# Do it again, what's happened?

Do it again, what's happened?

## Abbreviations

* 0xYY: Y is a value in hexadecimal presentation
* 3R: Re-amplification, Reshaping and Retiming
* ACT: Activation (in the TCM ACT byte)
* AI: Adapted Information
* AIS: Alarm Indication Signal
* APS: Automatic Protection Switching
* BDI: Backward Defect Indication
* BEI: Backward Error Indication
* BIAE: Backward Incoming Alignment Error
* BIP: Bit Interleaved Parity
* CBR: Constant Bit Rate
* CI: Characteristic Information
* CM: Connection Monitoring
* CRC: Cyclic Redundancy Check
* DAPI: Destination Access Point Identifier
* EXP: Experimental
* ExTI: Expected Trace Identifier
* FAS: Frame Alignment Signal
* FDI: Forward Defect Indication
* FEC: Forward Error Correction
* GCC: General Communication Channel
* IaDI: Intra-Domain Interface
* IAE: Incoming Alignment Error
* IrDI: Inter-Domain Interface
* JOH: Justification Overhead
* LSB: Least Significant Bit
* MFAS: Multi-Frame Alignment Signal
* MFI: Multi-frame Indicator
* MS: Maintenance Signal
* MSB: Most Significant Bit
* MSI: Multiplex Structure Identifier
* NNI: Network Node Interface
* OCh: Optical channel with full functionality
* OCI: Open Connection Indication
* ODU: Optical Channel Data Unit
* ODUk: Optical Channel Data Unit-k
* ODTUjk: Optical channel Data Tributary Unit j into k
* ODTUG: Optical channel Data Tributary Unit Group
* ODU-Xv: X virtually concatenated ODUk's
* OH: Overhead
* OMS: Optical Multiplex Section
* OM-OH: Optical Multiplex Section Overhead
* OMU: Optical Multiplex Unit
* ONNI: Optical Network Node Interface
* OOS: OTM Overhead Signal
* OPS: Optical Physical Section
* OPU: Optical Channel Payload Unit
* OPUk: Optical Channel Payload Unit-k
* OPUk-Xv: X virtually concatenated OPUk's
* OSC: Optical Supervisory Channel
* OTH: Optical Transport Hierarchy
* OTM: Optical Transport Module
* OTN: Optical Transport Network
* OTS: Optical Transmission Section
* OTS-OH: Optical Transmission Section Overhead
* OUT: Optical Channel Transport Unit
* OTUk: Optical Channel Transport Unit-k
* PCC: Protection Communication Channel
* PM: Path Monitoring
* PMI: Payload Missing Indication
* PMOH: Path Monitoring OverHead
* Ppm: parts per million
* PRBS: Pseudo Random Binary Sequence
* PSI: Payload Structure Identifier
* PT: Payload Type
* RES: Reserved for future international standardization
* RS: Reed-Solomon
* SAPI: Source Access Point Identifier
* Sk: Sink
* SM: Section Monitoring
* SMOH: Section Monitoring OverHead
* So: Source
* TC: Tandem Connection
* TCM: Tandem Connection Monitoring
* TS: Tributary Slot
* TxTI: Transmitted Trace Identifier
* UNI: User-to-Network Interface
* VCG: Virtual Concatenation Group
* VCOH: Virtual Concatenation Overhead
* vcPT: virtual concatenated Payload Type

## The key words

The following layers are defined in OTN:

* OPUk: Optical payload unit k (k = 0, 1, 2, 3, 4)
* ODUk: Optical data unit k (k = 0, 1, 2, 3, 4)
* OTUk: Optical transport unit k (k = 1, 2, 3, 4)
* OCh: Optical channel, a single wavelength
* OMSn: Optical multiplex section of order n (Capacities for n = 0 and n = 16 are defined)
* OTSn: Optical transmission section of order n (Capacities for n = 0 and n = 16 are defined)
* OTM-n.m: Optical transport module of rate m with n optical channels. Possible values for m are:
  * 1: 2.5 Gb/s
  * 2: 10 Gb/s
  * 3: 40 Gb/s
  * 4: 100 Gb/s
* OMU: Optical Multiples Unit
* OSC: Optical Supervisory Channel
* OLA: Optical in-Line Amplifier
* OPA: Optical Pre-Amplifier
* OBA: Optical Booster Amplifier