The MPLS-OPS Archive

["McCoy, Chris" <Chris.McCoy@spirentcom.com>]

Sylvia,

  It isn't really a hop count, it reflects the stability of the clock source
used by the upstream node.  If a node is externally timed by a Stratum 1
Primary Reference Source (PRS) like GPS or Cesium Beam frequency standard,
its priority will be higher, than say, a freerun node that is on its own
internal oscillator (Stratum 3E or lower).  If the node in question picks a
stratum 1 source, it will send on its links an SSM indicator of being
stratum 1 timed so all the downstream neighbors can pick a better timing
source if they need.

  Sorry for not including the list.

Chris M.

-----Original Message-----
From: Spice Sylvia [mailto:falsesylvia@yahoo.co.uk] 
Sent: Monday, March 21, 2005 10:15 AM
To: McCoy, Chris
Subject: RE: [MPLS-OPS]: question...


Hi,

So do we use signal strength as a measure in this
case?

Or is it  more of "the one closer to my preferred
clock source"?

Do you mind if I post this back to the list? I am sure
other people would be interested.

--- "McCoy, Chris" <Chris.McCoy@spirentcom.com> wrote:
> Sylvia,
> 
>   I don't know if anyone wrote you back on this.  I
> know SONET uses
> something called Sync Status Messaging which is the
> S1 byte in the overhead.
> It's a very basic system that has values that
> reflect the timing source
> stability for the upstream node (stratum 1 vs.
> stratum 2, free run, etc.).
> A node listens to the S1 byte on all links and picks
> the link with the
> highest priority from which to derive timing for the
> node.  It isn't really
> a vector system.
> 
> Chris M.
> 
> -----Original Message-----
> From: Spice Sylvia [mailto:falsesylvia@yahoo.co.uk]
> Sent: Monday, March 21, 2005 6:29 AM
> To: mpls-ops@mplsrc.com
> Subject: [MPLS-OPS]: question...
> 
> 
> Do SONET or SDH use somethig like MSDP to vector
> towards stratum clocks when deciding which clock
> source to sync up... (if clock is derived from line)
> 
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