[zeromq-dev] QoS support

[Erich Heine]

On Sat, Nov 7, 2009 at 10:58 AM, Steven McCoy <steven.mccoy at miru.hk> wrote:

> 2009/11/7 Alexander <mittspamkonto at gmail.com>
>
>> I'm doing some research about using message queuing for an application
>> currently using a reliable multi-cast solution. This app has some
>> requirements related to speed and safety, so I will need to be able to
>> control QoS (TOS, DiffServ or any equivalent network-level QoS
>> support) of the packages in the network.
>>
>
> QoS only works at routers, it has limited meaning at other network
> elements.  Generally you configure the gateway routers to add the tags to
> traffic instead of trusting the software to do it properly.
>
>
There is a strong argument for end-to-end QoS, as opposed to gw-to-gw. There
are two different reasons for this:

1.  Better application support -- Provided a host is (fairly) trusted, and
there is a good network admission layer, applications themselves can
internally prioritize their traffic. Instead of requiring 3 connections
managed by the application, it just calls send(...,PRIORITY_X). The
middleware of course could just set up 3 connections, which would certainly
be easy enough. With a QoS integration that is more than just connection
oriented however, there is a benefit from an adminstrative point of view as
well, not needing to know each possible communication set an application
will need/use.

2. Host protection -- ingress and egress rate controls and priority queues
(and etc.) allow critical traffic through, even in the face of a crowded
network, or a crowded network card. Say for example you have a low priority
task that is generating a lot of traffic, just sending your high priority
packet from the same host without QoS measures on the NIC does not ensure
timely sending, no matter what the network is set up to do. A priority queue
certainly goes a long way to help this. Example:  I have tc set up on my
home desktop to put torrents in the lowest priority and skype in the
highest, and everything else in the middle. I recently torrented the new
Ubuntu, and it came through very quickly, utilizing as much of my connection
as it could, however my skye session w/ my sister did not suffer at all.

A final note, when integrating QoS to the endpoints, it opens up a perfect
way to integrate middleware to signal back to the network when QoS is not
being met.

Steven is absolutely correct in that gw-to-gw style QoS does take reduce the
need to trust every app developer out there, but I think that the gateways
should sanity check edge QoS instead of obviating it.

Regards,
Erich
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