X.25 is an ITU-T standard protocol suite for packet-switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, leased lines, plain old telephone service connections, or ISDN connections as physical links. X.25 was defined by the International Telegraph and Telephone Consultative Committee in a series of drafts and finalized in a publication known as The Orange Book in 1976. X.25 networks were popular during the 1980s with telecommunications companies and in financial transaction systems such as automated teller machines. However, most uses have moved to Internet Protocol systems instead. X.25 is still used and available in niche applications such as Retronet that allows vintage computers to use the internet. X.25 is one of the oldest packet-switched services available. It was developed before the OSI Reference Model; the protocol suite is designed as three conceptual layers, which correspond to the lower three layers of the seven-layer OSI model.
It supports functionality not found in the OSI network layer. X.25 was developed in the ITU-T Study Group VII based upon a number of emerging data network projects. Various updates and additions were worked into the standard recorded in the ITU series of technical books describing the telecommunication systems; these books were published every fourth year with different-colored covers. The X.25 specification is only part of the larger set of X-Series specifications on public data networks. The public data network was the common name given to the international collection of X.25 providers. Their combined network had large global coverage into the 1990s. Publicly accessible X.25 networks were set up in most countries during the 1970s and 1980s, to lower the cost of accessing various online services. Beginning in the early 1990s, in North America, use of X.25 networks started to be replaced by Frame Relay services offered by national telephone companies. Most systems that required X.25 now use TCP/IP, however it is possible to transport X.25 over TCP/IP when necessary.
X.25 networks are still in use throughout the world. A variant called AX.25 is used by amateur packet radio. Racal Paknet, now known as Widanet, is still in operation in many regions of the world, running on an X.25 protocol base. In some countries, like the Netherlands or Germany, it is possible to use a stripped version of X.25 via the D-channel of an ISDN-2 connection for low-volume applications such as point-of-sale terminals. Additionally X.25 is still under heavy use in the aeronautical business though a transition to modern protocols like X.400 is without option as X.25 hardware becomes rare and costly. As as March 2006, the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with Air Route Traffic Control Centers. France was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as Minitel it was based on Videotex, itself running on X.25. In 2002, Minitel had about 9 million users, in 2011, it still accounted for about 2 million users in France when France Télécom announced it would shut down the service by 30 June 2012.
As planned, service was terminated 30 June 2012. There were 800,000 terminals still in operation at the time; the general concept of the X. 25 was to create a global packet-switched network. Much of the X.25 system is a description of the rigorous error correction needed to achieve this, as well as more efficient sharing of capital-intensive physical resources. The X. 25 specification defines only the interface between an X. 25 network. X.75, a protocol similar to X.25, defines the interface between two X.25 networks to allow connections to traverse two or more networks. X.25 does not specify how the network operates internally – many X.25 network implementations used something similar to X.25 or X.75 internally, but others used quite different protocols internally. The ISO protocol equivalent to X.25, ISO 8208, is compatible with X.25, but additionally includes provision for two X.25 DTEs to be directly connected to each other with no network in between. By separating the Packet-Layer Protocol, ISO 8208 permits operation over additional networks such as ISO 8802 LLC2 and the OSI data link layer.
X.25 defined three basic protocol levels or architectural layers. In the original specifications these were referred to as levels and had a level number, whereas all ITU-T X.25 recommendations and ISO 8208 standards released after 1984 refer to them as layers. The layer numbers were dropped to avoid confusion with the OSI Model layers. Physical layer: This layer specifies the physical, electrical and procedural characteristics to control the physical link between a DTE and a DCE. Common implementations use X. 21, EIA-449 or other serial protocols. Data link layer: The data link layer consists of the link access procedure for data interchange on the link between a DTE and a DCE. In its implementation, the Link Access Procedure, Balanced is a data link protocol that manages a communication session and controls the packet framing, it is a bit-oriented protocol that provides orderly delivery. Packet layer: This layer defined a packet-layer protocol for exchanging control and user data packets to form a packet-switching network based on virtual calls, acco
Bezeq is an Israeli telecommunications company. Bezeq and its subsidiaries offer a range of telecom services, including fixed-line, mobile telephony, high-speed Internet and pay TV. Bezeq was founded in 1984 as a government-owned corporation, taking over the provision of telephony services in Israel, which were run directly by the Ministry of Communications; the drive for creating the company was the bureaucratic and inefficient nature of the government run service, requiring customers to wait several years until they got a phone line installed. In the late 1980s Anat Hoffman founded a group, Bezeq-Afflicted Clients Association, to protect the interests of Bezeq customers. A major complaint was that Bezeq refused to offer customers itemized bills, so they had no assurance they were paying for services they received. National hearings were held where customers had the opportunity to share their grievances against Bezeq. Hoffman notes that of 46 cases handled through small claims court, the consumers prevailed against Bezeq in 43.
