70-402: Signalling System No. 7 ( SS7 ) is a set of telephony signaling protocols developed in the 1970s that is used to set up and tear down telephone calls on most parts of the global public switched telephone network (PSTN). The protocol also performs number translation, local number portability , prepaid billing, Short Message Service (SMS), and other services. The protocol was introduced in
140-556: A T1 facility. One or more signaling links can be connected to the same two endpoints that together form a signaling link set. Signaling links are added to link sets to increase the signaling capacity of the link set. In Europe, SS7 links normally are directly connected between switching exchanges using F-links. This direct connection is called associated signaling . In North America, SS7 links are normally indirectly connected between switching exchanges using an intervening network of STPs (Signalling Transfer Points). This indirect connection
210-604: A German mobile service provider, confirmed that the SS7 vulnerabilities had been exploited to bypass two-factor authentication to achieve unauthorized withdrawals from bank accounts. The perpetrators installed malware on compromised computers, allowing them to collect online banking account credentials and telephone numbers. They set up redirects for the victims' telephone numbers to telephone lines controlled by them. Confirmation calls and SMS text messages of two-factor authentication procedures were routed to telephone numbers controlled by
280-510: A charter that describes its focus; and what it is expected to produce, and when. It is open to all who want to participate and holds discussions on an open mailing list . Working groups hold open sessions at IETF meetings, where the onsite registration fee in 2024 was between US$ 875 (early registration) and $ 1200 per person for the week. Significant discounts are available for students and remote participants. As working groups do not make decisions at IETF meetings, with all decisions taken later on
350-674: A cooperative agreement, No. NCR-8820945, wherein CNRI agreed to create and provide a "secretariat" for the "overall coordination, management and support of the work of the IAB, its various task forces and, particularly, the IETF". In 1992, CNRI supported the formation and early funding of the Internet Society, which took on the IETF as a fiscally sponsored project, along with the IAB, the IRTF, and
420-556: A high-speed and high-performance packet-based communications protocol, can communicate significant amounts of information when setting up a call, during the call, and at the end of the call. This permits rich call-related services to be developed. Some of the first such services were call management related, call forwarding (busy and no answer) , voice mail , call waiting , conference calling , calling name and number display , call screening , malicious caller identification , busy callback . The earliest deployed upper-layer protocols in
490-586: A phone, and detect IMSI-catchers that allow call interception and other activities. In February 2016, 30% of the network of the largest mobile operator in Norway, Telenor , became unstable due to "unusual SS7 signaling from another European operator". The security vulnerabilities of SS7 have been highlighted in U.S. governmental bodies, for example when in April 2016 Congressman Ted Lieu called for an oversight committee investigation. In May 2017, O2 Telefónica ,
560-478: A transport based upon IP, the SIGTRAN protocols are not an SS7 variant, but simply transport existing national and international variants of SS7. Signaling in telephony is the exchange of control information associated with the setup and release of a telephone call on a telecommunications circuit. Examples of control information are the digits dialed by the caller and the caller's billing number. When signaling
630-477: A voice channel, leading to significant savings and performance increases in both signaling and channel usage. Because of the mechanisms in use by signaling methods prior to SS7 (battery reversal, multi-frequency digit outpulsing , A- and B-bit signaling ), these earlier methods cannot communicate much signaling information. Usually only the dialed digits are signaled during call setup. For charged calls, dialed digits and charge number digits are outpulsed. SS7, being
700-746: A voice channel. Since 1975, CCS protocols have been developed by major telephone companies and the International Telecommunication Union Telecommunication Standardization Sector (ITU-T); in 1977 the ITU-T defined the first international CCS protocol as Signaling System No. 6 (SS6). In its 1980 Yellow Book Q.7XX-series recommendations ITU-T defined the Signalling System No. 7 as an international standard. SS7 replaced SS6 with its restricted 28-bit signal unit that
770-540: Is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and all its participants are volunteers. Their work is usually funded by employers or other sponsors. The IETF was initially supported by the federal government of the United States but since 1993 has operated under
