile 6 device Skype 2.2, running on a Windows Mobile 6 device   Skype 2.7, running on Mac OS X Leopard Skype 2.7, running on Mac OS X Leopard   Skype 5.1, running on Mac OS X Snow Leopard Skype 5.1, running on Mac OS X Snow Leopard   Skype 5.1.0.935, running on Mac OS X Snow Leopard   Skype 1.0.2 running on iPhone Skype 1.0.2 running on iPhone   Skype 2.6 running on an Android device Skype 2.6 running on an Android device   Skype Mobile on Verizon 1.6 running on an Android 2.2 device Skype Mobile on Verizon 1.6 running on an Android 2.2 device   Skype 2.2 beta, running on a Linux desktop Skype 2.2 beta, running on a Linux desktop

Before and during the Microsoft acquisition, Skype withdrew licensing from several third parties producing software and hardware compatible with Skype. The Skype for Asterisk product from Digium was withdrawn as "no longer available for sale".^[79] The Senao SN358+ long-range (10–15 km) cordless phone were discontinued due to loss of licenses to participate in the Skype network as peers. In combination these two products made it possible to create roaming cordless mesh networks with robust handoff.

Security and privacy[link]

Skype is claimed to be a secure communication; encryption cannot be disabled, and is invisible to the user. Skype reportedly uses publicly documented, widely trusted encryption techniques: RSA for key negotiation and the Advanced Encryption Standard to encrypt conversations.^[80] However, it is impossible to verify that these algorithms are used correctly, completely and at all times as there is no public review possible without a protocol specification and/or the program source code. Skype provides an uncontrolled registration system for users with no proof of identity. Instead, a free choice of nicknames permits users to use the system without revealing their identity to other users. It is trivial to set up an account using any name; the displayed caller's name is no guarantee of authenticity. A third party paper analyzing the security and methodology of Skype was presented at Black Hat Europe 2006. It analyzed Skype and found a number of security issues with the current security model.^[81]

Skype incorporates some features which tend to hide its traffic, but it is not specifically designed to thwart traffic analysis and therefore does not provide anonymous communication. Some researchers have been able to watermark the traffic so that it is identifiable even after passing through an anonymizing network.^[82]

In an interview Kurt Sauer, the Chief Security Officer of Skype, said, "We provide a safe communication option. I will not tell you whether we can listen or not."^[83] Skype's client uses an undocumented and proprietary protocol. The Free Software Foundation (FSF) is concerned by user privacy issues arising from using proprietary software and protocols and has made a replacement for Skype one of their high priority projects.^[84] Security researchers Biondi and Desclaux have speculated that Skype may have a back door, since Skype sends traffic even when it is turned off and because Skype has taken extreme measures to obfuscate their traffic and functioning of their program.^[85] Several media sources reported that at a meeting about the "Lawful interception of IP based services" held on 25 June 2008, high-ranking unnamed officials at the Austrian interior ministry said that they could listen in on Skype conversations without problems. Austrian public broadcasting service ORF, citing minutes from the meeting, reported that "the Austrian police are able to listen in on Skype connections". Skype declined to comment on the reports.^[86][87]

The United States Federal Communications Commission (FCC) has interpreted the Communications Assistance for Law Enforcement Act (CALEA) as requiring digital phone networks to allow wiretapping if authorized by an FBI warrant, in the same way as other phone services. In February 2009 Skype said that, not being a telephone company owning phone lines, it is exempt from CALEA and similar laws which regulate US phone companies, and in fact it is not clear whether Skype could support wiretapping even if it wanted to.^[88] According to the ACLU, the Act is inconsistent with the original intent of the Fourth Amendment to the U.S. Constitution;^[89] more recently, the ACLU has expressed the concern that the FCC interpretation of the Act is incorrect.^[90][91]

On 20 February 2009 the European Union's Eurojust agency announced that the Italian Desk at Eurojust would "play a key role in the coordination and cooperation of the investigations on the use of internet telephony systems (VoIP), such as 'Skype'. ... The purpose of Eurojust’s coordination role is to overcome the technical and judicial obstacles to the interception of internet telephony systems, taking into account the various data protection rules and civil rights"^[92]

In 2012, Skype introduced automatic updates to better protect users from security risks, but received some challenge from users of the Mac product, as the updates cannot be disabled from version 5.6 on^[93] both on Mac OS and Windows versions, although in the latter, and only from version 5.9 on, automatic updating can be turned off in certain cases^[94].

