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Configuring T1 Cards
Configuring clocking
APX 8000/MAX TNT/DSLTNT Physical Interface Configuration Guide Preliminary May 9, 2000 7-17
Configuring clocking
You can configure the TAOS unit to use any of the T1 lines as a master phase-locked loop
(PLL) clock source for synchronous connections for an entire system. In synchronous
transmission, both the sending device and the receiving device must maintain synchronization
to determine where one block of data ends and the next begins.
From the T1 lines configured as eligible clock sources, the TAOS unit chooses a clock source
on the basis of priority. If multiple T1 lines are configured as eligible clock sources and have
an equal clock priority, the TAOS unit chooses one of them at random. Once chosen as the
clock source, the line used until it becomes unavailable or a higher-priority source becomes
available.
If no eligible external sources are available, the system uses an internal clock generated from
the primary shelf controller. Using the internal clock is generally not recommended.
The Clock-Source diagnostic command displays the current master clock source and any
available clock source. Sources from layer 2 up, which are preferred, are marked with an
asterisk.
To specify a clock source and set a priority, proceed as follows after reading in the line’s T1
profile:
admin> set clock-source = eligible
admin> set clock-priority = high-priority
admin> write
Configuring the front-end transceiver
The front-end type of the T1 transceiver can be CSU or DSX.
If you are connecting the TAOS unit to a DSX, set the Front-End-Type to DSX. With this
setting you must also specify the length of the physical T1 line in feet. The value must reflect
the longest line length you expect to encounter in your installation, up to a maximum of
655 feet (200m).
If you are not connecting the TAOS unit to a DSX, set Front-End-Type to CSU. You might also
have to set a line buildout value to specify the amount of attenuation, in decibels, that the
TAOS unit must apply to the line. If the TAOS unit is too close to a repeater, you need to add
some attenuation to reduce the strength of the signal. Ask your service provider whether you
need attenuation and, if so, how much.
To specify DSX settings, proceed as in the following example after reading in the line’s T1
profile:
admin> set front-end-type = dsx
admin> set dsx-line-length = 1-133
admin> write