Re: [PCN] PCN admission marking algorithm

Anna has pointed out to me that this email should talk about "PCN
threshold marking" rather than "PCN Admission marking". Similarly the
other email should be about "PCN excess marking" rather than "PCN
termination marking". This reflects what we agreed a couple of ietfs ago
& also the phrasing in the architecture draft. Sorry & thanks anna for
spotting the mistake

phil

-----Original Message-----
From: pcn-bounces@ietf.org [mailto:pcn-bounces@ietf.org] On Behalf Of
philip.eardley@bt.com
Sent: 27 February 2008 11:02
To: pcn@ietf.org
Subject: [PCN] PCN admission marking algorithm - consensus?

I think we have consensus on the admission marking behaviour. This is a
first attempt to capture that in Stds language, is it any use?

If an interface of the PCN-domain performs PCN Admission Marking then it
performs three functions, which are outlined in
draft-ietf-pcn-architecture as follows:

   o  Packet classify - decide whether an incoming packet is a PCN-
      packet or not.  Another PCN WG document will specify encoding,
      using the DSCP and/or ECN fields.

   o  PCN-meter - measure the 'amount of PCN-traffic'.  The measurement
      is made as an aggregate of all PCN-packets, and not per flow.

   o  PCN-mark - algorithms determine whether to PCN-mark PCN-packets
      and what packet encoding is used (as specified in another PCN WG
      document).

These functions are now described in more detail.

Note: The PCN-node MAY implement these three functions on either its
ingoing or outgoing interfaces. The same choice MUST be made for every
PCN-node in one PCN-domain. 

Classify function:

If a packet's ECN/DSCP fields have the value PCN, as defined in
[RFC-encoding], then it MUST be classified as a PCN-packet.

If a packet's ECN/DSCP fields do not have the value PCN, as defined in
[RFC-encoding], then it MUST NOT be classified as a PCN-packet.

Meter function:

Note: The meter is described as a 'token bucket with threshold', however
the implementation is not standardised. For example, it could equally
well be implemented as a virtual queue (which operates with negative
tokens).

A packet classified as a PCN-packet MUST be metered as follows. 

The interface MUST have:

[1] a configured bit rate, termed PCN-lower-rate

[2] a meter for PCN-packets, which MUST have the following behaviour:

a token bucket, which 

1A tokens are added at the PCN-lower-rate, to a maximum TB.size

1B tokens are removed equal to the size of the PCN-packet, to a minimum
TB.size=0

2 if TB.fill < TB.threshold, then the meter indicates "admission mark"
to the Mark function

Note: Step 1A can be triggered by a packet and so can be done at the
same time as Step 1B.

Note: Step 2 can be performed before or after step 1

If TB.fill < size of the PCN-packet, then the meter MAY:

a. leave TB.fill unaltered and indicate "admission mark" to the Mark
function

b. set TB.fill = 0 and indicate "admission mark" to the Mark function

c. set TB.fill = 0 and check if TB.fill < TB.threshold and if it is,
then indicate "admission mark" to the Mark function        

Note: Option a is expected to be the simplest to implement. 

Mark function:

If the meter indicates to "admission mark" a PCN-packet, then:

[1] this step is REQUIRED, unless [RFC-encoding] standardises an
encoding that allows a PCN-packet to be simultaneously "admission
marked" and "termination marked":

If the PCN-packet's codepoint is already "termination mark" then it MUST
NOT be altered, ie the following step is not performed.

[2] the PCN-packet's ECN/DSCP fields MUST be set to the codepoint
"admission marked", as defined in [RFC-encoding]

we could also add an example algorithm, such as that in
http://www.ietf.org/internet-drafts/draft-charny-pcn-comparison-00.txt
Fig 10.1
<http://www.ietf.org/internet-drafts/draft-charny-pcn-comparison-00.txt%
20Fig%2010.1>  on page 21.

Comments?

phil

Re: [PCN] PCN admission marking algorithm - consensus?