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#1732790487535840-506: Is able to convey multiple items of formation (e.g. multiple digits of the called telephone number). Subscriber signaling refers to the signaling between the telephone and the telephone exchange . Trunk signaling is the signaling between exchanges. Every signaling system can be characterized along each of the above axes of classification. A few examples: Whereas common-channel signaling systems are out-of-band by definition, and in-band signaling systems are also necessarily channel-associated,
910-421: Is also standardizing protocols for autonomic networking that enables networks to be self managing. It is a network of physical objects or things that are embedded with electronics, sensors, software and also enables objects to exchange data with operator, manufacturer and other connected devices. Several IETF working groups are developing protocols that are directly relevant to IoT . Its development provides
980-700: Is available from these statistics. The IETF chairperson is selected by the NomCom process for a two-year renewable term. Before 1993, the IETF Chair was selected by the IAB. A list of the past and current chairs of the IETF: The IETF works on a broad range of networking technologies which provide foundation for the Internet's growth and evolution. It aims to improve the efficiency in management of networks as they grow in size and complexity. The IETF
1050-426: Is called C7 (CCITT number 7), number 7 and Common Channel Interoffice Signaling 7 (CCIS7). In Germany, it is often called Zentraler Zeichengabekanal Nummer 7 (ZZK-7). Signaling System No. 5 and earlier systems use in-band signaling , in which the call-setup information is sent by generating special multi-frequency tones transmitted on the telephone line audio channels, also known as bearer channels . Since
1120-538: Is called quasi-associated signaling , which reduces the number of SS7 links necessary to interconnect all switching exchanges and SCPs in an SS7 signaling network. SS7 links at higher signaling capacity (1.536 and 1.984 Mbit/s, simply referred to as the 1.5 Mbit/s and 2.0 Mbit/s rates) are called high-speed links (HSL) in contrast to the low speed (56 and 64 kbit/s) links. High-speed links are specified in ITU-T Recommendation Q.703 for
1190-531: Is called the Network Service Part (NSP). SCCP completes the functions of the OSI network layer: end-to-end addressing and routing, connectionless messages (UDTs), and management services for users of the Network Service Part (NSP). Telephone User Part (TUP) is a link-by-link signaling system used to connect calls. ISUP is the key user part, providing a circuit-based protocol to establish, maintain, and end
1260-407: Is concerned with conveying addressing information, such as the calling and/or called telephone number . In the early days of telephony , with operator handling calls, the addressing formation is by voice as "Operator, connect me to Mr. Smith please". In the first half of the 20th century, addressing formation is done by using a rotary dial , which rapidly breaks the line current into pulses , with
1330-609: Is identified on the network by a number, a signaling point code. Extended services are provided by a database interface at the SCP level using the SS7 network. The links between nodes are full-duplex 56, 64, 1,536, or 1,984 kbit/s graded communications channels. In Europe they are usually one (64 kbit/s) or all (1,984 kbit/s) timeslots ( DS0s ) within an E1 facility; in North America one (56 or 64 kbit/s) or all (1,536 kbit/s) timeslots ( DS0As or DS0s) within
1400-428: Is network efficiency. With in-band signaling, the voice channel is used during call setup which makes it unavailable for actual traffic. For long-distance calls, the talk path may traverse several nodes which reduces usable node capacity. With SS7, the connection is not established between the end points until all nodes on the path confirm availability. If the far end is busy, the caller gets a busy signal without consuming
1470-407: Is not the predominant choice of modes in North America. When operating in the quasi-associated mode , SS7 signaling progresses from the originating switch to the terminating switch, following a path through a separate SS7 signaling network composed of signal transfer points . This mode is more economical for large networks with lightly loaded signaling links. The quasi-associated mode of signaling
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#17327904875351540-598: Is on implementing code that will improve standards in terms of quality and interoperability. The details of IETF operations have changed considerably as the organization has grown, but the basic mechanism remains publication of proposed specifications, development based on the proposals, review and independent testing by participants, and republication as a revised proposal, a draft proposal, or eventually as an Internet Standard. IETF standards are developed in an open, all-inclusive process in which any interested individual can participate. All IETF documents are freely available over
1610-452: Is on the IETF meetings page. The IETF strives to hold its meetings near where most of the IETF volunteers are located. IETF meetings are held three times a year, with one meeting each in Asia, Europe and North America. An occasional exploratory meeting is held outside of those regions in place of one of the other regions. The IETF also organizes hackathons during the IETF meetings. The focus
