Re: [rtcweb] STUN for keep-alive

Christer Holmberg <> Wed, 14 September 2011 10:27 UTC

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From: Christer Holmberg <>
To: "Muthu Arul Mozhi Perumal (mperumal)" <>, "" <>
Date: Wed, 14 Sep 2011 12:29:17 +0200
Thread-Topic: [rtcweb] STUN for keep-alive
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Subject: Re: [rtcweb] STUN for keep-alive
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>|Because, eventhough the keep-alives messages aren't authenticated, and 
>|do not trigger responses, a gateway would still have to 
>|process them, and since a gateway typically would serve a large number of browser 
>|clients, that could have quite big performance impact (the number of 
>|STUN keep-alives sent per session of course depend on how much other 
>|media traffic there is, but still).
>STUN keepalives are required by ICE only in the absence of 
>media traffic.

Yes. That's what I meant with the:

	"(the number of STUN keep-alives sent per session of course depend on how much other media traffic there is, but still)"

...statement :)

>Here are the snip from RFC 5245:
>10.  Keepalives
>If there has been no packet sent on the candidate pair ICE is 
>using for a media component for Tr seconds (where packets 
>include those defined for the component (RTP or RTCP) and 
>previous keepalives), an agent MUST generate a keepalive on 
>that pair.  Tr SHOULD be configurable and SHOULD have a 
>default of 15 seconds.  Tr MUST NOT be configured to less 
>than 15 seconds.
>20.2.3.  Keepalives
>STUN keepalives (in the form of STUN Binding Indications) are 
>sent in the middle of a media session.  However, they are 
>sent only in the absence of actual media traffic. In 
>deployments that are not utilizing Voice Activity Detection 
>(VAD), the keepalives are never used and there is no increase 
>in bandwidth usage.  When VAD is being used, keepalives will 
>be sent during silence periods.  This involves a single 
>packet every 15-20 seconds, far less than the packet every 
>20-30 ms that is sent when there is voice.  Therefore, 
>keepalives don't have any real impact on capacity planning.
>Do you think there is still a problem?

Well, it depends on the amount of outgoing media traffic, but in cases where you only receive media you would still need to send keep-alives.