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The customer CPE is a DSL modem, which may or may not also be a router. The [[Speedstream 4200]] is an example of a CPE that is both a DSL modem and router, but capable of acting as a pass through modem that may be used with a separate router. The CPE can use either FDM or Echo Cancellation to divide an allocate the available bandwidth of the line. POTS are low pass filters that are used on the customer line to separate low frequency voice signals from high frequency data signals, so that one doesn’t interfere with the other. Voice speech is below 4KHz so the filter blocks anything above that. Modulation is used to modify the data signal transmitted over the phone line. QAM is a modulation method used and can be implemented in either one of two different competing standards, CAP or DMT. CAP is less common and not considered as "standard" as DMT. Many providers started using CAP and then migrated to DMT. DMT allows for the connection of customers living further from the DSLAM location, and is capable of higher speed. The telcos that switched from CAP to DMT also implement PPPoE with the change. The Cisco 675 was a common CAP only DSL modem/router while the Cisco 678 is capable of both CAP and DMT (with limited speed) after a firmware upgrade. The [[Speedstream 4200]] is a common DMT router/modem used in moden ADSL installations and is made by the Siemens Corporation.* DSL - Digital Subscriber Line* DSL - Digital Subscriber Line* CPE - Customer Premises Equipment* PPPoE - Point-to-Point Protocol over Ethernet