Re: [Detnet-dp-dt] Providing unique Flow-ID

[Jouni Korhonen <[e-mail]>]

Hi,

We refer to the naming found in slides we used & shared in past two or so calls.

- Jouni

--
Jouni Korhonen, Broadcom Ltd.
M: [phone]

> On Feb 21, 2017, at 7:27 PM, Jiangyuanlong <[e-mail]> wrote:
> 
> Hi,
> 
> What is I-label and what is L-label? Are they in the same label stack as the d-pw label? It will help us to be aligned to the same picture;)
> In the past, we have PW label and LSP label (maybe multiple LSP labels in hierarchy) for a service. 
> 
> Thanks,
> Yuanlong
> -----Original Message-----
> From: Detnet-dp-dt [mailto:[e-mail]] On Behalf Of Jouni Korhonen
> Sent: Wednesday, February 22, 2017 5:34 AM
> To: Balázs Varga A
> Cc: [e-mail]
> Subject: Re: [Detnet-dp-dt] Providing unique Flow-ID
> 
> Hi,
> 
> I have few comments inline.
> 
> 
> --
> Jouni Korhonen, Broadcom Ltd.
> M: [phone]
> 
>> On Feb 21, 2017, at 9:05 AM, Balázs Varga A <[e-mail]> wrote:
>> 
>> Hi,
>> 
>> question to be answered:
>> - how to ensure that detnet flows can be unique recognized during transport?
>> 
>> Labels used by DetNet flows so far in our discussions:
>> - d-pw: DetNet flow specific
>> - l-label: FRER specific label to identify replica (member) flows
>> - t-label: transport label (FEC of T-PE or S-PE nodes)
>> Note: Text below assumes an l-label present, what may not be always the case.
> 
> To my understanding the l-labels “connect” x-PE nodes i.e. create the desired overlay topology over all LSRs/PEs. L-labels also identify which packets will receive FRER processing and which not i.e., whether a specific PW gets terminated in an x-PE or whether x-PE just acts as a transit.
> 
> 
>> Before discussing uniqueness/allocation/usage of these labels let's 
>> list the scenarios requiring flow identification during transport. They can be separated in two groups:
>> 1, DetNet function related scenarios:
>> - congestion protection: usage of allocated resources (queuing, policing, shaping).
>> - explicit routes: select/apply the flow specific path.
>> - service protection: recognize compound / member flows for 
>> replication an elimination.
>> 
>> 2, OAM function related scenarios:
>> - troubleshooting (e.g., identify misbehaving flows, etc.)
>> - recognize flow(s) for analytics (e.g, increase counters, etc.)
>> - correlate events with flows (e.g., volume above threshold, etc.)
>> - others ...
>> 
>> We can distinguish 3 node types:
>> - T-PE: d-pw starts/terminates here
>> - S-PE: place of detnet specific function (e.g., FRER)
>> - P: intermediate node (transport only functions)
>> 
>> T-PE and S-PE nodes are fully aware of both the DetNet service and transport layers.
>> In case of PHP, they receive only "d-pw + l-label", so the x-PE node 
>> should recognize the DetNet flow based on these labels. DetNet 
>> specific functions are driven by the "d-pw label" and "l-label" pair. 
>> The "d-pw"+"l-label" pairs have to be locally unique on the x-PE.
> 
> I have an issue what “pair” means here. L-labels should only have simple rules and actions like pop, label swap, etc:
> 
> In the context of DetNet and L-labels, popping it would expose the d-pw label to the system, which would then do PW (+FRER) thing based on the top d-pw label. Label swap for L-label would allow making desired x-PW nodes to behave as transit nodes in the DetNet context.
> 
> Combining L-label into DetNet specific processing is IMHO a bad decision. Even if the hardware could be able to look up multiple labels in parallel, the next hop and action decisions would still be per label, not as a single result. Keeping this in mind, the system would also work as such when L-labels are not present i.e., the x-PE just receives a packet with d-pw label or T-label+d-pw label.. the assumption here is that the configuration at this point is such there is no ambiguity..
> 
>> The problematic points are the intermediate "P" nodes. Their detnet 
>> role is limited to ensure congestion protection from the above listed 
>> DetNet functions. Additionally OAM functions are also nice to have at each hop (as usual).
>> 
>> We have two options for P nodes:
>> - Option-A, P node can recognize only "t-label" and cannot consider 
>> the whole label stack for flow recognition. This is the scenario, 
>> where we have pre-established tunnels over the network, where the 
>> DetNet flows are mapped to appropriate tunnels to be transported over 
>> the network. This can be treated as a form of aggregation as many 
>> DetNet flows may use the same tunnel. Of course with this aggregation we lost per flow identification, that is the price for scalability.
>> - Option-B, P-nodes can consider the whole label stack and they can 
>> identify each individual flow. That represents additional requirement 
>> on P nodes, which may not be acceptable in some network scenarios.
>> 
>> So, what labels should be unique and how should we allocate labels?
>> - d-pw: allocated by egress PE node. Label value is unique on that particular PE node.
>> Other PE nodes may allocate the same label value for a different detnet flow.
>> - l-label: allocated by the S-PE node. Label value is unique on that 
>> particular S-PE node.
> 
> How would the L-label assignment work in our A,B,C,D x-PE example? B would do downstream assignment to A and upstream assignment to D?
> 
>> - t-label: allocated by P node. Refer to the tunnel endpoint node 
>> (FEC) and the tunnel-ID. Value locally unique on the P node.
>> 
>> Such an allocation scheme ensure that all nodes in the network are 
>> able to identify uniquely the DetNet flows (or aggregate flows) and 
>> support the above listed
>> functions:
>> - T-PE (egress): DetNet flow(s) identified based on the "d-pw" value.
>> - S-PE: DetNet flow(s) identified based on the “l-label" value
> 
> How do you do the flow to seqnum pairing? It does not make sense to map multiple L-labels to a single seqnum counter & duplicate elimination function. A solution like this would need us to introduce kind of master and slave label relationships, or virtual labels that L-labels point at.
> 
>> - P-node (option-A): aggregated DetNet flow(s) identified based on the "t-label"
>> - P-node (option-B): DetNet flow(s) identified based on the "l-label + 
>> t-label" (no need to look for the “d-pw" label, unless “l-label” is 
>> not present)
>> 
>> Note, that as shown above globally unique “d-pw" labels are optional!
> 
> I realize that detnet domain wide global d-pw labels are a pain in a neck. It would, for example, required each ingress T-detnet-PE to have their own d-pw label ranges they assign labels to detnet flows (assuming upstream label assignment). However, I still think global d-pw labels are cleaner from the forwarding point of view.
> 
>> 
>> Good night and see You tomorrow early morning Bala'zs
>> 
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