Within two years of the well publicized campaign for itemized bills, they were offered to consumers. In 1994, Bezeq acquired 50% ownership of Pelephone, Israel's first mobile communication company, in 2004 acquired full ownership of the company from its co-owner Motorola. In 1998, Bezeq co-founded Yes, a direct-broadcast satellite provider, which began broadcasting in July 2000. In January 2012, Bezeq International Optical System was completed, a submarine telecommunication cable linking Tel Aviv and Bari in Italy; the system spans 2,300 km of cable, extended terrestrially from Bari through Interoute's network to major European cities. In April 2012, Bezeq acquired full ownership of Walla! Communications, Israel's leading Internet portal, which has more than 2.5 Million monthly unique users. Bezeq operates the B144 directory enquiries and yellow pages brand. In February 2015, Bezeq acquired full ownership of Yes, Israel's leading television provider, for ₪680 million. In 2018 the company announced.
She is one of several Bezeq employees under investigation by the Israel Securities Authority and the Israel Police regarding Bezeq's purchase of Yes shares and allegations of improper dealings with the Israeli Ministry of Communication. In 2018, board members Shaul Elovitch, Or Elovitch and Orna Elovitch resigned as a result of Case 4000, an ongoing corruption investigation involving the Israeli Prime Minister Benjamin Netanyahu. In 1994, Cellcom a new Mobile communication company was founded, breaking Pelephone's monopoly in this area. In 1999, a third competitor, Partner Communications Company, was established. In 1997, two new competitors were introduced in international calling services, Bezeq was obliged to establish a new subsidiarity to compete with them named Bezeq International; until the mid-first decade of the 21st century when it was owned by the Israeli government, Bezeq had a monopoly on landline telephony and Internet access infrastructure. Though still the most dominant provider of telephone services, it has had competition from the sole cable provider in the country, which offers a cables based telephone and internet access services as of 2005, with 012 Smile and more 013 netvision and Orange.
On 9 May 2005, Israel's Government Companies Authority, headed by Eyal Gabbai privatized Bezeq when 30% of its shares were sold by the state to the Apax-Saban-Arkin investment group for $972 million. The cellular communications provider Pelephone is a owned subsidiary of Bezeq. Bezeq is the largest shareholder in D. B. S. Satellite Services Ltd. known by its trademark name, the DBS television provider in Israel. In April 2010, the controlling interest in Bezeq, held by the Apax-Saban-Arkin group, was sold to B Communications, a subsidiary of Shaul Elovitch's Eurocom Group, for $1.75 billion. In late 2017, bank filed a petition against Elovitch to break up Eurocom Group to pay back loans totaling $275 million; this would directly impact the 10% shareholding in Bezeq, including Elovitch's 26% controlling stake. Meir Shamir has expressed interest in buying a controlling stake cancelling the debt to the banks. Two other investors have expressed interest in purchasing a stake in Bezeq, including Argentine investor Eduardo Elsztain and Elliott Management, who announced they had purchased a 4,8% stake.
