Hi,
I'd like to start a discussion on how to set speech signal level in an H323 environment.
Speech signal level is an important part of QoS. It directly impacts end user's perception of how good the system works. It is also an integral part of interoperability testing. After the interoperability issues at the protocol level have been ironed out, the signal levels from different vendors have to "match" in order to provide true interoperability for end users.
Some vendors make speech signal level a configurable parameter in their equipment and leave it to end user to decide. However, not all end users are capable of making intelligent decisions on this issue. When signal levels are set improperly, end users will complain about low volume, high volume, and/or echo. If the system consists of equipment from multiple vendors or involves interworking with PSTN/PBX, things can become complicated quickly.
So a set of guidelines on how to determine speech level can benefit equipment manufacturers as well as their customers, including end users and service providers.
I envision the guidelines should cover a number of topics:
1. desired end-end signal attenuation and acceptable range; 2. desired place of attenuation (tx or rx?) and how much; 3. desired level for DTMF and tones 4. desired level of echo cancellation; 5. connection scenarios: terminal-terminal, terminal-gateway, and gateway-gateway.
Issues that we have to contend with include: end user acceptance, voice coder and echo cancellor optimal operation ranges, idle noise levels.
For many of these issues, we can draw upon the wealth body of knowledge from the telephony world. Some of them may only take a reference to an existing standard. Others may require some serious thinking and, more importantly, agreement among multiple vendors.
The discussion certainly is not restricted to voice only applications. But I am not sure if video has an interoperability issue as serious as voice. I am open to any suggestions. We may continue the discussion online or we can discuss face to face at SuperOp next week.
Now here is my question #1: Is SourceInfo/DestinationInfo structure in H225 call setup messages a reliable way to distinguish end point type (terminal, gateway, gk)? What if in a GK-routed call? Does the GK modify that field?
Thanks,
Shan Lu
NexTone Communications, Inc 9700 Great Seneca Highway Rockville, MD 20850 +1 240-453-6315
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