Re: [Detnet-dp-dt] Using MS-PW concept for the d-pw

[Jouni Korhonen <[e-mail]>]

Yuanlong,


> On 25 Feb 2017, at 02:02, Jiangyuanlong <[e-mail]> wrote:
> 
> Loa,
> 
> -----Original Message-----
> From: Loa Andersson [mailto:[e-mail]] 
> Sent: Saturday, February 25, 2017 3:34 PM
> To: Jiangyuanlong; Jouni Korhonen
> Cc: [e-mail]
> Subject: Re: [Detnet-dp-dt] Using MS-PW concept for the d-pw
> 
> Yuanlong,
> 
> The L-laabel is ther to make the the intermediate not (S-PE) know what to do whit the packet, the d-pw label was not allocated by the S-PE, so it does not ahve any knowledge what it means.
> [YJ] d-pw can be allocated by the S-PE in MS-PW, just as you would like to allocate the L-labels. Very similarly, I think the same T-LDP protocol can be used.
> [YJ] As I said in the previous email, using PW to trigger FRER will be cleaner compared with using L-label since CW is inspected.

I think you are still getting it wrong what was intended with L-labels. They were specifically thought in the context of detnet global d-pw labels.

L-labels connected MS-PW nodes over the network topology. All FRER “triggering” etc is still and has always been tied to the d-pw. Within a S- or T-PE you need to pop the L-label and then inspect the top of stack d-pw label.. 

                                                 within
    LSR                         |------------- S- or T-PE -------------|
                    PHP                            POP 
                  -------->                     -------->
+------------+                  +------------+            +------------+
|  T-labels  |                  |  L-label   |            | d-pw label |
+------------+                  +------------+            +------------+
|  L-label   |                  | d-pw label |            |            |
+------------+                  +------------+            |  Payload   |
| d-pw label |                  |            |            |            |
+------------+                  |  Payload   |            +------------+
|            |                  |            |
|  Payload   |                  +------------+
|            |
+------------+


This allowed also bypassing S-PE easily for some L-labels.. instead of an L-label pop one would do a swap and just forward after that.


- Jouni


> If you let the S-PEs allocate and swap d-pw's, the next S-PE or a T-PE can't coordinate for the same packet coming in on from tow different nodes.
> [YJ] It's like the 1+1 PW protection case, though the operations of elimination and replication in the S-PE and the T-PE need to be specified.
> [YJ]Take VPLS as an example, several PWs can be directed into the same VSI in a PE and PW packets are processed there (for detnet, the processing is FRER now).
> 
> But I feel like we are going in circles, can we agree on the corner stones first?
> 
> Do we want all possible/conceivable control mechanism be within scope?
> [YJ] maybe we can take LDP as a first step. It seems the difficulty is how to decide the S-PEs for a detnet flow (a routing protocol may be needed for automatic selection). 
> [YJ] if all T-PEs and S-PEs are determined for a detnet flow, it is quite easy to set up PW segments and LSPs respectively with the help of LDP protocol. 
> Cheers,
> Yuanlong
> 
> /Loa
> 
> 
> On 2017-02-25 15:18, Jiangyuanlong wrote:
>> I agreed to alternative 2. L-label is not needed, S-PE must look into the PW label (further, extract sequence number in the CW) of a packet, and all FRER semantics can be coupled with the PW label.
>> 
>> -----Original Message-----
>> From: Jouni Korhonen [mailto:[e-mail]]
>> Sent: Saturday, February 25, 2017 3:07 PM
>> To: Jiangyuanlong
>> Cc: [e-mail]; Loa Andersson
>> Subject: Re: [Detnet-dp-dt] Using MS-PW concept for the d-pw
>> 
>> Hi,
>> 
>>> [YJ] I regard the L-Labels and T-labels are the same LSP layer. If we look into the full MPLS label stack of a packet in a PW, normally there is an LSP label at the top (unless PHP is enabled for the last hop).
>>> Not sure what is the L-Label in your picture, is it different from LSP label?
>> 
>> L-labels have been so far in the discussion between MS-PW PEs. 
>> T-labels are between any LSR. L-labels are not PHPed i.e., even if PHP 
>> is enable the L-Label stays and the label above it gets popped (that 
>> we have been referring as T-Labels). T- and L-labels are just a naming 
>> convention. IF you don’t have “between MS-PW PEs” semantic associated 
>> with the L-Label, it is the same as T-Label ;)
>> 
>> 
>> 
>> case L-labels are present.. (alternative 1)
>> 
>>                     PHP
>>                   -------->
>> +------------+                  +------------+
>> |  T-labels  |                  |  L-label   |
>> +------------+                  +------------+
>> |  L-label   |                  | d-pw label |
>> +------------+                  +------------+
>> | d-pw label |                  |            |
>> +------------+                  |  Payload   |
>> |            |                  |            |
>> |  Payload   |                  +------------+
>> |            |
>> +------------+
>> 
>> case no L-labels.. (alternative 2.. and also alternative 3 if you 
>> think T- and L-labels are the same)
>> 
>>                     PHP
>>                   -------->
>> +------------+                  +------------+
>> |  T-labels  |                  | d-pw label |
>> +------------+                  +------------+
>> | d-pw label |                  |            |
>> +------------+                  |  Payload   |
>> |            |                  |            |
>> |  Payload   |                  +------------+
>> |            |
>> +------------+
>> 
>> 
>> 
>> 
>> 
>> - Jouni
>> 
> 
> -- 
> 
> 
> Loa Andersson                        email: [e-mail]
> Senior MPLS Expert                          [e-mail]
> Huawei Technologies (consultant)     phone: [phone]
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