RE: [RPRWG] More comments on preemption
All,
Suppose there is an existing metro ring that wants to upgrade to RPR.
Suppose it uses 10G Ethernet with 8B10B encoding. If a new entry in the
line encoding table is used to support preemption, then the phy (the PCS is
in the phy) must be changed to support this. Might there not be equipment
that does not support this change? In that case, both the phy and MAC must
be replaced in order for the ring to support RPR. This would be an extra
cost to the ring operator, and could delay or discourage the operator from
implementing RPR.
It would also mean that the spec for the PCS would need to be changed to
accomodate this, unless 802.17 wants to define phy as well as mac.
I realize there are all kinds of semantics involved here, and I am the first
to admit that I don't know what a metro ring operator's plant or economics
are like, but the basic point is to go carefully along paths that require
changes to phy.
I have no stance on preemption, or any other RPR issue, really. My personal
preference is to be allowed to fade back into the noise and watch the very
interesting debate going on here. But maybe I blew that.
Regards,
Robin Uyeshiro
whose opinions are my own and do not reflect on my employer or anyone else.
-----Original Message-----
From: jeanlou.dupont@xxxxxxxxxxx [mailto:jeanlou.dupont@xxxxxxxxxxx]
Sent: Monday, May 07, 2001 8:37 AM
To: Uyeshiro, Robin
Cc: 'Raman Venkataraman'; Devendra Tripathi; William Dai;
stds-802-17@xxxxxxxx
Subject: RE: [RPRWG] More comments on preemption
Hi;
Could you emphasize on what you mean by: "Interoperability or usage of
existing
plant may be compromised." ?
jld.
Disclaimer: I am also not in favor of any preemption mechanism.
To: "'Raman Venkataraman'" <kvraman@xxxxxxxxxxxxxxxx>, Devendra Tripathi
<tripathi@xxxxxxxxxxxx>, Jeanlou Dupont/MAIN/MC1@MCMAIN
cc: William Dai <wdai@xxxxxxxxxxxx>, stds-802-17@xxxxxxxx
Subject: RE: [RPRWG] More comments on preemption
Sorry to interject, but I feel this may be relevant:
Preemption without retransmission requires stuff in a phy layer that may not
be there. It may mean that this limits which phy layers can be used, or it
may use a phy in ways for which it was not designed. Interoperability or
usage of existing plant may be comprimised. One should be very careful
about doing this.
Thanks, I feel better now.
Regards,
Robin Uyeshiro
-----Original Message-----
From: Raman Venkataraman [mailto:kvraman@xxxxxxxxxxxxxxxx]
Sent: Saturday, May 05, 2001 4:35 AM
To: Devendra Tripathi; jeanlou.dupont@xxxxxxxxxxx
Cc: William Dai; stds-802-17@xxxxxxxx
Subject: Re: [RPRWG] More comments on preemption
Hi Devendra,
You are correct about the Ethernet requirement. That is exactly my point.
Any preemption scheme that we propose should not have any implication on the
layers (encapsulation & transport) below 802.17 MAC. With this reference to
POS, the only advantage is that packet encapusulation may be considered to
be
within the 802.17 MAC layer; otherwise, embedding ESC sequence is not
providing
any significant advantage for preemption. In any case, I am not in favor
of
using ESC sequence for preemption.
Regards
Raman
----- Original Message -----
From: Devendra Tripathi <tripathi@xxxxxxxxxxxx>
To: Raman Venkataraman <kvraman@xxxxxxxxxxxxxxxx>;
<jeanlou.dupont@xxxxxxxxxxx>
Cc: William Dai <wdai@xxxxxxxxxxxx>; <stds-802-17@xxxxxxxx>
Sent: Friday, May 04, 2001 11:16 AM
Subject: RE: [RPRWG] More comments on preemption
> Hi Raman,
>
> >From my Ethernet background, the control symbols are differentiated only
> by PCS layer (or a small sub layer of MAC marked as re-conciliation
layer).
This is because in Ethernet there is no concept of extensive header per
> packet. Since RPR MAC is expected to operate with Ethernet PHYs, it is
> important to consider the implications there. Could you clarify how ESC
will
> be
> embedded by POS ?
