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OTN Introduction
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OTN Introduction
Optica l t ransport h ierarchy ………………………………………………Page4
OTN in te r face s t ructure…………………………………………………..Page8
Mult ip lexing/mapping pr inciples and bit rates……………...……….Page14
Overhead desc r ip t i on……………………………………………………Page19
Maintenance signals and function for different layers………………..Page39
Alarm and per formance events ……………………………………….Page50
OTN Introduction
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Foreword
This course will introduce OTN, includes:
Optical transport hierarchy (OTH) , interface structure, overhead
Maintenance signals, function for different layers
Alarm and Performance events
This Course is mainly based on:ITU-T G.872 Architecture of optical transport networks
ITU-T G.709 Interfaces for the Optical Transport Network (OTN)
ITU-T G.874 Management aspects of the optical transport network element
ITU-T G.798 Characteristics of optical transport network hierarchy equipmentfunctional blocks
OTN Introduction
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Objectives
Upon completion of this course, you will be able to:
Describe OTN frame structure, maintenance signals and function
for different layers
Outline alarm and performance events generation mechanism
Analyze the alarm and performance events and locate the failures
in OTN
Reference:
ITU-T G.709
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Contents
1. Optical transport hierarchy
2. OTN interface structure
3. Multiplexing/mapping principles and bit rates
4. Overhead description
5. Maintenance signals and function for different layers
6. Alarm and performance events
Objectives for this chapter:
Describe the features of OTN
Outline the protocols which supports OTN system
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OTN
OTN(Optical Transport Network)
An Optical Transport Network (OTN) is composed of a set of Optical
Network Elements connected by optical fiber links, able to provide
functionality of transport, multiplexing, routing, management,
supervision and survivability of client signals.
One important feature of OTN is that the transmission setting of any digital customer signal is independent of specific features of the customer, that is, independence of customer.
According to the requirements given in Rec. G.872.
The optical transport network supports the operation and management aspects of optical networks of various architectures.
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Features of OTN
Compared with SDH and SONET :
Ultra capacity with high accuracy, Terabit/second per fiber via
DWDM lines
Service transparency for client signals
Asynchronous mapping, powerful FEC function, predigest network
design and reduce the cost
Compared with traditional WDM
Enhanced OAM & networking functionality for all services
Dynamically electrical/optical layer grooming
Compared with SDH/SONET, the benefits of OTN are as follows:
Strong scalability of the capacity: The cross-connect capacity can be expanded to dozens of T bit/s.
The customer signal transparency covers payload and clock information.
The asynchronous mapping eliminates restriction on the synchronization in the whole network, with stronger FEC. The simplified system design can decrease the networking costs.
Up to 6-level TCM monitoring management capability.
Compared with the traditional WDM:
Effective monitoring capability: OAM&P and network survivability
Flexible optical/electrical grooming capability, carrier-class, manageable, and operable networking capability.
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OTN system
management
OTN
Jitter and
wander
Network protection
Equipment function and features
Structure and
mapping
Physic layer
featuresArchitecture
G.874G.874.1
G.8251G.8201
G.873.1G.873.2
G.798G.806
G.709G.7041G.7042
G.959.1G.693G.694
G.872G.8080
G.874, management features of optical transmission NE, describes the management feature of the OTN NE and transmission function of one or more network layers in the OTN. The management of the optical layer network is separated from the management of the customer layer network. Therefore, the same management method that is independent of the customer can be used. G.874 defines fault management, configuration management, billing management, and performance monitoring. G.874 describes the management network architecture model between the NE EMS and optical NE equipment management functions.
G.798, feature of equipment function block of the optical transport network, defines the function requirements of the optical transmission network in the NE equipment.
G.709, OTN interface, defines OTM-n signal requirements of OTN, including OTH, support of multi wavelength optical network overhead, frame structure, bit rate, and format of mapping customer signals.
G.872, OTN architecture, defines the relation between OTN hierarchical architecture, feature information and customer/service layer, and the function description of the network topology and layer network.
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Contents
1. Optical transport hierarchy
2. OTN interface structure
3. Multiplexing/mapping principles and bit rates
4. Overhead description
5. Maintenance signals and function for different layers
6. Alarm and performance events
Objectives for this chapter:
Draw the frame structure of OTN;
Outline the function of each part in OTN frame;
Brief introduce the difference between OTM-n.m and OTM-0.m;
Describe how does a client signal are encapsulated to OTN frame.
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OTN network layers and interface structure
ODUk
OPUk
OTUk OTUkV OTUk OTUkV
OCh OChr
OMSn
OTSnOPSn
IP/MPLS ATM Ethernet STM-NOPUk: Optical channel Payload Unit-k
ODUk: Optical channel Data Unit-k
OTUk: completely standardizedOptical channel Transport Unit-k
OTUkV: functionally standardized Optical channel Transport Unit-k
OCh: Optical Channel with full functionality
OChr: Optical Channel with reduced functionality
OMS: Optical Multiplex Section
OTS: Optical Transmission Section
OPS: Optical Physical Section
OTM: Optical Transport Module
OTM-0.mOTM-nr.m
OTM-n.m
Customer signals (for example, IP/MPLS, ATM, Ethernet, and SDH signals), served as OPU, plus the OPU payload are mapped to the OPUk, where, k is 1, 2, 3. k=1 indicates that the bit rate is about 2.5 Gbit/s, k=2 indicates that the bit rate is about 10 Gbit/s, and k=3 indicates that the bit rate is about 40 Gbit/s.
OPUk is added as the ODU payload. After ODUkP, ODUkT, frame alignment overhead, and all-zero OTU overhead are added, the ODUk is formed.
ODUk is combined into the OTU overhead and FEC region, and then mapped to the completely standardized optical channel transport unit k – OTUk, or standardized function optical channel transport unit k – OTUkV.
The OTUk is combined into OCh, and then mapped to the OCh with complete functions or, and simplified function optical channel OChr.
