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Cisco High Density Voice/Fax Network Modules

Field Notice: C5510 Based DSPFarm: Garbled Audio May Be Heard On a Cisco Conference Connection (CCC) Call


March 16, 2005


Products Affected

Product

Comment

2811 - CISCO2811

using c5510 DSP

2821 - CISCO2821

using c5510 DSP

2851 - CISCO2851

using c5510 DSP

3800 - CISCO3825

using c5510 DSP

3800 - CISCO3845

using c5510 DSP

MCEMOD - NM-HDV2-1T1/E1=

using c5510 DSP

MCEMOD - NM-HDV2-2T1/E1=

using c5510 DSP

MCEMOD - NM-HDV2=

using c5510 DSP

MCEMOD - PVDM2-16

using c5510 DSP

MCEMOD - PVDM2-32

using c5510 DSP

MCEMOD - PVDM2-48

using c5510 DSP

MCEMOD - PVDM2-64

using c5510 DSP

MCEMOD - PVDM2-8

using c5510 DSP

MCEVOIC - NM-HD-1V

using c5510 DSP

MCEVOIC - NM-HD-2V

using c5510 DSP

MCEVOIC - NM-HD-2VE

using c5510 DSP

2801 - CISCO2801

using c5510 DSP

Problem Description

Garbled audio may be heard when a Cisco Conference Connection (CCC) server plays the announcement. The root element is that there be a c5510 DSP used for conferencing or transcoding, whatever the platform or network module may be.

Garbled audio can be observed with Unity, CRA, IPCC Express, Extended Services or CCC. These products are known to produce the offending condition.

Certain products may send comfort noise packets that overlap with valid audio packets. Degraded audio may be experienced when the affected Cisco products convert these packets to a time-division multiplexing (TDM) or analog stream.

This issue can occur using all c5510 capable HW, including ISR's using onboard c5510 DSP's.

Conditions: This symptom is observed on a platform that is configured with a module that uses a 5510 DSP such as the products listed in the Products Affected list above. When remote IP phone users dial into the CCC, which supports only the G.711 codec, the transcoder is invoked because of a capability mismatch. The 5510 DSP intermittently generates garbled audio when it attempts to transcode the initial announcement that is played from the CCC.

Background

When Cisco Conference Connection (CCC) Server 1.2.2 sr2 is being used for conferences. It can only do G711ulaw. When calls are made to it that need to be G.729, (WAN) Transcoding resource on products using (c5510 DSP) dspfarm is invoked. When dialing into CCC server, there will be an initial announcement played. When hitting the CCC the call needs to transcode from G.729 to G.711 as CCC uses G.711 only.

Garbled audio was experienced for that initial announcement. Calls made using G.711 do not experience a problem. Problem is reproducible across all platforms using where the transcoding or conferencing resource is C5510 DSPfarm based. The 5510 transcoder does not handle the case where an RTP endpoint sends a comfort noise packet and then sends valid audio before before one packetization period has passed.

Problem Symptoms

Symptoms: Garbled audio may be heard when a CCC server plays the announcement.

Conditions: This symptom is observed on a platform that is configured with a module that uses a 5510 DSP such as an NM-HDV2 network module. When remote IP phone users dial into the CCC, which supports only the G.711 codec, the transcoder is invoked because of a capability mismatch. The 5510 DSP intermittently generates garbled audio when it attempts to transcode the initial announcement that is played from the CCC.

Workaround/Solution

The current workaround is to configure the G.711 codec across the WAN.

An alternate workaround is to configure the platform with a module that uses a 549 DSP as a transcoding resource such as NM-HDV module types.

Another valid workaround is to:

  1. Avoid using the transcoder or

  2. Modify the RTP endpoints so they do no send RTP comfort noise packets.

The DDTs has been resolved and will be integrated into DSPWare 4.4.704, which is currently targeted for Cisco IOS® software version 12.3.11T5.

The current posting for Cisco IOS software version 12.3.11T5 is planned for the end of May.

DDTS

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DDTS

Description

CSCeg87592 (registered customers only)

New 5510 dsp used for transcoding may cause garbled audio with CCC

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

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