Subject: [ippm] I-D ACTION:draft-ietf-ippm-twamp-08.txt

From: [email-masked]
Date: Mon, 9 Jun 2008 11:15:01 -0700 (PDT)

A New Internet-Draft is available from the on-line Internet-Drafts 
directories.
This draft is a work item of the IP Performance Metrics Working Group of the IETF.

	Title		: A Two-way Active Measurement Protocol (TWAMP)
	Author(s)	: J. Babiarz
	Filename	: draft-ietf-ippm-twamp-08.txt
	Pages		: 25
	Date		: 2008-6-9
	
The One-way Active Measurement Protocol [RFC4656] (OWAMP) provides 
  a common protocol for measuring one-way metrics between network 
  devices.  OWAMP can be used bi-directionally to measure one-way 
  metrics in both directions between two network elements.  However, 
  it does not accommodate round-trip or two-way measurements.  This 
  memo specifies a Two-way Active Measurement Protocol (TWAMP), based 
  on the OWAMP, that adds two-way or round-trip measurement 
  capabilities.  The TWAMP measurement architecture is usually 
  comprised of two hosts with specific roles, and this allows for 
  some protocol simplifications, making it an attractive alternative 
  in some circumstances.

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http://www.ietf.org/internet-drafts/draft-ietf-ippm-twamp-08.txt

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From: David Scheibelhut <[email-masked]>
Date: Mon, 09 Jun 2008 14:35:30 -0500

All,

It would be nice if this protocol could operate on hosts which lack a 
NTP/GPS synchronized clock.

I recommend that unsynchronized hosts (sender or receiver) be required 
to set their clock error estimate in the TWAMP-Test Packet to its 
maximum value, 0xFFFF, 65535.  On seeing this value, a program using 
TWAMP would not attempt to calculate one way timing statistics.  One way 
loss statistics would still be possible.

David Scheibelhut

Alcatel-Lucent

[email-masked] wrote:
> ------------------------------------------------------------------------
>

---

From: "Murtaza Chiba (mchiba)" <[email-masked]>
Date: Mon, 9 Jun 2008 19:14:14 -0700

I believe the 'S' bit indicates whether the clock is synchronized or
not.  So S = 0 is a valid setting indicating no NTP/GPS sync.

-Murtaza

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of David Scheibelhut
> Sent: Monday, June 09, 2008 12:36 PM
> To: IPPM
> Subject: Re: [ippm] I-D ACTION:draft-ietf-ippm-twamp-08.txt
> 
> All,
> 
> It would be nice if this protocol could operate on hosts 
> which lack a NTP/GPS synchronized clock.
> 
> I recommend that unsynchronized hosts (sender or receiver) be 
> required to set their clock error estimate in the TWAMP-Test 
> Packet to its maximum value, 0xFFFF, 65535.  On seeing this 
> value, a program using TWAMP would not attempt to calculate 
> one way timing statistics.  One way loss statistics would 
> still be possible.
> 
> David Scheibelhut
> 
> Alcatel-Lucent
>

---

From: Henk Uijterwaal <[email-masked]>
Date: Tue, 10 Jun 2008 07:25:14 +0200

Hi,

> NTP/GPS synchronized clock.

It can, see RFC 4656.  There is a a clock error word:

  The Error Estimate specifies the estimate of the error and
    synchronization.  It has the following format:

          0                   1
          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |S|Z|   Scale   |   Multiplier  |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The S bit should be 0 if the clock isn't synchronized.

> TWAMP would not attempt to calculate one way timing statistics.

Replace this by a check that the word is less than 0x7FFF  (or actually
0x3FFF, as the second bit must be 0).

 >  One way

TWAMP is about Two way, OWAMP about One way,

Henk

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