11.92 Year 28 13.11 Year 29 14.42 Year 30 15.86 Year 31 17.45 Even in long-haul applications, design considerations aimed at optimiz- ing the cost profile are not always straightforward. In particular, TDM-only solutions supporting increasing speed have kept pace with a number of advances in WDM technology during the mid to late 1990s, at least for medium-size trunking applications (up to 10 Gbps). For example, a TDM- based solution has only one 10-Gbps SONET terminal, as shown at the top of Figure 5-7. A WDM system that transports an aggregate capacity of 10 Gbps requires four 2.5-Gbps terminals in addition to a WDM terminal per end (shown at the bottom of the figure). Because TDM technology has typ- ically quadrupled its capacity for a cost multiplier of 2.5, the 10-Gbps solu- tion appears to be more cost effective. However, if the TDM system also requires four 2.5-Gbps terminals to provide the first stage of multiplexing, the 10-Gbps solution might actually be more costly. (Note that if the Chapter 5 OC-48 OC-48 Figure 5-7 OC-48 OC-48 arrangement. SONET SONET OC-48 (OC-192) (OC-192) OC-48 OC-48 OC-48 First Multiplex Stage (If Required) SONET SONET SONET SONET SONET SONET SONET SONET 2.5-Gbps terminals are already in the network, they represent a sunk cost and might not be included in the cost analysis.) Before optical line amplifiers (OLAs) were developed and deployed, higher-speed TDM-based systems were more cost effective than WDM because the TDM systems allowed multiple lower-speed electronic regener- ators at one point in the network to be replaced with a single higher-speed regenerator at that point in the network. Originally, this was not the case with the WDM design (as implied in Figure 5-7). The introduction of OLAs with the capability to amplify the entire ITU grid frequencies (which reside in the erbium-doped fiber amplifier [EDFA] passband) simultaneously enables multiple lower-speed electronic regenerators at a site to be replaced with one optical amplifier, as shown in Figure 5-8, making WDM more