Re: [Dyncast] CAN BoF issues and the next steps

Hi, Jens

    It is a choice about the decision point, and it leads to different solutions. The decision point may be the UE, the Ingress node, some centralized point (such as a controller), etc.

    If the UE is that smart, it can choose the proper server after knowing the needed information.
    If the Ingress node can handle the anycast/Dyncast job, the UE can be less complicated.
    Or a controller can give a suggestion about the selected path and/or the selected server to the UE or Ingress node.

    Some tradeoff needs to be considered here, and perhaps they have different suitable scenarios.

Best Regards
Zongpeng Du

duzongpeng@foxmail.com & duzongpeng@chinamobile.com

From: Jens Finkhaeuser
Date: 2022-04-13 17:07
To: tony.li; wangaijun
CC: dyncast; liupengyjy; luigi.iannone=40huawei.com
Subject: Re: [Dyncast] CAN BoF issues and the next steps
Hi all,

speaking from practical experience with the edge case of streaming video from the "best" source, it may be desirable for the UA to make the decision locally, as it's also best suited to deciding if a response no longer matters.

We'd query a central repository for likely sources with some compute aware ordering, and then use path aware ordering at the UA for narrowing down the candidate list.

In our use case, we would query all sources, update their ordering on actual RTT, and send ACK equivalents to all, independent of which source provided each packet.

This list then periodically got refreshed.

This could conceivably be done by the ingress, use unicast for all sources, etc. but it would need some transparency. That is, E2EE would likely place this at the UA rather than an ingress router.

The point here is probably that it's likely best to differentiate between where the path aware and the compute aware metrics get aggregated and evaluated, at least for some types of application. 

Hope that makes sense,
Jens

-------- Original Message --------
On 13 Apr 2022, 05:27, Tony Li < tony.li@tony.li> wrote:

Hi Aijun,
My understanding of the requirements was that a particular UE was supposed to be bound to a server for the lifetime of a ’transaction’ and that includes across the UE rehoming to a different source. Thus, the entire network needs to make a consistent and fixed decision per UE. Doing so in a dynamic environment would seem to be most challenging: you would need to synchronize forwarding state across the entire network instantly.
Making a single decision at the ingress and propagating that state seems somewhat easier.
And easier still is Joel’s proposal: have the UE pick one (from a centralized broker?) and then rely on unicast. :-)
Regards,
T
> On Apr 12, 2022, at 7:59 PM, Aijun Wang <wangaijun@tsinghua.org.cn> wrote:
>
> Hi, Joel:
> If you use binding address behind the ANYCAST address, it is possible. But if you use the ANYCAST address directly, you can't.
> For my understanding, the latter scenario is more popular.
>
>
> Best Regards
>
> Aijun Wang
> China Telecom
>
> -----Original Message-----
> From: Joel M. Halpern <jmh@joelhalpern.com>
> Sent: Wednesday, April 13, 2022 10:55 AM
> To: Aijun Wang <wangaijun@tsinghua.org.cn>; 'Luigi IANNONE' <luigi.iannone=40huawei.com@dmarc.ietf.org>; liupengyjy@chinamobile.com; 'dyncast' <dyncast@ietf.org>
> Subject: Re: [Dyncast] CAN BoF issues and the next steps
>
> If the ingress edge does the calculation, makes the determination, and tunnels the traffic to the right place then the underlay routing system does not need to know anything about these metrics or the decision processes made by the edge.
>
> Yours,
> Joel
>
> On 4/12/2022 10:52 PM, Aijun Wang wrote:
>> Hi, Luigi:
>> Why only the ingress need such decision? I think all the routers
>> in-path need such information(routing metric +compute metric), to
>> achieve the optimal "instance selection".
>>
>> Best Regards
>>
>> Aijun Wang
>> China Telecom
>>
>> -----Original Message-----
>> From: dyncast-bounces@ietf.org <dyncast-bounces@ietf.org> On Behalf Of
>> Luigi IANNONE
>> Sent: Tuesday, April 12, 2022 3:04 PM
>> To: Aijun Wang <wangaijun@tsinghua.org.cn>; 'Joel M. Halpern'
>> <jmh@joelhalpern.com>; liupengyjy@chinamobile.com; 'dyncast'
>> <dyncast@ietf.org>
>> Subject: Re: [Dyncast] CAN BoF issues and the next steps
>>
>> Hi,
>>
>>> But, with the placement of the ANYCAST application servers closing to
>>> the users in different sites, the bottleneck to influence the E2E
>>> application performance is not only the network metric, the metric
>>> for the application servers play a major role now.
>>> It is time to consider both the network metric and application server
>>> metric together to achieve such goals.
>>
>> I think that Joel is not against the above (routing metric +compute
>> metric = instance selection).
>> I think that he is more inline with Dirk's position, meaning that it
>> is not necessarily the routing layer that has to be "enhanced" with
>> compute metrics.
>> Rather, an in-path decision based on both metrics should be made by
>> some (CAN ) element.
>> My personal take is that the ingress is well suited for that (since
>> for sure it is in-path).
>> Then you have the choice of various ways on how to steer the traffic.
>>
>> Ciao
>>
>> L.
>>
>>
>>
>>
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>>
>
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