700-712-100-01, Revision 01
Functional Description
UTU-712 and ETU-762 List 1
May 10, 1999
13
Timing for the signals transmitted over the HDSL link is nominally derived from the selected primary timing
source. In case of failure of the primary timing source, the system utilizes the internal 2.048 MHz oscillator as the
backup timing source.
The external reference clock option is available only for UTUs plugged into an Exchange Office Management
Shelf (EMS-83x) with an Exchange Office Management Unit (EMU-830) installed in the same shelf.
The Transmit Clock option for the data port interface enables selection of the input clock source for the Transmit
Data (SD) fed to the unit from the Data Terminal Equipment (DTE) device. The options are:
•
INT RISING: Rising edge of the internal Send Timing (ST) clock.
•
INT FALLING: Falling edge of the internal ST clock.
•
EXT: External Terminal Timing (TT) clock from the DTE.
illustrates the Transmit Clock circuit function. When the data port has Nx64k selected as its primary
timing source, the transmit clock is fixed to External.
Figure 7.
Data Port Transmit Timing
When the selected primary timing source is Internal, HDSL, or External, the transmit clock may be selected as
Internal or External. The purpose of this selection is to compensate for a possible phase shift between SD and ST
due to long interface cables or delay added by the DTE. Not all DTE equipment allows the DCE transmit clock
(ST) to be sent back out as the transmit timing signal (TT), and the External transmit clock selection will not work
with such equipment.
In general, it is best to always set the Transmit Clock option to External, as long as the DTE provides TT. Only if
the DTE does not provide TT should one of the Internal options be used.
Processor
This device runs a program which in real-time:
•
monitors the HDSL framer performance
•
responds to user requests
•
maintains a history of system performance.
