DSL Network Guide Chapter 4: The Telco Central Office

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The CO is where a lot of the magic happens, unless it is an RT based order (see Chapter 11 RTs). If your telco has spent the money (about a half million dollars) to make your CO DSL ready and you meet other requirements (see Chapter 12: DSL Availability), then you can have DSL.
Once the signal reaches the CO the Main Distribution Frame splits the lines that only have telephone service and the lines that have DSL and telephone service. Lines with only telephone service are sent directly to the OE block. The OE block handles all the POTS service like dial-tone and placing phone calls.
DSL ready lines go to the DSLAM Block. The DSLAM Block passes this on to the LP card. This card splits the POTS service from the DSL service. The POTS service is passed on to the OE block and the DSL signal is sent to the LT Card.
The LT card is the modem on the other end. It transforms the DSL signal into an ATM signal and passes that onto the Telco ATM switch.
The ATM Switch is responsible for communicating between the Telco CO and the ISP CO. From here your signal is passed on to the ISP CO.

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