Lossy cogent p2p experiences?

Wed Sep 6 17:25:23 UTC 2023

On Wed, 6 Sept 2023 at 19:28, Mark Tinka <mark at tinka.africa> wrote:

> Yes, this has been my understanding of, specifically, Juniper's
> forwarding complex.

Correct, packet is sprayed to some PPE, and PPEs do not run in
deterministic time, after PPEs there is reorder block that restores
flow, if it has to.
EZchip is same with its TOPs.

> Packets are chopped into near-same-size cells, sprayed across all
> available fabric links by the PFE logic, given a sequence number, and
> protocol engines ensure oversubscription is managed by a request-grant
> mechanism between PFE's.

This isn't the mechanism that causes reordering, it's the ingress and
egress lookup where Packet or PacketHead is sprayed to some PPE where
it can occur.

Can find some patents on it:
https://www.freepatentsonline.com/8799909.html
When a PPE 315 has finished processing a header, it notifies a Reorder
Block 321. The Reorder Block 321 is responsible for maintaining order
for headers belonging to the same flow, and pulls a header from a PPE
315 when that header is at the front of the queue for its reorder
flow.

Note this reorder happens even when you have exactly 1 ingress
interface and exactly 1 egress interface, as long as you have enough
PPS, you will reorder outside flows, even without fabric being
involved.

-- 
  ++ytti