Pseudowire Control Word Negotiation Mechanism Analysis and Update

draft-jin-pwe3-cbit-negotiation-01

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PWE3 IETF79

Lizhong Jin Raymond Key

Thomas Nadeau Simon Delord

Vishwas Manral

Introduction

• This draft is an outcome from many face-to-face and email discussions with:– Stewart Bryant, Andrew Malis, Nick Del Regno, Sami

Boutros, Luca Martini, Venkatesan Mahalingam, Alexander Vainshtein, Adrian Farrel, and etc.

• This draft describes the problem of control word negotiation mechanism specified in [RFC4447].

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Relations with other draft

• draft-delregno-pwe3-mandatory-control-word also solve the problem of control word negotiation, and briefly described in option 4 in this draft.

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Problem Statement

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CW: PREFERRED

Label Map: Cbit=0CW: NOT-PREFERRED

Label Map: Cbit=0

CW: PREFERRED

Label Map: Cbit=0

Configuration changed to

Label Withdraw

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According to the control word negotiation mechanism, the received label mapping on PE2 from PE1 indicates Cbit=0, therefore PE2 will still send label mapping with Cbit=0.

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PW Negotiated Cbit=0

PW Negotiated Cbit=0 Wrong

Option 1: Control Word Re-Negotiation by Label Request

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CW: PREFERRED

Label Map: Cbit=0CW: NOT-PREFERRED

Label Map: Cbit=0

CW: PREFERRED

Label Request

Configuration changed to

Label Withdraw

PW Negotiated Cbit=0

PW Negotiated Cbit=1

Label Map: Cbit=1

Label Map: Cbit=1

Option 1: Control Word Re-Negotiation by Label Request

• When PE doing the CW changing operation, it should send label request to peer PE, even if it has already received the label mapping message.

• Request message processing for PW:– The request message should be processed in ordered

mode in MS-PW case.– PE1 SHOULD send label mapping with locally

configured CW parameter.• Option1 is backward compatible.

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Option 2: Make CW Non-Configurable

• Option 2: Make CW Non-Configurable– Default value is PREFERRED which can be degraded to NOT

PREFERRED by negotiation automatically;– But: there is explicit requirement from service providers to allow

control word to be configurable.

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Option 3: Manual Configuration Process for CW

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CW: PREFERRED

Label Map: Cbit=1CW: NOT-PREFERRED

Label Map: Cbit=0

CW: PREFERRED

Configuration changed to

Label Withdraw

PW Negotiated Cbit = 0 AND 1 = 0

PW Negotiated Cbit = 1 AND 1 = 1

Label Map: Cbit=1

1. Abandon the control word negotiation mechanism described in [RFC4447];2. Local PE should simply do “AND” operation between receiving CW with local configuration (PREFERRED or not-PREFERRED).

Option 4: Make CW Capability Mandatory

• Option 4: Make CW Capability Mandatory– The PW will only be in operation UP when both PW end-points

support control word capability.

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Next steps

• Which option should be accepted?• Need comments from work group

Thank you

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