Re: [Apn] Problem statement

[Joel Halpern <[e-mail]>]

I am not sure I understand your points.

Your scenario 1 says that the two VPNs have the same "set of QoS values" 
but then says that one should use low latency and one should avoid low 
latency.  (Note that "avoid low latency" is probably not meaningful.)  
latency is a QoS parameter.  So the two VPNs do not have the saem "set 
of QoS Values".  They don't even have the same set of queueing 
parameters since queueing treatment is an important part of achieving 
low latency.  As for path selection, we have both source routing and 
flex-algo as tools to achieve differentiated path selection.

Your second scenario says that operators using IGP always use the 
default metric.  This is not the case.  The IGPs advertise additional 
metrics which can be used with soruce routing (MPLS or SRv6) to achieve 
suitable path selection.  Further, one can us Flex-Algo (with IPv6, 
MPLS, or SRv6) to have even better control over the path selection 
algorithm.

Your third scenario talks about differing discard priorities. DSCP 
alreayd supports this at a coarse level with three different AF 
classes.  It can support significantly more nuanced drop priorities as 
there are a good number of code points for IP DSCP (there are fewer with 
SR-MPLS; that is being addressed).  Further, the NRP structures from 
TEAS allow even more detailed control over traffic treatment, and the 
community will determine what markings are needed for that.  We do not 
need a new working group for it.

