External Reference Clock - Juniper CTP2000 Series Hardware Manual

NOTE: BITS input is a T1/E1 line interface unit (LIU), with AMI (alternate mark inversion) encoding
enabled and B8ZS/HDB3 (Zero Suppression) disabled. The equalization is set for a 0-133 feet
cable. An internal 100 ohm termination is present, although it might need to be externally
augmented based on the type of cabling used. Any valid AMI signal works properly and it is not
restricted to only the "all 1" BITS signal but the ones density must be sufficient to prevent LOS
(according to the ITU G.775 recommendation). The TTL input has a slice point of 3.3V/2 = 1.65V
relative to chassis ground (GND). Therefore, any signal on the coaxial center conductor that
transitions through that voltage registers a transition. There are many signals, besides TTL, that
satisfy this criteria. An external termination must be provided that matches the impedance of
the cable that goes to the BNC connector.
If you can configure the rate in CTP menu, then the TTL supports a frequency of 2048 KHz for
the TTL clock input, provided the signal is good and noise-free (terminated properly). TTL is
rate-agile, while BITS is restricted to T1/E1 frequencies.
The TTL input is high-impedance (no on-board termination provided) because a variety of cable
types might exist that you can use to drive signal to this connector, such as RG-58 coax (50 ohm),
RG-59 coax (75 ohm), or twisted pair (100-120 ohm). Instead of applying a particular impedance
termination on the board and have it incorrectly done, we recommend that you configure the
impedance termination based on your network environment. For example, a 50 ohm termination
is needed if you are using RG-58/U coax cable, which has 50 ohm impedance.

External Reference Clock

The CTP2000 device can receive the external reference clock from any of the following inputs on the
clock main module:
The DB-25 connector. The clock input is provided on pins 24 and 11.
The T1/E1 BITS inputs
NOTE: The latest version of the clock main module does not have the BITS connector and no
longer supports a BITS input. If you need a BITS timing reference to or from a CTP2000 node,
you can use any of ports te-0/0 through te-0/3 if you have a T1/E1 interface module in the
first slot.
The T1/E1 TTL input
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