Chapter 1. Introduction
10
May 2011
When loop back is selected from the LCD menu system, the unit generates one of fourteen
different test patterns, according to ITU, for direct end-to-end integrity testing. The Error indicator
flashes for each bit error detected.
Multiple clock source selection provides maximum flexibility in connecting both the E1 and
user data interface. The E1 link may be clocked from the recovered receive clock, from the user
data port or from the internal oscillator.
1.3 System Timing Considerations
The ETU-01A has the flexibility to meet the timing requirements of various system
configurations. The timing mode for the E1 link and the user channel is selected through the LCD
menu system, a serial console or via optional SNMP management.
Master timing
The ETU-01A E1 link receive path always operates on the receive clock. The ETU-01A
recovers the receive clock from the received E1 link data signal. The source of the ETU-01A E1
link transmit clock may be selected by the user. The following E1 link transmit timing modes are
available:
Recovery timing:
The ETU-01A E1 link transmit clock is locked to the recovered receive clock. This is
usually the timing mode selected for network operation.
Internal timing:
The ETU-01A E1 link transmit clock is derived from the internal clock oscillator. This
timing mode is necessary in point-to-point applications over leased line. In this case, one
ETU-01A must use the internal oscillator, and the other may operate from the recovered
clock.
The ETU-01A has three data channel clocking modes:
Clock mode DTE1: The ETU-01A data channel accepts the user transmit clock from the
connected DTE (from the ETC pin) and provides a receive clock (Transparent timing) to the
synchronous equipment connected to the data channel.
Clock mode DTE2: The ETU-01A data channel accepts the user transmit clock (from ETC
pin) and receive clock (from ERC pin) provided by the DTE equipment connected to the
data channel. Note: The X.21 data channel cannot be operated in this mode.
Clock mode DTE3: The ETU-01A data channel operates as a DCE and accepts both the user
transmit and receive clock (All from ETC pin) provided by the DTE equipment connected to
the data channel.
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