[AusNOG] Deep buffer switches and CDN networks

[Paul Wilkins]

Deep buffers of transit routers do not add bandwidth, nor do they improve
your bandwidth/delay product.

The only use case I've ever found for deep buffers is remote sites on low
bandwidth links, where with the right QoS maps you can shunt bulk transfer
traffic aside, meaning user traffic eg voice, isn't contending with say
email.

Once you have 10 or more concurrent users, the law of large numbers means
deep buffers just take longer to fill before buffer drop. Buffer drop never
means you need deeper buffers, it means you need more bandwidth.

Perhaps there's a case for shunting update traffic between CDN caches, but
again, this relies on there being a benefit in delaying CDN cache update
packets from a user traffic peak to a user traffic trough, (where the delay
between peak and trough < 1s), the absence of user traffic freeing
bandwidth for the cache update. Again, the law of large numbers makes this
unlikely.


Kind regards

Paul Wilkins

On Fri, 24 May 2019 at 23:32, Tom Paseka <tom at cloudflare.com> wrote:

> Timely presentation from Netflix On this exact topic.
> https://ripe78.ripe.net/archives/video/128/
>
> On Thu, May 23, 2019 at 7:52 AM Tom Paseka <tom at cloudflare.com> wrote:
>
>> everything depends on your application and how you're moving traffic.
>>
>> if you lots of east-west flow (between equal speed interfaces, especially
>> in many to one) you'll need buffers. If you're doing north to south traffic
>> with interface change, you'll likely need buffers.
>>
>> The choice here might not have been for deep buffer, but for other
>> capabilities (forwarding, route table size, etc). Dave mentions from a
>> question there is no east-west traffic, everything is south-north.
>>
>> On Wed, May 22, 2019 at 5:46 AM Jason Leschnik <jason at leschnik.me> wrote:
>>
>>> Hi Noggers,
>>>
>>> I just finished watching the NANOG presentation of Netflix
>>> openconnect[1], I noticed that their core switch of choice was an Arista
>>> 7500E which is a deep buffer switch. I remember seeing a lot of comments
>>> around buffer bloat for deep buffer switches. Would this be considered an
>>> acceptable use case for this type of switch in the DC?
>>>
>>> Has anyone got experience with ideal switch types (shallow, deep
>>> buffers) for edge CDN network deployments?
>>>
>>> [1] - https://www.youtube.com/watch?v=tbqcsHg-Q_o
>>>
>>> Regards,
>>> Jason.
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>>> AusNOG at lists.ausnog.net
>>> http://lists.ausnog.net/mailman/listinfo/ausnog
>>>
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