Ethernet switches from many manufacturers has caused Ethernet switch prices to drop. Moreover, because of its standardization by the Institute of Electrical and Electronics Engineers (IEEE), vendors produce compatible Ethernet gear SO that providers are not locked into a single vendor's equipment. Gigabit Ethernet and Ethernet are often used in conjunction with Passive Optical Networks (PONs), discussed later in this chapter. PONs are a lower-cost method of extending fiber to premises and www.TechnicalPDF.com neighborhoods because they enable single strands of fiber to be shared between multiple homes and small businesses. Circuit-Switched Voice-Unsuitable for Packetized Traffic After 2012, carriers began carrying most traffic over Gigabit Ethernet both because of its suitability for data and because of decreases in the amount of analog voice and TDM traffic. Prior to 2012, SONET, a North American standard for multiplexing streams of traffic onto fiber-optic cabling was the predominant protocol for transporting traffic at Optical Carrier (OC) speeds. SONET was developed to aggregate (multiplex) and carry TDM (Time Division Multiplexed) and circuit-switched voice traffic from multiple sources. TDM multiplexing saves capacity for voice and data in predictable time slots. However, its top speed of 40Gbps is inadequate for today's long haul traffic. See Table 4-2 in the "Appendix" section at the end of this chapter for SONET speeds. Using Ring Topology-Greater Reliability and Carrier Gigabit Ethernet can operate as a straight point- to-point line between sites, in the more fail-safe ring, or in mesh topologies. Topology refers to the design of how devices are physically connected. It is the "the view from above." When fiber in a point-to-point arrangement is cut, service is lost. Reliability on fiber is critical because each failure affects potentially hundreds or thousands of customers, particularly if a failure occurs in long-haul networks. www.TechnicalPDF.com When a medium such as copper carries a conversation or