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

[Norman Finn <[e-mail]>]

Also, they define the overlay topology over which the pseudowires are created.

I think.

-- Norm
________________________________________
From: Detnet-dp-dt [[e-mail]] on behalf of Loa Andersson [[e-mail]]
Sent: Tuesday, February 21, 2017 10:06 PM
To: [e-mail]
Subject: Re: [Detnet-dp-dt] Providing unique Flow-ID

Bala'zs,

The tunnel might carry more the just one PW, and in the general case it
might come from more than one node.

/Loa

On 2017-02-22 13:56, Balázs Varga A wrote:
> Hi,
>
>> 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.
>
> Why do we need l-label to connect x-PE nodes? t-lables do that for free.
> I agree that the next label after the t-label will tell x-PE what to do.
> Terminate the PW or just act as transit.
>
> See You soon
> Bala'zs
>
> -----Original Message-----
> From: Jouni Korhonen [mailto:[e-mail]]
> Sent: Tuesday, February 21, 2017 10:34 PM
> To: Balázs Varga A <[e-mail]>
> 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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--


Loa Andersson                        email: [e-mail]
Senior MPLS Expert                          [e-mail]
Huawei Technologies (consultant)     phone: [phone]

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