Network Working Group H. Ohta Request for Comments: 3429 NTT Category: Informational November 2002 Assignment of the 'OAM Alert Label' for Multiprotocol Label Switching Architecture (MPLS) Operation and Maintenance (OAM) Functions Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved.
AbstractThis document describes the assignment of one of the reserved label values defined in RFC 3032 (MPLS label stack encoding) to the 'Operation and Maintenance (OAM) Alert Label' that is used by user- plane Multiprotocol Label Switching Architecture (MPLS) OAM functions for identification of MPLS OAM packets. RFC 3032 (MPLS label stack encoding ) to the 'OAM Alert Label' that is used by user-plane MPLS OAM functions for identification of MPLS OAM packets as described in the ITU-T Recommendation Y.1711  (on MPLS OAM functions).
- Reporting the defect/failure information: Defect information is given to other management entities (e.g., Operation Support System) in order to provide the appropriate indications to the maintenance staff for maintaining the Quality of Service (QoS) level offered to customers. - Defect/failure localization: Determination by internal or external test systems of a failed entity is performed if defect information is insufficient. - Performance monitoring: Performance (packet losses, transfer delay, bit errors, etc.) of the user information transport is measured in order to estimate the transport integrity. 1] uses a special label called 'OAM Alert Label' to differentiate OAM packets from the normal user packets. One of the reserved label values defined in RFC 3032 (MPLS label stack encoding ) is assigned to 'OAM Alert Label'. A value of 14 is used for this purpose. 3] (2) Corrigendum 1 to Recommendation Y.1710  (3) Recommendation Y.1711 (OAM mechanisms for MPLS networks)  (4) Draft Recommendation Y.1720 (Protection switching for MPLS networks)  relies on OAM mechanisms in Y.1711, under last call as of Nov. 2002. 1] are applied to MPLS networks where PHP is in effect.
1]. "1 Scope This Recommendation provides mechanisms for user-plane OAM (Operation and Maintenance) functionality in MPLS networks according to the requirements and principles given in Recommendation Y.1710. OAM functions specified in this Recommendation can be applied to both non-PHP and PHP cases unless otherwise stated. The current version of this recommendation is designed primarily to support point-to-point and multipoint-to-point explicit routed LSPs (ER-LSPs)." RFC 3032 . Case 2: The ultimate node has no MPLS label look up and processing capability and does not recognize labeled packets. This node asks for PHP, using the MPLS reserved label 3 (implicit null label) as defined in RFC 3032 . Currently, MPLS OAM functions defined in ITU-T Recommendation Y.1711  can only be applied to Case 1. The next subsection describes the node behavior in Case 1. Application for Case 2 needs further study. Also, application to carrier supporting carrier scenarios is for future study. 5]. - If the ultimate LSR supports MPLS OAM, it understands that a received packet with an OAM label on top is an OAM packet, since the original top label has been removed by the penultimate LSR. It also knows the ingress LSR that originated the MPLS OAM packet from the TTSI (Trail Termination Source Identifier) value of the
received MPLS OAM packet. TTSI is a unique identifier for ingress LSR that is contained in MPLS OAM packets (see ITU-T Recommendation Y.1711 ). - If the ultimate LSR does not support MPLS OAM, the OAM packet is discarded as per section 3.18 of RFC 3031 . section 3 for additional information. 1] can detect mis-connections, and therefore can prevent customers' traffic being exposed to other customers.  ITU-T Recommendation Y.1711, "OAM mechanism for MPLS networks", November 2002.  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinaccia, D., Li, T. and A. Conta, "MPLS label stack encoding", RFC 3032, January 2001.  ITU-T recommendation Y.1710, "Requirements for OAM functionality for MPLS networks" July 2001.  ITU-T Corrigendum 1 to Recommendation Y.1710, November 2002.  Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, January 2001.
 ITU-T Draft Recommendation Y.1720, "Protection switching for MPLS networks", under last call as of November 2002.
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