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NTT 2002 © 1 General Principles and Requirements for OAM Functions July 10, 2002 Hiroshi Ohta (NTT, Q.3/13 rapporteur)
NTT 2002 © 2 Contents Purposes, principles and requirements of OAM functions OAM functions for SDH-based ATM networks OAM functions for emerging networks (MPLS and Ethernet) Study issues
NTT 2002 © 3 Purposes, principles and requirements of OAM functions
NTT 2002 © 4 Purpose of the OAM functions OAM (Operation and Maintenance) functions are used to detect defects and performance degradation and localize them in order to maintain and guarantee the service performance –When an operator receives complaints from a customer, they need to Localize the defect and report it to the customer Arrange corrective action –When a defect or performance degradation occurs, they should be reported to the operator automatically and recovered automatically extent possible. –When a service is released to a user, it should be tested beforehand to ensure its availability and QoS
NTT 2002 © 5 OAM principles OAM functions are designed to meet the following objectives Defect detection Defect localization Defect information (reporting to OSS/NMS) Performance monitoring System protection (protection switching, redundancy of network elements)
NTT 2002 © 6 Defects and performance degradation Examples of defects and performance degradation Defects –Fiber/wire cut –Defect in equipment –mis-connection –swapped connection –Loop Performance degradation –Bit errors –Packet/Cell/Frame losses –Delay and its variation Although there are several technologies to build a network, problems are similar
NTT 2002 © 7 Requirements to OAM functions On-demand diagnosis and continuous monitoring Defect should be automatically detected, localized and reported to OSS/NMS. Customers should not be used as a defect detector Availability and QoS should be able to be measured OAM functions should not be dependent of the dynamic behavior of customer traffic The OAM function should perform reliably even under degraded link conditions Requirements are similar regardless of the technology (OTN, SDH, ATM, MPLS, etc.)
NTT 2002 © 8 Methods to realize OAM functions Hierarchical maintenance entity (ME) Fault management and performance management functions for each ME/layer –SDH –ATM –MPLS … under standardization –Ethernet … under study/standardization OAM functions are categorized into: –Continous surveillance for detection of defects and performance degradation (e.g., CC, AIS/RDI, PM for ATM) –On-demand diagnosis test for defect localization (e.g., Loopback and on-demand non-intrusive monitoring for ATM) Methods are also similar regardless of the technology (OTN, SDH, ATM, MPLS, etc.)
NTT 2002 © 9 Situation of standardization For ATM –OAM for ATM: Rec. I.610 –Protection switching for ATM: Rec. I.630 For MPLS –OAM requirements for MPLS: Rec. Y.1710 –OAM mechanisms for MPLS: Draft Rec. Y.1711 –Protection switching for MPLS: Draft Rec. Y.1720 For Ethernet –Under standardization within IEEE/EFM for OAM for Ethernet access networks –Under study within ITU-T SG13/15
NTT 2002 © 10 OAM functions for SDH-based ATM networks
NTT 2002 © 11 Protocol stack Regenerator Section Multiplex Section Transmission Path (TP) Virtual Path (VP) Virtual Channel (VC) Segment VC End-to-end VC Segment VC
NTT 2002 © 12 Hierarchical maintenance entity VPH VCH VPH VC VP Transmission Path Multiplex Section Regenerator Section VPH TPH Rep Transmission Path *VCH: VC Handler, VPH: VP Handler, TPH: Transmission Path Handler, Rep: Repeater/regenerator
NTT 2002 © 13 Defect detection VPH TPH Rep LOS is detected MS-AIS P-AIS VPH VCH VPH VP-AIS VC-AIS *VCH: VC Handler, VPH: VP Handler, TPH: Transmission Path Handler, Rep: Repeater/regenerator MS: Multiplex Section
NTT 2002 © 14 Defect detection and performance monitoring method Regenerator Section Multiplex Section Transmission Path Virtual Path (VP) Virtual Channel (VC) Detection of LOS/LOF at a regenerator Detection of LOS/LOF/LOP Reception of MS-AIS Path trace (J1) Signal Label (C2) (Seg/EE) VP Continuity Check (CC) (Seg/EE) VC Continuity Check (CC) Layer Methods for defect detection Methods for performance monitoring (Seg/EE) VC Performance Monitoring (PM) (Seg/EE) VP Performance Monitoring (PM) Bit error monitoring (B3) Bit error monitoring (B2) Bit error monitoring (B1)