The company's fixed-line domestic communications segment offers domestic carrier services, including basic telephony, Internet infrastructure and access services, transmission and data communications services. This segment provides infrastructure, billing, leasing space, related services for other communications operators and maintains radio transmitters, carries out set-up and operation works of networks or sub-networks for various customers and offers virtual private networks, data center, search engine services; as of December 2012 Bezeq has: 2.27 million fixed-line customers 2.80 million mobile customers 1.17 million high-speed broadband customers 578,000 pay TV customers Pelephone Communications Ltd.: Israel's first cellular phone operator Bezeq International Ltd.: Provides customers with solutions in international telecom, data hosting, data communication, information security solutions. Yes: Yes is Israel's only provider of multi-channel television broadcasts via satellite to subscribers, was the first company to offer digital broadcasts and interactive television services.
Bezeq On-Line Ltd.: Provides outsourcing and call-center services. Walla! Communications: Israel's leading Internet portal. Bezeq Interna
A set-top box or set-top unit is an information appliance device that contains a TV-tuner input and displays output to a television set and an external source of signal, turning the source signal into content in a form that be displayed on the television screen or other display device. They are used in cable television, satellite television, over-the-air television systems, as well as other uses. According to the Los Angeles Times, the cost to a cable provider for a set-top box is between $150 for a basic box to $250 for a more sophisticated box in the United States. In 2016, the average pay-TV subscriber paid $231 per year to lease their set-top box from a cable service provider; the signal source might be an Ethernet cable, a satellite dish, a coaxial cable, a telephone line, broadband over power lines, or an ordinary VHF or UHF antenna. Content, in this context, could mean any or all of video, Internet web pages, interactive video games, or other possibilities. Satellite and microwave-based services require specific external receiver hardware, so the use of set-top boxes of various formats has never disappeared.
Set-top boxes can enhance source signal quality. Before the All-Channel Receiver Act of 1962 required US television receivers to be able to tune the entire VHF and UHF range, a set-top box known as a UHF converter would be installed at the receiver to shift a portion of the UHF-TV spectrum onto low-VHF channels for viewing; as some 1960s-era 12-channel TV sets remained in use for many years, Canada and Mexico were slower than the US to require UHF tuners to be factory-installed in new TVs, a market for these converters continued to exist for much of the 1970s. Cable television represented a possible alternative to deployment of UHF converters as broadcasts could be frequency-shifted to VHF channels at the cable head-end instead of the final viewing location. However, most cable systems could not accommodate the full 54-890 MHz VHF/UHF frequency range and the twelve channels of VHF space were exhausted on most systems. Adding any additional channels therefore needed to be done by inserting the extra signals into cable systems on nonstandard frequencies either below VHF channel 7 or directly above VHF channel 13.
These frequencies corresponded to non-television services over-the-air and were therefore not on standard TV receivers. Before cable-ready TV sets became common in the late 1980s, an electronic tuning device called a cable converter box was needed to receive the additional analog cable TV channels and transpose or convert the selected channel to analog radio frequency for viewing on a regular TV set on a single channel VHF channel 3 or 4; the box allowed an analog non-cable-ready television set to receive analog encrypted cable channels and was a prototype topology for date digital encryption devices. Newer televisions were converted to be analog cypher cable-ready, with the standard converter built-in for selling premium television. Several years and marketed, the advent of digital cable continued and increased the need for various forms of these devices. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCR compatibility and the ability to drive multiple TV sets, albeit with a somewhat nonstandard channel numbering scheme.
Newer television receivers reduced the need for external set-top boxes, although cable converter boxes continue to be used to descramble premium cable channels according to carrier-controlled access restrictions, to receive digital cable channels, along with using interactive services like video on demand, pay per view, home shopping through television. Set-top boxes were made to enable closed captioning on older sets in North America, before this became a mandated inclusion in new TV sets; some have been produced to mute the audio when profanity is detected in the captioning, where the offensive word is blocked. Some include a V-chip that allows only programs of some television content ratings. A function that limits children's time watching TV or playing video games may be built in, though some of these work on main electricity rather than the video signal; the transition to digital terrestrial television after the turn of the millennium left many existing television receivers unable to tune and display the new signal directly.
