Re: [BEHAVE] [rtcweb] FW: New Version Notification for draft-chenxin-behave-turn-websocket-00.txt

Bernard Aboba <> Wed, 15 May 2013 17:20 UTC

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From: Bernard Aboba <>
To: "Hutton, Andrew" <>, "Chenxin (Xin)" <>, "" <>, "" <>
Date: Wed, 15 May 2013 10:19:53 -0700
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Subject: Re: [BEHAVE] [rtcweb] FW: New Version Notification for draft-chenxin-behave-turn-websocket-00.txt
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Andrew Hutton said: 

> When we wrote the draft we did not include this option because we did not see the benefit of additional transport options for TURN given that the existing options (E.g. TURN/TCP and TURN/TLS) seem to be meet our needs.
> So what would be the benefits that justify this addition transport option for TURN?

[BA] In my experience,  institutions with very restrictive security policies (e.g. those that don't allow UDP in or out) also tend to deploy other measures such as deep packet inspection.   So just because some traffic is allowed in or out on port 80 does not mean that TURN/TCP will be allowed on that port - a DPI box may examine the traffic and complain if it doesn't see HTTP being used.  On the other hand, unless the DPI box is upgraded, it will also complain about websockets.  So I think draft-chenxin only helps in a situation where TURN over Websockets would be allowed when TURN/TCP would not be.  That scenario is rare, at least at the moment. 
The argument for TURN over Websocket/TLS is even more difficult to make. While DPI boxes may examine traffic destined to port 443 carefully to make sure that TLS is really being used,  assuming that the DPI box does not see anything it considers fishy, the TLS exchange will complete and the DPI box will lose visibility.  After TLS is running, the DPI box does not have much information available to distinguish TURN/TLS from HTTP over TLS, with or without websockets -- and those things it does have (such as packet size) are as likely to result in an objection to websocket transport as TURN/TLS.  So I'm not sure that draft-chenxin will help in that situation either.