Subject: [TICTOC] Unicast discovery in 1588

From: Richard Cochran <[email-masked]>
Date: Sat, 5 Apr 2014 16:13:35 +0200

Dear list,

Recently I have been considering how to implement the unicast bits of
1588 in linuxptp. It looks like to me that unicast is one of those
grey areas of the standard. I wanted to request an "interpretation",
but it looks like 1588 has been dropped, and so I ask my question
here.

Clause 17.5.1 talks about slaves wanting to use unicast when the
network doesn't provide multicast. In this case, they are supposed to
use unicast message negotiation with the masters in their table.

However, the way to ask for unicast service and the way to configure
the table are both via management messages. These are never unicast,
as far as I can tell. So it seems impossible to use this option.

Does anyone have any insight into this?

Thanks,
Richard

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From: Douglas Arnold <[email-masked]>
Date: Sat, 5 Apr 2014 07:22:50 -0700

Hello Richard,

Systems which use unicast, such as those implementing the ITU G.8265
Telecom Profile, use an Acceptable Master List or equivalent.  In other
words a list of masters and their IP addresses must be created by a sys
admin via a user interface.

Doug

On Sat, Apr 5, 2014 at 7:13 AM, Richard Cochran <[email-masked]>wrote:

> _______________________________________________
> TICTOC mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/tictoc
>

-- 
Doug

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From: Richard Cochran <[email-masked]>
Date: Sat, 5 Apr 2014 16:47:10 +0200

> admin via a user interface.

Yes, I got that part.

But how can a slave send a REQUEST_UNICAST_TRANSMISSION if the network
does not support multicast?

The slave's management request will get dropped.

Thanks,
Richard

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From: Richard Cochran <[email-masked]>
Date: Sat, 5 Apr 2014 17:17:07 +0200

On Sat, Apr 05, 2014 at 08:03:39AM -0700, Douglas Arnold wrote:
> In the implementations I know of, unicast mode is assumed from the start
> and configured via the user interfaces of all devices involved.  The PTP
> management messages are not used.

Okay, I see.

Getting back to the 1588 standard, would you agree then that clause
17.5.1 doesn't make any sense?

Thanks,
Richard

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From: Douglas Arnold <[email-masked]>
Date: Thu, 17 Apr 2014 19:49:38 -0700

---------- Forwarded message ----------
From: Douglas Arnold <[email-masked]>
Date: Thu, Apr 17, 2014 at 7:49 PM
Subject: Re: [TICTOC] Unicast discovery in 1588
To: Richard Cochran <[email-masked]>

Hello Richard,

My reading of the section 17.5.1 is that it states that Unicast Message
Negotiation should be used.  These are unicast messages which would have to
be sent to specific master ports, by unicast, one at a time.  But perhaps I
am too close to the standard, and already know what was "intended".  And,
since you are a smart person, then presumably others are confused by the
vague language as well.  I will pass this on to the maintenance
subcommittee of the 1588 Working Group.

Doug

-- 
Doug

-- 
Doug