Re: [802.3_NGEPON] Questions about fragmentation in EPON

[Frank Effenberger <frank.effenberger@xxxxxxxxxx>]

All,
Yes, this is the application of fragmentation that we want.

As a thought experiment, one can imagine a single channel Epon with fragmentation. The big deal is that the size of the grants can be delinked from the size of the frames. All that stuff about water marks could go away.
Frank E



(null)

From:Glen Kramer

To:STDS-802-3-NGEPON

Date:2016-07-01 05:49:36

Subject:Re: [802.3_NGEPON] Questions about fragmentation in EPON

Mark,

Agree, we need to focus on the problem we are solving. 

Just to remind everyone (the issue was first discussed in Macao), if the ONU sends frames across all enabled (granted) lanes in FIFO order, it would be extremely easy for the OLT to recover the frame sequence (by frame start time, same as in downstream) and without any buffering at all.  But the problem with this approach was that a combination of frames that gets in each grant will be different from the combination of frames that were reported by the ONU to the OLT, so every grant will be under-utilized, and a significant portion of bandwidth will be wasted (see picture on the left below). So, the proposal at that time was to pack frames in grants as they were reported (see picture on the right). That solves the grant utilization problem, but requires the OLT to buffer multiple bursts to restore frame sequence. 

In Whistler, I proposed to revisit the fragmentation option so that we are not constrained by the frame delineation boundaries anymore. In this approach, the ONU will start transmitting the next frame in an earliest available grant. If that grant ends, the rest of the frame will continue in the another currently-active grant, if any. Otherwise, it will wait for the future grant. At most one frame per LLID  will remain split between the OLT and ONU, while waiting for a future grant. I do not have full proposal or even a clear picture of how this would work, but Duane's proposal to do it in RS and have a signal line from MPCP to RS may help.

Glen

On Thu, Jun 30, 2016 at 1:16 PM, Mark Laubach <000006d52ee8f1bc-dmarc-request@xxxxxxxx> wrote:

Duane, all,

 

The motivation, as I recall, for exploring upstream fragmentation was to answer the question of does it reduce buffer memory requirements in the OLT.  I would suggest if possible to focus on that question first before we get too deep into the details.   If there isn’t a clear win on memory savings, then I suggest not getting into the fragmentation complexity and staying with whole packets.   Perhaps select one or two “scheduling” models, then focusing on the re-assembly details in the OLT?

 

Mark

 

From: Duane Remein [mailto:Duane.Remein@xxxxxxxxxx]
Sent: Thursday, June 30, 2016 12:14 PM
To: STDS-802-3-NGEPON@xxxxxxxxxxxxxxxxx
Subject: [802.3_NGEPON] Questions about fragmentation in EPON

 

Glen/Marek,

During the call today you both expressed concerns about fragmentation. Do the following two questions adequately capture your expressed concerns? If not please clarify.

1)      In a multi-lane mixed capability network (mix of 25G, 50G & 100G ONUs) how would fragmenting avoid loss of capacity due to gaps between bursts?

2)      In a multi-lane mixed capability network how could fragmenting allow an ONU that is bursting on X lanes expand its transmission to X+m (ex. go from 2 lane transmission to 4 lane transmission) smoothly?

Best Regards,

Duane

 

FutureWei Technologies Inc.

duane.remein@xxxxxxxxxx

Director, Access R&D

919 418 4741

Raleigh, NC