Call drops on analog phones

[gullsinn]

i connected two nortel cs1K sites through PRI cards distance could be around 2.5KM which i covered with SHDSL ntu 5099b
site B can dial within site fine however site B calls are getting dropped within 15 to 20 seconds weather call is ringing or picked
digital (m3902)sets do not drop calls.
same happening for outside network calls too on site B
if site A call to site B on m3902 works fine but drops call on analog (500)
my call routing to dial each other is VNR

what could be the issue

 

[trvlr1]

Check your clocking in LD 60, make sure its not in freerun or clocking off a this new PRI you put in