RE: [RPRWG] More comments on preemption
If I may answer to it, I would give example of 1/10 G Ethernet PHY which
need
support special symbols which can be inserted at pre-emption point. Since
PHY design has not forseen any such requirement, there is likelyhood of
interoperability problem here.
Regards,
Devendra Tripathi
VidyaWeb Inc.
Pune, India
Tel: +91-20-433-1362
> -----Original Message-----
> From: jeanlou.dupont@xxxxxxxxxxx [mailto:jeanlou.dupont@xxxxxxxxxxx]
> Sent: Monday, May 07, 2001 11:37 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