[Standards] Coping with low bandwidth channels in Jingle
paulrw at codian.com
Wed Feb 13 14:13:33 UTC 2008
Dave Cridland wrote:
> On Wed Feb 13 13:13:26 2008, Lauri Kaila wrote:
>> If I understood you, a client should know its network capacity. Then
>> it tells that infromation to the other end so they can agree on the
>> best media fromat that doesn't exceed the limit. But isn't it almost
>> impossible to know actual end-to-end bandwidth beforehand unless some
>> kind of QoS is present?
> Sometimes the user knows the bandwidth of the immediate upstream link.
> Often, though, they don't - people usually know the advertized maximum
> downlink bandwidth, but usually don't know either the upstream, nor
> the actual bandwidth of either direction.
> The actual device may know it's immediate link rate. Sometimes, at
> least - often actual link rates are deeply buried inside weird APIs,
> and finding overhead, latency, and other somewhat related link
> characteristics isn't usually possible.
> But there is indeed no practical way to know the end to end bandwidth
> short of measuring it, and that measurement is quite tricky. There's a
> very interesting paper on the subject of intermediate link measurement
> by van Jacobson, actually. People interested in this sort of thing can
> probably find it with a Google for pathchar, or download pchar (an
> open source implementation). You'll note it takes several minutes for
> each hop, and uses quite a bit of traffic to do so.
Fortunately, actually knowing the bandwidth is not necessary:
More information about the Standards