After the OCh is modulated to the optical channel carrier (OCC), n OCCs performs the Wavelength Division Multiplexing (WDM), and then are combined into the OMS overhead to form the OMSn interface.
After the OMSn is combined into the OTS overhead, the OTSn unit is formed.
The OChr is modulated to the OCCr. N OCCr perform the WDM to form the optical physical section OPSn. The OPSn is combined with the OMS without the monitoring information and the transport function of the OTS layer network.
To be continued in the next page
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OTN network layers and interface structure
ODUk(ODUkP,ODUkT)
OPUk
OTUk OTUkV OTUk OTUkV
OCh OChr
OMSn
OTSnOPSn
IP/MPLS ATM Ethernet STM-NOPUk: Optical channel Payload Unit-k
ODUk: Optical channel Data Unit-k
OTUk: completely standardizedOptical channel Transport Unit-k
OTUkV: functionally standardized Optical channel Transport Unit-k
OCh: Optical Channel with full functionality
OChr: Optical Channel with reduced functionality
OMS: Optical Multiplex Section
OTS: Optical Transmission Section
OPS: Optical Physical Section
OTM: Optical Transport Module
OTM-0.mOTM-nr.m
OTM-n.m
As shown in the figure above, the OTM-n.m (n ≥1) is composed of OTSn, OMSn, OCh, OTUk/OTUkV, and ODUk.
“n” indicates the number of the maximum wavelength supported by the interface in case of the minimum bit rate supported by the wavelength. When n is 0, it indicates one wavelength.
“m” indicates the bit rate or bit rate set supported by the interface.
“r” indicates the reduced function. OTM-0.m need not label “r”, because one wavelength indicates the reduced function.
OTM-nr.m and OTM-0.m is composed of OPSn, OChr, OTUk/OTUkV, and ODUk.
The information structure that supports the OTN interface is called “OTM-n”, that is, the optical transport module-n. The OTM-n includes two structures: OTM with full functionality OTM-n.m, OTM with reduced functionality OTM-0.m and OTM-nr.m.
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OTM-n.m Containment Relationships
n represents the maximum number of wavelengths that can be supported at the lowest bit rate supported on the wavelength, m=1,2,3,12,23,123;OTS_OH, OMS_OH, OCh_OH and COMMS OH information fields are contained within the OOS
OSC:Optical Supervisory Channel used to transmit OOS
OMSn payload
OCCp OCCp OCCp
OCh payload
ODUk FECOH
OPUkOH
Client signal
OPUk payloadOHOPUk
ODUk
OTUk[V]
OCh
OCG-n.m
OTM-n.m OTSn payloadOTSn OH
OMSn OH
OC
Co
OChOH
OC
Co
OC
Co
OMU-n.m
Non
-ass
ocia
ted
OH
OOS
com
ms
OH
OTM
-n.m
OTM Overhead Signal (OOS)
λ2
λ1
λn
λOSC
The figure on the right shows the composition of the OTM-n.m signals of the OTM interface with complete function. The OTM-n.m is composed of up to n multiplexing wavelengths and OTM overhead signals that support the non-associated overhead, m can be 1, 2, 3, 12, 23, or 123.”m=1” indicates the signals are OTU1/OTU1V. m=2: indicate the signals are OTU2/OTU2V. “m=3” indicates the signals are OTU3/OTU3V. “m=12” indicates partial signals are OTU1/OTU1V and partial signals are OTU2/OTU2V. “m=23” indicates partial signals are OTU 2/OTU2V and partial signals are OTU3/OTU3V. “m=123” indicates partial signals are OTU 1/OTU1V, partial signals are OTU2/OTU2V, and partial signals are OTU3/OTU3V. The physical optical feature specifications of OTM-n.m signals are determined by the suppliers. The recommendations do not have specific specifications.
The optical layer signal OCh is composed of OCh payload and OCh overhead. After the OCh is modulated to the OCC, multiple OCC time division multiplexes (TDM) constitute the OCG-n.m unit. OMSn payload and OMSn overhead constitute the OMU-n.m. OTSn payload and OTSn overhead constitute the OTM-n.m unit.
The overhead and generic management information of the optical layer units constitute the OTM overhead signal (OOS), which is transmitted by 1-channel independent OSC in the non-associated overhead.
The overhead of electrical layer units such as OPUk, ODUk, and OTUk are the associated channel overheads, which are transmitted together with the payload.
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OTM-nr.m Containment Relationships
Fixed channel spacing, irrespective of signal level
1<n≤16, m=1,2,3,12,23,123
Without optical supervisory channel
OPSn
OCCp OCCp OCCp
OCh payload
ODUk FECOH
OPUkOH
Client signal
OPUk payloadOHOPUk
ODUk
OTUk[V]
OChr
OCG-nr.m
OTM-nr.m
OTM
-16r
.m
λ2
λ1
λ16
The OTM-nr.m signals are composed of up to n optical channel multiplexing, and does not support the non-associated overhead. At present, m of OTM-16r.m can be 1, 2, 3, 12, 23, or 123, where, the physical optical feature specifications of OTM-16r.1 and OTM-16r.2 are defined in G959.1 of ITU-T. The physical optical feature specifications of other four signals are in need of the further study.
The electrical layer signal structures of OTM-nr.m and OTM-n.m are the same. The optical layer signals do not support the non-associated overhead OOS, without the optical monitor channel. Therefore, it is called the OTM interface with the reduced function.
This OTM-16r.m supports 16 optical channels on a single optical span with 3R regeneration at each end. The OTM-16r.m signal is an OTM-nr.m signal with 16 optical channel carriers (OCCr) numbered OCCr #0 to OCCr #15. An optical supervisory channel (OSC) is not present and there is no OOS either.
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OTM-0.m Containment Relationships
The OTM 0.m supports a non colored optical channel on a single optical span with 3R
regeneration at each end.
m=1,2,3
Without optical supervisory channel
OCh payload
ODUk FECOH
OPUkOH
Client signal
OPUk payloadOHOPUk
ODUk
OTUk[V]
OChr
OTM-0.m OPS0
OTM
-0.m
The OTM-0.m supports a non-coloured optical channel on a single optical span with 3R regeneration at each end.
