Cisco Systems IPMUX-1E operation manual Network Timing Schemes, External Network Timing

Chapter 1 Introduction IPmux-1/1EInstallation and Operation Manual

ISDN/FXS/FXO/E&M

The available timing modes for the PCM clock are:

•Loopback Timing – available only when IPmux-1E ISDN BRI is configured as TE (not available in ISDN BRI NT mode or for FXS/FXO/E&M 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, above).

•Internal Mode – the clock is received from an internal oscillator.

Network Timing Schemes

The following paragraphs describe typical timing schemes and the correct timing mode settings for achieving end-to-end synchronization.

External Network Timing

When the edges of the network are synchronized by an external network clock source, all the IPmux-1 units should be configured to work in loopback timing mode (see Figure 1-11). This topology enables any-to-any connectivity.

Clock from External Distribution Network

E1/T1					E1/T1
E1/T1					E1/T1
		IPmux-1
E1/T1 Device				IPmux-1		E1/T1 Device
	LBT Mode		IP/Ethernet		LBT Mode
					E1/T1
					E1/T1
		IPmux-1
E1/T1 Device	LBT Mode			IPmux-1 LBT Mode		E1/T1 Device

Figure 1-11. IPmux-1 in Loopback Timing Mode

External timing from the network can also be issued to IPmux-1 by External Clock input; in this case, the E1/T1 device will use the LBT mode.

1-14 Functional Description