Subject: CLP bit to QoS mapping

From: "Fabio Poggi" <[email-masked]>
Date: Mon, 21 Jun 2004 16:52:19 +0200

Hi all,
I've read draft-martini-l2circuit-encap-mpls-07 and I've one question
regarding cap. 4.2.4 "CLP bit to Quality of Service mapping":
How this mapping is resolved in case of 'ATM Cells mode' encapsulation ?
For example, in the diagram illustrating 'ATM Cells mode' encapsulation
with two different ATM cells provided in the document. Conceptually the two
ATM cells could have different CLP values. How these, probably different,
values are used to set the 'unique' QoS field in the MPLS label stack ?

Is it possible to assume the same rule defined in 'ATM AAL5 CPCS-SDU Mode'
for L (CLP) bit ?

Fabio

---

From: [email-masked]
Date: Wed, 23 Jun 2004 09:40:30 +0100

Luca,

Your suggestion seems to be more like the fragmentation mechanism that can
be used in AAL5 PDU mode to allow OAM cells to pass in correct order. i.e.
you stop building the MPLS packet and ship it based on the value of some
bit in the ATM cell header.

Best regards,

Matthew

|---------+--------------------------->
|         |           Luca Martini    |
|         |           <lmartini@cisco.|
|         |           com>            |
|         |           Sent by:        |
|         |           pwe3-bounces@iet|
|         |           f.org           |
|         |                           |
|         |                           |
|         |           23/06/2004 01:27|
|         |                           |
|---------+--------------------------->
  >-------------------------------------------------------------------------------------------------------------------------------|
  |                                                                                                                               |
  |        To:      [email-masked]                                                                                 |
  |        cc:      [email-masked]                                                                                                 |
  |        Subject: Re: [PWE3] CLP bit to QoS mapping                                                                             |
  >-------------------------------------------------------------------------------------------------------------------------------|

Mustapha Aissaoui wrote:

>
>MA> Are you suggesting concatenation be aborted when a cell of a
>different CLP value than the "currently concatenated cells" arrives?
>I think this could be too disruptive and may not achieve the
>objective of bandwidth efficiency. In my view, it is much easier to
>use a rule similar to the one described for the AAL5 modes. Note
>that such a rule would only apply to CLP-significant service
>categories. For a CLP-transparent service category, there is no need
>to differentiate between CLP0 and CLP1 cells.
>
>
>
>
Well , the method described for AAL5 modes will cause ATM analyzers to
detect errors. In AAL5 more this is not much of a problem as it ends up
being a packet anyway. But in cell mode, an ATM analyzer will see the
wrong data dropped by the mpls network. Not much, but still some people
are very picky about it.
I am not saying that using the described AAL5 method for CPL to MPLS EXP
bit marking is wrong, as it will probably be fine for 99% of the
applications. But there is no reason why the concatenation timer cannot
be triggered , and the packet sent if a cell with different CLP setting
arrives ...

Luca

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