RE: A Question about "Inter Packet Gap and SOP Lane alignment"
Boaz,
The random /A/ or /K/ in the first IPG column will statistically provide
opportunities to obtain and maintain word sync and lane de-skew within a
stream of packets. It is more important to have an /R/ column appearing
between packets deterministically because you need to know a worst case
spacing between /R/'s in order to properly size clock tolerance adjustment
buffers.
The only way to deterministically guarantee /A/ and /K/ and /R/ between
every packet is to require 3 full columns *following the column containing
the /T/ character*. This means minimum IPGs of 13-16 bytes. You cannot get
/A/ and /K/ and /R/ columns in a 12 byte IPG.
Steve
-----Original Message-----
From: Boaz Shahar [mailto:boazs@mysticom.com]
Sent: Monday, July 17, 2000 9:00 AM
To: 'Brown, Ben [BAY:NHBED:DS48]'; 802.3ae
Subject: RE: A Question about "Inter Packet Gap and SOP Lane alignment"
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@baynetworks.com]
> 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@nSerial.com
> > 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@nortelnetworks.com
> -----------------------------------------
>