History of International Telephony Standards

Electric telegraphy became available to the general public in the late 1850s. But messages could not electrically cross national borders because each country used different coding systems. Messages had to be handed over at frontiers after someone transcribed and translated them. The messages then had to be retransmitted in the telegraph network of the neighboring country. Because of the overhead and the bottleneck created by this cumbersome way of working, many countries decided to make arrangements to aid the interconnection of their national networks. These arrangements were managed on a national level, meaning that countries often ended up having a huge number of separate agreements, depending on how many frontier localities they had on their borders. Because of the complexity of these arrangements, countries began making bilateral or regional agreements to simplify matters. But again, because of rapid expansion, a large number of bilateral or regional agreements had come into existence by 1864.

For the first time, 20 European countries were forced to develop a framework for international interconnection. This framework entailed uniform operating instructions, tariff and accounting rules, and common rules to standardize equipment to facilitate an international interconnection. It was published in 1865 and was known as the International Telegraph Convention. The International Telegraph Union (ITU) was established to facilitate subsequent amendments to this initial agreement. Ten years later, because of the invention and rapid deployment of telephony services, the ITU began recommending legislation governing the use of telephony.

By 1927 there were subcommittees known as the Consultative Committee for International Radio (CCIR), the Consultative Committee for International Telephone (CCIF), and the Consultative Committee for International Telegraph (CCIT).

In 1934 the International Telegraph Union changed its name to the present-day meaning—the ITU. By this time the ITU covered all forms of wireline and wireless communication.

In 1947 the ITU became a United Nations (UN) specialized agency. It has always operated from Geneva, Switzerland. The UN is responsible for worldwide telecommunications standardization. The ITU functions to this day under the auspices of the UN. Historically, nearly all national networks have been run by government-operated agencies (the "incumbents")—hence, the placement of the ITU within the UN.

In 1956 the CCIF and CCIT were combined and became the CCITT—the Consultative Committee for International Telegraph and Telephone.

When telecommunication networks were government monopolies, the ITU could have been considered the Parliament of monopoly telecommunications carriers. But during the 1980s, competition began to be seen in some countries following market deregulation. This is still putting pressure on the ITU to change and adapt.

In 1992 the ITU was dramatically remodeled with the aim of giving it greater flexibility to adapt to today's increasingly complex, interactive, and competitive environment. It was split into three sectors corresponding to its three main areas of activity: telecommunication standardization (ITU-T), radio communication (ITU-R), and telecommunication development (ITU-D). The CCITT that had been established in 1956 as part of the ITU ceased to exist and became the ITU-T.

The ITU-T continues to refine and develop international standards for SS7 protocols, intelligent networks, and bearer/signaling transport over IP.

ITU-T (Formerly CCITT) International Standards

The ITU has been creating worldwide telephony standards since the invention of the telephone network. It is the international standards body for the telecom industry worldwide. The ITU first appeared in 1865 when it produced the first cross-country telegraphy standards. Membership in the ITU is open to all governments that belong to the UN; these are called member states. Equipment vendors, telecommunication research institutions, and regional telecommunication organizations can now also hold membership; they are called sector members. For example, Cisco Systems and the European Telecommunications Standards Institute (ETSI) are vendor and regional organization sector members. Members are required to pay a membership fee.

The CCITT had a fixed four-year study period in which to publish standards, which it called recommendations. The term recommendation reflects the fact that member states do not have to adopt them, although they are proposed as an international standard. The industry, however, views them as standards. With the role of government diminishing, it makes even greater sense as time goes by to view the recommendations as standards. Recommendations are available for a fee.

If a recommendation was ready before the end of the four-year period, it could not be endorsed until it was approved by the CCITT at the end of the four-year period at a formal meeting (plenary assembly meeting). After being endorsed, the recommendations were published en bloc in sets. The covers were a different color for every study period. For example, Blue Book refers to the 1988 recommendations, and Red Book refers to the 1984 recommendations.

A fresh set of standards every four years did not fare well in the accelerating telecommunications industry. When the CCITT was rebranded the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) in 1992, the notion of a fixed four-year period was dropped. Instead, the study groups were given greater autonomy so that they could approve their recommendations themselves without having to wait for a full ITU meeting at the end of every four years. The last issue of the "CCITT colored books" was the Blue Book (1988). From 1992 onward, the recommendations were published in separate booklets and weren't grouped for publishing en bloc every four years (at the end of every study period). Because the ITU-T recommendations had no cover color as they had under the CCITT, people have referred to them as "White Book" editions. Therefore, references to White Books implies separate booklets and not grouped books.

This book is primarily focused on ITU-T international standards and the North American American National Standards Institute (ANSI) regional standards. The C7 protocols are covered in the ITU Q series of recommendations, switching and signaling—specifically, the Q.7xx series—because these specifications are concerned with what we may now, in hindsight, call the core/traditional C7 protocols. Table 2-1 lists the ITU Q.7xx series.

