Specifications

Reference Guide
2-19
Applications ADPCM Voice Compression Server
The remote systems must be configured with the TCP/IP CPU software option. Remote units
send management information in IP packets over the FDL to an intervening AT&T DACS II.
The DACS II can be configured to convert the IP management information from the FDL
channel into a full DS0 using a link level protocol called Bit-7 Redundant (B7R). Even though
the management information is only 4 Kbps it will occupy the full 64 Kbps DS0. The resulting
8 DS0s are then routed over T1 link(s) to the integrated access system that contains the 8228.
Physically the 8228 is the same card as the 8220 SRU card. Both have ten RJ-48 interface
ports, but on the 8228 the first eight are physically disabled and, effectively, replaced by eight
“internal” ports used for the DS0s. The ninth RJ-48 port is available for maintenance and the
tenth RJ-48 port is used for the aggregate SLIP line to the terminal server.
2.5 ADPCM Voice Compression Server
The 8871 ADPCM (Adaptive Differential Pulse Code Modulation) server card is designed to
compress digital and analog voice traffic for transmission over wide area network links. The
level of compression for an individual channel is software configurable at 24Kbps, 32Kbps or
40Kbps. A single ADPCM card is capable of compressing 64 channels of voice
simultaneously. Since the ADPCM card is a server card, these 64 channels can be originated
from a variety of interfaces, including FXS, FXO, E&M, SRU, BRI, and T1/E1. Up to two
ADPCM server cards can be supported per integrated access system for a total of 128
compressed voice channels. A third ADPCM server card can be utilized for 1:N redundancy.
The sum of the compression rates for the engine pair must equal 64Kbps. A 32Kbps circuit
can only be paired with a 32Kbps circuit. A 40Kbps circuit can only be paired with a 24Kbps
circuit and vice-versa. The ADPCM server card can also pair a low speed asynchronous data
transmission (19.2Kbps or less) from an SRU port with a 40kbps engine. This data path will
occupy a 24Kbps engine. Group II FAX is supported in 32Kbps channels and Group III FAX
is supported in 40Kbps channels.
Modem support up to 4.8Kbps, and V.32bis to 9.6Kbps is supported in 32Kbps channels.
Modem speeds up to 12Kbps, and V.32bis speeds up to 14.4Kbps is supported in 40Kbps
channels. Modem data is not supported in 24Kbps channels.
The ADPCM card supports Transition Signaling as defined by ANSI T1.302-1989 with the
exception of the Alarm bits. ANSI T1.302 specifies signaling at the 32Kbps compression rate.
The ADPCM card uses this scheme for 24Kbps and 40Kbps although it is not included in the
standard.
The ADPCM card can be used in a variety of applications to reduce the number of
transmission lines for efficient transport of voice traffic. It can be used in:
•
PBX to PBX trunk application
•
Automatic Call Distribution application
•
Efficient wireless base station/hub application