high. The SeaMeWe-4 cabling system is an example of upgraded undersea routes. It was installed in December 2005 with an initial capacity of 160Gbps. The lit capacity at the end of 2009 between Europe and Egypt was 1,580Gbps. Upgrading is costly because electronics must be changed or added at every drop-off city where speed is intended to be increased, not just at the ocean's edges. In addition, older fiber that has had a number of fiber cuts and repairs does not support the same high speeds as newer fiber cabling. TECHNOLOGIES USED IN CARRIER NETWORKS Carriers use a mix of Synchronous Optical Network (SONET), Gigabit Ethernet, and older technologies to support legacy networks based on Time-Division Multiplexing (TDM) (T1 and T3) as well as analog circuit-switched voice. Newer networks deploy Optical Transport Network (OTN)-compliant gear athat can efficiently carry both SONET for legacy circuit-switched voice and Gigabit Ethernet for IP data and VoIP traffic. Legacy is a term used to describe networks and equipment that are based on older technologies such as TDM and analog voice service. Circuit-Switched Voice and T1/T3 over Fiber SONET is a North American standard for multiplexing streams of traffic onto fiber- optic cabling and transporting it at Optical Carrier (OC) speeds. SONET was devel- oped to aggregate (multiplex) and carry TDM and circuit-switched voice traffic from multiple sources. The international version of SONET is Synchronous Digital Hierar- chy (SDH). SONET SDH carries traffic at Synchronous Transfer Mode (STM) rates. Traffic carried between cities in Europe or in undersea cables is often referred to as being carried at STM-1 (155Mbps) or STM-16 (2.5Gbps) speeds. See Table 4-1 in the "Appendix" section at the end of this chapter for optical carrier and synchronous trans- fer mode speeds. SONET equipment using STM speeds can communicate with North American-type SONET gear. When SONET was first introduced in 1994, all public network traffic was essen- tially based on TDM. Although most public net