Session Begins Soon
OTN Primer
Steven Surek Consulting Engineer, Ciena Corporation December 3, 2008
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Outline
!! OTN Objectives and Requirements !! OTN Layered Model !! OTN Multiplexing Structure !! OTN Frame Structures !! OTN Overhead Descriptions !! OTN New Standardization Efforts !! OTN Standards and References
The Original DWDM Problem
Proprietary DWDM systems
Carrier A Domain
Vendor A Domain Vendor B Domain
NE
NE
NE
NE End Customer Carrier C Domain NE NE
Carrier B Domain NE NE
Vendor interop only at client level
End Customer
Lack of end-to-end service management
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The OTN Solution
Allow DWDM systems with non-standard Intra-domain Interfaces (IaDI)
Carrier A Domain
Vendor A Domain Vendor B Domain
NE
NE
NE
NE End Customer Carrier C Domain NE NE
Carrier B Domain NE NE
Standarize Inter-domain Interfaces (IrDI)
End Customer
End-to-end OTN-standard service management
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OTN Objectives and Requirements
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Standardize Inter-domain Interfaces
!! Single and multiple wavelength !! With or Without COMMS capability (Optical Supervisory Channel) !! Standard rates and formats (2.5G, 10G, 40G)
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Address Lack of Management Capability of Pure Optical Networks
!! Digital wrapper supporting payload transport and management functions !! Provide signal alignment functions, signal quality monitoring, connection and connectivity monitoring, maintenance signal generation and detection, management communications channels, etc. !! Support multiplexing/demultiplexing of services for efficient bandwidth utilization for various line rates
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Standardize Forward Error Correction Functions
OTN Layers End-to-End
ODUk Trail OTUk Trail OCh OMS OTS
ADM OADM LA
OTS
OADM ADM
Client Trail
Client EQPT
LA = Line Amplifier OADM = Optical Add/Drop Multiplexer
Client EQPT
OTN Layer Descriptions Optical Layers
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Optical Transmission Section (OTS)
!! Physical optical signal consisting of multiplexed payload wavelengths plus an optical supervisory channel wavelength !! Provides optical amplification, dispersion compensation, and management overhead for the physical optical transmission section
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Optical Multiplex Section (OMS)
!! Optical signal consisting of multiplexed payload wavelengths (each wavelength representing an individual optical channel) !! Provides optical amplification, dispersion compensation, and management overhead for the physical optical multiplex section !! Provides multiplexing/demultiplexing of optical channels and management overhead for the optical multiplex section
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Optical Channel (OCh)
!! Represents a single traffic signal (single wavelength), contains optical and electrical functions some of which reside in the OTU frame !! Provides traffic signal generation and recovery (framing, scrambling, FEC, etc.) and management overhead for the optical channel
OTN Layer Descriptions Digital Layers
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Optical Channel Transport Unit (OTU)
!! Provides the electrical functions to support the management of an optical channel section, i.e., section monitor (section trail trace identifier, section error detection code (BIP-8), defect indication functions, general communications channel) !! Provides for transport of the optical channel data unit
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Optical Channel Data Unit (ODU)
!! Provides the electrical functions to support the management of an optical channel data path, i.e., path monitor (path trail trace identifier, path error detection code (BIP-8), defect indication functions, general communications channel, automatic protection switching channel) !! Provides the electrical functions to support the management of tandem optical channel data paths, i.e., tandem connection monitors (tandem connection trail trace identifier, tandem connection path error detection code (BIP-8), defect indication functions, automatic protection switching channel) !! Provides for transport of the optical channel payload
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Optical Channel Payload Unit (OPU)
