[Bloat] Packet reordering and RACK (was The "Some Congestion Experienced" ECN codepoint)

Ingemar Johansson S ingemar.s.johansson at ericsson.com
Thu Mar 14 04:26:20 EDT 2019


In addition to the below, in NR (=New Radio, a part of 5G) the RLC layer will 
no longer ensure
in sequence delivery to higher layers. Packet reordering can occur on the MAC 
layer as several HARQ (Hybrid ARQ) run simultaneously to transmit packets, 
some processes need to retransmit and there you get packet reordering.
The PDCP layer can however (optionally) enforce in sequence delivery, 
personally I am sceptic about the benefits of this as it adds extra HoL 
blocking to solve a problem that RACK can solve. In addition it costs more 
memory in nodes that potentially need to transmit 10s of GByte of data.


Date: Tue, 12 Mar 2019 21:39:42 -0700 (PDT)
From: David Lang <david at lang.hm>
To: Sebastian Moeller <moeller0 at gmx.de>
Cc: Mikael Abrahamsson <swmike at swm.pp.se>,  "Holland, Jake"
	<jholland at akamai.com>,  Cake List <cake at lists.bufferbloat.net>,
	"codel at lists.bufferbloat.net" <codel at lists.bufferbloat.net>,  bloat
	<bloat at lists.bufferbloat.net>,  "ecn-sane at lists.bufferbloat.net"
	<ecn-sane at lists.bufferbloat.net>
Subject: Re: [Bloat] [Cake] The "Some Congestion Experienced" ECN
	codepoint - a new internet draft -
Message-ID: <nycvar.QRO. at qynat-yncgbc>
Content-Type: text/plain; charset=US-ASCII; format=flowed

On Mon, 11 Mar 2019, Sebastian Moeller wrote:

> How is packet reordering for anybody but the folks responsible for
> operating the "conduits" in any way attractive?

It's more that not worrying about maintaining the order, and just moving the
packets as fast as possible reduces the overhead.

The majority of the time, packets will be in order, but race conditions and
corner cases are allowed to forward packets out of order rather than having
the delay some packets to maintain the order.

David Lang

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