you can wire a pri between the two.. rj45 pins 1,2 4,5 on the db-9 side that translates to 1,3 9,11.. you do not need a csu.. the switch sets the framing to esf the clock sets the bandwidth to 1.54.. the d makes it simple for msg lamps names etc to work transparent..
you will need to add steering codes for all the ext in the remote switch so that your dial plan works..those can be entered in blocks..
john poole
bellsouth business
columbia,sc