In the United States, where analog shutdown was completed in 2009 for full-service broadcasters, a federal subsidy was offered for coupon-eligible converter boxes with deliberately limited capability which would restore signals lost to digital transition. Professional set-top boxes are referred to as IRDs or integrated receiver/decoders in the professional broadcast audio/video industry, they are designed for rack mounting environments. IRDs are capable of outputting uncompressed serial digital interface signals, unlike consumer STBs which don't because of copyright reasons. Hybrid set-top boxes, such as those used for Smart TV programming, enable viewers to access multiple TV delivery methods. By integrating varying delivery streams, hybrids enable pay-TV operators more flexible application depl
In fiber-optic communications, wavelength-division multiplexing is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity; the term wavelength-division multiplexing is applied to an optical carrier, described by its wavelength, whereas frequency-division multiplexing applies to a radio carrier, more described by frequency. This is purely conventional because frequency communicate the same information. A WDM system uses a multiplexer at the transmitter to join the several signals together and a demultiplexer at the receiver to split them apart. With the right type of fiber, it is possible to have a device that does both and can function as an optical add-drop multiplexer; the optical filtering devices used have conventionally been etalons. As there are three different WDM types, whereof one is called "WDM", the notation "xWDM" is used when discussing the technology as such.
The concept was first published in 1978, by 1980 WDM systems were being realized in the laboratory. The first WDM systems combined only two signals. Modern systems can handle 160 signals and can thus expand a basic 100 Gbit/s system over a single fiber pair to over 16 Tbit/s. A system of 320 channels is present WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fiber. By using WDM and optical amplifiers, they can accommodate several generations of technology development in their optical infrastructure without having to overhaul the backbone network. Capacity of a given link can be expanded by upgrading the multiplexers and demultiplexers at each end; this is done by use of optical-to-electrical-to-optical translation at the edge of the transport network, thus permitting interoperation with existing equipment with optical interfaces. Most WDM systems operate on single-mode fiber optical cables. Certain forms of WDM can be used in multi-mode fiber cables which have core diameters of 50 or 62.5 µm.
Early WDM systems were complicated to run. However, recent standardization and better understanding of the dynamics of WDM systems have made WDM less expensive to deploy. Optical receivers, in contrast to laser sources, tend to be wideband devices. Therefore, the demultiplexer must provide the wavelength selectivity of the receiver in the WDM system. WDM systems are divided into three different wavelength patterns: normal and dense. Normal WDM uses the two normal wavelengths 1550 on one fiber. Coarse WDM provides up to 16 channels across multiple transmission windows of silica fibers. Dense WDM uses the C-Band transmission window but with denser channel spacing. Channel plans vary, but a typical DWDM system would use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing; some technologies are capable of 12.5 GHz spacing. New amplification options enable the extension of the usable wavelengths to the L-band, more or less doubling these numbers. Coarse wavelength division multiplexing, in contrast to DWDM, uses increased channel spacing to allow less-sophisticated and thus cheaper transceiver designs.
To provide 16 channels on a single fiber, CWDM uses the entire frequency band spanning the second and third transmission windows including the critical frequencies where OH scattering may occur. OH-free silica fibers are recommended if the wavelengths between second and third transmission windows is to be used. Avoiding this region, the channels 47, 49, 51, 53, 55, 57, 59, 61 remain and these are the most used. With OS2 fibers the water peak problem is overcome, all possible 18 channels can be used. WDM, CWDM and DWDM are based on the same concept of using multiple wavelengths of light on a single fiber but differ in the spacing of the wavelengths, number of channels, the ability to amplify the multiplexed signals in the optical space. EDFA provide an efficient wideband amplification for the C-band, Raman amplification adds a mechanism for amplification in the L-band. For CWDM, wideband optical amplification is not available, limiting the optical spans to several tens of kilometres; the term coarse wavelength division multiplexing was generic and described a number of different channel configurations.
