Table of Contents - G.709/Y.1331 (2020) Amd. 4 (07/2025) -
1 Scope
2 References
3 Definitions
3.1 Terms defined elsewhere
3.2 Terms defined in this Recommendation
4 Abbreviations and acronyms
5 Conventions
6 Optical transport network interface structure
6.1 Basic signal structure
6.2 Information structure for OTN interfaces
7 Multiplexing/mapping principles and bit rates
7.1 Mapping
7.2 Wavelength division multiplex
7.3 Bit rates and capacity
7.4 ODUk timedivision multiplex
7.5 Interconnection of Ethernet UNI and FlexE Group UNI in two administrative domains in the OTN
8 OTN Interfaces
8.1 Point-to-point interface, type I
8.2 Point-to-point interface, type II
8.3 Optical networking interface, type II
8.4 Optical networking interface, type I
9 Media Element
10 OCh and OTSiA
10.1 OCh
10.2 Optical tributary signal assembly (OTSiA)
11 Optical transport unit (OTU)
11.1 OTUk (k=0,1,2,3,4,4-SC) frame structure
11.2 Scrambling for OTUk (k=0,1,2,3,4)
11.3 OTUCn frame structure
11.4 OTU25 and OTU50 frame structure
12 Optical data unit (ODU)
12.1 ODU frame structure
12.2 ODU bit rates and bit-rate tolerances
13 Optical payload unit (OPU)
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14 Overhead information carried over the OSC and OCC
14.1 OSC
14.2 OCC
15 Overhead description
15.1 Types of overhead
15.2 Trail trace identifier and access point identifier definition
15.3 OTS-O description
15.4 OMS-O description
15.5 OCh-O and OTSiG-O description
15.6 OTU/ODU frame alignment OH description
15.7 OTU OH description
15.8 ODU OH description
15.9 OPU OH description
16 Maintenance signals
16.1 OTS maintenance signals
16.2 OMS maintenance signals
16.3 OCh and OTiSA maintenance signals
16.4 OTU maintenance signals
16.5 ODU maintenance signals
16.6 Client maintenance signal
17 Mapping of client signals
17.1 OPU client signal fail (CSF)
17.2 Mapping of CBR2G5, CBR10G, CBR10G3 and CBR40G signals into OPUk
17.3 Blank clause
17.4 Mapping of GFP frames into OPUk (k=0,1,2,3,4,flex)
17.5 Mapping of test signal into OPU
17.6 Mapping of a non-specific client bit stream into OPUk
17.7 Mapping of other constant bit-rate signals with justification into OPUk
17.8 Mapping a 1000BASE-X and FC-1200 signal via timing transparent transcoding into OPUk
17.9 Mapping a supra-2.488 Gbit/s CBR signal into OPUflex using BMP
17.10 Mapping of packet client signals into OPUk
17.11 Mapping of 64B/66B encoded packet client signals into OPUflex using IMP
17.12 Mapping of FlexE aware signals into OPUflex
17.13 Mapping a 64B/66B PCS coded signal into OPUflex using BMP and 2-bit alignment of 66B code words
17.14 Mapping a 256B/257B PCS coded signal into OPUflex
18 Blank clause
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19 Mapping ODUj signals into the ODTU signal and the ODTU into the OPUk tributary slots
19.1 OPUk tributary slot definition
19.2 ODTU definition
19.3 Multiplexing ODTU signals into the OPUk
19.4 OPUk multiplex overhead and ODTU justification overhead
19.5 Mapping ODUj into ODTUjk
19.6 Mapping of ODUj into ODTUk.ts
20 Mapping ODUk signals into the ODTUCn signal and the ODTUCn into the OPUCn tributary slots
20.1 OPUCn tributary slot definition
20.2 ODTUCn definition
20.3 Multiplexing ODTUCn signals into the OPUCn
20.4 OPUCn multiplex overhead and ODTU justification overhead
20.5 Mapping ODUk into ODTUCn.ts
Annex A – Forward error correction using 16-byte interleaved RS(255,239) codecs
Annex B – Adapting 64B/66B encoded clients via transcoding into 513B code blocks
B.1 Transmission order
B.2 Client frame recovery
B.3 Transcoding from 66B blocks to 513B blocks
B.4 Link fault signalling
Annex C – Adaptation of OTU3 and OTU4 over multichannel parallel interfaces
Annex D – Generic mapping procedure principles
D.1 Basic principle
D.2 Practical application of GMP
D.3 Applying GMP in an ODU
