[asterisk-dev] extend IAX2 IE proposal

[Russell Bryant]

Mihai Balea wrote:
> That is the theoretical maximum UDP packet size.  As I mentioned in one 
> of my previous emails, Mac OSX limits UDP packets to approx. 9K.  I'm 
> sure there are other systems out there that would enforce similar limits 
> (I am thinking embedded systems).

Ah.  Well, for this reason, as well as concerns of having to retransmit an 
extremely large Full frames, I would say that the text in the RFC describing 
this new segmented information element method should only be used in situations 
where the payload is "slightly" larger than 255 bytes, such as the case with the 
OSP token information, which will take 4 segments.  However, the text should 
strongly discourage use of this method for extremely large amounts of data.

> Even if ~ 64K would be achievable, what if I need to transmit 65K? The 
> solution does not scale well and limits like this can be easily exceeded 
> in today's applications.

If we come to a point where we would like to implement the ability to do 
transfers of this size, then we will have to handle it with a separate method.

>> On the topic of holding up the link while transmitting a large packet, 
>> this isn't something that would be newly introduced into IAX2.  In 
>> fact, it is normal to have extremely large IAX2 trunk frames which get 
>> transmitted a lot more often than any signaling frames.
> 
> Trunk frames do not require retransmission.

True.  I was just trying to address the concern about blocking the link while 
the single large packet is transmitted.

> If we're extending the protocol, I would be in favor of defining a new 
> type of large frame plus a packetization mechanism that would be able to 
> transfer an unlimited amount of data.  We could have a separate 
> mechanism of retransmission if needed, as long as we do not impact the 
> existing control and media frames.

I agree with you if we decide to implement a method for doing something like 
peer-to-peer file transfers over IAX2.  However, I still think this generic IE 
segmentation method is perfect for OSP tokens, and perhaps other applications in 
the future which would only take a few segments.

-- 
Russell Bryant
Software Engineer
Digium, Inc.
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