[asterisk-dev] extend IAX2 IE proposal

[Derek Smithies]

Hi,
On Fri, 8 Dec 2006, Markku Korpi wrote:
> 
> A new full frame type would provide cleaner protocol architecture, if we could
> start 'on green meadows'. Due to the fact that it would need to be mandatory,
> it would basically be incompatible with the current IAX2 protocol.
> 
> We could avoid introduction of a new full frame type, if we modify Di-Shi
> Sun's segmented OSPTOKEN proposal slightly and turn it to a generic
> segmentation method. It can then be used with any long IE in any message.
> 
||
|| A very excellent suggestion on implementation deleted for brevity.
||
> This method should provide easier backwards compatibility, because an IAX2
> entitity that has not implemented the SEGMENT IE would ignore it.
> 
> Comments?

I am a little concerned about the proposal- it has some aspects that are a 
little concerning.
Suppose someone uses this mechanism to send a 100 K datablock. I know, 
this does seem a little extreme, but it will happen. Given the range of 
users of iax, and the number of users, it is inevitable.
On transmitting the packet, it will be assigned an oseqno.
The network will, because of mtu requirements, break it up into 70 smaller 
packets. - all sent as UDP. On an slightly lossy network, there is a 
chance of one of those packets being dropped. Consequently, the whole
packet fails in the transmission process.

At this point, the IAX2 retry mechanism will be required to resend the 
packet. During this resend period, all other full frames between the two 
iax entities are delayed. The receiving node of the big packet cannot 
acknowledge subsequent full frames - this will imply it has successfully 
received the 100 k datablock.

What do I mean by a slightly lossy network? A network that drops 1/1000 
UDP packets will have troubles with the 100 K data block, on every 13th 
datablock.


yes, I know my scenario here is dependant on two things
 a) the desire to send large blocks of data
 b) a slightly lossy network.

Derek.
-- 
Derek Smithies Ph.D.
IndraNet Technologies Ltd.
Email: derek at indranet.co.nz
ph +64 3 365 6485
Web: http://www.indranet-technologies.com/