Subject: Re: [MMUSIC] RTSPv2 bandwidth indication

From: Magnus Westerlund <[email-masked]>
Date: Wed, 06 Oct 2010 16:03:52 +0200

Hi,

New text proposal for the bandwidth header. Comments appreciated:

The Bandwidth request-header field describes the estimated bandwidth
available to the client, expressed as a positive integer and measured in
kilobits per second. The bandwidth available to the client may change
during an RTSP session, e.g., due to mobility, congestion, etc.

Clients may not be able to accurately determine the available bandwidth,
for example due to that first hop is not a bottleneck. For example most
local area networks (LAN) will not be a bottleneck if the server is not
in the same LAN. Thus link speeds of WLAN or Ethernet networks are
normally not a basis for estimating the available bandwidth. Cellular
devices or other devices directly connected to an modem or connection
enabling device may more accurately estimate the bottleneck bandwidth
and what is reasonable share of it for RTSP controlled media. It is
RECOMMENDED that only clients that has accurate and explicit information
about bandwidth bottlenecks uses this header.

This header is not a substitute for proper congestion control. Only a
method providing an initial estimate and coarsely determine if the
selected content can be delviered at all.

Cheers

Magnus Westerlund

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From: "James M. Polk" <[email-masked]>
Date: Fri, 08 Oct 2010 14:58:30 -0500

Magnus

comments in-line

At 09:03 AM 10/6/2010, Magnus Westerlund wrote:
>kilobits per second.

a minor (by important distinction) - Is this 
basically the interface speed of the client, or 
is this the available BW that isn't being used at 
this time by the client? For example, if the 
client is doing a massive file download (e.g. a 
movie file), the interface speed can be 
significantly different than what is available to RTSP for a new session.

>The bandwidth available to the client may change
>RECOMMENDED that only clients that has

s/has/have

>accurate and explicit information

otherwise, the rest is good to me

James

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From: Magnus Westerlund <[email-masked]>
Date: Tue, 12 Oct 2010 09:56:22 +0200

> significantly different than what is available to RTSP for a new session.

No, it should be what the client believes is available for use. Thus
known consumptions should be deducted.

I can clarify the second paragraph by including that based on link speed
or bottleneck speed the client also needs to deduct known usages or
assign only a certain fraction of the known bottleneck.

Thus my proposal would be:

Clients may not be able to accurately determine the available bandwidth,
for example due to that first hop is not a bottleneck. For example most
local area networks (LAN) will not be a bottleneck if the server is not
in the same LAN. Thus link speeds of WLAN or Ethernet networks are
normally not a basis for estimating the available bandwidth. Cellular
devices or other devices directly connected to an modem or connection
enabling device may more accurately estimate the bottleneck bandwidth
and what is reasonable share of it for RTSP controlled media. The client
will also need to take into account other traffic sharing the
bottleneck. For example by only assigning a certain fraction to RTSP and
its media streams. It is RECOMMENDED that only clients that has accurate
and explicit information about bandwidth bottlenecks uses this header.

Is that clearer?

Cheers

Magnus Westerlund

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From: "James M. Polk" <[email-masked]>
Date: Tue, 12 Oct 2010 12:47:38 -0500

>and explicit information about bandwidth bottlenecks uses this header.

this is good

Thank you

James