Service in the People's Republic of China[link]

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Since September 2007, users in China trying to download the Skype software client have been redirected to the site of TOM Online, a joint venture between a Chinese wireless operator and Skype, from which a modified Chinese version can be downloaded.^[95] The TOM client participates in China's system of Internet censorship, monitoring text messages between Skype users in China as well as messages exchanged with users outside the country.^[96][97] Niklas Zennström, then chief executive of Skype, told reporters that TOM "had implemented a text filter, which is what everyone else in that market is doing. Those are the regulations." He also stated: "One thing that’s certain is that those things are in no way jeopardising the privacy or the security of any of the users."^[98]

In October 2008, it was reported that TOM had been saving the full message contents of some Skype text conversations on its servers, apparently focusing on conversations containing political issues such as Tibet, Falun Gong, Taiwan independence, and the Chinese Communist Party. The saved messages contain personally identifiable information about the messages' senders and recipients, including IP addresses, usernames, land line phone numbers, and the entire content of the text messages, including the time and date of each message. Information about Skype users outside China who were communicating with a TOM-Skype user was also saved. A server misconfiguration made these log files accessible to the public for a time.^{[97][99][100]}

Customer service[link]

As of February 2012, Skype provides support through their web support portal, support community, @skypesupport on Twitter, and Skype Facebook page. Direct contact via email and live chat is available through their web support portal. Chat Support is a premium feature available to Skype Premium and some other paid users.

In January 2010 Skype rescinded their policy of seizing funds in Skype accounts that have been inactive (no paid call) for 180 days. This was in settlement to a class action lawsuit.^[101] A settlement of up to US$4 was paid to persons who opted in to the action.

Skype's refund policy states that they will provide refunds in full if a client has used less than 1 euro of their Skype Credit. "Upon a duly submitted request, Skype will refund you on a pro rata basis for the unused period of a Product".

Use of Skype for Language Exchange and other educational purposes[link]

Although Skype is a commercial product, its free version is being used with increasing frequency among teachers and schools interested in global education projects.^[102]. For example Skype is being used to facilitate language exchange. Students in different parts of the world are paired off, each is a native speaker of the language that the other wishes to learn. In conversations over Skype they alternate between the two languages.^[103][104]

Outages and downtime[link]

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On 16 August 2007, Skype became unavailable to a majority of its users. Millions of users were requesting to log-in at the same time following a routine Windows update and this flooded the peer-to-peer system. The event lasted for about two days.^[105]

On 22 December 2010, it was reported that Skype experienced an outage estimated to represent 8 million foregone calls.^[106] Skype administrators placed the following message on their Twitter page: "Some of you may have problems signing in to Skype -- we're investigating, and we're sorry for the disruption to your conversations...engineers and site operations are working non-stop to get things back to normal."^[107][108] The problem came down to the limited availability of "supernodes", affecting some versions of Skype.^[109] Later in the day, Skype's CEO, Tony Bates, issued an apology. He said that the matter was being taken very seriously and was being thoroughly investigated. He said that malicious attack was not being ruled out as a problem cause and he put his estimate of the foregone calls at about 10 million.^[110] On 23 December 2010, Skype's blog with Tony Bates issued another apology through a video posted on YouTube for the Skype outage.^[111]

The problem persisted across the North America, Latin America, Europe and Asia. It had started to subside by 8:30 pm UTC; however users were warned it might take several hours for the program to be fully operative again.^[112] It was reported at 9:27 am 23 December UTC that most users were able to log in again although some still could not.^[113] On the other hand into Thursday only about a third of the expected traffic was actually using Skype, relative to the time-period.^[114] On 23 December 2010, Skype said on its blog that the system had stabilized, and a detailed explanation of the incident was published six days later.^[115] Bates offered all Pay As You Go and Pre-Pay customers a free call to any landline as compensation.^[116] Subscribers had their subscription extended by one week.

See also[link]

Internet portal

• Comparison of instant messaging clients
• Comparison of instant messaging protocols
• Comparison of VoIP software
• Mobile VoIP
• Presence information
• Secure communication
• Unified communications
• Caller ID spoofing

References[link]

External links[link]

• Official website
• Compilation of research and technology articles involving Skype
• An Experimental Study of the Skype Peer-to-Peer VoIP System
• "Skype, Going Public, Hopes for $100 Million From First Offering" Eric Pfanner, The New York Times, 9 August 2010
• Skype Journal, an independent blog covering Skype since its 2003 launch.
• A Brief History Of Skype - The "Skype Idea", early development and history.