ey additionally carry the decreasing amounts of legacy traffic from analog circuit-switched voice on these networks. Legacy is a term used to describe networks and equipment that are based on older technologies such as TDM and analog voice service. Carrier Gigabit Ethernet Gigabit Ethernet is used in both Local Area Networks (LANs) and Wide Area Networks (WANs). It operates over fiber-optic cabling. When it is used in telecommunications and cable TV networks, it is sometimes referred to as Carrier Gigabit Ethernet. There are six capacities of Gigabit Ethernet (also referred to as GigE): 1, 2.5, 10, 100, 400, and terabit. These are used in core, Metropolitan Area Networks (MANs), and access networks. Carrier Gigabit Ethernet is used for VoIP and www.TechnicalPDF.com all IP-packetized traffic. This includes video, data, and graphics traffic that is bundled in packets. A timing source is included in GigE to make it suitable for switched voice, because it does not natively have timing sources. A timing source provides fixed, guaranteed capacity that circuit-switched voice requires. Without it, circuit-switched voice sounds choppy because of brief, intermittent delays, which are otherwise imperceptible in IP data. An International Telecommunications Union (ITU) 2010 standard called Synchronous Ethernet was developed for chips with timing sources. Timing sources are now standard in most Synchronous GigE switches. The Drive for Higher-Capacity Carrier Gigabit Ethernet Large providers such as AT&T and Verizon support 400Gbps capacity in their backbones. The impetus behind 00Gbps Ethernet is the increasing amount of high-definition streaming TV, personal videos uploaded to social networks, network-based storage, cloud based data centers, and mobile broadband backhaul traffic. Backhaul networks "backhaul" traffic from cellular antennas to mobile companies' data centers. Gigabit Ethernet was expressly developed for IP traffic and is less costly to purchase, maintain, and install than SONET. The wide availability of Gigabit 