RE: restoration time requirement (was Re: Last Call on RSVP Label Allocation for Backup Tunnels)

[Heiles Juergen <Juergen.Heiles@icn.siemens.de>]

Curtis

	>Then again, this is second hand, so I could be completely wrong. This is not a measurement I've made myself and the SONET equipment is not something I'm familiar with .... 

you are completely wrong and I suggest you better make measurments and get familiar with SONET before making such statements.. SONET/SDH equipment will not shut down/drop connections. Today SONET connections are permanent connections setup via the management system. An automatic drop of a conneciton as it is the case for switched connections will not occur. What you will see is the insertion of AIS (alarm indication signal) after the detection of an defect. But as soon as the defect is gone the AIS is removed and the connection is running again. AIS is nothing harmful as due to the defect the connection is interupted in any case. Furthermore the AIS avoids downstream alarms (alarm storms).

What could be of concern are the following points. I talk about a server layer for a SONET/SDH network  (e.g. an Optical Network) providing protection/restoration:

Stacked protection/restoration:
If you use protection/restoration at an optical network layer (server) and a SONET/SDH network layer (client) the server layer switching times should be faster than the client layer reaction times, so that the server layer does the protection/restoration and the client layer doesn't react.

Automatic power reduction/automatic laser shutdown APR/ALS
APR is used for safety reasons in order to avoid harmful emission of laser light in case of a fiber cut. One implementation switches off the transmit laser in case of loss of signal at the receiver. A restart action which is triggered automatically in intervals of several seconds is required in order to test if the link is repaired. Normally the APR function can be switched off if not needed. The APR function needs some careful consideration in case of protection/restoration and automatic connection setup in all optical networks.

Regards

Juergen

> -----Original Message-----
> From:	Curtis Villamizar [SMTP:curtis@workhorse.fictitious.org]
> Sent:	Monday, April 09, 2001 4:37 AM
> To:	Lazer, Monica A, NNAD
> Cc:	'neil.2.harrison@bt.com'; raszuk@cisco.com; mpls@UU.NET; ccamp@ops.ietf.org
> Subject:	restoration time requirement (was Re: Last Call on RSVP Label Allocation for Backup Tunnels)
> 
> 
> In message <31236E6272C7D2119F1C0000C0A8E4F40324083D@nj0200po04.bm.att.com>, "L
> azer, Monica A, NNAD" writes:
> > Voice switches will drop the connections after 2.5 seconds. A large number
> > of dropped calls will cause FCC reportable events, which is something that
> > US carriers need to avoid. So restoration within this time frame is needed
> > for support of trunks carrying voice traffic.
> > 
> > Monica A. Lazer
> > Advanced Transport Technology and Architecture Planning
> > 
> > 908 234 8462
> > mlazer@att.com
> 
> 
> Monica,
> 
> We're off topic, so I changed the subject.
> 
> Thanks for providing the 2.5 second figure.
> 
> I've heard carrier transport people grumble about SONET equipment
> they'd be please to get rid of that will shut down even when used as
> linear SONET with no protect path and as a result would require
> <100msec restoration.  Since there is enough of this SONET gear, the
> carriers can't really get rid of it although it will probably
> disappear over time and so they will make fast restoration a
> requirement of people they buy from.  To be safe, the request for
> <50msec has been made.
> 
> If you are not blessed with such equipment or you are able to work
> around it when doing VoIP, then you are among the fortunate.
> 
> Then again, this is second hand, so I could be completely wrong.  This
> is not a measurement I've made myself and the SONET equipment is not
> something I'm familiar with such that I could say with confidence that
> it could not be configured to hold on longer or to not shut down at> 
> all if there was no protect.
>  
> OTOH there are those who (claim to) want to configure SONET on some
> links but not on others and don't want a fast restoration.  They want
> to be assured that restoration will occur only after it is safe to
> assume that SONET restoration is not available.
> 
> Curtis