Subject: [PCN] Second thoughts on detail in draft-moncaster-pcn-baseline-encoding

From: Bob Briscoe <[email-masked]>
Date: Wed, 16 Jul 2008 19:20:15 +0100

Toby,

Commenting on my own draft to the list...

Section 4: Encoding two PCN States in IP
----------------------------------------
>Any packet that belongs to a PCN capable flow MUST have the ECN 
>field set to one of the two ECT codepoints 10 or 01 at the PCN-ingress-node.

Delete 'or 01'

Reasoning: By saying either 10 or 01 it limits future flexibility. It 
would allow a future use of ECT(1) if we made up our minds and 
specified the PCN ingress must only set ECT(0).

And a terminology nit:

>The PCN encoding states are defined using the Type of Service field
>of the IP header which is a combination of the DSCP field and ECN field.

Change to:
'The PCN encoding states are defined using a combination of the 
Differentiated Services field and ECN field.'

Reasoning: When RFC2780 split the TOS field into the DS field and the 
ECN field, I don't think it intended the pair of fields to still be 
called the TOS field. It would be safer to just use 'modern' terminology.

Appendix A. Tunnelling Constraints
----------------------------------
I think we should refer to draft-briscoe-tsvwg-ecn-tunnel-01.txt from 
the last para of this appendix, saying we're trying to fix this 
problem so PCN doesn't have to be an exception.

When I introduced the -00 version to tsvwg a year ago, it attracted 
general support (Sally Floyd, David Black etc), as it makes all IP in 
IP tunnelling consistent with what IPsec now does since RFC4301.

I agreed with the Transport Area Directors' request to hold this 
ecn-tunnel draft back for a year - until it was clearer what the PCN 
wire encoding would be. So I've just posted -01, as I think PCN 
encodign is now converging. Pls comment on tsvwg about ecn-tunnel 
(support please!), cross-posting to PCN if relevant.

Appendix B.
----------
I've lost touch with what the proper PCN terminology is, but this 
appendix seems to be inconsistent. Ignore me if I'm wrong.

Bob

____________________________________________________________________________
Bob Briscoe, <[email-masked]>      Networks Research Centre, BT Research
B54/77 Adastral Park,Martlesham Heath,Ipswich,IP5 3RE,UK.    +44 1473 645196 

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