Re: A Question about "Inter Packet Gap and SOP Lane alignment"
Boaz,
Turning on your receiver in the middle of a packet stream
is an unlikely situation. When your receiver is disabled,
your transmitter is either disabled or reporting break link
(somehow). This should tell your link partner (remember,
these are all point-to-point links) to stop sending data
because there's no one on this end to receive it. In this
manner, when your receiver turns on, it should be receiving
nothing but IDLEs meaning it has time to gain sync before
it starts getting packets. Once it starts getting packets,
the requirement for frequent /A/s and /K/s is gone and the
occasional columns are sufficient to make sure lane alignment
and deskew are still okay.
If your link partner is sending data in light of your
reporting break link, all bets are off.
In order to satisfy the 12-byte average minimum IPG, some
IPGs will be as short as 9 bytes while others may be as
long as 15 bytes (see Steve Haddock's presentation):
http://grouper.ieee.org/groups/802/3/ae/public/jul00/haddock_1_0700.pdf
The longer IPGs are the ones Rich is referring to. Also,
not all links are 100% utilized so there will be cases when
there are no packets to send and longer IPGs will exist.
Regards,
Ben
Boaz Shahar wrote:
>
> Ben and Rich,
> Thank you for the explanations. However, there are some things which I'm not
> so sure about:
>
> 1.Refering the state diagram at the end, after transmitting /A/ or /K/ and
> /R/ columns, we randomize the distance to the next A (Which is uniformly
> distributed between 16 to 31).
>
> Now, if it happened to be /K/, /R/ columns, then the next /A/ could be a
> distance of 16 columns away (Or may never come, if a new packet starts
> before). And, on the contrary, if it was /A/, /R/ and the next packet starts
> immediately, then the next /K/ can be far away. Since the synchronization
> condition requires 3x/K/ per lane and then /A/ for de skewing, due to this
> randomization, if you turn on your receiver at the "middle", you don't know
> when you will be synchronized! Actually, your time for synchronization is a
> random variable.
>
> I think this is a disadvantage relative to the previous proposed /A/, /K/,
> /R/ minimal sequence. Here, you can bound the time for synchronization,
> avoiding the "Random Time" parameter.
>
> At least, if we MUST support this 12 bytes, I would suggest that the third
> column will always be "the other one", i.e. if the first is /A/, and there
> is a third column, it will always be /K/. And if the first is /K/, let the
> third always be /A/, and only then start the randomization process.
>
> In addition, I saw that Rich mentioned again the minimal gap of /A/,/K/,/R/,
> so it still an option? (The MIN IPG is 12 to 16 in this case, instead of 9
> to 12, and the "time to sync" is deterministic.)
>
> Boaz
>
> > -----Original Message-----
> > From: Brown, Ben [BAY:NHBED:DS48] [mailto:bebrown@xxxxxxxxxxxxxxx]
> > Sent: Sunday, July 16, 2000 10:15 PM
> > To: 802.3ae
> > Subject: Re: A Question about "Inter Packet Gap and SOP Lane
> > alignment"
> >
> >
> >
> >
> > Rich,
> >
> > Allow me to clean up a few editing errors to avoid confusion:
> >
> > Rich Taborek wrote:
> > >
> > > 1) No change to EOP column which contains the first 1 to 4
> > columns of the IPG.
> > > Note that the EOP counts towards IPG.
> >
> > The EOP column contians the first 1 to 4 BYTES of the IPG.
> >
> > > 2) Transmit /A/ or /R/ randomly while maintaining minimum
> > 16 column /A/ spacing.
> >
> > Transmit /A/ or /K/ randomly.
> >
> > Enjoy,
> > Ben
> >
> > Rich Taborek wrote:
> > >
> > > Boaz,
> > >
> > > Your question is answered in a presentation made at the La
> > Jolla meeting:
> > > "8B/10B Idle Pattern for 12-byte IPG" by
> > > Rich Taborek and Don Alderrou of nSerial,
> > >
> > http://grouper.ieee.org/groups/802/3/ae/public/jul00/taborek_1
> > _0700.pdf
> > >
> > > This proposal modifies the fixed starting /A/K/R/ Idle
> > pattern for all
> > > applications of 8B/10B encoded 4-lane streams was accepted
> > into the set of
> > > baseline proposals along with the core XAUI/XGXS proposal.
> > The specific change
> > > is as follows:
> > >
> > > 1) No change to EOP column which contains the first 1 to 4
> > columns of the IPG.
> > > Note that the EOP counts towards IPG.
> > > 2) Transmit /A/ or /R/ randomly while maintaining minimum
> > 16 column /A/ spacing.
> > > 3) Transmit /R/
> > > 4) Transmit /K/, /R/ or /A/ randomly while maintaining
> > minimum 16 column /A/
> > > spacing until SOP detected.
> > >
> > > Note that this proposal works for IPGs as small as 9.
> > Detailed state machines
> > > are included at the end of the PDF file.
> > >
> > > Best Regards,
> > > Rich
> > >
> > > --
> > >
> > > Boaz Shahar wrote:
> > > >
> > > > Hello Steve,
> > > > I have a question in regards to your presentation "Inter
> > Packet Gap..." in
> > > > the last meeting:
> > > >
> > > > You suggest to use only 2 columns of Idle as a minimum
> > for IPG. In previous
> > > > proposals (e.g.
> > > >
> > http://grouper.ieee.org/groups/802/3/ae/public/may00/taborek_2
> > _0500.pdf
> > > > slide 14) the suggested gap is a minimum of 3
> > columns-/A/, /K/, and /R/. So:
> > > > Can you please say which of them should be eliminated, or
> > define a procedure
> > > > which say which type of Idle columns should be inserted?
> > > >
> > > > Thanks,
> > > > Boaz
> > >
> > > -------------------------------------------------------
> > > Richard Taborek Sr. Phone: 408-845-6102
> > > Chief Technology Officer Cell: 408-832-3957
> > > nSerial Corporation Fax: 408-845-6114
> > > 2500-5 Augustine Dr. mailto:rtaborek@xxxxxxxxxxx
> > > Santa Clara, CA 95054 http://www.nSerial.com
> >
> >
> > --
> > -----------------------------------------
> > Benjamin Brown
> > Router Products Division
> > Nortel Networks
> > 1 Bedford Farms,
> > Kilton Road
> > Bedford, NH 03110
> > 603-629-3027 - Work
> > 603-624-4382 - Fax
> > 603-798-4115 - Home
> > bebrown@xxxxxxxxxxxxxxxxxx
> > -----------------------------------------
> >
--
-----------------------------------------
Benjamin Brown
Router Products Division
Nortel Networks
1 Bedford Farms,
Kilton Road
Bedford, NH 03110
603-629-3027 - Work
603-624-4382 - Fax
603-798-4115 - Home
bebrown@xxxxxxxxxxxxxxxxxx
-----------------------------------------