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RE: A Question about "Inter Packet Gap and SOP Lane alignment"

I agree with Howard: Why do you need to be aligned during the IDLE?
And about the technical problems:

1.Whats the problem to do alignmenet on the LSS column as well?
And if you want to avoid it:
2.You can avoid Doing alignement on LSS column, and do very robust scheme a

Just do alignement on two (Or even three) consequtive Data columns. Minimal
packet is about 16 data columns.


> -----Original Message-----
> From: Rich Taborek [mailto:rtaborek@xxxxxxxxxxxxx]
> Sent: Wednesday, July 19, 2000 2:28 AM
> To: HSSG
> Subject: Re: A Question about "Inter Packet Gap and SOP Lane 
> alignment"
> Howard,
> I believe that you realize full well that your suggestion is 
> a subversive
> maneuver to derail LSS whose "words" have a similar "look and 
> feel" to a
> Start-of-Packet delimiter.
> The format of an LSS word is /K/D/D/D/ where K is a special 
> character with the
> meaning LSS. The format of a Start-of-Packet delimiter is an 
> SOP word /K/D/D/D/
> where K is a special character with the meaning SOP. The same 
> general encoded
> format is defined for transport on the XGMII, XAUI, the 
> 8B/10B PCS and the
> 64B/66B PCS. The reason for this format is it allows a single 
> LSS word to carry
> three bytes of data, plenty enough to function as an OAM&P transport. 
> Your proposal to reconsider the use of /A/ for alignment and 
> instead perform the
> alignment on the Idle-to-Data transition is not sufficiently 
> robust due to the
> potential presence of LSS words in the Idle stream and 
> insufficient hamming
> distance between the special characters for the various 
> interfaces which may be
> traversed.
> Additionally, alternative PMDs such as the 1550 WWDM proposed 
> by Mr. Michael
> Fisk of Luminent and Mr. Fred Mohamadi of Broadcom in May in 
> Ottawa may impart
> significantly more skew between lanes than can be handled by 
> the current and
> simple /A/ spacing. The spacing may need to be increased 
> significantly for the
> 50 km 1550 WWDM links proposed in that presentation and 
> publicly exhibited at
> N+I in May by you know who. It is a simple matter to increase 
> the /A/ spacing
> since we currently use a simple counter. However, it is not 
> possible to use
> Idle-to-Data transitions as you propose since the skew (I'm 
> still trying to
> assess the exact number) may be larger than the minimum 
> Ethernet frame size
> spacing.
> What is it about this "/A/K/R/O/ stuff during IDLE" that is 
> getting out of hand?
> This sounds like more FUD. I still haven't heard a valid 
> technical argument
> against LSS, only FUD. I also have not seen any robust 
> counter proposals. 
> It is true that the current initialization protocol (for 
> 8B/10B based links)
> allows for a link to initialize only when a packet occurs. 
> However, I hope that
> the reader recognizes that this will result in needlessly 
> dropped packets and
> that link initialization does not require packets. 8B/10B 
> links are continuously
> signaled whenever the link hardware is powered. The 
> continuous signal is Idle.
> The link initializes during Idle and is ready to go when a 
> packet arrives.
> Whenever a packet transfer is requested by the MAC, the Idle stream is
> interrupted. This operation is as simple, straightforward and 
> robust as can be.
> Howard Frazier wrote:
> > 
> > Maybe we should reconsider the use of /A/ for alignment.  We don't
> > really need to use a special character for lane alignment.  We could
> > just as well perform the alignment on the IDLE->DATA transition at
> > the start of each packet.
> > 
> > All of this /A/K/R/O/ stuff during IDLE is getting out of hand.
> > We would be better off with simpler rules for IDLE, like a 
> randomized
> > sequence of Ks and Rs.
> > 
> > In fact, if we did the alignment based on the transition from
> > lane[0:3]=IDLE to (lane[0]=SOP & lane[1:3]=data), then we wouldn't
> > need to maintain columns of Ks and Rs during IDLE.  We 
> would just need
> > to send a complete column of R once during IPG, for instance, on the
> > column immediately following the T. IDLE could be random per-lane Ks
> > and Rs at all other times.
> > 
> > The IDLE insert/delete rules would remain unchanged.
> > 
> > We don't really need to be aligned until there is a packet 
> to receive,
> > and the first packet that a receiver gets can be used to 
> establish the
> > lane alignment. If a receiver looses alignment, it will re-establish
> > the alignment at the next start of packet.
> > 
> > Howard Frazier
> > Cisco Systems, Inc.
> -- 
> Best Regards,
> Rich
> ------------------------------------------------------- 
> 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