!! Supports the mapping of a variety of client signal types (GFP, constant bitrate (SDH), etc.) !! Provides payload type defect detection
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OTN Rates
Level k=1 OTU Rate (20 ppm) 255/238 x 2.48832Gbps = ~2.666057Gbps k=2 255/237 x 9.95328Gbps = ~10.709225Gbps k=3 255/236 x 39.81312Gbps = ~43.018414Gbps ODU Rate (20 ppm) 239/238 x 2.48832Gbps = ~2.498775Gbps 239/237 x 9.95328Gbps = ~10.037274Gbps 239/236 x 39.81312Gbps = ~40.319219Gbps 238/237 x 9.95328Gbps = ~9.995277Gbps 238/236 x 39.81312Gbps = ~40.150519Gbps OPU rate (20 ppm) 2.48832Gbps
Note 1: OTN networks operate asynchronously and do not require network synchronization Note 2: Non-standard rates exist at k=2,3 levels as a result of transparent 10GbELAN mappings
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OTN Information Containment Structure
OTM - Optical Transport Module COMMs - Communications OTS - Optical Transport Section OH - Overhead OMU - Optical Multiplex Unit OMS - Optical Multiplex Section OCG Optical Channel Group OCCo Optical Channel Carrier overhead OCCp Optical Channel Carrier payload OCh Optical Channel OTU Optical channel Transport Unit FEC Forward Error Correction ODU Optical channel Data Unit TCMOH Tandem Connection Monitoring Overhead TC Tandem Connection L1, Lm Level 1, Level m PMOH Path Monitoring Overhead OPU Optical channel Payload Unit
OCh
Client
OPUk
OPUk OH
OPUk Payload
ODUk path
ODUk PMOH
OPUk ODUk TC L 1 ODUk TCMOH
ODUk tandem connection
ODUk TCMOH
ODUk TC Lm ODUk TCMOH
1 to 6 levels of tandem connection monitoring
OTUk section
OTUk OH
OTUk FEC
OCh OH
OCh payload
OCG-n.m
...
OCCp
OCCp
... .
OCCp
OTM COMMs
OOS
OMU-n.m
OMSn OH
OMSn payload
OTM -n.m
OTSn OH
OTSn payload
k = 1,2,3 (2.5G, 10G, 40G bit rates) m = 1,2,3,12,123,23 (represents set of bit rates supported) n = maximum number of wavelengths supported
OCCo
OCCo
OCCo
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OTN Multiplexing and Mapping Structure
! Client signals mapped directly to optical channel payload unit frame (OPUk) ! OPUk mapped into corresponding optical channel data unit frame (ODUk) ! ODUk frames mapped to corresponding optical channel transport unit frame (OTUk) or multiplexed to higher order ODUk ! OTUk frames mapped to optical channels (OCh) ! Optical channels mapped to optical channel carrier (OCC) ! Optical channel carriers optically multiplexed into carrier group (OCG) ! OCG combined with optical supervisory channel (OSC) to create the optical transport module (OTM)
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OTN Overhead Signals (OOS): Bit Signaling
Each Layer Signal consists of two parts:
!! Payload Signal (-P): Physical signal carrying service payload !! Overhead Signal (-O): Logical signal mainly for fault management purpose
!! OTS OH: TTI, PMI, BDI-P, and BDI-O !! OMS OH: PMI, FDI-P, FDI-O, BDI-P, and BDI-O !! OCh OH: FDI-P, FDI-O, and OCI
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Signaling transported between nodes over the OSC signal (not standardized) Signaling function termination/generation
!! !! !! !! OTS OHs are always terminated/sourced at every node OMS OHs are always terminated/sourced at every OADM, but pass thru LA nodes OCh OHs are terminated/sourced at node where channels are dropped/added Express OCh OHs are forwarded thru the node
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OTN Frame Structure
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OTUk and ODUk Overhead
ACT Activation/deactivation control channel APS Automatic Protection Switching channel BDI Backward Defect Indication BEI Backward Error Indication BIAE Backward Incoming Alignment Error BIP-8 Bit Interleaved Parity level 8 DAPI Destination Access Point Identifier EXP Experimental FTFL Fault Type and Fault Location channel GCC General Communications Channel IAE Incoming Alignment Error MFAS Multi-frame Alignment Signal PCC Protection Communication Channel PM Path Monitor RES Reserved SAPI Source Access Point Identifier SM Section Monitor STAT Status TCM Tandem Connection Monitor TTI Trail Trace Identifier
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Overhead Descriptions Alignment
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Frame Alignment Signal (FAS)
!! Provided in the OTU frame to allow determination of the beginning of the OTU frame !! Detection of framing failure results in Loss of Frame (LOF) indication
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Multiframe Alignment Signal (MFAS)
