Subject: RE: [Capwap] Local MAC

From: "Bob O'Hara" <[email-masked]>
Date: Wed, 1 Sep 2004 12:13:54 -0700

Lily,
 
If the description of the local MAC in the taxonomy is accurate, both
local MAC and split MAC perform your first example identically.  For the
second example (drawn from 802.11e), both should behave the same, as
well, performing the 5-step process.  Otherwise, the AC isn't providing
any "C".

 -Bob

-----Original Message-----
From: Yang, Lily L [mailto:[email-masked]] 
Sent: Wednesday, September 01, 2004 11:37 AM
To: Bob O'Hara; Pat R. Calhoun; Chunduru Rama Krishna Prasad;
[email-masked]
Subject: RE: [Capwap] Local MAC

Is there any difference in terms of the sequence of request and response
events that happen? The sequence that I understand for Split MAC, e.g.
for an association request is:

1)       request from STA to WTP

2)       request forwarded from WTP to AC

3)       AC talks to AS, and gets a response from AS

4)       AC sends response to WTP

5)       WTP forwards the response to STA

Does the Local MAC follow the exact same sequence, even though using
different PDU between WTP and AC for step 2) and 4)? 

Even if they follow the same sequence of events for association request,
does that hold true in general for all the management frame handling,
esp. those that don't involve backend AS? For example, take ADDTS
request in the 11e. I can imagine two different sequences here:

1)       ADDTS request from STA to WTP

2)       ADDTS request forwarded from WTP to AC

3)       ADDTS response made by AC 

4)       AC sends ADDTS response to WTP

5)       WTP forwards the response to STA

Or,

1)       ADDTS request from STA to WTP

2)       ADDTS response made by WTP

3)       WTP sends response to STA  

4)       WTP report the response to AC

The round trip time for the former sequence is obviously longer than the
latter. Is there difference in Split MAC and Local MAC on that aspect?

  _____  

From: [email-masked] [mailto:[email-masked]] On
Behalf Of Bob O'Hara
Sent: Wednesday, September 01, 2004 10:05 AM
To: Pat R. Calhoun; Chunduru Rama Krishna Prasad; [email-masked]
Subject: RE: [Capwap] Local MAC

I think the difference can be summed up like this:

The protocol between an AC and the Local MAC and the Split MAC is
semantically identical.  Each uses a different syntax for this protocol.

 -Bob

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Pat R. Calhoun
Sent: Wednesday, September 01, 2004 6:32 AM
To: Chunduru Rama Krishna Prasad; [email-masked]
Subject: RE: [Capwap] Local MAC

Great question.

As you observed below, the primary difference (from what I can tell)
between

split and local MAC is that while the former simply sends the frames
untouched

the latter reformulates the 802.11 messages into another format before
sending

them to the AC. So sure the PDUs look different, but in reality they are
not really

that different, right?

I mean what's the difference between sending a straight association
request to the

AC vs. breaking the association request down into small components and
using the

resulting information to create a message to be sent to the AC?

One could easily argue that using the straight association request will
ensure forward

compatibility with any new IEEE 802.11 related standard. Let's use
802.11k for instance,

there are some new extensions that are added to existing MAC mgmt
frames. So while

a protocol that simply forwards the MAC mgmt frames to the AC will be
able to handle

802.11k transparently, the other approach would require that the IETF WG
get together

and define a way to map the new 802.11k extensions into whatever
protocol was created.

Clearly, we cannot afford to have the IETF's protocol lag behind IEEE
standards.

On the data path, what is the difference between sending the straight
802.11 frame

vs. sending an 802.3 frame with some associated control information that
was derived

from the 802.11 frame to begin with? What happens when protocols like
802.11e change

the actual format of the frame by inserting 2 bytes in the protocol
header? Sending the

straight 802.11 frame to the AC ensures that whatever solution we've
come up with will

be able to support these future extensions, while a protocol that breaks
down the PDU

into an 802.3 frame will cause these extensions to be lost.

It's really not like understanding the 802.11 protocol is a complex
thing - there are

plenty of implementations of 802.11 based products, and some of these
are even available

as open source. So I would argue that parsing 802.11 packets is much
simpler than 802.3

with some control information since those stacks are publicly available.

PatC

  _____  

From: [email-masked] on behalf of Chunduru Rama Krishna
Prasad
Sent: Tue 8/31/2004 10:52 PM
To: [email-masked]
Subject: [Capwap] Local MAC

Hi ,

Please correct if my interpretation of LOCAL MAC is wrong.
WTP terminates 802.11 control packets and nothing is sent to AC .
WTP terminates 802.11 mangement frames and corresponding events are sent
to
AC.
WTP terminates 802.11 data frames, does decryption/encryption based on
unique keys correspond to wireless stations, extracts 802.3 packet from
the
frame and send the frame across to AC. If needed, it might also send
some control information along with each 802.3 packet.
In this case, AC does not have knowledge of 802.11 header. It only needs
knowledge of
CAPWAP protocol, 802.1x termination, specific wireless related
parameters.

What makes it split MAC? My understanding is that, if AC terminates
802.11
frames and
does encyption/decryption and has knowledge of 802.11 frames, then it is
Split MAC.
Is this understanding correct?

Thanks
Rama Krishna

Ch. Rama Krishna Prasad
Intoto Software(I) Pvt Ltd,
Uma Plaza, Nagarjuna circle,
Panjagutta. Hyderabad, AP
Tel No:s  2335 8927/8928/8434

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