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to be decoded at the remote end. When overdriven, both modules will not
correctly reproduce the VF signal input, and the CELP will reproduce a
lower quality VF signal (due to the larger number of errors in the digital
signal).
When the data is transmitted across an aggregate trunk, the CELP Voice
channel data bits are bit interleaved in a proprietary format, along with
data bits from other types of channel modules. This means that each 64
kHz DS0 channel on a E1 or T1 aggregate could contain bits from many
different channels. This makes it impossible for the Carrier provider or
installation technician to monitor and check levels at any point within
the CELP circuit.
When testing CELP voice circuits using a 1 milliwatt test tone, the digital
equivalent of a 0 dBm VF signal should appear on the Aggregate trunk in
digital format, but the data bits are not contained within any single 64
kHz DS0 channel, i.e., if a Voice channel were installed in a TMS-3000
node, and the Voice channel's transmit attenuator and gain switches
were set for 0 dB, then a 0 dBm 1004 Hz tone injected into the Voice
channel should produce a digital equivalent of the 0 dBm 1004 Hz signal
within the aggregate bit stream, but the bits will be spread out amongst
multiple DS0 channels of the aggregate trunk. Because of the bit
interleaved technique, the digital signal transmitted from the CELP
module cannot be monitored on the aggregate trunk by any test equip-
ment that is available.
The Echo Canceller in the CELP requires an echo return loss of greater
than 6 dB measured at the CODEC to function properly. This was also the
case with the VEC-1 on the ADPCM. The terminal equipment must be
tested to assure that it meets this requirement. It is recommended that the
echo return loss be at least 18 dB in order to preserve a margin of safety,
although only six dB is required (refer to Echo Return Loss later in this
appendix).
This section of the appendix covers the various aspects of alignment and
OUTLINES OF
their associated concepts. Since many of the terms used may not be
SPECIFIC
familiar, a Detailed Reference subsection is presented to provide you with
PROCEDURES
further explanation of terms. This section is broken down into subsec-
tions as follows:
1. Detailed Reference.
2. 4-wire circuits such as 4-wire phones or 4-wire PBXs. No hybrids pre-
3. 2-wire circuits such as PBXs or telephones, which have to be connected
4. Hoot 'n holler or shoutdown circuits which are commonly encountered
5. Analog bridging circuits which are used to implement conference
sent.
through 2- to 4-wire hybrid converters or term sets.
in brokerage applications. These circuits have speakers at one or both
ends.
phone networks.
APPENDIX D
D-3
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