OTM-0.m is composed of the single optical channel. It does not support the associated overhead OOS and is without specific wavelength configuration. Only one optical channel is contained; therefore, m can be 1, 2, or 3 only. The physical optical feature specifications of OTM-0.1, OTM-0.2, and OTM-0.3 are defined in G.959.1 and G.693.
The electrical layer signal structure of three OTM interfaces are the same, the electrical layer signals are monitored through the associated overhead. The difference is: The OTM-n.m optical layer signals supports the transmission of the non-associated overhead through 1-channel OSC. The OTM-nr.m and OTM-0.m do not support the optical layer overhead.
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Contents
1. Optical transport hierarchy
2. OTN interface structure
3. Multiplexing/mapping principles and bit rates
4. Overhead description
5. Maintenance signals and function for different layers
6. Alarm and performance events
Objectives for this chapter:
Draw the mapping route of OTM;
List the rate of all types of OTUk,ODUk and OPUk signals;
Describe how does a lower rate ODUk multiplex to a higher rate ODUk.
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OTM multiplexing and mapping structure
Mapping
Multiplexing
ODTUG3
ODTUG2
OChr
OChr
OChr
OCh
OCh
OCh
OTU3[V]
OTU2[V]
OTU1[V]
Client signal
Client signal
OPU3ODU3
OCCr
OCCr
OCCr
OCC
OCC
OCC
OCG-nr.m
1 ≤ i+j+k ≤ n
OCG-n.m
1 ≤ i+j+k ≤ n
OPU2ODU2
×1OPU1ODU1
OTM-nr.m
OTS, OMS, OCh, COMMSOSC OOS
OTM-n.m
×4
×1
×1×4
×16×1
×1×1
×1
×1
×1
×1
×1
×1
×1
×1
×1
×1
×1
×1
×1
×1
× i
× j
× k
× i
× j
× 1
Client signal
×1
OTM-0.m
× k
Customer signals or ODTUGk is mapped to OPUk; OPUk is mapped to ODUk; ODUk is mapped to OTUk or OTUkV; OTUk or OTUkV is mapped to OCh or OChr. Finally, OCh or OChr is modulated to OCC or OCCr.
The multiplexing includes the TDM from low-level ODU to high-level ODU and the WDM from up to n OCC or OCCr to one OCG-n.m or OCG-r.m (here, n ≥1).
The TDM is used to transmit multiple low-rate optical channel signals on one high-rate optical channel, and to perform the end-to-end path maintenance for these low-rate channels. Through the TDM, up to four ODU1 signals can be multiplexed to one ODTUG2. Then, the ODTUG2 is mapped to the OPU2. Meanwhile, j ODU2 and 16-4j ODU1 signals can be multiplexed to one ODTUG3, where j≤4. ODTUG3 is mapped to OPU3. OPU2 and OPU3 can be multiplexed to the corresponding large granularity customer signals.
For the WDM, the OCC or OCCr unit of OCG-n.m or OCG-r.m can adopt various rates. OTM-n.m or OTM-r.m transmits OCG-n.m or OCG-r.m. In addition, OTM-n.m interface can multiplex the OSC to the OTM-n.m through the WDM.
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Types and capacity
40 150 519.322 kbit/sOPU3
9 995 276.962 kbit/sOPU2
2 488 320 kbit/sOPU1
40 319 218.983 kbit/sODU3
10 037 273.924 kbit/sODU2
2 498 775.126 kbit/sODU1
43 018 413.559 kbit/sOTU3
10 709 225.316 kbit/sOTU2
±20 ppm
2 666 057.143 kbit/sOTU1
bit rate tolerancenominal bit rateTypes
As we know,the size of OTUk is fixed, that is, OTU1, OTU2, and OTU3 are 4-line and 4080-column. For OTU1 frames, from Column 1 to Column 16, there are OTU1, ODU1, and OPU1 overhead. From Column 17 to Column 3824 (with 3808 columns in total), there are customer signals. From column 3825 to column 4080 (with 256 columns in total), there are FEC areas. Assume the customer signals are STM-16 SDH signals, the rate is 2 488 320kbit/s, the calculations are as follows:
Customer signal /OTU frame = Customer signals rate / nominal OTU frame rate
3808/4080 = 2 488 320 / nominal OTU1 frame rate
That is, nominal OTU1 frame rate = 255/238 x 2 488 320 kbit/s
For OTU2 frames, four ODU1s are combined to ODTUG2 through the TDM. Four ODU1s operate as the OPU2 payload, occupying 3808 columns. In OPU2 payload, there are 16 columns of OTU1, ODU1, and OPU1 overhead. Therefore, the customer signals are 3792 columns. The calculation is as follows:
3792/4080 = 2 488 320 x 4 / nominal OTU2 frame rate
That is, nominal OTU2 frame rate = 255/237 x 9 953 280 kbit/s
The nominal OTU3 frame rate = 255/236 x 39 813 120 kbit/s
For OTU1/2/3 frame rate, the conclusion is as follows:
OTUk rate = 255/(239-k) x STM-N frame rate , k=1, 2, 3 correspond to the frame rate of STM-16, STM-64, and STM-256 respectively.
The OTU bit rate tolerance is ± 20 ppm.
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ODUk(TDM)
Low rate ODUk signals are multiplexed into high rate ODUk
signals using time-division multiplexing :
Up to 4 ODU1 signals are multiplexed into an ODU2 using
time-division multiplexing
A mixture of j (j ≤ 4) ODU2 and 16-4j ODU1 signals can be
multiplexed into an ODU3 using time-division multiplexing.
Two customer/service relationships are defined:
One ODU2 transmits four ODU1.
One ODU3 transmits 16 ODU1, or four ODU2, or other combinations in this range, where, one ODU2 is equivalent to four ODU1.