Yours,

Joel

On 5/23/2023 9:14 AM, Mohammed Umair wrote:
> Hi,
>
> Apologies for my late entry into this discussion.
>
> In my opinion the operators domain faces most of the problem is not 
> with the QoS but rather in the treatment of a packet in it's network.
> I have tried to capture a few of the scenarios/points below.
>
>
> Scenario 1 : latency dependent application/traffic.
> ==========================================
> VPN-A and VPN-B both when traversing the network have traffic with 
> same set of QoS values to the same Destination, but VPN-A should 
> always has to be steered on low latency network, and VPN-B can take 
> the path other than low latency, so basically we can think of using 
> the Fine Grained values which are carried directly into the packet 
> takes the decision Hop by Hop using the Performance measurement data 
> or end-to-end performance measurement Data.
>
>
> Scenario 2:  Network operators who use IGP.
> =====================================================
> In these networks IGP Metric always gets considered for steering of 
> the traffic, so there is a need for few packets to take the metric 
> other than the IGP as well.
> These values can be added at the ingress/source of the network and can 
> also be modified in the middle of the network as well, something like 
> remarking of QoS Values.
>
>
>
> Scenario 3: Treatment of traffic in Congestion.
> ====================================================
> When a middle device receives two different VPN'S traffic with same 
> QoS values, Device should have the capability to understand which 
> traffic needs to be dropped, but since the QoS values are same 
> sometimes the drop happens randomly in the congested network (there 
> are few techniques, where using SIP/DIP someone can steer the traffic 
> to different queues, but sometimes becomes complex), by using current 
> QoS values and Values in the New header device can take the decisions.
>
>
> Regards,
> Umair
>
>
> On Sat, May 20, 2023 at 8:16 AM Joel Halpern <[e-mail]> wrote:
>
>     As Jim likes to point out to me, SFC can steer to whatever you
>     want.  So I think it is important to specify what problem we have
>     that SFC does not address.  Targeting specific queues on specific
>     nodes is clearly within SFC. Targeting specific classes of service
>     across all nodes is DSCP.
>
>     Yours,
>
>     Joel
>
>     On 5/19/2023 7:28 PM, Pengshuping (Peng Shuping) wrote:
>>
>>     Hi,
>>
>>     I agree with your capture, that is, it is more like a SFC-like
>>     approach. The current SFC is the chain of service functions, but
>>     here we want to do more than just service functions. Actually
>>     both underlay and overlay network elements are involved,
>>     including network nodes and service functions.
>>
>>     Regarding particular uses, I am thinking whether we could
>>     categorize them into several types, for example,
>>
>>     1.Steering: into queues of nodes, or paths going through nodes
>>     and service functions, or virtual instance on each service function
>>
>>     2.Triggering: certain services such as various performance
>>     measurement mechanisms
>>
>>     3.Identifying: the packets belonging to which traffic groups in
>>     the middle of the network, i.e. VPN, sites, access interfaces, to
>>     enforce group-level policies efficiently
>>
>>     Please find more responses in line. Thank you!
>>
>>     *From:*Ted Hardie [mailto:[e-mail]
>>     <mailto:[e-mail]>]
>>     *Sent:* Wednesday, May 17, 2023 9:44 PM
>>     *To:* Pengshuping (Peng Shuping) <[e-mail]>
>>     <mailto:[e-mail]>
>>     *Cc:* [e-mail]; [e-mail]
>>     *Subject:* Re: [Apn] Problem statement
>>
>>     My apologies for taking so long to reply; I started a reply and
>>     lost track after I  put it aside.
>>
>>     Some comments in-line.
>>
>>     On Sat, May 6, 2023 at 11:25 AM Pengshuping (Peng Shuping)
>>     <[e-mail]> wrote:
>>
>>         Hi,
>>
>>         These are very good points and suggestions. Thank you!
>>
>>         I try to first summarize the current discussions, which
>>         actually lead to three key questions that need to be answered.
>>
>>         1.What are the core problem?
>>
>>         2.What are the uses?
>>
>>         3.What are the key items?
>>
>>     I think this is missing a critical question:  what is it about
>>     this set of uses that makes an omnibus solution the right
>>     approach?  Unless I have missed something basic, this appears to
>>     encompass a fairly broad swath of potential use cases, some of
>>     which already have well-established alternate approaches outside
>>     the data plane.  Some description of why these signals belong
>>     together is necessary, unless you are suggesting that the
>>     eventual scope will be a single use case.
>>
>>     Shuping> The thing is that we would need to somehow keep the
>>     description more abstract. Considering the uses people have
>>     explained so far in the mailing list and previous discussions.
>>     Whether it would be good if we could categorize the uses into
>>     types, as I listed before: steering, triggering, identifying, …
>>
>>         Let’s focus on them one by one.
>>
>>         1.What are the core problem?
>>
>>         Maybe we could first try to use one sentence to describe this
>>         core problem. Considering the discussions, I am thinking that
>>         this sentence would be something like “How to maintain
>>         continuously the fine granularity within the network in an
>>         efficient manner”. Please suggest better wording.
>>
>>         I like the following paragraph extended by Adrian and further
>>         add this summary sentence at the end. Your comments and
>>         suggestions are welcome.
>>
>>         “In a network operator controlled domain, the ingress edge
>>         devices usually have access to rich information, such as
>>         VLAN/QinQ, VPN ID, and access interface, which is used to
>>         classify the packets into fine granular virtual groups of
>>         flows at the edge. However, after the packets enter the
>>         network operator’s domain, all such information is not
>>         immediately visible at transit nodes: it may be hidden inside
>>         encapsulation, masked by encryption, mapped to other protocol
>>         fields, or stripped from the packets completely. Furthermore,
>>         many mapping schemes, where they are used, lose some level of
>>         granularity from the information available at the network
>>         edge. For example, when the information is mapped into small
>>         fields like DSCP (6 bits) or MPLS EXP (3 bits) the result is
>>         that only relatively coarse grained QoS treatment can be
>>         provided. How to maintain continuously the fine granularity
>>         within the network in an efficient manner is the core problem
>>         to focus upon. ”
>>
>>         2.What are the uses?
>>
>>         I fully agree with both of you on making the uses clear.
>>
>>         First of all, I need to clarify that “to affect queuing
