[Asterisk-Dev] Increasing reliability on lossy connections

[Steve Kann]

On Jan 12, 2005, at 8:48 PM, Mike M wrote:

> On Wed, Jan 12, 2005 at 02:07:31PM -0500, John Todd wrote:
>> At 12:54 PM -0600 1/12/05, Michael Giagnocavo wrote:
>>>
>>> So, what I was thinking is that if duplicate IAX2 packets were sent, 
>>> then
>>> most packets would get there, at least once. IAX2 would discard the
>>> duplicates, and things would work better, at double the bandwidth. I 
>>> was
>>> thinking about adding an iax.conf option to configure this per user.
>>
>> The better solution would be to implement iLBC's packet concealment
>> methods, and then use that codec for your IAX2 trunking.  I am
>> currently under the impression (someone correct me if I'm wrong!
>> It's been a while since this was discussed...) that the iLBC code in
>> * is not completely implemented due to timing issues, so that iLBC's
>> great packet concealment methods are unused.
>>
>> Sending packets twice is... a frightening hack.
>
> Actually  it's a small form of the PCR error correction method used on
> satellite links.  Preventive Cyclic Retransmission periodically resends
> unacknowledged PDUs until they are ack'd.

The problem with any error-recovery scheme based on retransmissions is 
that it will triple or so your latency, because the retransmission 
can't arrive until about  1.5RTT or so.


-SteveK