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RE: ATM Label stack processing

  • From: Javier Antich <javier.antich@telindus.es>
  • Date: Thu, 28 Jun 2001 12:40:49 +0200
  • Resent-Date: Thu, 28 Jun 2001 07:44:49 -0400
  • To: John Black <john_black66@hotmail.com>, mpls-ops@mplsrc.com
  • X-MIME-Autoconverted: from quoted-printable to 8bit by host.secure4-hosting.net id f5SAhNs28778

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Javier Antich Romaguera
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> -----Mensaje original-----
> De:	John Black [SMTP:john_black66@hotmail.com]
> Enviado el:	jueves 28 de junio de 2001 11:24
> Para:	mpls-ops@mplsrc.com
> Asunto:	ATM Label stack processing
> 
> My understanding of label stack processing in ATM is that top most label
> is 
> encoded as VPI/VCI pair, the rest of stack is encoded in AAL5 PDUs.
> 1.Does it mean that every ATM switch has to reassemble AAL5 frame to read 
> the next label from the stack?
	[Javier Antich]  ATM switches acting as LSRs do not need to read the
next label. They do only ATM switching based on the VPI/VCI values with are
the MPLS outer-most label. They would need to reassemble if they act as LER.
> 2. When LSP over ATM setup is completed - is there any need in label
> stacks 
> any more or cells just follow each other and switch swaps labels based on 
> information read from original label stack?
	[Javier Antich]  I do not understand actually the question, but
cells are switched like normal ATM cells based on the VPI/VCI values. No
matter if inside them a frame is encapsulated which has more labels.
Remember that an ATM-LSR is not able to push or pop labels, it is only able
to swap the outer label (encoded as VPI/VCI).

> thanks
> jb
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