Re: [MMUSIC] ICE aggressive nomination problem

Folks,

This aggressive nomination bug is still an open issue for ICE. If time 
permits, I'm hoping to discuss this tomorrow. As a solution, I'm leaning 
towards the updated offer, but would like to hear your opinions on this.

Cheers,
Ari

On 12/19/12 9:50 AM, Ari Keranen wrote:
> Hi all,
>
> Going through the ICE spec reminded me of one old problem with
> aggressive nomination that I discussed with Philip Matthews back when
> ICE was published:
>
> Two endpoints L and R. L is the offerer and controlling end. There are
> two possible paths, and just one component.
>
> Since L is using aggressive nomination, it sets the USE-CANDIDATE flag
> in each Binding request. However, the Binding response for the first
> path does not make it back to L. When the second check succeeds, L
> immediately stops ICE processing and uses the second path. However, R
> thinks the first path is being used.
>
> Initially, L will use path 2 for data, while R will use path 1.
> Eventually, both paths will fail, because L is only sending keep-alives
> on path 2, while R is only sending them on path 1.
>
> L                                         R
>   <--------- Bind req ---------------------  ]
>   ---------- Bind resp ------------------->  ]  Path 1
>   ---------- Bind req, USE-CAND ---------->  ]
>        X <-- Bind resp --------------------  ]
>
>   <--------- Bind req ---------------------  ]
>   ---------- Bind resp ------------------->  ]  Path 2
>   ---------- Bind req, USE-CAND ---------->  ]
>   <--------- Bind resp --------------------  ]
>
> ---
>
>
> Any good ideas how to fix this? Should the controlling agent just keep
> retransmitting even after successful nomination (for how long)?
>
> The updated offer (if we make that MUST in all cases) will help to
> detect the problem though and this could also be added to the list of
> "reasons for not using aggressive nomination unless you really have to".
>
>
> Cheers,
> Ari
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