I reckon 21CN dates for exchanges may have something to do with the ages of DSLAMs in exchanges. For example, in my situation, my exchange was one of the first to be enabled for ADSL in 2003 in the area and so it has older DSLAMs than most others (Which have not been announced for 21CN).
The ones which have even older ones like the nearby town exchange enabled for ADSL in 2001 was enabled for 21CN in 2009 - 2 years ago and it is almost exactly 2 years older than the ADSL date was for my exchange - 2003.
Could it be that BT Wholesale want to get rid of the older DSLAMs and replace it with newer MSANs due to support expiration?
By the figures, it appears as though BT Wholesale replace the older ADSL DSLAMs with newer MSANs after around 8 years?
-------------------------------------------------------------------
6851kbps Throughput:

Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 13.0 db 10.0 db
Max(Kbps): 11616 1056
6851kbps Throughput:

Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 13.0 db 10.0 db
Max(Kbps): 11616 1056
Edited by chris6273 (Wed 27-Jul-11 20:57:45)