In general, the choice of channel spacings and frequency in these configurations precluded the use of erbium doped fiber amplifiers. Prior to the recent ITU standardization of the term, one common definition for CWDM was two or more signals multiplexed onto a single fiber, with one signal in the 1550 nm band and the other in the 1310 nm band. In 2002, the ITU standardized a channel spacing grid for CWDM using the wavelengths from 1270 nm through 1610 nm with a channel spacing of 20 nm. ITU G.694.2 was revised in 2003 to shift the channel centers by 1 nm so speaking, the center wavelengths are 1271 to 1611 nm. Many CWDM wavelengths below 1470 nm are considered unusable on older G.652 specification fibers, due to the increased attenuation in the 1270–1470 nm bands. Newer fibers which conform to the G.652. C and G.652. D standards, such as Corning SMF-28e and Samsung Widepass, near
Network convergence refers to the provision of telephone and data communication services within a single network. In other words, one company provides services for all forms of communication. Network convergence is driven by development of technology and demand. Users are able to choose among more service providers. On the other hand, convergence allows service providers to adopt new business models, offer innovative services, enter new markets. One dictionary definition of “convergence” provides a starting point for the analysis: “the act of converging and esp. moving toward union or uniformity.” Convergence implies the integration of telecommunication and Internet network services. It allows a variety of providers to use different paths to transmit voice, video signals, data to homes and business. In the past, it was restricted to either communicating people by wire line or watching broadcast programming at the same time. Two-way communication has been limited to text by the limited availability of bandwidth.
Nowadays technology development, fierce competition, deregulation have transformed several distinct communications service markets into a converged market. In the telecommunications world, convergence has come to mean a moving towards the use of one medium as opposed to manipulation of all forms of information including voice and video across all types of network instead of carrying information separately within distinct networks. In the convergent network, different forms of information can be re-engineered to provide better, more flexible service to the user. For example, telephone networks can transmit data and video and cable networks are able to provide voice services... Convergence is of interacting with society; the basic type of network convergence is the combination and connection across platforms and networks, which allows several types of networks to connect with each other within certain common standard and protocol. The second type is the convergence of telecommunication service, which allows firms to use a single network to provide several communication services that traditionally required separate networks, called the triple play or quadruple play in the USA.
The third type is market convergence. The convergent network will stimulate mergers and collaborations among corporations. New business entities are created to offer multiple services and new, address different markets. Digital technology allows both traditional and new communication services – whether voice, sound or pictures – to be provided over many different networks. Whether at home, at the office, or in the classroom, people enjoy the conveniences and entertainment brought by convergence like video-on-demand, interactive television, the Internet, personal digital assistants, so on. Examples of products and services being delivered include: Home-banking and home-shopping over the Internet, Voice over Internet protocol. Unlike other countries or regions, the U. S. never adopted a formal convergence policy. Technological change is driving convergence from distinct telecommunications and media markets; the U. S. communications infrastructure is evolving from circuit-based networks, in which individual applications are woven into the network architecture, to Internet Protocol network, in which multiple applications ride on top of the physical network layer.
The Telecommunications Act of 1996 is a fundamental document for network convergence in the US. Before that time, the industry was characterized by service-specific networks that did not compete with another: circuit-switched networks provided telephone service and coaxial cable networks provided cable service; the 1996 Act introduced full competition into all telecommunications markets by abolishing the remaining legal entry barriers into local telecommunications services. The objective of the Act was to open up markets to competition and to create a regulatory framework for the transition from monopoly provision to competitive provision of telecommunications services: The conference report refers to the bill “to provide for a pro-competitive, de-regulatory national policy framework designed to accelerate private sector deployment of advanced information technologies and services to all Americans by opening all telecommunications markets to competition....” The Act created distinct regulatory regimes for these service-specific telephone networks and cable networks that included provisions intended to foster competition from new entrants that used network architectures and technologies similar to those of the incumbents.