TDM includes two cases: ODU1 multiplexing to ODU2, and ODU1/ODU2 multiplexing to ODU3.
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ODU1 into ODU2 multiplexing methodODU1floats in ¼ of the OPU2 payload area.
An ODU1 frame will cross multiple ODU2 frame boundaries.
OTU2 OTU2FEC
Client layer signal(e.g., STM-16, ATM, GFP)
ODU1ODU1OH
Alignm
ODU2
x4
Client Layer Signal(e.g. STM-16)ODU1 OH O
PU
1 O
H
Client Layer Signal(e.g. STM-16)ODU1 OH O
PU
1 O
H
Client Layer Signal(e.g. STM-16)ODU1 OH O
PU
1 O
H
Client layer signal(e.g., STM-16, ATM, GFP)ODU1 OHODU2 OH
OP
U2 O
H
OPU2 PayloadODU2 OH
Alignm
OP
U2 O
H
OTU2OH
Client Layer Signal(e.g. STM-16)ODU1 OH O
PU
1 O
H
Client Layer Signal(e.g. STM-16)ODU1 OH O
PU
1 O
H
Client Layer Signal(e.g. STM-16)ODU1 OH O
PU
1 O
H
Client layer signal(e.g., STM-16, ATM, GFP)ODU1 OH
OP
U1 O
H
Alignm
Alignm
OP
U1 O
H
OP
U1 O
H
ODU1floats in ¼ of the OPU2 payload area. An ODU1 frame will cross multiple ODU2 frame boundaries.
A complete ODU1 frame(15296 bytes) requires the bandwidth of (15296/3808 =) 4.017 ODU2 frame
The figure shows the ODU1 frame, including the frame alignment overhead and all-zero OTUk overhead. The ODU1 adapts to the clock synchronization of the ODU2 signal through the asynchronous mapping.
As shown in the frame structure in the figure, four ODU1 after adaptation is multiplexed to the OPU2 payload area in the byte interleaved mode; JC and NJO are inserted to OPU2 overhead area.
After ODU2 overhead is added, ODU2 is mapped to OTU2 (or OTU2V). After OTU2 (or OTU2V) overhead, frame alignment overhead, and FEC area are added, the OTU2 signals transmitted through the OTM are formed.
The frame size of ODU1 and ODU2 are the same, that is, 4 lines and 3824 columns, where, the payload is 3808 column. How can OPU2 take four ODU1 frames? The ODU1 frame must cross one ODU2 frame border, occupying 3824/3808, that is, 1.004 ODU2 frame. The frame frequency of the ODU1 differs from that of ODU2. The frame frequency of the ODU2 is higher than ODU1. Therefore, it is feasible when ODU1 is multiplexed to ODU2 with occupying one ODU2 frame.
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Contents
1. Optical transport hierarchy
2. OTN interface structure
3. Multiplexing/mapping principles and bit rates
4. Overhead description
5. Maintenance signals and function for different layers
6. Alarm and performance events
Objectives for this chapter:
List the overheads in OTN frame;
Describe the function of each overhead.
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OTN frame formats (k=1,2,3)
3825
40801 7 8 14 15 16 17
3824
1
2
3
4
OPU k payload
OP
Uk
OH
OPUk - Optical Channel Payload Unit
ODUkOH
ODUk – Optical Channel Data Unit
Client signal mapped in
OPUk payload
Client signal
OTUKFEC
OTUkOH
OTUk – Optical Channel Transport Unit
Alignm
Alignment
k :1 - 2.5G2 - 10G3 - 40G
The OPUk is in the area from row 15 to row 3824, where, OPUk overhead area is from column 15 to column 16, OPUk payload area is from column 17 to column 3824, customer signals are in the OPUk payload area.
The ODUk is in the block structure with 4 lines and 3824 columns, which is composed of ODUk overhead and OPUk, where ODUk overhead area is from row 1 to row 4 and from column 1 to column 14. The frame alignment overhead area is from column 1 to column 7 in the first line. Column 8 to 14 in the first line are all-zero.
The OTUk overhead area is from column 8 to column 14 in the first line, and the FEC area is from column 3825 to column 4084 (256 columns in total) on the right of the frame. The frame alignment overhead area is from Column 1 to column 7 of the first line in the frame header.
The customer signal rate corresponding to OTU1/2/3 is respectively 2.5G/10G/40Gbits/s. The OTUk frame structure of each level is the same. The OTUk signals at the ONMI must have the sufficient bit timing information. Therefore, the OTUk provides the scramble function, to construct an appropriate bit pattern by using a scrambler, with the avoidance of long “1” or long “0” series. With the consideration of the framing, the OTUk overhead FAS should not be scrambled. The scrambling operation is performed after FEC calculation and insertion of OTUk signals.
The transmission sequences of the bytes in the OTUk frame is from left to right, from top down
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OTN electrical overhead overview
ODUk OHTCMACT: Tandem Connection Monitoring
Activation/deactivation control channel
TCMi:Tandem Connection Monitoring i
FTFL:Fault Type & Fault Location reporting
channel
PM: Path Monitoring
EXP:Experimental
GCC1/2: General Communication Channel 1/2
APS/PCC:Automatic Protection Swiching
coordination channel/Protection Communication
Control channel
Alignment OHFAS: Frame Alignment Signal
MFAS: multi-frame Alignment SignalOTUk OH
SM: Section Monitoring
GCC0:General Communication Channel0
RES: Reserved for future international
standardisation
OPUk OH PSI: Payload Structure Identifier
JC: Justification Control
NJO: negative justification opportunity
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4
PM
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS MFAS SM GCC0 RES JCRES
The figure shows the overall electrical layer overhead, include frame alignment overhead, OTUk layer overhead, ODUk layer overhead, and OPUk layer overhead.
The frame alignment overhead is used for the framing. It is composed of 6-byte frame alignment signal overhead FAS and 1-byte multi-frame alignment overhead MFAS.
