chase any transponders in office B. Transponders are only needed at the "tails" of the connection to shift the wavelength back to the standard client interface. A transceiver converts the electrical inputs into optical outputs and vice versa. Today's transceiv- ers are packaged as hot pluggable modules that are accessible from the front of the equipment and interchangeable by the user. They are available at many speeds, reaches, fiber type (single mode and multimode) and can be sourced from a variety of suppliers due to multisource agreements that create electromechanical commonalities. Pluggable optics have several advantages over integrated optics: 1. Modularity-the failure rate of optics is higher than integrated circuits. When the optics fail, a pluggable can be replaced in the field as opposed to replacing an entire line card. Supplier independence-in theory, a service provider can purchase the optics indepen- dently of the line cards. In practice, many telecom original equipment manufacturers (OEMs) require that you purchase the optics from them, usually at a premium to open mar- ket prices. The OEMs argue that they are responsible for the entire system from a mainte- nance perspective and must control the optics. They typically implement firmware-based validation checks that will reject optics they have not sourced. As part of the new architec- ture, AT&T has taken a firm stance with its suppliers that they must support AT&T's use of third-party optics. 3. Pay as you grow-line cards on a packet fabric box support tens of interfaces. The cost of optics is now dominating the overall cost of a packet/optical reference connection. As The term "degree" refers to the number of distinct fiber pairs a ROADM can support. If a ROADM terminated separate N, E, S, and W fiber pairs, we would refer to it as having four degrees. Network Core Standard client Standard client Standard client interface interface interface Colored Colored wavelength (a) wavelength (i) Router xponder xponder xponder xponder Router First genera