Perle Systems PERLE P850 - Manual (Page 13)

Installation
7
it must be configured to the type of connection service that will be
used; please see the following section for this procedure.
The V.35 module and Universal WAN module in V.35 mode require
interface converters that convert from a DB25 connector to a male 34
pin (V.35) connector used for the V.35 service interface. Be sure to
secure the cable connector to the router and the communications
equipment with connector screws to prevent accidental disconnection.
The T1/E1 and LX411 CSU-DSU interfaces connect with a standard
RJ-45 (RJ-48C specification for T1/E1, RJ-48S specification for
CSU/DSU) connector
After the P850 is powered up and the router has established
communications with its partner across the WAN, the “Tx” LED will
turn green.