>>         behaviours”is not my main focus. Queuing is at the node
>>         level, but I look more at the network level, like traffic
>>         steering along appropriate paths or slices. On the contrary,
>>         this sentence of Adrian is in my scope, “this information
>>         might be used to supplement routing information and help send
>>         traffic from different flows onto different paths according
>>         to the capabilities of the network and the demands of the
>>         traffic”
>>
>>     How fine grained will this actually be?  It cannot realistically
>>     be more fine grained than the number of paths with differing
>>     capabilities.  That's why there has been an aggregation step in
>>     production networks for a long time. If the boxes along the path
>>     don't have the ability to queue these differently, this ends up
>>     being more like service function chaining than differential
>>     network capabilities, right?
>>
>>     Shuping> “Fine” may be a bit misleading? “Flexible” might be a
>>     good word? I found that when we talk about “Fine”, people will
>>     relate it immediately with QoS. We are actually targeting more
>>     uses than QoS. Even for QoS, the actual case is that the nodes
>>     have much high capability, not only a few queues, just this
>>     capability is not fully utilized yet. Something needs to be done
>>     here to change this status.
>>
>>     Shuping> It is indeed more like a SFC-like approach, just not
>>     only including SF. Thank you!
>>
>>         Basically, as we listed before, “to apply various policies in
>>         different nodes along a network path onto a traffic flow
>>         altogether, for example, at the headend to steer into
>>         corresponding path, at the midpoint to collect corresponding
>>         performance measurement data, and at the service function to
>>         execute particular policies. Currently there is still no way
>>         to efficiently realize this composite network service
>>         provisioning along the path.”
>>
>>         Therefore, I further extend this sentence as the followings.
>>         Please let me know how you think.
>>
>>         “The packet treatments needed may vary at different parts of
>>         the packet’s path within the domain, andgeneric enough
>>         information is needed to determine these treatmentsin an
>>         efficient and unified way. Thus, the continuous fine grained
>>         network services within the network domain cannot be provided
>>         efficiently.  For example, at the headend to steer into
>>         corresponding path, at the midpoint to collect corresponding
>>         performance measurement data, and at the service function to
>>         execute particular policies. Currently there is still no way
>>         to efficiently realize this composite network service
>>         provisioning along the path.
>>
>>     Does packet treatment always mean steer, or does it have other
>>     meanings?
>>
>>     Shuping> Steering, triggering, identifying… what I have
>>     summarized above, please suggest more or revisions.
>>
>>
>>     I'm also afraid that "Currently there is still no way to
>>     efficiently realize this composite network service provisioning
>>     along the path" falls into a fairly common charter trap:
>>     presuming that the new thing is better than the existing thing
>>     before you have built it and assessed the trade-offs.
>>
>>         This information can be carried directly in the packet or
>>         achieved through a mapping from an opaque tag. Existing
>>         protocols such as SFC/NSH, SR/SRv6, MPLS, VXLAN, and IPv6,
>>         can be taken as implementation basis, but in each case the
>>         protocol may need extensions.”
>>
>>     Could I ask for an example of what extension MPLS might need to
>>     accomplish this traffic engineering?  Or did you have a different
>>     packet treatment in mind?
>>
>>     Shuping> The required MPLS extensions are up to the MPLS folks to
>>     explore. Currently there are on-going activities in IETF. The
>>     work here was also considered as one of their use cases.
>>
>>         3.What are the key items?
>>
>>         Yes, considerations on privacy and security need to be taken
>>         as the key work items. We will need to specify the potential
>>         privacy and security aspects, mitigation mechanisms, and
>>         principles with particular emphasis on reducing the exposure
>>         of confidential/private information outside the network.
>>
>>         Please also suggest other work items.
>>
>>         Best Regards,
>>
>>         Shuping
>>
>>     Sorry again for the long delay in replies.
>>
>>     Ted
>>
>>     Thank you!
>>
>>     Best Regards,
>>
>>     Shuping
>>
>>         *From:*Adrian Farrel [mailto:[e-mail]]
>>         *Sent:* Friday, May 5, 2023 2:36 AM
>>         *To:* 'Ted Hardie' <[e-mail]>; Pengshuping (Peng
>>         Shuping) <[e-mail]>
>>         *Cc:* [e-mail]
>>         *Subject:* RE: [Apn] Problem statement
>>
>>         Hi all,
>>
>>         Reasonable points, Ted.
>>
>>             In a network operator controlled domain, the ingress edge
>>             devices usually have access to much richer information,
>>             such as VLAN/QinQ, VPN, and access interface, which is
>>             used to classify the packets into fine granular virtual
>>             groups of flows at the edge. However, after the packets
>>             enter the network operator’s domain, all such information
>>             is lost together with the continuous fine granularity
>>             within the network.
>>
>>         "all such information is lost together with the continuous
>>         fine granularity within the network" seems to be the core of
>>         the problem statement.  I think it is not quite correct as
>>         stated, in that the information is not lost; it is
>>         distributed.  Because this is within a single operator's
>>         domain, the operator can construct the network to map data
>>         like VLAN to specific address announcements or DHCP
>>         assignments; even if there is a later NAT or CGNAT, the
>>         operator should control all of the devices which implement
>>         those mappings. That means the operator has (or can have)
>>         this information now; it's just distributed through the network.
>>
>>         I think you need to be clear about this because it makes it
>>         more obvious that you are describing a potential
>>         optimization, rather than truly new functionality.
>>
>>         In a network operator controlled domain, the ingress edge
>>         devices usually have access to much richer information, such
>>         as VLAN/QinQ, VPN, and access interface, which is used to
>>         classify the packets into fine granular virtual groups of
>>         flows at the edge. However, after the packets enter the
>>         network operator’s domain, all such information is lost
>>         together with the continuous fine granularity within the
