[Standards] IBB fallback in SI file transfer

Goffi goffi at goffi.org
Mon May 2 08:53:23 UTC 2016

The IBB fallback is not clearly defined in SI. As there is Jingle now which 
define it in a clear way, it's just a matter of time to see SI being deprecated 
and Jingle pushed more forward.

The current issue blocking the move, is that Jingle File Transfert is still in 
experimental state, and evolving (we still lack an URI scheme for instance).

In our client we have implemented SI with both S5B and IBB to be compatible 
with older clients, but we have no fallback mechanism there, and use jingle 
when available.

So in my opinion, we should not try to fix SI fallback and deprecate it as soon 
as Jingle File Transfert is a draft standard.


Le lundi 2 mai 2016, 10:25:01 CEST Christian Schudt a écrit :
> Hi,
> I've had a brief discussion [1] about how the fallback to IBB works in SI
> filetransfer. 
> It's mentioned twice in XEP-0096 and it reads like a fallback to IBB is
> intended to work but it lacks a proper description about how it actually
> works. 
> My interpretion is this:
> 1. Initiator initiates file transfer offering S5B and IBB
> 2. Receiver chooses S5B
> 3. Initiator offers at least one stream host
> 4. Receiver can't connect to any host and returns <item-not-found/>
> 5. Initiator then opens an IBB session (same session id)
> 6. Receiver should always be prepared for the incoming IBB <open/>, because
> it's a mandatory technology. 
> Another interpretion is to start from 1. again after receiving
> <item-not-found/>, i.e. starting a new file transfer session, but this time
> only offering IBB. I think this probably leads to poor user experience due
> to a new file transfer request. 
> I know there's Jingle File Transfer, which specifies the fallback more
> precisely, but it's rarely implemented yet, experimental and doesn't help
> with the existing specification and implementations. 
> Do you have any thoughts about it?
> -- Christian
> [1]: https://community.igniterealtime.org/thread/58601
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