Subject: Re: [ippm] Synchonization state: consistency among owdp and ippm mib

From: stanislav shalunov <[email-masked]>
Date: 02 Aug 2002 03:41:10 -0400

"Robert Holley" <[email-masked]> writes:

> The sender can know where the reciever gets it time source. The
> information is maintained in the NTP MIB. This may be accessed by
> the "separate communication channel" reference in the thread below.

The measurement protocol has to work for clocks that are not
disciplined using NTP.  (For example, Surveyor normally goes across a
PCI bus to a GPS receiver each time it needs a timestamp.)

Even in a world where each clock is disciplined using NTP, NTP source
will only tell you the immediate parent.  Running ntptrace for each
packet isn't an option (and ntptrace doesn't always work).

Even if running ntptrace for each packet were an option, not getting
to the same ultimate parent means what?  It's obviously perfectly OK
to use, e.g., two different (local to each host) GPS cards for the
sender and the receiver.

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

"You wake me up early in the morning to tell me I am right?  Please
wait until I am wrong."	-- John von Neumann, on being phoned at 10 a.m.
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From: "Robert Holley" <[email-masked]>
Date: Fri, 2 Aug 2002 09:36:27 -0400

Stanislav,

In your example, the Surveyor system would be considered an "authoritative
source" since it obtains it time from a GPS. But that is very implementation
specific. What if a system has a GPS, but only checks it once a day or less
(perhaps on initialization). Then it is dependent on the accuracy and
resolution of the system clock (high/low or malfunction) quality may drift
from true time.

In the Internet time synch network, authoritative servers that provide
synchronization to a sizeable population of clients normally operate as a
group of three or more mutually redundant servers, each operating with three
or more stratum 1 or stratum 2 servers in client/server modes, as well as
all other members of the group in symmetric modes. This provides protection
against malfunctions in which one or more servers fail to operate or provide
incorrect time.

In other words, even with the presence of stratum 1 servers, the time is
compared with other stratum 1 servers for protection.

So, even though a system may be connected to a GPS, it is not a guarantee
that it will provide true time.

It is reasonable to say that running ntptrace is not practical. But it may
be practical to say that the end-point needs to support ntpd so that it can
DESCRIBE its synchronization state in clear and well defined terms.

Even if it is an authoritative source (e.g. GPS) and it is the only node in
the synch tree, using ntpd, it will be able to accurately describe it's
state wrt time and provide sufficient information to infer whether the time
should be "trusted".

NTP is the current state-of-the-art with regards to describing time in a
network environment.

Since a critical component of this work is a concept of agreement in time
between two network clocks, it seems reasonable that utilization of NTP
concepts should be a requirement.

If IPPM is expected to work with systems that are not disciplined by using a
well known system as NTP, then an alternative mechanism would be needed to
insure credibility of the measurements.

I suggest that it would be a simpler implementation effort, if it was
accepted that the current NTP concepts be utilized and required.

Even using NTP, a problem still exists. Namely what is the algorithm and
which NTP parameters should be collected and deemed sufficient for a Server
to validate that the collected IPPM data is accurate?

regards
============================================
Robert Holley
Network Consulting Engineer
Global Solutions Engineering

Cisco Systems
7025 Kit Creek Road.
Research Triangle Park, NC 27709
Phone:  +1 919-392-2359
Pager:   +1 800-796-7363 pin 100-9187
============================================

> -----Original Message-----
> From: stanislav shalunov [mailto:[email-masked]]
> Sent: Friday, August 02, 2002 3:41 AM
> To: Robert Holley
> Cc: [email-masked]
> Subject: Re: [ippm] Synchonization state: consistency among owdp and
> ippm mib
>
>

---

From: stanislav shalunov <[email-masked]>
Date: 02 Aug 2002 10:13:00 -0400

"Robert Holley" <[email-masked]> writes:

> [...] the end-point needs to support ntpd so that it can DESCRIBE
> its synchronization state in clear and well defined terms.

So you want to make running NTP a prerequisite to running OWAMP.
This would be a reversal of decisions made on this list in February
2001 (http://mailhost.advanced.org/archives/ippm/2001-February/001308.html
and its thread).

I don't see a compelling case to make a little Ethernet switch that
might run OWAMP run NTP as well.

"Nuclear war can ruin your whole compile."          -- Karl Lehenbauer
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From: "Robert Holley" <[email-masked]>
Date: Fri, 2 Aug 2002 11:27:47 -0400

Stanislav,

Thanks for the historical perspective. I'm reading through the thread now.

In general I feel that if one wishes his opinions to be considered, then
they should be offered at the appropriate time.

If this was decided in Feb 2001 and if there are not very compelling reasons
to re-visit the issue, then I would agree that the status quo should be
unchanged.

regards
Bob

> Sent: Friday, August 02, 2002 10:13 AM
> To: Robert Holley
> Cc: [email-masked]