OTUk layer overhead supports the transmission operation function connected through one or more optical channel. It is composed of 3-byte SM, 2-byte GCC0, and 2-byte RES. It is terminated at the OTUk signal assembly and dissemble places.
ODUk layer overhead is used to support the operation and maintenance of the optical channel. It is composed of 3-byte PM for end-to-end ODUk channel monitoring, 6-level TCM1-TCM6 with 3 bytes respectively, 1-byte TCMACT, 1-byte FTFL, 2-byte EXP, 2-byte GCC1, 2-byte GCC2, 4-byte APS/PCC, and 6-byte reservation overhead. The ODUk overhead is terminated at the ODUK assembly and disassemble places. TC overhead is added at the source, and is terminated at the sink.
OPUk overhead is used to support the customer signal adaptation. It is composed of 1-byte PSI, 3-byte JC, 1-byte NJO, and 3-byte reservation overhead. It is terminated at the OPUk assembly and disassemble places.
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Frame Alignment Signal
byte 1 byte 2 byte 3 byte 4 byte 5 byte 6
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
OA1 OA1 OA1 OA2 OA2 OA2
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4
PM
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS MFAS SM GCC0 RES JCRES
17
FAS (Frame Alignment Signal)
A six byte OTUk-FAS signal is defined in row 1, columns 1 to 6 of the OTUk
overhead.
OA1 is 0xF6(1111 0110 ) ,OA2 is 0x28(0010 1000).
Frame Alignment Signal (FAS) is used for the frame alignment and positioning, with the length of six bytes. It is located in Column 1 to Column 6 of Line 1. The contents are shown in the figure: three OA1 plus three OA2 series. The value of OA1 is 0xF6, and the value of OA2 is 0x28.
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Multi-Frame Alignment Signal
MFAS OH Byte
MFA
S sequen
ce
1 2 3 4 5 6 7 8
0 0 0 0 0 0 0 00 0 0 0 0 0 0 10 0 0 0 0 0 1 00 0 0 0 0 0 1 10 0 0 0 0 1 0 0
....
.
.
1 1 1 1 1 1 1 01 1 1 1 1 1 1 10 0 0 0 0 0 0 00 0 0 0 0 0 0 1
..
MFAS (Multi-Frame Alignment Signal)
defined in row 1, column 7;
The value of the MFAS byte will be incremented each
OTUk/ODUk frame and provides as such a 256 frame
multi-frame.
Individual OTUk/ODUk overhead signals may use this
central multi-frame to lock their 2-frame, 4 frame, 8-
frame, 16-frame, 32-frame, etc., multi-frames to the
principal frame.
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4
PM
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS SM GCC0 RES JCRES
17
MFAS
Multi-Frame Alignment Signal (MFAS) follows the FAS. Some OTUk and ODUk overheads, for example, TTI, should cross multiple OTUk/ODUk frames. These overheads must implement the OTUk/ODUk frame alignment and multi-frame alignment processing. The MFAS is used for the multi-frame alignment.
The length of the overhead is one byte, and is located in Line 1 Column 7.
The value of the MFAS bytes increases with the increase of the OTUk/ODUk basic frame number, from 0 to 255 (with up to 256 basic frames). For the overhead of each multi-frame structure, the length can be adjusted. For example, if an overhead uses the multi-frame structure with 16 basic frames, bit1-bit4 are not calculated when the multi-frame signals are extracted.
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OTUk section monitoring overhead
TTI (Trail Trace Identifier)
a one-byte overhead is defined to transport the 64 byte TTI
signal
The 64-byte TTI signal shall be aligned with the OTUk
multi-frame and transmitted four times per multi-frame.
TTI struture:16 bytes SAPI:Source Access Point Identifier
16 bytes DAPI:Destination Access Point Identifier
32 bytes operator specific
Operatorspecific
TTI BIP-8
BEI/BIAE BDI
RES
1 2 3 4 5 6 7 8
1 2 3
IAE
63
32
0
15
16
31
SAPI
DAPI
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4
PM
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS GCC0 RES JCRES
17
MFAS SM
The SM overhead is composed of three bytes.
The trail trace identifier (TTI), with the length of one byte, is located in the first byte of the SM overhead. It is used to transmit 64-byte OTUk-level trail trace identifier signals. The content sequence of 64 bytes are:
Byte 0 includes SAPI[0] character, with the fixed value of all zeroes.
Byte 1-byte5 include 15-character SAPI.
Byte 16 includes DAPI[0] character, with the fixed value of all zeroes.
Byte 17-byte 31 include 15-character DAPI.
Byte 32- byte 63 are the contents designated by the operator.
The 64-byte TTI signal should align with the OTUk multi-frame. Transmit for four times in each multi-frame. Each multi-frame contains 256 frames.
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OTUk section monitoring overheadBIP-8 (Bit Interleaved Parity-8)
For section monitoring, a one-byte error detection code signal is defined.
This byte provides a bit interleaved parity-8 (BIP-8) code ;
The OTUk BIP-8 is computed over the bits in the OPUk (columns 15 to 3824) area
of OTUk frame i, and inserted in the OTUk BIP-8 overhead location in OTUk frame
i+2
BIP8
OPUk
1 14 15 3824
Frame i
Frame i+1
Frame i+2
Bit Interleaved Parity-8 (BIP-8) byte is used for the detection of the OTUk-level bit error detection. The code is in the even parity inserted among bits. Its length is one byte, located in the second byte of the SM overhead. For BIP8 parity, calculate the bit in the whole OPUK frame area of the No.i OTUk frame to obtain the OTUk BIP-8. Insert the results to No.(i+2) OTUk frame OTUk BIP-8 overhead position. In No.(i+2) frame, as shown in the figure, compare this value with the DIP8 calculation results of the current frame. If both values mismatch, detect the bit error block of the near end.