NTT 2002 © 15 Reports to OSS (1) – Physical layer defect OSS (Operation Support System) VPH VCH VPH VCH Report (LOS) VP-AIS VP-CC Detection of Loss of VP-CC (LOC) But it is not reported because VP-AIS is received VC-AIS Detection of Loss of VC-CC (LOC) But it is not reported because VC-AIS is received VC-CC *LOS: Loss of Signal
NTT 2002 © 16 Reports to OSS (2) – VP layer defect OSS (Operation Support System) VPH VCH VPH VCH Report (LOC) VP-CC Detection of Loss of VP-CC (LOC) It is reported because VP-AIS is NOT received. VC-AIS Detection of Loss of VC-CC (LOC) But it is not reported because VC-AIS is received VC-CC VP layer defect (e.g., table corruption) *LOC: Loss of Continuity
NTT 2002 © 17 Multi-operator environment – VP layer defect OSS (Operation Support System) VPH VCH VPH VCH Report (LOC) VP-CC Detection of Loss of VP-CC (LOC) VC-AIS Detection of Loss of VC-CC (LOC) VC-CC VP layer defect (e.g., table corruption) Operator AOperator B OSS (Operation Support System) Operator A Detects VP-LOC defect at the VP terminating point. Understands it is the root-cause because there is no AIS. Operator A is responsible to handle this defect. Operator B Detects VC-LOC at the VC terminating point. Understands that the cause of this defect is already detected in upstream because there is VC-AIS. Operator B is not responsible for this defect. *LOC: Loss of Continuity
NTT 2002 © 18 OAM functions for emerging networks
NTT 2002 © 19 OAM aspects for MPLS and Ethernet MPLS and Ethernet are widely used recently for providing services for corporate users such as: –MPLS based IP-VPN –Transparent LAN Service (TLS) / Ethernet based on optical pure Ethernet or MPLS There services are replacing leased line services based on SDH and ATM because they are cheaper in terms of the cost per bandwidth However, although services for corporate users require high reliability in general, OAM functions for MPLS and Ethernet have not been fully developed yet.
NTT 2002 © 20 OAM for MPLS networks (1) Functions below are specified in Draft Rec. Y.1711 Defect detection: Connectivity Verification (CV) –Verify connectivity by sending CV packet periodically –Verify TTSI (Trail Termination Source Identifier) at the sink of an LSP to detect the following defects Misconnection, swapped connection, unintended replication, loop Alarm signal transfer: Forward Defect Indication (FDI) and Backward Defect Indication (BDI) –Notify defects downstream and upstream –Suppress unnecessary reporting to OpS (because it has been already reported by the NE generating FDI)
NTT 2002 © 21 OAM for MPLS networks (2) Functions below are under study Performance monitoring Loopback LSP trace
NTT 2002 © 22 OAM for Ethernet (1) OAM for access network is under study (IEEE/EFM, SG13/15) No OAM functions which cover entire network Link up/down can be reported by L2 switches to OSS but (for example) it does not cover the cases where: –there are regenerators between L2 switches –there are WDM systems between L2 switches There is no OAM functions to indicate defects to other operators in multi-operator case Link up at all L2 switches does not mean defect-free end-to-end connectivity because switches can have defects such as VLAN table corruption.
NTT 2002 © 23 OAM for Ethernet (2) Ethernet is a connectionless mesh network. Ethernet OAM functions must be applied to this. Following OAM functions are envisaged: –connectivity verification –alarm signal transfer (forward/backward) –performance monitoring –Loopback –Trace Ethernet OAM functions should be coordinated with lower layer OAM functions (e.g., OAM for WDM, regenerator spans) so that operator can grasp all the defects in the network.
NTT 2002 © 24 Ethernet over MPLS, SDH/SONET, ATM Ethernet services can be provided by emulations such as: –MPLS (Ethernet over MPLS … several Internet-Drafts) –SDH/SONET (Ethernet over SDH/SONET with GFP … G.7041) –ATM (Multiprotocol Encapsulation over AAL5 … RFC2684) If the paths (LSPs, Transmission paths, VPs/VCs) spans UNI to UNI or edge to edge, OAMs for these lower layer can be used as OAM for Ethernet services.
NTT 2002 © 25 Study issues
NTT 2002 © 26 Study issues Clarification of the requirements to OAM functions, in particular, for emerging networks such as MPLS and Ethernet –Defect detection and localization –Performance monitoring Development of the standard methods to realize necessary OAM functions Clarification of the trade-off between cost/complexity and OAM functions Clarification of what OAM functions should be performed by what layer
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