The deployment of digital technologies in these distinct networks has led to market convergence and “intermodal” competition, as telephone and wireless networks are able to offer voice and video services over a single broadband platform. Timeline o
The Internet is the global system of interconnected computer networks that use the Internet protocol suite to link devices worldwide. It is a network of networks that consists of private, academic and government networks of local to global scope, linked by a broad array of electronic and optical networking technologies; the Internet carries a vast range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web, electronic mail and file sharing. Some publications no longer capitalize "internet"; the origins of the Internet date back to research commissioned by the federal government of the United States in the 1960s to build robust, fault-tolerant communication with computer networks. The primary precursor network, the ARPANET served as a backbone for interconnection of regional academic and military networks in the 1980s; the funding of the National Science Foundation Network as a new backbone in the 1980s, as well as private funding for other commercial extensions, led to worldwide participation in the development of new networking technologies, the merger of many networks.
The linking of commercial networks and enterprises by the early 1990s marked the beginning of the transition to the modern Internet, generated a sustained exponential growth as generations of institutional and mobile computers were connected to the network. Although the Internet was used by academia since the 1980s, commercialization incorporated its services and technologies into every aspect of modern life. Most traditional communication media, including telephony, television, paper mail and newspapers are reshaped, redefined, or bypassed by the Internet, giving birth to new services such as email, Internet telephony, Internet television, online music, digital newspapers, video streaming websites. Newspaper and other print publishing are adapting to website technology, or are reshaped into blogging, web feeds and online news aggregators; the Internet has enabled and accelerated new forms of personal interactions through instant messaging, Internet forums, social networking. Online shopping has grown exponentially both for major retailers and small businesses and entrepreneurs, as it enables firms to extend their "brick and mortar" presence to serve a larger market or sell goods and services online.
Business-to-business and financial services on the Internet affect supply chains across entire industries. The Internet has no single centralized governance in either technological implementation or policies for access and usage; the overreaching definitions of the two principal name spaces in the Internet, the Internet Protocol address space and the Domain Name System, are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers. The technical underpinning and standardization of the core protocols is an activity of the Internet Engineering Task Force, a non-profit organization of loosely affiliated international participants that anyone may associate with by contributing technical expertise. In November 2006, the Internet was included on USA Today's list of New Seven Wonders; when the term Internet is used to refer to the specific global system of interconnected Internet Protocol networks, the word is a proper noun that should be written with an initial capital letter.
In common use and the media, it is erroneously not capitalized, viz. the internet. Some guides specify that the word should be capitalized when used as a noun, but not capitalized when used as an adjective; the Internet is often referred to as the Net, as a short form of network. As early as 1849, the word internetted was used uncapitalized as an adjective, meaning interconnected or interwoven; the designers of early computer networks used internet both as a noun and as a verb in shorthand form of internetwork or internetworking, meaning interconnecting computer networks. The terms Internet and World Wide Web are used interchangeably in everyday speech. However, the World Wide Web or the Web is only one of a large number of Internet services; the Web is a collection of interconnected documents and other web resources, linked by hyperlinks and URLs. As another point of comparison, Hypertext Transfer Protocol, or HTTP, is the language used on the Web for information transfer, yet it is just one of many languages or protocols that can be used for communication on the Internet.
The term Interweb is a portmanteau of Internet and World Wide Web used sarcastically to parody a technically unsavvy user. Research into packet switching, one of the fundamental Internet technologies, started in the early 1960s in the work of Paul Baran and Donald Davies. Packet-switched networks such as the NPL network, ARPANET, the Merit Network, CYCLADES, Telenet were developed in the late 1960s and early 1970s; the ARPANET project led to the development of protocols for internetworking, by which multiple separate networks could be joined into a network of networks. ARPANET development began with two network nodes which were interconnected between the Network Measurement Center at the University of California, Los Angeles Henry Samueli School of Engineering and Applied Science directed by Leonard Kleinrock, the NLS system at SRI International by Douglas Engelbart in Menlo Park, California, on 29 October 1969; the third site was the Culler-Fried Interactive Mathematics Center at the University of California, Santa Barbara, followed by the University of
IP Multimedia Subsystem
The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem is an architectural framework for delivering IP multimedia services. Mobile phones have provided voice call services over a circuit-switched-style network, rather than over an IP packet-switched network. Alternative methods of delivering voice or other multimedia services have become available on smartphones, but they have not become standardized across the industry. IMS is an architectural framework to provide such standardization. IMS was designed by the wireless standards body 3rd Generation Partnership Project, as a part of the vision for evolving mobile networks beyond GSM, its original formulation represented an approach for delivering Internet services over GPRS. This vision was updated by 3GPP, 3GPP2 and ETSI TISPAN by requiring support of networks other than GPRS, such as Wireless LAN, CDMA2000 and fixed lines. IMS uses IETF protocols wherever possible, e.g. the Session Initiation Protocol. According to the 3GPP, IMS is not intended to standardize applications, but rather to aid the access of multimedia and voice applications from wireless and wireline terminals, i.e. to create a form of fixed-mobile convergence.