!! Provided in the OTU frames to align overhead functions that require multiple frame operation (e.g., Trail Trace Identifier (TTI) functions at OTU/ODU layers; fault type and fault locate, tandem connection activation, mapping functions, and automatic protection switch functions at ODU layer) !! Detection of multi-framing failure results in Loss of Multi-frame (LOM) indication
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Incoming Alignment Error (IAE)
!! Provided in the OTU and ODU frames to detect frame alignment errors detected by upstream equipment (occurs for through-timed equipment when incoming clock signal is lost) !! Detection of alignment error results in suppression of near-end and far-end performance monitoring data for current and previous seconds
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Backward Incoming Alignment Error (BIAE)
!! Provided in the OTU and ODU frames to detect frame alignment errors detected by downstream equipment (due to a detection of an IAE at a downstream node) !! Detection of alignment error results in suppression of far-end performance monitoring data for current and previous seconds
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IAE and BIAE Processing
Detect incoming IAE, Suppress near/far end PM for current and previous second
frame slip IAE BIAE
Detect incoming BIAE, Suppress far end PM for current and previous second
Generation/detection of IAE/BIAE in ODU layer are used for tandem connection functions not for endto-end path monitoring
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Overhead Descriptions Signal Quality
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FEC (Forward Error Correction)
!! Provided in the OTU frame to allow detection and correction of line bit errors
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BIP-8 (Bit Interleaved Parity-8)
!! Provided in the OTU/ODU frame to allow detection of near-end bit errors and support performance monitoring and protection switching functions (Signal Degrade, Note: signal fail due to BER detection not provided) !! Detection of bit error counts are reported to the far end via the backward error indication field (BEI) on a frame-by-frame basis !! Detection of bit errors within a frame generates an errored block (errored block counts are the basis for near-end PM parameter value determination) !! Detection of N successive degraded seconds (based on percentage of errored blocks) results in a Degraded (DEG) indication
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BEI (Backward Error Indication)
!! Provided in the OTU/ODU frame to allow detection of far-end bit errors and support performance monitoring (single-ended maintenance) !! Detection of bit errors within a frame generates an errored block (errored block counts are the basis for far-end PM parameter value determination) which are reported back to the near-end via BEI bits
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BIP-8 and BEI Computations
1 Frame i 2 3 4
BIP-8
BIP-8 Generation
Frame i+1
BIP-8
1 2 3 4
BIP-8
1 Frame i 2 3 4 1 Frame i+1 2 3 4
BIP-8 BIP-8
BIP-8 Error Detection and BEI Generation
BIP-8
XOR
# of BIP Errors
BEI
BBE count used to trigger DEG defect through user provisionable Degraded seconds threshold and degraded seconds monitoring interval
>0
BBE
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Overhead Descriptions Connectivity and Continuity
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TTI (Trail Trace Identifier)
!! Provided in the OTS overhead or OTU/ODU frame to allow detection of connectivity errors !! Supports provisioning of transmitted and expected values and allows retrieval of accepted value !! Provides disabled, source access point identifier (SAPI), destination access point identifier (DAPI), and SAPI+DAPI modes; provides mode for disabling automatic actions due to trace identifier mismatch !! Detection of trace identifier mismatch results in Trail trace Identifier Mismatch (TIM) indication
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OCI (Open Connection indication)
!! Provided in the OCh overhead or ODU frame to allow detection of continuity errors by indicating that a loss of signal is due to an output connection point is not connected to an input connection point !! At the OCh layer OCI indicates a wavelength not cross-connected !! At ODU layers indicated through 0110 pattern in STAT fields
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Trail Trace Identifier Format
CC = ISO 3166 Country Code ICC = ITU Carrier Code as per ITU-T Rec. M.1400 UAPC = Unique Access Point Code is carrier specific
