Subject: SONET APS Question

From: "Nakum, Vimal" <[email-masked]>
Date: Thu, 6 Jun 2002 15:08:44 -0700

> Hi,
> 
> In SONET standards, it is mentioned that K1/K2 bytes carry APS Protocol
> bytes on protection line when signal degrade happens on working line.
> Suppose after some times, working line becomes up. Now, when signal
> degrade happens on protection line, how link switches back to working line
> ? Does working line carries K1/K2 bytes, indicating switchover to working
> line  or  both ends assume that now transfer will be on working line ?
> 
> Thanks,
> 
> Vimal Nakum

---

From: "Sivaram Namakal Balakrishnan" <[email-masked]>
Date: Fri, 7 Jun 2002 09:48:01 +0530

There are two things to be noted here.

Traffic in a 1+1 fashion – that is a non-revertive protection switching.

or Traffic in 1:1 fashion – that is revertive protection switching.

In the first case, K1/K2 byte in protection fiber indicates and performs
a traffic switch. Since traffic is not expected to be reverted here, it
stays in the protection fiber. A manual switch is performed to revert
the traffic.

In the second case, a timer mechanism is built into the system. This is
normally called “Wait to restore”. In most of the cases this period is
user configurable. So when the traffic stabilizes in the working fiber,
the configured period has to be passed (say for example 5 minutes.) and
then the traffic switches back to the working fiber. This is referred to
as automatic reverting of traffic.

So there is nothing like K1/K2 bytes in working fiber.

Sivaram Balakrishnan
WIPRO Technologies
WIPRO ~ NORTEL LAB
OPTera Management Framework & Solutions Verification
* +91-80-8520408 x3315      ESN 877-8523
* email: [email-masked] 
72, Electronic City, Hosur Road, Bangalore 561 229 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Nakum,
Vimal
Sent: Friday, June 07, 2002 3:39 AM
To: [email-masked]'
Subject: SONET APS Question

Hi, 

In SONET standards, it is mentioned that K1/K2 bytes carry APS Protocol
bytes on protection line when signal degrade happens on working line.
Suppose after some times, working line becomes up. Now, when signal
degrade happens on protection line, how link switches back to working
line ? Does working line carries K1/K2 bytes, indicating switchover to
working line  or  both ends assume that now transfer will be on working
line ?

Thanks, 

Vimal Nakum

---

From: Stephen Trowbridge <[email-masked]>
Date: Fri, 07 Jun 2002 13:47:25 -0600

Vimal,
Actually, while K1/K2 MAY be carried on both Working and Protection,
for SONET and (normal ETSI style) SDH, the control of protection
switching occurs according to K1/K2 carried on the Protection section.
If protection is no good, there is no point in trying to switch
from working to protection.

The exception is the (Japanese style) 1+1 bi-directional optimized
flavor that you find in Annex B of ITU-T Rec. G.841. Here, we label
one section as Primary and the other as Secondary, carrying the APS
bytes on the Secondary section (similar starting condition to normal
SONET or SDH). However, after a switch occurs and the fault cause
clears, instead of reverting back to restore service to the primary
section, the sections are renamed so that the newly active section
(previously called Secondary) is now called Primary and vice-versa.
At this point, APS bytes are recieved from the other section. In
this flavor of linear switching, APS bytes are always transmitted
on both sections, but received from whichever section is Secondary
at the moment.

Regards,
Steve Trowbridge

> "Nakum, Vimal" wrote:
> 
> Hi,
> 
> In SONET standards, it is mentioned that K1/K2 bytes carry APS Protocol bytes on protection line when signal degrade happens on working line. Suppose after some times, working line becomes up. Now,
> when signal degrade happens on protection line, how link switches back to working line ? Does working line carries K1/K2 bytes, indicating switchover to working line  or  both ends assume that now
> transfer will be on working line ?
> 
> Thanks,
> 
> Vimal Nakum