Annex E – Adaptation of parallel 64B/66B encoded clients
E.1 Introduction
E.2 Clients signal format
E.3 Client frame recovery
E.4 Additions to Annex B transcoding for parallel 40GBASE-R clients
Annex F – Improved robustness for mapping of 40GBASE-R into OPU3 using 1027B code blocks
F.1 Introduction
F.2 513B code block framing and flag bit protection
F.3 66B block sequence check
Annex G – Mapping ODU0 into a low latency OTU0 (OTU0LL)
G.1 Introduction
G.2 Optical transport unit 0 low latency (OTU0LL)
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Annex H – OTUCn sub rates (OTUCn-M)
H.1 Introduction
H.2 OTUCn-M frame format
Annex I
Annex J – Recovery of xB/yB encoded clients from parallel 256B/257B interfaces
Annex K – Transporting 200GbE, 400GbE and 800GbE am_sf<2:0> information through a single optical link between two Ethernet/OTN transponder entities in the OTN
K.1 Introduction
K.2 Client Degrade Indication (CDI) overhead
Annex L – OTU25u and OTU50u interfaces
L.1 Introduction
L.2 Bit rates
Annex M – Fine grain flexible ODU (fgODUflex) path layer network
M.1 fgODUflex frame structure
M.2 fgODUflex frame alignment signal and overheads
M.3 fgODUflex maintenance signals
M.4 fgODUflex bit rates and bit-rate tolerances
M.5 Mapping of client signals into fine grain flexible OPU (fgOPUflex)
Annex N – Mapping fgODUflex signals into the fgODTU signal and the fgODTU into the OPU fine grain tributary slots
N.1 Fine grain tributary slot number and multiplex structure of OPU
N.2 fgODTU.M structure and multiplexing fgODTU.M signals into the OPU
N.3 OPU multiplexing overhead and fgODTU justification overhead
N.4 Mapping fgODUflex into fgODTU.M
Annex O – Hitless bandwidth adjustment of fgODUflex
O.1 Resizing control overheads
O.2 Resizing procedure
O.3 Resizing parameters
Appendix I – Range of stuff ratios for asynchronous mappings of CBR2G5, CBR10G, and CBR40G clients with 20 ppm bit-rate tolerance into OPUk, and for asynchronous multiplexing of ODUj into ODUk (k > j)
Appendix II – Examples of functionally standardized OTU frame structures
Appendix III – Example of ODUk multiplexing
Appendix IV – Blank appendix
Appendix V – ODUk multiplex structure identifier (MSI) examples
Appendix VI – Parallel logic implementation of the CRC-9, CRC-8, CRC-5, CRC-6 and CRC-4
Appendix VII – OTL4.10 structure
Appendix VIII – CPRI into ODU mapping
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Appendix IX – Overview of CBR clients into OPU mapping types
Appendix X – Overview of ODUj into OPUk mapping types
Appendix XI – Derivation of recommended ODUflex(GFP) bit-rates based on n × ODUk.ts clock and examples of ODUflex(GFP,n,k) clock generation
XI.1 Introduction
XI.2 Tributary slot sizes
XI.3 Example methods for ODUflex(GFP,n,k) clock generation
Appendix XII – Terminology changes between ITU-T G.709 Edition 4, Edition 5 and Edition 6
Appendix XIII – OTUCn sub rates (OTUCn-M) Applications
XIII.1 Introduction
XIII.2 OTUCn-M frame format and rates
XIII.3 OTUCn-M fault condition
Appendix XIV – Examples of interconnection of Ethernet UNI and FlexE Group UNI in two administrative domains in the OTN for the case that these UNIs deploy different mapping methods
Appendix XV – Examples of ODUflex(GFP) and ODUflex(IMP) clock generation methods
Appendix XVI – Implications of OTSiG (de)modulator processes and OCh|OTSiG overhead trail termination functions being located in adjacent network elements
XVI.1 Introduction
XVI.2 Black link deployment without co-location of OTSiG (de)modulator and OTSiGO_TT/OCh-O_TT function
XVI.3 Failure correlation for black link deployment without colocation of OTSiG (de)modulator and OTSiG-O_TT/OCh-O_TT function
Appendix XVII – fgOFCS test vectors for mapping of packet clients into fgOPUflex
Bibliography
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