1680-569: Is overseen by an area director (AD), with most areas having two ADs. The ADs are responsible for appointing working group chairs. The area directors, together with the IETF Chair, form the Internet Engineering Steering Group (IESG), which is responsible for the overall operation of the IETF. The Internet Architecture Board (IAB) oversees the IETF's external relationships. The IAB provides long-range technical direction for Internet development. The IAB also manages
1750-401: Is performed on the same circuit as the conversation of the call, it is termed channel-associated signaling (CAS). This is the case for analogue trunks, multi-frequency (MF) and R2 digital trunks, and DSS1/DASS PBX trunks. In contrast, SS7 uses common channel signaling , in which the path and facility used by the signaling is separate and distinct from the signaling without first seizing
1820-561: Is responsible for day-to-day management of the IETF. It receives appeals of the decisions of the working groups, and the IESG makes the decision to progress documents in the standards track . The chair of the IESG is the area director of the general area, who also serves as the overall IETF chair. Members of the IESG include the two directors, sometimes three, of each of the following areas: Liaison and ex officio members include: The Gateway Algorithms and Data Structures (GADS) Task Force
1890-476: Is the exchange of call control information within the same physical channel, or within the same frequency band, that the message (the callers' voice) is using. An example is dual-tone multi-frequency signaling (DTMF), which is used on most telephone lines to customer premises. Out-of-band signaling is telecommunication signaling on a dedicated channel separate from that used for the message. Out-of-band signaling has been used since Signaling System No. 6 (SS6)
1960-535: Is the exchange of signaling information during the middle of a call. SS7 also enables Non-Call-Associated Signaling, which is signaling not directly related to establishing a telephone call. This includes the exchange of registration information used between a mobile telephone and a home location register database, which tracks the location of the mobile. Other examples include Intelligent Network and local number portability databases. Apart from signaling with these various degrees of association with call set-up and
2030-434: Is the predominant choice of modes in North America. SS7 separates signaling from the voice circuits. An SS7 network must be made up of SS7-capable equipment from end to end in order to provide its full functionality. The network can be made up of several link types (A, B, C, D, E, and F) and three signaling nodes – Service Switching Points (SSPs), Signal Transfer Points (STPs), and Service Control Points (SCPs). Each node
2100-740: The BT IUP , Telephone User Part (TUP) , or the ISDN User Part (ISUP), the User Part provides layer 7. Currently there are no protocol components that provide OSI layers 4 through 6. The Transaction Capabilities Application Part (TCAP) is the primary SCCP User in the Core Network, using SCCP in connectionless mode. SCCP in connection oriented mode provides transport layer for air interface protocols such as BSSAP and RANAP . TCAP provides transaction capabilities to its Users (TC-Users), such as
2170-701: The Bureau of Investigative Journalism revealed that the SS7 protocol was exploited in an attempt to locate Sheikha Latifa bint Mohammed Al Maktoum (II) on 3 March 2018, a day before her abduction. In 2024, Kevin Briggs, an official at the Cybersecurity and Infrastructure Security Agency , reported to the FCC that hacks related to SS7 and Diameter had been used "numerous attempts" to acquire location data, voice and text messages, deliver spyware, and influence voters in
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2240-648: The European Telecommunications Standards Institute (ETSI). National variants with striking characteristics are the Chinese and Japanese Telecommunication Technology Committee (TTC) national variants. SS7 has been shown to have several security vulnerabilities, allowing location tracking of callers, interception of voice data, intercept two-factor authentication keys, and possibly the delivery of spyware to phones. The Internet Engineering Task Force (IETF) has defined
2310-722: The Internet Protocol . The protocols for SIGTRAN are M2PA , M2UA , M3UA and SUA . The SS7 protocol stack may be partially mapped to the OSI Model of a packetized digital protocol stack. OSI layers 1 to 3 are provided by the Message Transfer Part (MTP) and the Signalling Connection Control Part (SCCP) of the SS7 protocol (together referred to as the Network Service Part (NSP)); for circuit related signaling, such as
2380-635: The Internet Research Task Force (IRTF), with which the IETF has a number of cross-group relations. A nominating committee (NomCom) of ten randomly chosen volunteers who participate regularly at meetings, a non-voting chair and 4-5 liaisons, is vested with the power to appoint, reappoint, and remove members of the IESG, IAB, IETF Trust and the IETF LLC. To date, no one has been removed by a NomCom, although several people have resigned their positions, requiring replacements. In 1993
