Verilink C100 (880-502893-001) Product Manual - Manual (Page 31)

Configuration Using the DIP Switches
06/17/97 C100 and C150 T1/FT1 CSU/DSU 3-7
Another common timing option is Internal. Many T-1 facilities
provided to the user such as T-SPAN do not go through switched
services. In these applications, the T-1 CSU/DSU must supply timing
at one end. Therefore, the CSU/DSU at one end must be programmed
for Internal. With Internal Timing selected, position 7 Off and 8 On, the
unit’s internal oscillator will be the timing source. When using this
mode, the remote unit at the other end must be programmed for
Network supplies Timing. This mode is also selected when using the
unit as a Limited Distance Modem (LDM) over Customer-owned
wiring.
Channel or DSX-1 timing
The other selections, Channel or DSX-1 supplies Timing is used when
the timing on the DSX-1 or Channel is derived from a Public Network
or an extremely accurate timing source.
DSX-1 timing is set if timing is provided by CPE equipment such as a
PBX or Channel Bank.
Channel timing is set when customer DTE is supplying timing (very
rare). It is most commonly used in tail circuit timing.