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

[<[e-mail]>]

We've got to have *one* metering function for termination (& one for
adm). 

 

I thought the idea was that lc-pcn would get into anna's comparison
draft, ie in the same format & the same general level of understanding
of how it works (the latter being a pre-requisite to getting it in
there!). 

 

Even so, I looked at the latest lc-pcn & S4.3.1 (interior node &
termination) and it says:

The PCN-interior-nodes can measure the PHB aggregated PCN traffic
   that exceeds a configured-admissible-rate and mark this excess PCN

   traffic

 

which is exactly what the email below does.

                          

Please explain what youre concerned about!

thanks.

 

Phil/

 

-----Original Message-----
From: Georgios Karagiannis [mailto:[e-mail]] 
Sent: 28 February 2008 13:08
To: Eardley,PL,Philip,CXR9 R; [e-mail]
Subject: RE: [PCN] PCN termination marking algorithm - consensus?

 

Hi Phil

 

I am not in favour of using the token bucket as the only metering
function that can be used in PCN!

Regarding the comparison, I think that if you want to base any decission
on it, then 

the LC-PCN algorithm should also be included in this comparison!

 

Best regards,

Georgios

 

 

 

 

 

	 

	
________________________________


	From: [e-mail] [mailto:[e-mail]] On
Behalf Of [e-mail]
	Sent: woensdag 27 februari 2008 14:13
	To: [e-mail]
	Subject: [PCN] PCN termination marking algorithm - consensus?

	Here also is an attempt for consensus on the termination marking
behaviour.

	 

	 

	 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. 

	[Lars has commented: do we need to allow this choice?]

	 

	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. However, if
the PCN-packet is already "termination marked", as defined in
[RFC-encoding], then the Meter function SHOULD NOT be performed. (*)

	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', however the
implementation is not standardised.

	 

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

	The interface MUST have:

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

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

	 

	a token bucket, operating in bits: 

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

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

	2 if TB.fill = 0, then the meter indicates "termination 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

	 

	The following SHOULD be done (**) instead of Step 2 above (Step
2 is then superfluous).

	if TB.fill < maximum size of PCN-packet, then the meter
indicates "termination mark" to the Mark function

	The "maximum size of PCN-packet" is the MTU in bits of any
PCN-packets in the PCN-domain. 

	Note: Step 1B above is still performed. 

	 

	 

	Mark function:

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

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

	 

	 

	(*) Explanation: for CL termination (ie the termination based on
rates, rather than the 3SM termination based on marked pkts), if the
meter counts pkts that are already termination marked then there'll be
over-termination in the event of multiple bottlenecks. However, since
this option is probably more complicated to implement than a normal
classifier (?), I suggest it is a SHOULD.

	 

	(**) Explanation: this captures the point that Michael makes in
http://www3.informatik.uni-wuerzburg.de/staff/menth/Publications/Menth08
-PCN-MFT.pdf
<http://www3.informatik.uni-wuerzburg.de/staff/menth/Publications/Menth0
8-PCN-MFT.pdf>  & Bob makes in
http://www.ietf.org/internet-drafts/draft-briscoe-tsvwg-byte-pkt-mark-02
.txt
<http://www.ietf.org/internet-drafts/draft-briscoe-tsvwg-byte-pkt-mark-0
2.txt>  Otherwise flows with big pkts get marked more than flows with
small pkts. However, since this option is more complicated to implement
than a normal token bucket, I suggest it is a SHOULD.

	 

	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

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