RE: [RPRWG] Phy Layer question
Regarding the issue of RPR MAC being phy agnostic we voted and it was
approved. Nevertheless the RPR standard will have to deal with some issues
that are phy dependent:
- Are we going to rely only on RPR alarms to perform protection switch ? My
position here is that we have to take into consideration layer 1 alarms
also, then:
- Which layer 1 alarms are the ones that trigger the protection mechanism.
For example SONET phys can monitor for LOS, LOF, AIS (Line and Path), TIM
(Section and Path), ... alarms, while GE phys monitor RxLOS. GR-253 defines
that protection should be performed for LOS, LOF, AIS-L.
- SONET APS uses also BER monitoring as a trigger to switch. Is RPR going to
have a BER monitoring capability to provide a similar behavior ?.
- Is RPR going to support all the SONET APS stack (Lockout, Forced, SF, SD,
Manual, Exercise) ?
- As Mike noted, the user should decide which protection mechanism should be
allowed first, this means that RPR should allow enough flexibility in the
protection timers to cope with all the protection mechanisms provided by
layer 1 phys that we consider candidates for RPR.
I recommend that the RPR WG come up with a list of "preferred" phys for RPR
(My opinion: SONET/SDH and GE) and define their interface with RPR in some
detail, and have a general statement for other phys.
Leon
-----Original Message-----
From: Mike Takefman [mailto:tak@xxxxxxxxx]
Sent: Thursday, April 19, 2001 5:08 AM
To: Karighattam, Vasan
Cc: stds-802-17@xxxxxxxx
Subject: Re: [RPRWG] Phy Layer question
Vasan,
With my Chair hat on.
A SONET framer does not have to be de-featured to work with an
RPR MAC. It is my technical opinion that 802.17 will not use
every feature of SONET but that there is no advantage
to trying to create a reduced functionality SONET framer.
There are plenty of SONET chips out there and no-one will
want to redesign and reverify to save a few thousand gates.
We want 802.17 to flow packets through SONET clouds, DWDM
clouds and dark fiber. Therefore, we want to make sure we
do not throw away any features of the layer 1 that are
required to operate in the appropriate environment.
With my Cisco Hat on.
SRP does not use K1/K2 or any of the SONET APS signalling.
It uses the SONET frame as a way to get a PDU from one
node to the next. Most of our customers prefer SONET to
GE due to the performance monitoring features.
That being said, SRP can work in a SONET cloud when provided
with a protected circuit and the SRP protection mechanism
can be configured to allow Layer 1 to try to protect first.
We do not encourage this mode of operation and suggest to
customers that they use unprotected circuits and allow SRP
to do the protection.
cheers,
mike