Subject: Re: [Capwap] Data channel policy negotiation

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Thu, 14 Sep 2006 09:58:26 -0700

I feel that there are few ambiguities in the capwap 02 draft
related
	to the tunnel creation and data plane policy negotiation.
Forgive me
	if these points have already been brought up and discussed over
this
	list.
	
	1. Draft -02 does not talk about when the capwap data tunnel is
	   created or deleted. Is it implicitly assumed that data tunnel
is
	   created once WTP and AC reach join state?
<PRC> Yes, that is correct.
	
	2. From the draft, WTP can encapsulate and tunnel wireless
packets
	    differently for different wlans. That is why, tunnel mode is
passed
	    to WTP in dot11 add wlan message element.
<PRC> Both MAC mode and Tunnel mode are present. Tunnel mode is not
about having different encapsulation schemes across WLANs, but more
about allowing a WTP to provide local MAC with some SSIDs, and split MAC
with others. In all cases, the encapsulation is the same. I do wonder
whether including MAC Mode on a WLAN basis makes sense, though.
	
	    But how different type of tunneled packets are identified
over
	    the data plane? For e.g., bss0 tunnels 802.3 frames whereas,
	    bss1 tunnels 802.11 frame. So when a capwap data packet
	    arrives at AC, how the employed tunnel mode is identified?
<PRC> Based on the BSSID.

	    Capwap transport header does not carry any payload
	    encapsulation type. Moreover, the radio mac address optional
	    field in capwap transport header may need to carry bssid
instead
	    of radio address -- there are multiple bss on a radio.
<PRC> Correct. I disagree with this decision, but if AC vendors can
figure out a way to provide service, I guess it's up to them.
	
	3. Draft does not also talk about how WTP is informed whether
DTLS
	    is used over data channel or not. Since it is a modifiable
parameter,
	    administrator can decide to turn on DTLS for say wtp0. But
how wtp0
	    would know that administrator has changed this setting? wtp0
might
	    still be sending plain packets which get discarded by the
AC. Actually AC
	    should inform this change over the capwap control plane to
the WTP.
	    But there is no such notification to WTP for this.
<PRC> I don't believe it can be changed "mid-stream". However, a clear
way to signal the need for DTLS over the data channel is required. I've
created issue 221 to track this.
	
	Is that the data plane policy is supposed to be vendor specific
information,
	and it is exchanged through vendor specific payload message
element?
<PRC> Sorry, I don't understand what you mean.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems

________________________________

	From: Hasan Raza [mailto:[email-masked]] 
	Sent: Friday, September 08, 2006 8:03 AM
	To: [email-masked]
	Subject: [Capwap] Data channel policy negotiation

	Hi,

	Thanks
	Hasan 
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