Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

RE: Minimum IPG w/ WIS ?


I have been tracking this IPG thread, because I too am trying
to understand what is intended for minimum IPG (actually IFG -
Inter Frame Gap, no ?) in the 10Gb/s WIS application, and I
would like to pose the following observation for clarification
by those who understand it better.

If I read the algorithm correctly in section 4.2.8, specifically
page 32, lines 16-22, it looks like the MAC is taking the minimum
IPG/IFG called out in the table in section 4.4.2 (page 41, lines
15-16), into account when counting bits to determine its "stretch
size" (bytes/octets that will be added in the IFG/IPG to adapt for
the WIS rate). As well as, the preamble and SFD bytes (header size).

So, if I understand it all correctly, that should mean that in a
PCS+WIS application, the MAC generated data stream into the XGMII
inputs of the PCS will contain:
     1. 12 bytes/octets minimum of IPG/IFG for a minimum size
        packet/frame per frame, and
     2. 26 bytes/octets minimum of IPG/IFG for a maximum size
        packet/frame per frame
In both cases the "interFrameGap" AKA "interFrameSpacing" as
defined in the present version of D2.1, is maintained.

My confusion comes in with the note on page 41, lines 42-45,
in section 4.4.2, as you were discussing earlier;
This notes says that this "interFrameGap shrinkage" to 5
bytes/octets is;
 "... as measured at the XGMII receive signals at the DTE."

Keeping in mind that +/-100ppm is only one 4-byte column to
be deleted/added every 10,000 4-byte columns, worst case.
I guess I am not clear on how this would ever bring the IFG/IPG
down to 4-5 bytes (1 column) of IPG/IFG on a frame-by-frame
basis ?

Your clarification on this matter would be sincerely
appreciated. (-:

Thanks, & Best Regards,

pat_thaler@xxxxxxxxxxx on 02/20/2001 01:02:24 PM
From: pat_thaler@xxxxxxxxxxx on 02/20/2001 01:02:24 PM
To:   sanjeev@xxxxxxxxx, pat_thaler@xxxxxxxxxxx, pat_thaler@xxxxxxxxxxx,
      stds-802-3-hssg@xxxxxxxx, yariv@xxxxxxxxxxxxx
Subject:  RE: RS minimum IPG


I can't quite parse what you've said. In any case, Shimon has pointed
where it is specified in 4.4.2. Note that the numbers in 4.4.2 are

   10 Mb/s   47 BT
   100 Mb/s  not specified
   1 Gb/s    64 BT
   10 Gb/s   40 BT (= 5 Phy characters)

As you can see, consistancy between speeds was not particularly a goal.


-----Original Message-----
From: Sanjeev Mahalawat [mailto:sanjeev@xxxxxxxxx]
Sent: Tuesday, February 20, 2001 12:45 PM
To: pat_thaler@xxxxxxxxxxx; pat_thaler@xxxxxxxxxxx; sanjeev@xxxxxxxxx;
stds-802-3-hssg@xxxxxxxx; yariv@xxxxxxxxxxxxx
Subject: RE: RS minimum IPG

At 01:10 PM 02/20/2001 -0700, pat_thaler@xxxxxxxxxxx wrote:
>I dashed off my response too quickly. I meant to say "I don't know of
>anyplace a minimum receive IPG of 4 is stated for 10 Gb/s."

The original question was why everybody is talking about
shrinking the IPG to 4 bytes. The receive IPG is never shrinked
to 4 bytes and and it is never less than 5 bytes at RS receive
for explained or unexplaned reasons, it is an issue that
specify the preamble and the min IPG that
are "consistence" with the slower speeds those are 4 bytes
min IPG and SFD at RS. I am not sure of you chasing the the place.


>-----Original Message-----
>From: pat_thaler@xxxxxxxxxxx [mailto:pat_thaler@xxxxxxxxxxx]
>Sent: Tuesday, February 20, 2001 9:48 AM
>To: sanjeev@xxxxxxxxx; stds-802-3-hssg@xxxxxxxx; yariv@xxxxxxxxxxxxx
>Subject: RE: RS minimum IPG
>Where do you find such a definition in the standard? I don't know of
>anyplace a minimum receive IPG of 5 is stated. Further, that is a
>that has varied based on speed so what it was at 100/1000 Mb/s does not
>limit our choice at 10 Gig.
>-----Original Message-----
>From: Sanjeev Mahalawat [mailto:sanjeev@xxxxxxxxx]
>Sent: Monday, February 19, 2001 11:25 AM
>To: stds-802-3-hssg@xxxxxxxx; yariv@xxxxxxxxxxxxx
>Subject: Re: RS minimum IPG
>The min IPG varies from 9 bytes to 15 bytes
>based on the packet size and due to clock compensation
>the PHY may delete a column that will lead to min
>IPG of 5 Bytes. So, thoeritically it should not be
>less than 5 bytes but the spec. always defines it
>to be 4 bytes as this was in the 100/1000 mbps