Re: [rtcweb] Requiring ICE for RTC calls

Eric Rescorla <ekr@rtfm.com> Fri, 30 September 2011 02:35 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 29 Sep 2011 19:37:40 -0700
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To: Hadriel Kaplan <HKaplan@acmepacket.com>
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Cc: Randell Jesup <randell-ietf@jesup.org>, "<rtcweb@ietf.org>" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Requiring ICE for RTC calls
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On Thu, Sep 29, 2011 at 5:18 PM, Hadriel Kaplan <HKaplan@acmepacket.com>wrote;wrote:

>
> On Sep 29, 2011, at 6:25 PM, Matthew Kaufman wrote:
>
> > Ridiculous. We're not talking something like one SHA-1 HMAC per packet
> received... this is one SHA-1 per connectivity test. That's one or two
> packets *per call*. No way that increases the cost/complexity of any
> possible device that might be terminating or transcoding media.
>
> Not as far as I know; the SHA-1 hash is calculated on every single STUN
> request and response packet, because it covers the STUN header which
> includes the transaction-id, which is unique per request; and the request
> has different content than the response.  So per ICE-pair connectivity
> check, it could be two STUN requests and two responses (for the "normal"
> mode).  And since I'm assuming v4/v6 dual-stack, that's potentially double
> that number.
>
> And yes while 8 SHA-1's per call isn't a lot compared to transcoding or
> terminating media, I wasn't talking about this being done in the PSTN
> TDM-facing gateways themselves, but rather in the "media-plane gateway"
> interworking RTCWeb with the legacy SIP world. (ie, SBCs)  At least I
> assumed that's what people here meant by "media gateways" - it's not like
> real PSTN-TDM gateways are eager to do ICE... nor are MTAs, voicemail
> servers, announcement servers, conference servers, IVRs, etc.
>

Absent some measurements, I tend to agree with Matthew here.
My Macbook Air can do roughly 3x10^3 SHA-1 operations per
second on a single core. In order for this to be 10% of your load,
you would need to be processing on the order of
75K STUN requests/sec/core. How many total calls/second
can you do/core w/o STUN?

-Ekr