Table 2-1. ITU Core/Traditional C7 Recommendations

Recommendation	Title
Q.700	Introduction to CCITT SS7
Q.701	Functional description of the message transfer part (MTP) of SS7
Q.702	Signaling data link
Q.703	Signaling link
Q.704	Signaling network functions and messages
Q.705	Signaling network structure
Q.706	Message transfer part signaling performance
Q.707	Testing and maintenance
Q.708	Assignment procedures for international signaling point codes
Q.709	Hypothetical signaling reference connection
Q.710	Simplified MTP version for small systems
Q.711	Functional description of the signaling connection control part
Q.712	Definition and function of signaling connection control part messages
Q.713	Signaling connection control part formats and codes
Q.714	Signaling connection control part procedures
Q.715	Signaling connection control part user guide
Q.716	SS7— Signaling connection control part (SCCP) performance
Q.721	Functional description of the SS7 Telephone User Part (TUP)
Q.722	General function of telephone messages and signals
Q.723	Telephone user part formats and codes
Q.724	Telephone user part signaling procedures
Q.725	Signaling performance in the telephone application
Q.730	ISDN user part supplementary services
Q.731.1	Direct dialing in (DDI)
Q.731.3	Calling line identification presentation (CLIP)
Q.731.4	Calling line identification restriction (CLIR)
Q.731.5	Connected line identification presentation (COLP)
Q.731.6	Connected line identification restriction (COLR)
Q.731.7	Malicious call identification (MCID)
Q.731.8	Subaddressing (SUB)
Q.732.2	Call diversion services
Q.732.7	Explicit Call Transfer
Q.733.1	Call waiting (CW)
Q.733.2	Call hold (HOLD)
Q.733.3	Completion of calls to busy subscriber (CCBS)
Q.733.4	Terminal portability (TP)
Q.733.5	Completion of calls on no reply
Q.734.1	Conference calling
Q.734.2	Three-party service
Q.735.1	Closed user group (CUG)
Q.735.3	Multilevel precedence and preemption
Q.735.6	Global Virtual Network Service (GVNS)
Q.736.1	International Telecommunication Charge Card (ITCC)
Q.736.3	Reverse charging (REV)
Q.737.1	User-to-user signaling (UUS)
Q.741	SS7— Data user part
Q.750	Overview of SS7 management
Q.751.1	Network element management information model for the Message Transfer Part (MTP)
Q.751.2	Network element management information model for the Signaling Connection Control Part
Q.751.3	Network element information model for MTP accounting
Q.751.4	Network element information model for SCCP accounting and accounting verification
Q.752	Monitoring and measurements for SS7 networks
Q.753	SS7 management functions MRVT, SRVT, CVT, and definition of the OMASE-user
Q.754	SS7 management Application Service Element (ASE) definitions
Q.755	SS7 protocol tests
Q.755.1	MTP Protocol Tester
Q.755.2	Transaction capabilities test responder
Q.756	Guidebook to Operations, Maintenance, and Administration Part (OMAP)
Q.761	SS7— ISDN User Part functional description
Q.762	SS7— ISDN User Part general functions of messages and signals
Q.763	SS7— ISDN User Part formats and codes
Q.764	SS7— ISDN User Part signaling procedures
Q.765	SS7— Application transport mechanism
Q.765bis	SS7— Application Transport Mechanism: Test Suite Structure and Test Purposes (TSS & TP)
Q.765.1bis	Abstract test suite for the APM support of VPN applications
Q.765.1	SS7— Application transport mechanism: Support of VPN applications with PSS1 information flows
Q.765.4	SS7— Application transport mechanism: Support of the generic addressing and transport protocol
Q.765.5	SS7— Application transport mechanism: Bearer Independent Call Control (BICC)
Q.766	Performance objectives in the integrated services digital network application
Q.767	Application of the ISDN user part of CCITT SS7 for international ISDN interconnections
Q.768	Signaling interface between an international switching center and an ISDN satellite subnetwork
Q.769.1	SS7— ISDN user part enhancements for the support of number portability
Q.771	Functional description of transaction capabilities
Q.772	Transaction capabilities information element definitions
Q.773	Transaction capabilities formats and encoding
Q.774	Transaction capabilities procedures
Q.775	Guidelines for using transaction capabilities
Q.780	SS7 test specification—General description
Q.781	MTP level 2 test specification
Q.782	MTP level 3 test specification
Q.783	TUP test specification
Q.784	TTCN version of Recommendation Q.784
Q.784.1	Validation and compatibility for ISUP '92 and Q.767 protocols
Q.784.2	Abstract test suite for ISUP '92 basic call control procedures
Q.784.3	ISUP '97 basic call control procedures—TSS & TP
Q.785	ISUP protocol test specification for supplementary services
Q.785.2	ISUP '97 supplementary services—TSS & TP
Q.786	SCCP test specification
Q.787	Transaction Capabilities (TC) test specification
Q.788	User network interface-to-user network interface compatibility test specifications for ISDN, non-ISDN, and undetermined accesses interworking over international ISUP
Q.795	OMAP

Within the ITU-T, Study Group 11 (SG11) is responsible for signaling recommendations. The output from SG11 (recommendations), in addition to setting a standard for the global level, also serves as the basis for study at regional, national, and industry levels. SG11 is also responsible for signaling protocols for ISDN (narrowband and broadband), network intelligence, mobility, and signaling transport mechanisms.