[asterisk-dev] "cRTP, anyone?" and more crackpot ideas

[Klaus Darilion]

John Todd schrieb:
> On Dec 17, 2008, at 3:50 PM, Steve Underwood wrote:
> 
>> John Todd wrote:
>>> Abdul -
>>>   I would disagree with you slightly on the statement that "Anything
>>> other than RTP header compression is bound to fail using the public
>>> internet."  This is already not the case - take a look at how IAX2
>>> does multi-session trunking. (http://www.voip-info.org/wiki-Asterisk+bandwidth+iax2
>>> )  There is always a risk of reordering in transit, but that is a  
>>> risk
>>> that is inherent in any RTP or RTP-like session.
>>>
>> Packets reorder quite frequently, especially when the path has high
>> jitter. RTP packets are sequenced, and a good receiver attempts to
>> reorder them in its jitter buffer. So, any RTP like session has no
>> problems, though many implementations of an RTP channel don't handle
>> things well.
>>
>> I didn't realise how often packets reorder in the real world until I
>> started investigating T.38 failures. If you simply say "packets X and
>> X+2 arrived, so X+1 must be a lost packet" you get significantly worse
>> results than waiting a while to see if packet X+1 appears.
>>
>> Steve
> 
> 
> Interesting that it happens that frequently.
> 
> How frequently is frequently?  Is this endemic in certain network  
> locations, or do you see out-of-order packets with some regularity on  
> any RTP stream that travels a reasonable number of internet segments?

In our office we have Internet access via 2 load balanced DSL lines and 
this setup introduces packet reordering very often.

klaus