LLB – Local Loop Back
The LLB mode loops back the currently received data stream. This mode
is often referred to as a THROUGH mode. Individual channels may be
dropped to the speaker and errors may be inserted into the out-going
data stream. The received data is passed back to the transmitter
undisturbed. The unit no longer does an auto-evaluate in this mode.
TLB – Test Loop Back
This mode is similar to the LLB mode with one major difference. The
receiver will continue to BERT the data as in the LLB mode but the
receiver will correct any BPV errors and re-time the data before sending
it back out the transmitter. Individual channels may still be dropped to
the speaker and errors may also be inserted into the transmit data
stream.
DLAY – Round Trip Loop Delay Measurement Mode
This mode is an out-of-service test that measures the amount of time it
takes for a single bit to propagate through the network. The test set
must be in PATTERN SYNC.
By pressing the logic error inject key, the test set will insert a single
logic error into the E1 payload. At the same time, a 1-millisecond
counter is started and the receiver will start looking for the bit error.
Once the bit error has been detected, the counter will stop and display
the information in the results screen as [LoopDly XXXXXXXX]. The
measurement has a 1-millisecond resolution.
CO64 – Co-directional Interface 64 kbps
The interface used between the data terminal equipment (DTE) and the
data communication equipment (DCE) depends on the method used to
synchronize the 64kbps signals to the 2048kbps signal. It the DTE and
the multiplexer are synchronized from an external clock source, a so-
called co-directional interface is used. Synchronous operation is achieved
by transmitting the data signal and associated timing signal from the
terminal equipment to the multiplexer.
The term co-directional is used to describe an interface across which the
information and its associated timing signal are transmitted the same
direction. This mode provides 64 kbps transmit and receive as per ITU-T
G.703.
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