Technical data
dbri(7D) Devices SunOS 5.5
B-channels can be configured for µ-law, A-law, or HDLC encoding of data. The µ-law
and A-law formats are always at 8000 Hz, 8-bit, mono. Although a BRI H-channel is
actually 16 bits wide at the physical layer and the 16-bit sample occurs at 8 kHz, the
HDLC encodingalways presents the data in 8-bit quantities. Therefore, 56 bit-per-second
(bps), 64 bps, and 128 bps formats are all presented to the programmer as 8-bit wide,
mono, AUDIO_ENCODING_NONE format streams at different sample rates. A line rate of
56kbps results in a 8-bit sample rate of 7000 Hz. If the bit stuffing and un-stuffing of
HDLC were taken into account, the data rate would be slightly less.
For the sake of compatibility,AUDIO_GETINFO will return one of the following on a ISDN
channel:
BRI Audio Data Formats
Sample Rate Encoding Precision Channels
8000 Hz µ-law or A-law 8 1
- AUDIO_ENCODING_NONE - -
ISDN_GET_FORMAT
will return one of the following for an ISDN channel:
BRI Audio Data Formats
Mode Sample Rate Encoding Precision # Ch Available on
HDLC 2000 Hz NONE 8 1 D
HDLC 7000 Hz NONE 8 1 B1,B2
HDLC 8000 Hz NONE 8 1 B1,B2
HDLC 16000 Hz NONE 8 1 B1,B2
TRANS 8000 Hz µ-law 8 1 B1,B2
TRANS 8000 Hz A-law 8 1 B1,B2
TRANS 8000 Hz NONE 8 1 B1,B2
TRANS 8000 Hz NONE 16 1 B1 only
In the previous table,HDLC = ISDN_MODE_HDLC, TRANS = ISDN_MODE_TRANSPARENT.
Audio Ports Audio ports are not relevant to ISDN D or B channels.
The record.avail_ports and play.avail_ports fields of the audio_info structure report the
available input and output ports. The dbri device supports two input ports, selected by
setting the record.port field to either AUDIO_MICROPHONE or AUDIO_LINE_IN. The
play.port field may be set to any combination of AUDIO_SPEAKER, AUDIO_HEADPHONE,
and AUDIO_LINE_OUT byOR’ing the desired port names together. As noted above, when
using the onboard Multimedia Codec on the SPARCstation LX, the Line In and Line Out
ports are not available.
Sample Granularity Since the dbri device manipulatesbuffers of audio data, at any given time the reported
input and output sample counts will vary from the actual sample count by no more than
the size of the buffers it is transferring. Programs should, in general, not rely on absolute
accuracy of the play.samples and record.samples fields of the audio_info structure.
Audio Status Change
Notification
As described in audio(7I), it is possible to request asynchronous notification of changes in
the state of an audio device. The DBRI driver extends this to the ISDN B-channels by
sending the signal up the data channel instead of the control channel. Asynchronous
notification of events on a B-channel only occurs when the channel is in a transparent
data mode. When the channelis in HDLC mode, no such notification will take place.
7D-74 modified 27 Feb 1995