tion First generation First generation First generation P2P DWDM P2P DWDM P2P DWDM P2P DWDM Office A Office B B2B transponders Office C Standard client Standard client interface interface Colored Colored wavelength (a) wavelength (2) Router xponder xponder Router ROADM ROADM ROADM Office A add a Office B express a Office C drop a FIGURE 13.5 Expressing wavelengths. FIGURE 13.6 100G Pluggable Form factors (CFP on left, QSFP28 on right). a result, a common practice is to purchase only the quantity of optics needed to support immediate capacity needs and to add more as the demand grows. 4. Right tool for the job-pluggables are available that support differing reaches (distances). Longer reach equates to better quality optics, higher power consumption (e.g., temperature stabilized lasers or higher output power lasers for longer reach), and higher cost. The pluggables supporting a new data rate start in a large footprint and get smaller as the tech- nology matures, enabling increased density with time. For 100G, it started with a "CFP" and the smallest footprint commercially available now is a "QSFP28" (Figure 13.6). A CFP is shown on the left. It has 24 Watt power dissipation and the physical size of roughly man's wallet. A QSFP 28 is shown on the right. It has 3.5 Watt power dissipation and is the size of a pack of gum. Note the optical connectors on the front panel. It is hard to see but there are electrical connections on the back of each unit that would mate with a receptacle on the router. Recently, pluggable optics is being used on the line side of the transponder as well. Today, all the high-speed connections (100 Gbit/s or more) above 80 km reach use coherent optics [5]. Earlier generation optical systems operated using simple on/off keying. The receiver sampled CFP stands for C Form-factor Pluggables. The use of the C is reference to the Roman numeral for 100, as the initial pur- pose of this form factor was for 100 Gbps optics. Building the Network of the Future the power of the incoming optical signal at e