History of SS7

The first specification (called a recommendation by the CCITT/ITU-T) of CCITT Signaling System No. 7 was published in 1980 in the form of the CCITT yellow book recommendations. After the yellow book recommendations, CCITT recommendations were approved at the end of a four-year study period. They were published in a colored book representing that study period.

Table 4-1 provides an evolutionary time line of CCITT/ITU-T SS7.

Table 4-1. CCITT/ITU-T SS7 Timeline

Year	Publication	Protocols Revised or Added
1980	CCITT Yellow Book	MTP2, MTP3, and TUP, first publication.
1984	CCITT Red Book	MTP2, MTP3, and TUP revised. SCCP and ISUP added.
1988	CCITT Blue Book	MTP2, MTP3, TUP, and ISUP revised. ISUP supplementary services and TCAP added.
1992	ITU-T Q.767	International ISUP, first publication.
1993	ITU-T "White Book 93"	ISUP revised.
1996	ITU-T "White Book 96"	MTP3 revised.
1997	ITU-T "White Book 97"	ISUP revised.
1999	ITU-T "White Book 99"	ISUP revised.

Under the CCITT publishing mechanism, the color referred to a published set of recommendations—that is, all protocols were published at the same time. The printed matter had the appropriate colored cover, and the published title contained the color name. When the ITU-T took over from the CCITT, it produced single booklets for each protocol instead of producing en bloc publications as had been the case under the supervision of the CCITT. Under the new mechanism, the color scheme was dropped. As a result, the ITU-T publications came to be known as "White Book" editions, because no color was specified, and the resulting publications had white covers. Because these publications do not refer to a color, you have to qualify the term "White Book" with the year of publication.

As Table 4-1 shows, when SS7 was first published, the protocol stack consisted of only the Message Transfer Part 2 (MTP2), Message Transfer Part 3 (MTP3), and Telephony User Part (TUP) protocols. On first publication, these were still somewhat immature. It was not until the later Red and Blue book editions that the protocol was considered mature. Since then, the SS7 protocols have been enhanced, and new protocols have been added as required.

Figure 4-1 shows how many pages the ITU-T SS7 specifications contained in each year. In 1980, there were a total of 320 pages, in 1984 a total of 641 pages, in 1988 a total of 1900 pages, and in 1999 approximately 9000 pages.

Figure 4-1. How Many Pages the ITU C7 Specifications Covered Based on Year (Source: ITU [Modified])

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The following section introduces the SS7 network architecture.