! All TTI characters are from the T.50 character set ! SAPI and DAPI fields are defined as above ! Operator Specific bytes are user specified
SAPI[0] and DAPI[0] are set to All-0s
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SAPI and DAPI Applications
Transmitted TTI Point-to-Point Application Expected SAPI Expected SAPI or SAPI+DAPI
Transmitted TTI Point-to-Multipoint Application
Expected SAPI
Expected SAPI Transmitted TTI
Transmitted TTI Multipoint-to-Point Application Transmitted TTI
Expected DAPI
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Overhead Descriptions Maintenance Signals
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FDI (Forward Defect Indication)
!! Provided in the OOS to indicate optical AIS condition
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PMI (Payload Missing Indication)
!! Provided in the OTS/OMS layers to indicate loss of optical payload for downstream LOS-P suppression
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STAT (Status AIS, LCK)
!! Provided in the ODU frame to allow detection of maintenance signal conditions !! Detection of All-1s results in Alarm Indication Signal (AIS) indication and detection of 0101 pattern results in Locked condition (LCK) indication
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BDI (Backward Defect Indication)
!! Provided in the OTS/OMS/OTU/ODU frame to allow detection of far-end defect conditions (single ended maintenance)
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Mapping Overhead
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PT (Payload Type, part of PSI multi-frame)
!! Provided in the ODU (OPU OH) frames to allow detection of client payload mismatches !! Detection of mismatch between expected and received payload types results in Payload Label Mismatch (PLM) indication
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JC (Justification Control), NJO/PJO
!! Provided in the ODU frames (OPU OH) to control +1/0/-1 stuffing operations for client signal rate adaptation and +2/+1/0/-1 stuffing operations for ODUjk multiplexing !! NJO/PJO provide positive and negative stuffing opportunities for +/-45ppm client and ~+/-80ppm ODUjk multiplexing rate adaptation
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Other Client Mapping/Multiplexing Specific Overhead
!! VCAT OH virtual concatenation overhead (NxODUk container creation) !! MSI multiplex structure identifier overhead (ODUjk multiplexing)
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Current OTN Standarization Efforts
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OTU4/ODU4 (100G)
!! Rate close to final definition (~112G) !! Proposed client signal list defined (ODUk, ODU2e, 100GbE, etc.) !! Support 10xODU2/ODU2e, 2xODU3+2/ODU2/ODU2e, 40xODU1, 80xODU0 !! New multi-lane formats and modulation formats being discussed
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Standardized support for ODU2e still being discussed
!! Supports transparent 10GbELAN mapping !! Likely rate is ~11.096Gbps
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ODU0 Standardization
!! 2xODU0 multiplexed into ODU1, ODU0 multiplexing into other rates being discussed !! Geared toward efficient transport of GbE services
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Standards and References
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ITU-T Recommendations
!! G.709 - Interfaces for the Optical Transport Network (OTN) !! G.798 - Characteristics of optical transport network hierarchy equipment functional blocks !! G.808 - Generic protection switching - Linear trail and subnetwork protection !! G.870 - Terms and definitions for Optical Transport Networks (OTN) !! G.871 - Framework for optical transport network Recommendations !! G.872 - Architecture of optical transport networks !! G.873.1 - Optical Transport Network (OTN): Linear protection !! G.874 - Management aspects of the optical transport network element !! G.874.1 - Optical transport network (OTN): Protocol-neutral management information model for the network element view !! G.959.1 - Optical transport network physical layer interfaces !! G.8201 - Error performance parameters and objectives for multi-operator international paths within the Optical Transport Network (OTN) !! G.8251 - The control of jitter and wander within the optical transport network (OTN) !! G.Sup43 - Transport of IEEE 10G Base-R in Optical Transport Networks (OTN)
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