IPmux-1/1E Installation and Operation Manual Chapter 1 Introduction
Functional Description 1-15
Timing Modes
The E1/T1 Tx clock, or ISDN/FXS PCM clock, can operate in several timing modes
to provide maximum flexibility for connecting the IPmux-1 E1, T1, ISDN or FXS
channels.
Each of the clocks must be configured correctly on both the Receive and Transmit
ends to ensure proper operation and prevent pattern slips (see Figure 1-12,
Figure 1-14, and Figure 1-15).

E1/T1

The E1/T1 available Tx modes are:
• Loopback Timing – the E1/T1 Tx clock is derived from the E1/T1 receive (Rx)
clock.
• Adaptive Timing – in this mode, the E1 or T1 Tx clock is regenerated using the
Adaptive method. In this method, the fill level of the buffer receiving packets is
monitored. If the buffer begins to overfill, the regenerated Tx clock frequency
increases to avoid overflow. If the buffer begins to empty, the Tx clock (toward
the TDM device) decreases to avoid underflow.
• Internal Clock Timing – in this mode, the Tx clock is received from an internal
oscillator.
• External Clock Timing – in this mode the Tx clock is taken from the external
clock input (Ordering option). The External Clock port also outputs the input
clock signal to allow connection to other units, if needed.
In Adaptive Timing mode the regenerated clock is subject to network Packet Del ay
Variation and may not comply with jitter and wander specifications.

FXS/BRI

The available timing modes for the PCM clock are:
• Loopback Timing – available only when IPmux-1E BRI is configured as TE (not
available in BRI NT mode or for FXS interface). In this mode the PCM clock is
derived from Channel 1.
It is recommended not to deactivate Channel 1 while it is in loopback clock so
that data will not be damaged. If Channel 1 is disconnected or deactivated (by
the NT side), the PCM clock will change to Internal clock and a momentary
disruption will occur to the other channels (2,3,4), if they are active.
• Adaptive Mode – the clock is regenerated using the Adaptive method, where
the rate of arriving packets is used to regenerate the clock (see E1/T1).
• Internal Mode – the clock is received from an internal oscillator.
Note
Warning
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