2450-541: The MTP and connection-oriented services of the SCCP . For each active mobile equipment one signalling connection is used by BSSAP having at least one active transactions for the transfer of messages. BSSAP provides two kinds of functions: In 2008, several SS7 vulnerabilities were published that permitted the tracking of mobile phone users. In 2014, the media reported a protocol vulnerability of SS7 by which anyone can track
2520-640: The Mobile Application Part , the Intelligent Network Application Part and the CAMEL Application Part . The Message Transfer Part (MTP) covers a portion of the functions of the OSI network layer including: network interface, information transfer, message handling and routing to the higher levels. Signaling Connection Control Part (SCCP) is at functional Level 4. Together with MTP Level 3 it
2590-627: The SIGTRAN protocol suite that implements levels 2, 3, and 4 protocols compatible with SS7. Sometimes also called Pseudo SS7 , it is layered on the Stream Control Transmission Protocol (SCTP) transport mechanism for use on Internet Protocol networks, such as the Internet . In North America, SS7 is also often referred to as Common Channel Signaling System 7 (CCSS7) (or CCS7). In the United Kingdom , it
2660-413: The 1.5 Mbit/s and 2.0 Mbit/s rates, and ANSI Standard T1.111.3 for the 1.536 Mbit/s rate. There are differences between the specifications for the 1.5 Mbit/s rate. High-speed links utilize the entire bandwidth of a T1 (1.536 Mbit/s) or E1 (1.984 Mbit/s) transmission facility for the transport of SS7 signaling messages. SIGTRAN provides signaling using SCTP associations over
2730-641: The Bell System in the United States by the name Common Channel Interoffice Signaling in the 1970s for signalling between No. 4E SS switch and No. 4A crossbar toll offices. The SS7 protocol is defined for international use by the Q.700-series recommendations of 1988 by the ITU-T . Of the many national variants of the SS7 protocols, most are based on variants standardized by the American National Standards Institute (ANSI) and
2800-591: The IETF changed from an activity supported by the US federal government to an independent, international activity associated with the Internet Society , a US-based 501(c)(3) organization . In 2018 the Internet Society created a subsidiary, the IETF Administration LLC, to be the corporate, legal and financial home for the IETF. IETF activities are funded by meeting fees, meeting sponsors and by
2870-523: The ISDN, and the predominant telephone service is still Plain Old Telephone Service . Due to its richness and the need for an out-of-band channel for its operation, SS7 is mostly used for signaling between telephone switches and not for signaling between local exchanges and customer-premises equipment . Because SS7 signaling does not require seizure of a channel for a conversation prior to
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2940-620: The ISOC's board of directors. In 2018, ISOC established The IETF Administration LLC, a separate LLC to handle the administration of the IETF. In 2019, the LLC issued a call for proposals to provide secretariat services to the IETF. The first IETF meeting was attended by 21 US federal government-funded researchers on 16 January 1986. It was a continuation of the work of the earlier GADS Task Force. Representatives from non-governmental entities (such as gateway vendors ) were invited to attend starting with
3010-644: The Internet Society via its organizational membership and the proceeds of the Public Interest Registry . In December 2005, the IETF Trust was established to manage the copyrighted materials produced by the IETF. The Internet Engineering Steering Group (IESG) is a body composed of the Internet Engineering Task Force (IETF) chair and area directors. It provides the final technical review of Internet standards and
3080-481: The Internet Standards process, the Internet Standards or their technical content". In 1998, CNRI established Foretec Seminars, Inc. (Foretec), a for-profit subsidiary to take over providing secretariat services to the IETF. Foretec provided these services until at least 2004. By 2013, Foretec was dissolved. In 2003, IETF's RFC 3677 described IETFs role in appointing three board members to
3150-588: The Internet and can be reproduced at will. Multiple, working, useful, interoperable implementations are the chief requirement before an IETF proposed specification can become a standard. Most specifications are focused on single protocols rather than tightly interlocked systems. This has allowed the protocols to be used in many different systems, and its standards are routinely re-used by bodies which create full-fledged architectures (e.g. 3GPP IMS ). Because it relies on volunteers and uses "rough consensus and running code" as its touchstone, results can be slow whenever
3220-645: The SS7 suite were dedicated to the setup, maintenance, and release of telephone calls. The Telephone User Part (TUP) was adopted in Europe and the Integrated Services Digital Network (ISDN) User Part ( ISUP ) adapted for public switched telephone network (PSTN) calls was adopted in North America. ISUP was later used in Europe when the European networks upgraded to the ISDN. As of 2020 North America has not accomplished full upgrade to
