A subscriber complains that his DSL rates are slower than the service he ordered. The customer ordered ADSL at 1 mpbs downstream and 256 kbps upstream, but the maximum bitrate observed during file downloads is never more than 128 kbps downstream. Initial troubleshooting shows that the subscriber’s DSL modem is trained at 1024 kbps downstream and 256 kbps upstream. Which one of the following presented choices is clearly the most appropriate information needed to begin troubleshooting the problem?

A.
The ATM QoS parameters assigned to the subscriber’s PVC in the DSLAM, ATM switch, and router.

B.
The software version running in the CPE and DSLAM.

C.
The manufacturer and model of ADSL CPE that is used, to determine correct interoperability with the DSLAM.

D.
The FEC parameters used for the subscriber’s ADSL port in the DSLAM, which could be causing the degraded throughput.