[EMAIL PROTECTED] wrote:
Its not a limitation. Its an architectural design which is based on
pulse code modulation (pcm) standards, which essentially says:
- 8,000 audio samples per second,
- each sample is an 8-bit value
- resulting in 64,000 bits/second (like g711 codec standard)
Thank you for your answer, but I don't think you read/understood my
question?
The Zaptel driver uses a 8 byte buffer for buffering G.711 in each
direction. This has nothing to do with the sample rate, but how large
packets you can buffer the voice for to be transported through the PCI
interface. I get the impression that the Digium boards are limited to
8 bytes (1 ms ) by reading the zaptel driver. But, I don't know this
cause I have no hardware manual that cover the PCI interface. I was
hoping that the Sangoma boards offered a more variable buffer size???
The current cards from Digium use bus mastering, so the amount of
buffering on the board should not be a big issue, unless the PCI latency
in really bad. The 1ms buffering is a driver issue, and was a design
choice which made a lot of sense originally. It might make less sense now.
- 1ms ensured the latency between E1/T1 ports bridged in the drievr was
low, and EC would not be an issue. The latest revision of the 4 port
E1/T1 cards from Digium now have on board bridging, so this is less of
an issue. It still matters when bridging between cards, though.
- 1ms ensured good EC convergence, using software EC. Adding delay
really degrades the performance of an EC adaption loop. It may be a
block size of 2 or 3 ms might have been a better compromise between
adaption performance, and the necessary response time of the software.
However, making the block size considerably bigger - say ta 20ms block,
which is what * generally works with in its core - would significantly
degrade EC adaption. Now there are cards with hardware EC, for which
20ms blocks seems to make a lot of sense. However, right now they still
all work in the same 1ms block manner.
Regards,
Steve
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