This is done by having a horizontal control layer that isolates the access network from the service layer. From a logical architecture perspective, services need not have their own control functions, as the control layer is a common horizontal layer. However, in implementation this does not map into greater reduced cost and complexity. Alternative and overlapping technologies for access and provisioning of services across wired and wireless networks include combinations of Generic Access Network, softswitches and "naked" SIP. Since it is becoming easier to access content and contacts using mechanisms outside the control of traditional wireless/fixed operators, the interest of IMS is being challenged. Examples of global standards based on IMS are MMTel, the basis for Voice over LTE and Rich Communication Services, known as joyn or Advanced Messaging. IMS defined by an industry forum called 3G. IP, formed in 1999. 3G. IP developed the initial IMS architecture, brought to the 3rd Generation Partnership Project, as part of their standardization work for 3G mobile phone systems in UMTS networks.
It first appeared in Release 5. Support for the older GSM and GPRS networks was provided. 3GPP2 based their CDMA2000 Multimedia Domain on 3GPP IMS, adding support for CDMA2000. 3GPP release 6 added interworking with WLAN, inter-operability between IMS using different IP-connectivity networks, routing group identities, multiple registration and forking, speech recognition and speech-enabled services. 3GPP release 7 added support for fixed networks by working together with TISPAN release R1.1, the function of AGCF and PES are introduced to the wire-line network for the sake of inheritance of services which can be provided in PSTN network. AGCF works as a bridge interconnecting the Megaco/H.248 networks. Megaco/H.248 networks offers the possibility to connect terminals of the old legacy networks to the new generation of networks based on IP networks. AGCF acts a SIP User agent towards the IMS and performs the role of P-CSCF. SIP User Agent functionality is included in the AGCF, not on the customer device but in the network itself.
Added voice call continuity between circuit switching and packet switching domain, fixed broadband connection to the IMS, interworking with non-IMS networks and charging control, emergency sessions. 3GPP release 8 added support for LTE / SAE, multimedia session continuity, enhanced emergency sessions and IMS centralized services. 3GPP release 9 added support for IMS emergency calls over GPRS and EPS, enhancements to multimedia telephony, IMS media plane security, enhancements to services centralization and continuity. 3GPP release 10 added support for inter device transfer, enhancements to the single radio voice call continuity, enhancements to IMS emergency sessions. 3GPP release 11 added USSD simulation service, network-provided location information for IMS, SMS submit and delivery without MSISDN in IMS, overload control. Each of the functions in the diagram is explained below; the IP multimedia core network subsystem is a collection of different functions, linked by standardized interfaces, which grouped form one IMS administrative network.
A function is not a node: An implementer is free to combine two functions in one node, or to split a single function into two or more nodes. Each node can be present multiple times in a single network, for dimensioning, load balancing or organizational issues; the user can connect to IMS in various ways, most of which use the standard IP. IMS terminals can register directly on IMS when they are roaming in another network or country; the only requirement is that they can run SIP user agents. Fixed access, mobile access and wireless access are all supported. Other phone systems like plain old telephone service, H.323 and non IMS-compatible systems, are supported through gateways. HSS – Home subscriber server: The home subscriber server, or user profile server function, is a master user database that supports the IMS network entities that actua