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OTUk section monitoring overhead
BEI/BIAE (Backward Error Indication/ Backward
Incoming Alignment Error)
BDI (Backward Defect Indication)
IAE (Incoming Alignment Error)
RES (Reserved)
Operatorspecific
TTI BIP-8
BEI/BIAE BDI
RES
1 2 3 4 5 6 7 8
1 2 3
IAE
63
32
0
15
16
31
SAPI
DAPI
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4
PM
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS GCC0 RES JCRESMFAS SM
Backward Error Indication (BEI) and Backward Incoming Alignment Error (BIAE) are used to return the detected bit errors to the upstream of the OTUk-level and to introduce the IAE. The length is four bits. It is located in the most significant four bits of the third byte of the SM overhead. In the IAE status, the field is set to 1011. The bit error number and non IAE state is omitted, insert the bit error number (0-8). Other six values may be caused by some irrelevant status. It should be explained as 0 bit error and BIAE inactivation.
The backward defect indication (BDI) is used for OTUk-level to return the signal invalidity status detected in the terminal sink function. The length is one bit. It is located in Bit5 of byte3 of the SM overhead. When the BDI is set to 1, it indicates OTUk backward defect. Otherwise, it is set to 0.
The Incoming Alignment Error (IAE) is used for the OTUk-level S-CMEP at the ingress point to notify the peer S-CMEP at the egress point that the alignment error is detected in the introduction signals. The S-CMEP egress point can use this information to stress the bit error number. These bit error may be caused by the ODUk frame phase change at the TC ingress point. The IAE length is one bit. It is located in bit6 of byte 3 of the SM overhead. The IAE bit is set to 1 to indicate the frame alignment error. Otherwise, it is set to 0.
The last two bits of the SM is reserved, and is set to “00”.
S-Connection Monitoring End Point (CMEP): Section-Connection monitoring end-points represent end points of trails and correspond as such with the trail termination functions.
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GCC0 (General Communication Channel)
Two bytes are allocated in the OTUk overhead to support a general
communications channel between OTUk termination points
A clear channel which are located in row 1, columns 11 and 12
RES (Reserved)
Two bytes of OTUk overhead are reserved for future international standardization
Located in row 1, columns 13 and 14
Set to all ZEROs
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4
PM
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS RES JCRES
17
MFAS SM GCC0
OTUk GCC0 and RES overhead
General Communication Channel 0 (GCC0) is used to support the general communication between OTUk terminals. The length is two bytes. It is located in Column 11 to Column 12 of line 1. The GCC0 is the transparent channel. The format specification is not discussed here in this course.
Then, it is the 2-byte OTUk reserved overhead, for the international standardization. It is located in column 13-column 14 of line 1. The reserved overhead is set to all zeroes.
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ODUk path monitoring overhead
TTI / BIP-8 / BEI / BDI
For path monitoring, this overheads’ function are the
same as OTUk SM signal, except BEI signal which
doesn’t support BIAE function.
In row 3, columns 10 to 12
Operatorspecific
TTI BIP-8
BEI BDI
STAT
1 2 3 4 5 6 7 8
1 2 3
63
32
0
1516
31
SAPI
DAPI
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS RES JCRES
17
MFAS SM GCC0
PM
The PM is similar to the SM.
The PM overhead is composed of three bytes. It is located in column 10-column 12 of line 3. The PM is composed of 1-byte TTI, 1-byte BIP-8, 4-bit BDI, 1-bit BEI, and 3-bit STAT. The definitions of TTI / BIP-8 / BEI / BDI are similar to those in SM. These parts support the channel monitor.
The PM overhead does not support IAE and BIAE function. In addition, BIP-8 of the PM overhead is parity of the whole OPUk frame (column 15- 3824). But, the parity position is in the PM overhead, which differs from the BIP regenerated node in the BIP8.The BEI field needs not to support the BIAE function. Therefore, one value is less that of the SM overhead to indicate the return of the IAE state. Four bits of BEI fields in the PM overhead have nine effective values in total. 0-8 indicates 0-8 bit errors respectively. The other seven values are caused by some irrelevant status, which can be interpreted as 0 bit error.
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ODUk path monitoring overhead
Operatorspecific
TTI BIP-8
BEI BDI
STAT
1 2 3 4 5 6 7 8
1 2 3
63
32
0
1516
31
SAPI
DAPI
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2 TCM1
TCM4TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS RES JCRES
17
MFAS SM GCC0
PM
Maintenance signal: ODUk - AIS 1 1 1
Maintenance signal: ODUk - OCI 1 1 0
Maintenance signal: ODUk - LCK 1 0 1
Reserved for future international standardization 1 0 0
Reserved for future international standardization 0 1 1
Reserved for future international standardization 0 1 0
Normal path signal0 0 1
Reserved for future international standardization 0 0 0
statusBit 6 7 8
STAT (Status)
For path monitoring, three bits are defined as status bits
They indicate the presence of a maintenance signal
The STAT field is used for the maintenance signals of ODUk channel level. The length is 3 bits. It is located in the least significant 3 bits of Column 12 of Line 3.
The table describes the meaning of the STAT field.
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ODUk TCM overhead
TTIi / BIP-8i / BEIi/BIAEi / BDIi
For each tandem connection monitoring field,
this overheads’ function are the same as OTUk
SM signal
Six fields of ODUk TCM overhead are defined in
row 2, columns 5 to 13 and row 3, columns 1
to 9 of the ODUk overhead
TTIi BIP-8i
BEIi/BIAEi BDIi
STATi
1 2 3 4 5 6 7 8
1 2 3
63
32
0
1516
31
SAPI
DAPI
Operatorspecific
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS RES JCRESMFAS SM GCC0
PMTCM1TCM2TCM3
TCM6 TCM5 TCM4
The ODUk overhead defines TCM1-TCM6 of six domains. The Tandem Connection Monitoring (TCM) overhead supports the monitoring of the ODUk connection. It is used to the scenarios such as one or more optical UNI to UNI, NNI to NNI serial line connection monitoring, linear and ring protection switch sub-layer monitoring, the fault location of the optical channel serial line connection, and the service delivery quality acceptance. TCM6-TCM1 are located in Column 5-Column 13 of line 2, Column 1-Column 9 of Line 3. Its format is similar to the SM of the OTUk overhead and the PM of the ODUk overhead.