>>         network. But maybe we should avoid trying to solve the
>>         problem statement and just focus on clarifying it.
>>
>>         But, anyway, you’re right that “lost” is the wrong word.
>>         Rather than “lost” we might have “not immediately visible”.
>>         But perhaps a few more words would help draw out this
>>         fundamental part of the problem statement and make clear the
>>         potential limitations of existing approaches (which leads on
>>         to the comment about “fine grained information”). So, perhaps…
>>
>>         In a network operator controlled domain, the ingress edge
>>         devices usually have access to rich information, such as
>>         VLAN/QinQ, VPN ID, and access interface, which is used to
>>         classify the packets into fine granular virtual groups of
>>         flows at the edge. However, after the packets enter the
>>         network operator’s domain, all such information is not
>>         immediately visible at transit nodes: it may be hidden inside
>>         encapsulation, masked by encryption, mapped to other protocol
>>         fields, or stripped from the packets completely. Furthermore,
>>         many mapping schemes, where they are used, lose some level of
>>         granularity from the information available at the network
>>         edge. For example, when the information is mapped into small
>>         fields like DSCP (6 bits) or MPLS EXP (3 bits) the result is
>>         that only relatively coarse grained QoS treatment can be
>>         provided.
>>
>>         The packet treatments needed may vary at different parts of
>>         the packet’s path within the domain, and enough information
>>         is needed to determine these treatments. Thus, the continuous
>>         fine grained network services within the network domain
>>         cannot be provided efficiently. This information can be
>>         carried directly in the packet or achieved through a mapping
>>         from an opaque tag. Existing protocols such as SFC/NSH,
>>         SR/SRv6, MPLS, VXLAN, and IPv6, can be taken as
>>         implementation basis, but in each case the protocol may need
>>         extensions.
>>
>>         I also believe that you need to include a statement about
>>         what the network is going to do with the "fine grained
>>         information", because you can't judge whether a proposal
>>         serves the purpose adequately without that. If your aim is to
>>         carry it to an orchestrator inside an operator network for
>>         action (as in the source quench example Adrian came up with),
>>         then this is a way of getting data to that orchestrator
>>         rather than using a set of database dips.  That has one set
>>         of characteristics, and my personal guess is that it would
>>         look much like service function chaining.
>>
>>         If your aim is to affect research consumption within the
>>         network, then you'd both need different data and you need the
>>         entire network to provide queues at the level of granularity
>>         that you're proposing.  As you point out, most things
>>         currently get mapped to things like DSCP or EXP, and I invite
>>         you to consider the tradeoff between complex queue management
>>         and additional capacity in that reality.
>>
>>         s/research/resource/
>>
>>         I think this is a fundamental point as well. Obviously(?) if
>>         there is no specific planned use for the information, then
>>         there is no point in making it available.
>>
>>         One of my previous thoughts was that this information might
>>         be used to supplement routing information and help send
>>         traffic from different flows onto different paths according
>>         to the capabilities of the network and the demands of the
>>         traffic, but I think that this is not in scope of Shuping’s
>>         proposal.
>>
>>         More in scope, from what I understand, is to affect queuing
>>         behaviours.
>>
>>         Now, as you say, “complex queue management” has historically
>>         been a significant drain on processing and hard to manage.
>>         There is a claim, however, that newer hardware can support
>>         very many queues and achieve fine-grained and complex
>>         scheduling and prioritisation.
>>
>>         But the message here is that the text needs to say what the
>>         purpose of the information is. I do believe that this is
>>         somewhat covered by the paragraph you quoted below (and I
>>         folded into my green text, above), but maybe it is not clear
>>         and clean enough what the use cases are. We need to be
>>         careful not to invent a tool and then look for uses: we need
>>         to have clear uses that drive the invention of the tool. (Of
>>         course, future uses may be discovered, and we should try to
>>         make the tool as generic as possible without losing the
>>         benefits of specialisation).
>>
>>         I also thought there was consensus that this proposal needed
>>         to have privacy considerations so that the same data that
>>         carries ingress port information did not carry information
>>         specific to the user.  While I am sure that the proponents
>>         are clear on this limitation, I think it would be appropriate
>>         to repeat that in the problem statement text, as that would
>>         help new participants understand that it is firmly out of scope.
>>
>>         I completely agree with this. I think it is very important to
>>         continue to make this clear because it is such a sensitive
>>         point for so many people.
>>
>>         Best,
>>
>>         Adrian
>>
>>         best regards,
>>
>>         Ted Hardie
>>
>>             Indeed, the information is mapped into small fields like
>>             DSCP (6 bits) or MPLS EXP (3 bits). However, such small
>>             fields are only able to provide relatively coarse grained
>>             QoS treatment. The packet treatments needed may vary at
>>             different parts of the packet’s path within the domain,
>>             and enough information is needed to determine these
>>             treatments. Thus, the continuous fine grained network
>>             services within the network domain cannot be provided
>>             efficiently. This information can be carried directly in
>>             the packet or achieved through a mapping from an opaque
>>             tag. Existing protocols such as SFC/NSH, SR/SRv6, MPLS,
>>             VXLAN, and IPv6, can be taken as implementation basis,
>>             but in each case the protocol may need extensions.
>>
>>             =================
>>
>>             Best Regards,
>>
>>             Shuping
>>
>>             -- 
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>>             https://www.ietf.org/mailman/listinfo/apn
>>             <https://www.ietf.org/mailman/listinfo/apn>
>>
>>
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