>
> Regards,
> Devendra Tripathi
> VidyaWeb Inc.
> Pune, India
> Tel: +91-20-433-1362
>
> > -----Original Message-----
> > From: Raman Venkataraman [mailto:kvraman@xxxxxxxxxxxxxxxx]
> > Sent: Friday, May 04, 2001 7:14 AM
> > To: Devendra Tripathi; jeanlou.dupont@xxxxxxxxxxx
> > Cc: William Dai; stds-802-17@xxxxxxxx
> > Subject: Re: [RPRWG] More comments on preemption
> >
> >
> > Hi,
> > My understanding of William's proposal for the IDLE/Escape marking is
> > in the 802.17 MAC level and it is not clear to me why PCS layer is
getting involved. It looks to me that if we use the POS transport, the
special
ESC sequence can be used for detecting the special markings. However, if we
use
the
> > GFP for the transport, the escape sequences will be stripped before
encapsulating the packets into the GFP. So, it looks like this method will
work
if we use the POS.
> > Regards
> > Raman
> > ----- Original Message -----
> > From: Devendra Tripathi <tripathi@xxxxxxxxxxxx>
> > To: <jeanlou.dupont@xxxxxxxxxxx>
> > Cc: William Dai <wdai@xxxxxxxxxxxx>; <stds-802-17@xxxxxxxx>
> > Sent: Thursday, May 03, 2001 6:17 PM
> > Subject: RE: [RPRWG] More comments on preemption
> >
> >
> > >
> > > Hi William,
> > >
> > > Actually, it is not just a question of symbol. The PCS layer of 1/10 G
> > > Ethernet PHY makes quite a few assumtions on where an IDLE can come.
IDLE
is also used to decide on clock compensation. In all likelyhood such a
> > packet will be declared erroneous ( I need to look this more seriously
to be
> > > conclusive).
> > > If we decide to use the reserve symbol to mark Escape, there may be
> > > compatibility (of PHY devices) issues.
> > >
> > > The other issue is related to frame format change at gateway (LAN/MAN)
> > > points.
> > > The default understanding which I had was that when a Packet from LAN
> > comes to Metro area, it requires add/delete of header and that is about
it
(as for as frame format is concerned). But this may not be strong issue
though.
> > >
> > > Regards,
> > > Devendra Tripathi
> > > VidyaWeb Inc.
> > > Pune, India
> > > Tel: +91-20-433-1362
> > >
> > > > -----Original Message-----
> > > > From: jeanlou.dupont@xxxxxxxxxxx [mailto:jeanlou.dupont@xxxxxxxxxxx]
> > > > Sent: Friday, May 04, 2001 4:53 AM
> > > > To: Devendra Tripathi
> > > > Cc: William Dai; stds-802-17@xxxxxxxx
> > > > Subject: RE: [RPRWG] More comments on preemption
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Could you clarify your statement "... definitely takes us away
> > > > from Ethernet"?
> > > >
> > > > If you are targeting your comment at the Ethernet PHY layer: the
> > > > Ethernet (100
> > > > & 1000) uses 8B/10B encoding.
> > > > There are some "spare symbols" not used (if I am not mistaken)
> > > > that could be
> > > > redefined to mean "IDLE/Escape".
> > > >
> > > > Jean-Lou Dupont
> > > > Marconi Networks.
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > To: "William Dai" <wdai@xxxxxxxxxxxx>, stds-802-17@xxxxxxxx
> > > > cc: (bcc: Jeanlou Dupont/MAIN/MC1)
> > > >
> > > > Subject: RE: [RPRWG] More comments on preemption
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > > 3. Each M and L packet transfer will be inserted an "IDLE/Escape"
> > > > > word for every 256 byte (for the sake of alignment/padding
> > concern)
> > > > > as the preemptive insertion point.
> > > >
> > > > This is very good idea to manage pre-emption and other QOS related
> > > > considerations but this definitely takes us away from Ethernet.
> > > >
> > > > Regards,
> > > > Devendra Tripathi
> > > > VidyaWeb Inc