TTIi / BIP-8i / BEIi / BIAEi / BDIi support the TCMi sub-layer monitoring, where, i ranges from 1 to 6. The definitions and functions of these parts are the same as the corresponding parts in SM. But, only the monitoring levels are different.
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ODUk TCM overhead
TTIi BIP-8i
BEIi/BIAEi BDIi
STATi
1 2 3 4 5 6 7 8
1 2 3
63
32
0
1516
31
SAPI
DAPI
Operatorspecific
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIGCC2 APS/PCC RES
EXP
FAS RES JCRES
17
MFAS SM GCC0
PMTCM1
Maintenance signal: ODUk -AIS 1 1 1
Maintenance signal: ODUk -OCI 1 1 0
Maintenance signal: ODUk -LCK 1 0 1
Reserved for future international standardization1 0 0
Reserved for future international standardization0 1 1
In use with IAE0 1 0
In use without IAE0 0 1
No source TC 0 0 0
statusBit 6 7 8
TCM2TCM3
TCM6 TCM5 TCM4
STAT (Status)For each tandem connection monitoring field, three bits are defined as status bits. They indicate the presence of a maintenance signal, if there is an incoming alignment error at
the source TC-CMEP, or if there is no source TC-CMEP active.
STAT is used for the maintenance signal of TCMi sub layer, whether the IAE error exists in the source TC-CMEP, whether the source TC-CMEP is activated. The length is 3 bits. It is located in the least significant 3 bits of the TCMi field.
It indicates the meaning of the STAT field.
TCMi overhead has more BIAE function than PM overhead. In the maintenance signals in the STAT field, there are more two meanings: No source TC, and TC in use but with IAE error.
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Nested and Cascaded ODUk monitored connections
A1 B1 C1 C2 B2 B3 B4 A2
A1 - A2
B1 - B2
C1 - C2
B3 - B4
TCM1 TCM1
TCM2
TCM1
TCM2
TCM3
TCM1
TCM2
TCM1 TCM1
TCM2
TCM1
TCM2
TCM3
TCM4
TCM5
TCM6
TCMi TCM OH field not in use TCMi TCM OH field in use
TCM2
TCM3
TCM4
TCM5
TCM6
TCM2
TCM3
TCM4
TCM5
TCM6
TCM3
TCM4
TCM5
TCM6
TCM3
TCM4
TCM5
TCM6
TCM3
TCM4
TCM5
TCM6
TCM4
TCM5
TCM6
Along one ODUk trail, the monitored connections range from 0 to 6. The monitored multi-level connections can be overlay, nesting, or cascading. At present, the overlay mode is applicable to the test only. Each TC-CMEP inserts or extracts the TCM overhead from six TCMi overhead domains. The corresponding network operator, network management system or switching control platform provides the TCMi overhead domain contents.
As shown in the figure, the monitored connects A1-A2, B1-B2, and C1-C2 are nested, A1-A2 and B3-B4 are nested, B1-B2 and B3-B4 are cascaded.
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Overlapping ODUk monitored connections
A1 B1 C1 C2B2 A2
A1 - A2
B1 - B2
C1 - C2
TCM1 TCM1
TCM2
TCM1
TCM2
TCM3
TCM1
TCM2
TCM1
TCMi TCM OH field not in use TCMi TCM OH field in use
TCM2
TCM3
TCM4
TCM5
TCM6
TCM2
TCM3
TCM4
TCM5
TCM6
TCM3
TCM4
TCM5
TCM6
TCM3
TCM4
TCM5
TCM6
TCM4
TCM5
TCM6
As shown in the figure, the monitored connects B1-B2 and C1-C2 are overlaid, A1-A2 and B1-B2 are nested, A1-A2 and C1-C2 are nested.
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ODUk GCC1/GCC2
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2
TCM4TCMACT
GCC1
FTFL RES JC
RES JC
NJOPSIAPS/PCC RES
EXP
FAS RES JCRES
17
MFAS SM GCC0
PMTCM1
GCC2
GCC1 / GCC2 (General Communication Channel)
Two fields of two bytes are allocated in the ODUk overhead to support two
general communications channels between any two network elements with
access to the ODUk frame structure (i.e., at 3R regeneration points).
The bytes for GCC1 are located in row 4, columns 1 and 2, and the bytes for
GCC2 are located in bytes row 4, columns 3 and 4 of the ODUk overhead.
GCC1 and GCC2 can be used to access to the ODUk frame structure (that is, located in 3R regeneration points) between any two NEs. The length is 2 bytes, respectively located in Column 1-2 and Column 3-4 of Line 1. It is the transparent channel. Its function is similar to OTUk overhead GCC0. The ESC function can be applied to the product.
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Other overheads 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2
TCM4TCMACT
GCC1 PSI
FAS RES
17
MFAS SM GCC0
PMTCM1
GCC2
TCMACT (TCM Activation/Deactivation)
APS/PCC (Automatic Protection Switching/Protection Communication
Control)
EXP (Experimental)
FTFL (Fault Type & Fault Location)
EXP
FTFL
APS/PCC
RES JC
RES JC
NJO
RES JC
RES
RES
TCM Activation/Deactivation (TCMACT) overhead is 1-byte long, and is located in Column 4 of Line 2. Its definition is not determined yet.
Automatic Protection Switching (APS)/Protection Communication Control (PCC) overhead is applicable to the protection protocol communication, with the length of four bytes. This field can appear in up to 8-level nested APS/PCC signals. It can be used by multiple protection mechanisms. In the multi-frame, the first eight basic frames (for MFAS, it is 0-7) APS/PCC are sequentially allocated to ODUk channel layer, ODUk TCM1-TCM6 sub layers, and OTUk section layer.
