[Dyncast] CAN BoF issues #19 #21 #23

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Dear All,

Based on the categories of the CAN BoF issues, here are the responses to the following issues #19 #21 #23, which are related to the service discovery and the potential cooperation with application layer.  Any comments are welcome. Thanks!

#19 For each application there might be a overlay plane, because the resources/metric is specific to the plane. #19 
Part of the work in CAN is to identify methods to describe metrics as well as decision making mechanisms in a manner that those may be utilized by many applications, while also minimizing the exposed semantics to the CAN provider. Furthermore, CAN may allow to act on categories of services rather than individual services themselves, where the metrics and decision making may be applied across the specific category.

#21 The CAN problem is not striked as a routing problem, it's all service discovery that can be done in higher layers. #21
Indeed, CAN be described as a service instance selection problem, where said instance is being chosen as one from possibly many while forwarding the packet from the client to the chosen instance. With this, it can be described as an on-path solution, while current solutions can be categorized as off-path solutions, often performing a dedicated service discovery/resolution step before engaging in direct communication between client and the discovered/resolved instance. This dedicated discovery/resolution step adds latency as well as additional complexity to the overall communication, which may cause issues in scenarios with dynamic re-assignment of clients to service instance.

#23 It needs application information too, so it can't just make a decision at the network layer. #23 
It is the scope of proposed work what information and which semantic needs exposure across business boundaries (e.g., from application to network provider) in order to make suitable decision. Opague decision making is possible through conveying utility functions operating on numerals only. 
There may be deployments in which network and service entities may be owned by the same entity(e.g operators), thereby simplifying the crossing of information, such as computing load, from the computing to the networking infrastructure and vice versa.

PS: The issues #1 #5 #6 #9 #20 #25 were updated according to the discussion, and will be still opened for a while to see if there are any more comments.

You can also add your comments to any of them(https://github.com/CAN-IETF/CAN-BoF-ietf113/issues). 

Regards,
Peng



[e-mail]
 
From: Linda Dunbar
Date: 2022-05-11 06:11
To: [e-mail]
Subject: [Dyncast] Categories of the CAN BoF issues
CAN BoF proponents:
 
Many thanks for creating the CAN BoF issues tracking  in the Github: https://github.com/CAN-IETF/CAN-BoF-ietf113/issues/created_by/CAN-IETF?page=1&q=is%3Aopen+is%3Aissue+author%3ACAN-IETF
 
I went through the issues captured in the Github and characterized them into groups. Some issues can be lumped together for the discussion. There are quite a few issues related to the requirements, which need to be clarified.
 
Best Regards, Linda
 
 
Issues associated with Applications vs. Underlay networks:
Consider not to load underlay network with application details. #35
We have multiple upper layer application. Do we have additional needs for routing(e.g. WG?) or we are using those applications and won't need such new WG? #30
It needs application information too, so it can't just make a decision at the network layer. #23
This is not striked as a routing problem; it's all service discovery that can be done in higher layers. #21
3GPP and URSP solve this based on UPF selection. It uses both endpoint + application. #20
One overlay plane per application. Resources/metric specific to the plane. #19
How does the application layer or the transport layer learn the network status to steering traffic? #16
 
Need more clear requirements for CAN (to be addressed by draft-liu-dyncast-ps-usecases):
Need to understand if three are requirement to avoid extra messages or 1ms of latency #36
Regarding the flow affinity, is it from network perspective or from application/computation perspective? #33
How to effectively compute paths? Shall we put CPUs into account? #32
What happens when the user moves? If so we also need to move application context. #25
It can only move the services around as fast as it can update the routing plane. which comes back to the point about service discovery (waiting for convergence/distribution as opposed to just updating the SD server) #24
Whether the interests of the organization deploying the application and the organization providing the network connectivity are aligned. Google doesn't worry about this because they are both. #17
The question is more what the scope and semantic of information is that will need to cross organizational boundaries. This needs further study, in particular when assuming stakeholder division between service and network provider.
It seems impossible to satisfy that requirement simultaneously with the latency requirement. #15
It wasn't clear that how hard of a requirement session persistence is. #13
A session usually creates ephemeral state. If execution changes from one (e.g., virtualized) service instance to another, state/context needs transfer to another. Such required transfer of state/context makes it desirable to have session persistence (or instance affinity) as the default, removing the need for explicit context transfer, while also supporting an explicit state/context transfer (e.g., when metrics change significantly).
Should it select UPF based on the application? Steering is done per user? or per application? #9
This seems to assume conventional non-distributed applications just running at the edge. what about modern frameworks like Sapphire? and Ray? #7
It would be good to understand the multi-site requirements of such framework, which I have understood to mainly run in single DCs.
Relation to 3GPP UPF #6
Relation to ALTO #5
Do the mobility issues and associated protocols are also in scope? There are scenarios where routing alone would not be sufficient. #4
What is the position in the edge location regarding to UPF? #3
Is there some sort of authorization model so that an edge can indicate whether or not it will provide compute services? #2
What is CNC and the relationship with CAN #1
 
Measurement of the Computing Resources (to be addressed by draft-du-computing-resource-representation):
It is hard to use existing work to measure the computation, but we can optimize the latency through the performance monitoring. We have performance/measurement matrix over there. #34
Clarifications on the computing resource, its requirements and characteristics would be helpful. #27
Each application may have a different definition of "resources" these then have to be boiled down into a single topology Network Aware Computing (NAC! :) does scale #14
Is computing resource measurable? #10
It is, and how to use the measurement would be solution related. See IFIP Networking 2022 paper on how to simply expose “computing capability” and achieve better steering with such simple measure.
Why compute resource is different with other resources? #8
 
Load Balance based solutions:
The point is that we need a standardized LB protocol #18
The LB as part of the application itself is superior (part of the distributed application itself is to obtain and keep updating the "best" unicast location to use). #22
If there is anything missing from current lbs that would prevent their use as-is? other than there is for market reasons no interop standard between different lbs? #12
For the load balance, should it learn the network’s status? #11
 
Dyncast based Solution issues:
For Dyncast, when the time is short, is it possible for the router to decide the routing? It is too fast. #31
Is dyncast proposed to encapsulate? #29
Will CAN dyncast impact each and every router? How to avoid loops? #28
What's the assumed scale of a D-router? 10 ^ 6 sessions? 100^ 8? What's the assumed update rate? !Gb? 1Tb? #26