RAD Data comm ASMI-450 operation manual System Timing, Internal timing

à￿External timing. With external timing, the ASMi-450 system timing is locked to the clock signal received from the user's equipment (this mode is not supported when the ASMi-450 is equipped with an Ethernet interface). This mode allows locking the system timing to the timing of the network to which the local ASMi-450 unit is connected, and thus it enables providing the network timing to the equipment on the customer's premises.

The local HDSL transmit timing is locked to the incoming clock signal, therefore the transmit path of the local ASMi-450 transparently transfers the timing from the user's equipment to the HDSL line.

Figure 1-3 shows the flow of timing signals through the ASMi-450 system in the external timing mode.

∙ The remote unit, located at the remote end of the link (customer side), serves as the network termination unit (NTU).

The ASMi-450 supports both the central (LTU) and the remote (NTU) operating modes; the actual operating mode (LTU or NTU) is user-selectable.

Introduction

System Timing	The ASMi-450 offers selectable timing options, which enable the distribution of
	timing over the HDSL system, from the central office to the remote end.
	∙ ASMi-450 Unit Configured as Central Unit (LTU). The ASMi-450 unit
	configured as central unit has two timing modes: external timing and
	internal timing.

	CENTRAL ASMi-450		REMOTE ASMi-450
			HDSL Line
Local	User	HDSL Line	HDSL Line	User	Remote
User's					User's
	Interface	Interface	Interface	Interface
DTE					DTE
Timing
Source

Figure 1-C. Flow of Timing Signals through ASMi-450 System in the External Timing Mode

à￿Internal timing. With internal timing, the ASMi-450 system timing is determined by the clock signal generated by an internal crystal oscillator. This clock signal is supplied to the HDSL transmit path and to the user's equipment.

The internal timing mode is suitable for point-to-point configurations.

Figure 1-4 shows the flow of timing signals through the ASMi-450 system in the internal timing mode.

1-4 ASMi-450 Installation and Operation Manual