gh DWDM lasers are more expen- sive than CWDM lasers, the cooled DFB lasers provide cost-effective solu- tions for long-haul transport and large metro rings requiring high capacity. In both of these applications, the cost of the DWDM systems is amortized over the large number of customers served by these systems. Metro access networks, on the other hand, require lower-cost and lower-capacity systems to meet market requirements, which are based largely on what the cus- tomer is willing to pay for broadband services. Chapter 6 Figure 6-5 CWDM drift. Uncooled 1550-nm DFB Laser-Wavelength as a Function of Temperature 25° C 50° C Filter Passband Wavelength Uncooled coarse WDM lasers drift in wavelength at the rate of approximately 0.08 nm/centigrade. The filter passband and laser channel spacing must be wide enough to accommodate this temperature dependent wavelength drift, plus any manufacturing variations. Primary market research shows that customers typically want to spend at most $4,000, $7,000, or $12,000 per month for a dedicated 10 Mbps, 100 Mbps, or 1 Gbps service for a two-point metropolitan transparent LAN ser- vice (TLS), respectively. The backbone fiber and the spurs (laterals) in the two buildings cost about $4,000 per month. The carrier's operations and sales, general, and administrative (SGA) costs are in the 40 percent range, or $1,600, $2,800, and $4,800 per month for the aforementioned 10 Mbps, 100 Mbps, and 1 Gbps services, respectively. This leaves a monthly charge of $1,600 for 10 Mbps, $200 for 100 Mbps, and $3,200 for 1-Gbps edge equip- ment at two building sites and central office (CO) equipment. Ignoring for a moment the CO equipment and assuming a 25-month payback on the edge equipment, the carrier can only invest $04 at each site for 10-Mbps TLS, $5,000 for 100-Mbps TLS ($2,500 per end), and $80,000 for 1-Gbps TLS ($40,000 per end). In addition, you need to add in some profit for the carrier and the carrier's shareholders. Currently, there are few customers who need 1 Gbps in the WAN; theref