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BT8110

High-Capacity ADPCM Processor

Conexant Systems 

E

Appendix E. E1 ADPCM Transcoder

E.1.1 Description

E.1 Introduction

This appendix describes an assembly of the Bt8110/B ADPCM Processor,

Bt8200 ADPCM Line Formatter, and Bt8510 E1 Framer or the Bt8370 T1/E1

Frame/LIU that realizes a single-board transcoder meeting the transcoding

requirements of ITU–T Recommendation G.726 and the interface requirements

given in ITU–T Recommendation G.761. An evaluation board is available for this

configuration (Bt8200EVM–E1).

G.726 is a transcoding algorithm between 64 kbit/s PCM and 32 kbit/s

ADPCM. G.761 is a line format for 32 kbit/s ADPCM compression of voice-band

signals on 2.048 Mbit/s primary-rate digital streams. Signaling conversion from

the full-rate source streams to the compressed digital stream is specified in G.761

as well. This signaling conversion requires processing of signaling history with a

scrambling algorithm to ensure that no multiframe alignment signal emulation

can occur on the compressed E1 stream.

The Bt8200EVM-E1 transcoder meeting the requirements of G.761 was

developed with three Conexant products: Bt8110/B, Bt8200, Bt8510. Two

Bt8110/B ADPCM processors provide transcoding for 60 channels. Two Bt8200

ADPCM Line Formatters buffer and synchronize the encoded and decoded

ADPCM and PCM signals, respectively, to obtain the required line formats. Three

Bt8510 E1 Framers are used, one each for the full-rate A and B ports and one for

the compressed C port.

Figure E-1 shows the transcoder assembly. Circuit elements required include a

microprocessor; two 16.384 MHz timing oscillators that can be synchronized to

any of the E1 signals or synchronized externally; and an optional RS-232C

interface to a supervisory data link. The encoder and the decoder operate with

separate time bases; normally the decoder is synchronized to the incoming clock

at the C port to meet the synchronization requirements of G.761.

The microprocessor sets the configuration of the transcoder and monitors all

status and alarm indications. Optional status (LED) indicators can also be set by

the microprocessor. The UART link to the RS-232C interface can be used to

transfer supervisory signaling to and from the Bt8200 ports, to set idle and

transparent (uncoded PCM or data) channels, to provide the signaling conversion

(G.761 signaling performed by microprocessor or external hardware) between the

100060C

Conexant

E-1

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