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ADMINISTRATION OPTIONS AND REQUIREMENTS — SYSTEM 85
7-9
Field 8
V1-V4
Offers the choice of 24th-channel or robbed-bit signaling (RBS). The choice of
signaling method used is dependent on the application. The DS1/DMI-BOS
applications may be translated for either option. However, ISDN-PRI applications
always require that 24th-channel signaling be selected.
With RBS, information is transmitted in the least-significant bit (LSB) position of
each channel every six frames. This effectively limits the channel’s use to voice and
voiceband analog data applications. Digital data ports connected to Digital
Communications Protocol (DCP) data modules must use the modem pooling
capability to transmit data over DS1/T1 RBS facilities. Analog data ports must be
configured with analog modems.
24th-channel signaling multiplexes all signaling information for channels 1 through
23 into the 24th channel. This makes available the full 64K-bps bandwidth (of
channels 1 through 23) for voice and/or digital data transmission called alternate
voice/data (AVD).
AVD allows pure 64K-bps digital data to be transmitted over those digital trunk
facilities that use 24th-channel signaling. Although AVD trunks are designed for
digital data transmission, they may also be used for voice transmission. However,
because of a modem-pooling limitation, AVD trunks cannot easily be used for
analog voice-grade data transmission.
24th-channel signaling is required for those trunk groups that are translated AVD
(from procedure 101, field 17).
Either the AT&T proprietary format or the DMI-BOS format may be used with
another System 85 or System 75. The DMI-BOS format is required to provide
24th-channel signaling capability with other vendors’ digital switches. 24th-channel
signaling (both methods) is not compatible with D4-channel banks. The AT&T
proprietary format is provided by the ANN11C version-8 (or later) circuit pack. All
previous versions will eventually be replaced via a class-A change. The DMI-BOS
format is provided by the ANN11D or ANN11E circuit pack. When 24th-channel
signaling is optioned, the ANN11D or ANN11E circuit pack automatically
interrogates the far-end and provides the required format. For System 75, the
proprietary format is administered by translating a n in the DMI-BOS field. To
select the DMI-BOS format, simply administer a y for the DMI-BOS field.
V3-V4
A mode 1 data call requires a Line+Trunk-mode circuit pack with RBS option.