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ADMINISTRATION OPTIONS AND REQUIREMENTS — SYSTEM 75
7-109
Signaling
The default option is common-channel. This option is the same as 24th-channel or
Mode
AVD for System 85. The alternate choice is robbed-bit. The choice of signaling
mode used is dependent on the application.
Common-channel signaling multiplexes all signaling information for channels 1-23
into the 24th-channel. This makes available the full 64K-bps bandwidth (of
channels 1-23) for voice and/or digital data transmission. This capability is
sometimes referred to as Alternate Voice Data (AVD).
The term AVD is a software attribute for a trunk. AVD allows pure 64K-bps
digital data to be transmitted over those DS1 trunks that use 24th-channel signaling.
Although AVD trunks are designed for digital data transmission they may also be
used for voice and voice-grade data transmission. However, a pooled modem is
required to transmit voice-grade data over AVD trunks.
CAUTION: Due to a change in the evolving DS1/DMI protocol specification,
two methods for providing 24th-channel signaling exist. The two methods are
not compatible with each other. The earlier method is known as the AT&T
proprietary format (conventional T1 test equipment cannot analyze it). This
latter version is known as the DMI-BOS format (T1 test equipment can analyze
this format).
Either the AT&T proprietary format or the DMI-BOS format, depending on the
circuit pack configuration, may be used with another System 75 or System 85. The
DMI-BOS format is required to provide 24th-channel signaling capability with other
vendors’ digital switches. Common-channel signaling (both methods) are not
compatible with channel banks and multiplexers.
CAUTION: The TN722 circuit pack provides the AT&T proprietary format;
the circuit pack does not provide DMI-BOS. The TN722B circuit pack may be
administered to provide either the proprietary format or DMI-BOS format.
DMI-BOS
Assigns the DS1’s format. Field encodes and their descriptions are:
n
y
AT&T proprietary. This option assumes that common-channel signaling is
selected; otherwise, RBS is used.
DMI. This option is equivalent to a 1 in field 14 of procedure 260.