3290-441: The US. Telephony signaling In telecommunications , signaling is the use of signals for controlling communications . This may constitute an information exchange concerning the establishment and control of a telecommunication circuit and the management of the network. Signaling systems may be classified based on several principal characteristics. In the public switched telephone network (PSTN), in-band signaling
3360-507: The above metering pulse example demonstrates that there exist channel-associated signaling systems which are out-of-band. Internet Engineering Task Force Early research and development: Merging the networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: The Internet Engineering Task Force ( IETF )
3430-459: The advent of digital trunks , supervision signals are carried by robbed bits or other bits in the E1-carrier dedicated to signaling. Line signaling is concerned with conveying information on the state of the line or channel, such as on-hook, off-hook (answer supervision and disconnect supervision, together referred to as supervision ), ringing , and hook flash . Register signaling
3500-471: The attackers. This enabled them to log into victims' online bank accounts and effect money transfers. In March 2018, a method was published for the detection of the vulnerabilities, through the use of open-source monitoring software such as Wireshark and Snort . The nature of SS7 normally being used between consenting network operators on dedicated links means that any bad actor's traffic can be traced to its source. An investigation by The Guardian and
3570-418: The auspices of the Internet Society , a non-profit organization with local chapters around the world. There is no membership in the IETF. Anyone can participate by signing up to a working group mailing list, or registering for an IETF meeting. The IETF operates in a bottom-up task creation mode, largely driven by working groups. Each working group normally has appointed two co-chairs (occasionally three);
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#17327904875353640-538: The bearer channels are directly accessible by users, they can be exploited with devices such as the blue box , which can replicate the tones used by the network for call control and routing. As a remedy, SS6 and SS7 implements out-of-band signaling, carried in a separate signaling channel, thus keeping the call control and speech paths separate. SS6 and SS7 are referred to as common-channel signaling (CCS) protocols, or Common Channel Interoffice Signaling (CCIS) systems. Another element of in-band signaling addressed by SS7
3710-431: The call being routed to a particular subscription switch at which service logic would be executed, but permits service logic to be distributed throughout the telephone network and executed more expediently at originating switches far in advance of call routing. It also permits the subscriber increased mobility due to the decoupling of service logic from the subscription switch. Another ISUP characteristic SS7 with NFAS enables
3780-622: The connections for calls. Transaction Capabilities Application Part (TCAP) is used to create database queries and invoke advanced network functionality, or links to Intelligent Network Application Part (INAP) for intelligent networks, or Mobile Application Part (MAP) for mobile services. BSS Application Part ( BSSAP ) is a protocol in SS7 used by the Mobile Switching Center (MSC) and the Base station subsystem (BSS) to communicate with each other using signaling messages supported by
3850-470: The event a deficit occurs, CNRI has agreed to contribute up to USD$ 102,000 to offset it." In 1993, Cerf continued to support the formation of ISOC while working for CNRI, and the role of ISOC in "the official procedures for creating and documenting Internet Standards" was codified in the IETF's RFC 1602 . In 1995, IETF's RFC 2031 describes ISOC's role in the IETF as being purely administrative, and ISOC as having "no influence whatsoever on
3920-405: The exchange of control information, non-facility associated signaling (NFAS) became possible. NFAS is signaling that is not directly associated with the path that a conversation will traverse and may concern other information located at a centralized database such as service subscription, feature activation, and service logic. This makes possible a set of network-based services that do not rely upon
3990-516: The facilities used to carry calls, SS7 is designed to operate in two modes: associated mode and quasi-associated mode . When operating in the associated mode , SS7 signaling progresses from switch to switch through the Public Switched Telephone Network following the same path as the associated facilities that carry the telephone call. This mode is more economical for small networks. The associated mode of signaling
4060-459: The fourth IETF meeting in October 1986. Since that time all IETF meetings have been open to the public. Initially, the IETF met quarterly, but from 1991, it has been meeting three times a year. The initial meetings were very small, with fewer than 35 people in attendance at each of the first five meetings. The maximum attendance during the first 13 meetings was only 120 attendees. This occurred at
