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Implementing Echo Cancel on a Conference Leg

Introduction

The following procedure details the steps for attaching an Echo Canceller to a conference leg, and then recording the output.

Prerequisites

You must have a DSP chip configured with the Echo Cancel function. See Connecting to an ASR (Automatic Speech Recognition) Server.

Guidelines

The Echo Canceller must be attached to the channel before you connect it to the conference or to another DSP receiver.

Procedure

1. Park the channel using the Park Channel 0x00BF message.

2. Create the conference using the Resource Create 0x0124 message.

3. Attach Echo Canceller to channel using the Resource Connect 0x0127 message.

AIBs

Resource A: Channel (Input to Echo Canceller)

Resource B: Slot (of card where conference resides)

Mandatory TLV

0x0602 Resource Type

Resource Type = Echo Cancel (0x0108)

Optional TLVs (to override default card parameters)

0x0673 Echo Cancel Tap Length

0x0674 Echo Cancel NLP Type

0x0675 Echo Cancel ADAPT

0x0676 Echo Cancel Bypass

0x0677 Echo Cancel G.176 Modem Answer Detection

0x0678 Echo Cancel NLP Threshold

0x0679 Echo Cancel CNG Noise Threshold

4. Connect Channel to Conference using Resource Connect 0x0127 message.

5. Attach other DSP Resources as required, such as Record Conference Leg using Record File Start 0x011E message.

6. Disconnect Echo Canceller using the Resource Disconnect 0x0128 message.

AIBs

Source Channel: Span/Channel

Mandatory TLV

0x0602 Resource Type

Resource Type = Echo Cancel (0x0108)

Optional TLVs

None

Example Call Trace

Park Channel span/channel 20/00

H->X

[00 12 00 bf 00 09 ff 00 02 0d 03 00 20 00 0d 03 00 20

00 00]

X->H

[00 07 00 bf 00 09 ff 00 10]

Resource Create - Conference

H->X

[00 20 01 24 00 0c ff 00 01 22 03 00 ff ff 00 03 06 02

00 02 01 00 06 03 00 02 00 00 06 13 00 02 00 06]

X->H

[00 1e 01 24 00 0c ff 00 10 00 01 22 03 04 06 02 00 02 06 10

00 04 00 00 fd fe 06 02 00 02 01 00]

Resource Connect 20/00- Echo Canceller, use slot 4

H->X

[00 17 01 27 00 00 ff 00 02 0d 03 00 20 00 01 01 04 00

01 06 02 00 02 01 08]

X->H

[00 19 01 27 00 00 ff 00 10 00 02 0d 03 00 20 00 01 01 04 00

01 06 02 00 02 01 08]

Resource Connect 20/00- Connect Leg to Conference

H->X

[00 1e 01 27 00 0e ff 00 02 0d 03 00 20 00 55 02 fd fe

00 02 06 02 00 02 01 00 06 12 00 02 00 00]

X->H

[00 1a 01 27 00 0e ff 00 10 00 02 0d 03 00 20 00 55 02 fd fe

00 01 06 02 00 02 01 00]

Record File Start 20/00

H->X

[00 46 01 1e 00 12 ff 00 02 0d 03 00 20 00 01 01 ff 00

06 05 e0 00 04 00 dc 5b 17 05 e1 00 02 00 01 05 e2 00

13 00 01 00 02 2f 50 61 74 45 63 68 6f 2f 6d 79 2e 72

61 77 05 e9 00 02 02 26 05 fb 00 01 ca 05 e6 00 01 0c]

X->H

[00 11 01 1e 00 12 ff 00 10 00 02 0d 03 00 20 00 01 01 04]

Digital Signal Processor
Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.
Range of channels provided by T1 or E1 transmission service. A physical span is a group of channels taking up a single physical wire. A logical span is a group of channels taking up less than a single logical wire, or carried over more than one physical wire.