Juniper Networks ERX Hardware 8 - Manual (Page 75)

Cabling ERX Routers
The SRP I/O module has two input ports for external clock sources.
These ports provide a way to ensure that the router system clock remains
synchronized with the network’s system clock. The primary clock is labeled
A; the secondary, redundant clock is labeled B.
Use the connectors appropriate for your locale (European or
North American standard):
European—Two 75-ohm E1 2.048-Mbps inputs with BNC connectors
North American—Two 100-ohm T1 inputs with three pin wire-wrap
connectors. Pins are labeled T (tip), G (ground), and R (ring). We recommend
using 26-AWG wire minimum.
NOTE: Use shielded cables to connect the external clock sources to the clock
source input ports.
Cabling the SRP I/O Module 57