4130-436: The movements of mobile phone users from virtually anywhere in the world with a success rate of approximately 70%. In addition, eavesdropping is possible by using the protocol to forward calls and also facilitate decryption by requesting that each caller's carrier release a temporary encryption key to unlock the communication after it has been recorded. The software tool SnoopSnitch can warn when certain SS7 attacks occur against
4200-506: The number of pulses conveying the address. Finally, starting in the second half of the century, address signaling is by DTMF . Channel-associated signaling (CAS) employs a signaling channel that is dedicated to a specific bearer channel . Common-channel signaling (CCS) employs a signaling channel which conveys signaling information relating to multiple bearer channels. These bearer channels, therefore, have their signaling channel in common. Compelled signaling refers to signaling where
4270-423: The number of volunteers is either too small to make progress, or so large as to make consensus difficult, or when volunteers lack the necessary expertise. For protocols like SMTP , which is used to transport e-mail for a user community in the many hundreds of millions, there is also considerable resistance to any change that is not fully backward compatible , except for IPv6 . Work within the IETF on ways to improve
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#17327904875354340-419: The organization of annual INET meetings. Gross continued to serve as IETF chair throughout this transition. Cerf, Kahn, and Lyman Chapin announced the formation of ISOC as "a professional society to facilitate, support, and promote the evolution and growth of the Internet as a global research communications infrastructure". At the first board meeting of the Internet Society, Cerf, representing CNRI, offered, "In
4410-473: The receipt of each signal from an originating register needs to be explicitly acknowledged before the next signal can be sent. Most forms of R2 register signaling are compelled, while R1 multi-frequency signaling is not. The term is only relevant in the case of signaling systems that use discrete signals (e.g. a combination of tones to denote one digit), as opposed to signaling systems which are message-oriented (such as SS7 and ISDN Q.931) where each message
4480-525: The speed of the standards-making process is ongoing but, because the number of volunteers with opinions on it is very great, consensus on improvements has been slow to develop. The IETF cooperates with the W3C , ISO / IEC , ITU , and other standards bodies. Statistics are available that show who the top contributors by RFC publication are. While the IETF only allows for participation by individuals, and not by corporations or governments, sponsorship information
4550-543: The twelfth meeting, held during January 1989. These meetings have grown in both participation and scope a great deal since the early 1990s; it had a maximum attendance of 2810 at the December 2000 IETF held in San Diego, California . Attendance declined with industry restructuring during the early 2000s, and is currently around 1200. The locations for IETF meetings vary greatly. A list of past and future meeting locations
4620-490: The working group mailing list , meeting attendance is not required for contributors. Rough consensus is the primary basis for decision making. There are no formal voting procedures. Each working group is intended to complete work on its topic and then disband. In some cases, the working group will instead have its charter updated to take on new tasks as appropriate. The working groups are grouped into areas by subject matter ( see § Steering group , below ). Each area
4690-573: Was Mike Corrigan, who was then the technical program manager for the Defense Data Network (DDN). Also in 1986, after leaving DARPA, Robert E. Kahn founded the Corporation for National Research Initiatives (CNRI), which began providing administrative support to the IETF. In 1987, Corrigan was succeeded as IETF chair by Phill Gross. Effective March 1, 1989, but providing support dating back to late 1988, CNRI and NSF entered into
4760-566: Was both limited in function and not amendable to digital systems. SS7 also replaced Signaling System No. 5 (SS5), while R1 and R2 variants are still used in numerous countries. The Internet Engineering Task Force (IETF) defined SIGTRAN protocols which translate the common channel signaling paradigm to the IP Message Transfer Part (MTP) level 2 (M2UA and M2PA), Message Transfer Part (MTP) level 3 ( M3UA ) and Signaling Connection Control Part (SCCP) (SUA). While running on
4830-501: Was introduced in the 1970s, and also in Signalling System No. 7 (SS7) in 1980 which became the standard for signaling among exchanges internationally. In the mid-20th century, supervision signals on long-distance trunks in North America were primarily in-band, for example at 2600 Hz , necessitating a notch filter to prevent interference. Late in the century, all supervisory signals had been moved out of band. With
4900-646: Was the precursor to the IETF. Its chairman was David L. Mills of the University of Delaware . In January 1986, the Internet Activities Board (IAB; now called the Internet Architecture Board) decided to divide GADS into two entities: an Internet Architecture (INARC) Task Force chaired by Mills to pursue research goals, and the IETF to handle nearer-term engineering and technology transfer issues. The first IETF chair
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