ies today have tied together some form of high bandwidth packet switched fibre transmission backbone with circuit switched voice lines. INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 - © OECD 2006 2. TELECOMS INFRASTRUCTURE TO 2030 Table 2.A1.2. Digitalisation development (1980-91)2 overview Company/Year AT&T3 BellSouth4 France Telecom6 NYNEX8 Televerket10 For all carriers except AT&T, digitalisation is defined as number of main lines in use connected with a digital (time-division switched) exchange. For AT&T, digitalisation is defined as traffic switched by a digital exchange. 2. For purposes of divestiture effective 1 January 1984, data for US companies start in 1984. 3. Source: Annual Report (1983, p. 10); Telephony (1987, Feb. 2, p. 13), Annual Report (1988, p. 4). 4. Source: BellSouth. 5. Source: BT Annual Report (1991, p. 37). 6. Source: France Telecom Annual Reports (1981-91). 7. Source: GTE. 8. Source: NTT. Year indicates fiscal year. 9. Source: NTT. 10. Source: Televerket, Sveriges officiella statistik (1980-86), Televerket, Annual Reports (1987-91). 11. Interpolation. Source: Bohlin, E., Techno-Economic Management of Investments, Ph.D. Dissertation, Chalmers University of Technology, 1995. To handle high-speed traffic for data and voice as a bitstream in the hundreds of Mbps and Gbps range, the CCITT ATM (Asynchronous Transfer Mode, or Broadband ISDN) transmission protocol was produced in the 1980s. A whole CCITT synchronous digital hierarchy (SDH) was progressively introduced in the 1990s for high-speed international fibre optic transmission (termed synchronous optical network, SONET, in the US Bellcore convention) to interwork with narrowband ISDN and broadband ATM over fibre. Recently, the need to handle multiple protocols for high-speed transmission with minimal switching delay has led to MPLS (multi-protocol label switching). In the late 1980s, inter-switch trunk signalling also evolved with CCITT standards to produce SS7 (signalling system 7). This sign