[asterisk-dev] Skinny protocol messages with recent Cisco phones-

Damien voip at facts.com.au
Tue Jun 5 15:24:29 MST 2007

Dan Austin wrote:
> I don't have wireshark, so I am open to suggestions.
> My sniffer is reporting it as 'extra bytes'.  At least
> one of structures in the current code is using :
> uint32_t space;
> To generate 4 bytes of padding, so I extended the concept.
> I have a patch that I am cleaning up right now, and I
> can/will open a bug with it attached.
> My 7940 is still functional after these changes, so the
> older phones do not care if the packet is padded, but the
> new ones choke if it is not.  Based on that observation, I
> would tend to think that this approach is valid not only
> for trunk, but also branches/1.4 since the code tries to
> support the new devices.
> An alternate approach is to duplicate all of the structures
> and have versions for old and new phones and make the general
> code aware of the difference so we send old style packets
> to legacy models and the new style for the current models (yuck).
> Dan
I think the older devices are fairly tolerant to different size packets. 
Some of the structures in chan_skinny are still not complete, meaning 
they are shorter than anticipated. If the phones needed all of the data, 
no devices would be working on the current code (example, 
CALL_INFO_MESSAGE is still missing some stuff at the end).

It's probably reasonable to assume that these devices accept longer 
packets and just grab the stuff they want. Your initial am/pm patch 
wouldn't have worked as you added another byte to the data structure, 
but it did, so I think it's safe to say that the old devices just ignore 
the extra data.


PS I don't like the idea of duplicating all the structures.

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