The ODUk overhead defines 2-byte EXP, which allows the equipment supplier or network operator to use the extra ODUk overhead on the subnet. The specific function of the EXP is not limited to the standard, which is not defined within G.709 range.
The ODUk overhead is allocated with one byte to transmit total 256-byte Fault Type & Fault Location (FTFL). The FTFL message is composed of forward area and backward area, with 128 bytes in each area, respectively containing the forward and backward fault type, operator identifier, and operator designated domain.
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OPUk payload structure identifier
PSI (Payload Structure Identifier)
One byte is allocated in the OPUk overhead
to transport a 256-byte payload structure
identifier (PSI) signal
Aligned with the ODUk multi-frame.
PSI[0] contains a one-byte payload type.
PSI[1] to PSI[255] are mapping and
concatenation specific .
255
0
1
PT
Mapping& concatenation
specific
RES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1
2
3
4
TCM3
TCM6 TCM5
TCM2
TCM4TCMACT
GCC1
RES JC
RES JC
NJOAPS/PCC RES
EXP
FAS RES JCRES
17
MFAS SM GCC0
PMTCM1
GCC2
FTFL
PSI
The OPUk overhead defines 1-byte payload structure identifier (PSI) overhead to transmit the 256-byte PSI to indicate the OPUk signal type. The PSI overhead is in Column 15 of Line 4. The 256-byte PSI signal aligns with the ODUk multi-frame. PSI[0] is a 1-byte payload type (PT); PSI[1]-PSI[255] are used for the mapping and cascading; PSI[1] is reserved, and PSI[2]-PSI[17] is the multiplex structure identifier (MSI). The MSI includes the ODU type and transmitted ODU tributary port number information. For OPU2, there are only four ODU1 tributary port number. Therefore, only four bytes PSI[2]-PSI[5] are needed, and the last 12 bytes of the MSI are set to 0.
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OOS
TTI: Trail Trace IdentifierPMI: Payload Missing Indication OCI: Open Connection Indication BDI-O: Backward Defect Indication –OverheadBDI-P: Backward Defect Indication – PayloadFDI-O: Forward Defect Indication –OverheadFDI-P: Forward Defect Indication – Payload
OTSn
n
32
OC
h
1
General Management Communications
OM
Sn
FDI-O
FDI-P
OCI
BDI-O
BDI-P
PMI
FDI-P
FDI-O
BDI-O
BDI-P
PMI
TTI
The OOS is the non-associated overhead, which is transmitted through the OSC. The optical layer overhead function should comply with the standard. The recommendation defines overheads and corresponding functions contained in the optical layer, and does not define the frame rate or frame structure. The optical layer overhead include OTS, OMS, OCh overheads, and generic management information overhead defined by the supplier, where,
The OTS overhead is used to support the maintenance and operation function of the optical transmission section, and is terminated at the OTM signal assembly and dissemble places, including:
TTI: Transmit the TTI consisting of 64-byte character string. The TTI includes the source access point indication, destination access point indication, and information designated by the operator.
BDI-P: Transmit the OTSn payload signal invalidity status detected from the OTSn terminal sink function to the upstream.
BDI-O: Transmit the OTSn overhead signal invalidity status detected from the OTSn terminal sink function to the upstream.
PMI: It is used to transmit the status of payload that is not added at the upstream of the OTS signal source terminal to the downstream, to suppress subsequent reporting of loss of signal.
To be continued in the next page
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OOS
TTI: Trail Trace IdentifierPMI: Payload Missing Indication OCI: Open Connection Indication BDI-O: Backward Defect Indication –OverheadBDI-P: Backward Defect Indication – PayloadFDI-O: Forward Defect Indication –OverheadFDI-P: Forward Defect Indication – Payload
OTSn
n
32
OC
h
1
General Management Communications
OM
Sn
FDI-O
FDI-P
OCI
BDI-O
BDI-P
PMI
FDI-P
FDI-O
BDI-O
BDI-P
PMI
TTI
The OMS overhead is used to support the maintenance and operation function of the optical MS, and is terminated at the OMU signal assembly and dissemble places, including:
FDI-P: Transmit OMSn payload signal status to the downstream direction.
FDI-O: Transmit OMSn overhead signal status to the downstream direction.
BDI-P: Transmit the OMSn payload signal invalidity status detected from the OMSn terminal sink function to the upstream.
BDI-O: Transmit the OMSn overhead signal invalidity status detected from the OMSn terminal sink function to the upstream.
PMI: Transmit the information with a OCCp containing optical channel signal information at the upstream of OMS signal source terminal to the downstream, to suppress subsequent reporting of signal invalidity status.
The OCh overhead is used to support the maintenance function of the fault management in the optical channel, and is terminated at the OCh signal assembly and dissemble places, including:
FDI-P: Transmit OCh payload signal status to the downstream direction.
FDI-O: Transmit OCh overhead signal status to the downstream direction.
OCI: It is the OCh open connection indication. The OCI is the signal sent to the downstream. It indicates that the matrix connection is opened when the upstream delivers the management commands in the connection function. Then, at the OCh terminal point, detect that the OCh signal loss status may be related to the open matrix.
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Contents
1. Optical transport hierarchy
2. OTN interface structure
3. Multiplexing/mapping principles and bit rates
4. Overhead description
5. Maintenance signals and function for different layers
6. Alarm and performance events
Objectives for this chapter:
List the maintenance signals type;
Describe the function and application of maintenance signals.
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OTN Maintenance LayersOChn
TTIBDI-PBDI-OPMI
FDI-OBDI-PBDI-OPMI
FDI-POTS OMS
FDI-PFDI-OOCI
OCh1
OCh2
General management communications (OSC)
1
2
3
4
FAS
EXP
TCMACT TCM4
TCM3 TCM2
TCM6
GCC1 GCC2
FTFL
PM
RES
RESAPS/PCC
SM RESGCC0MFAS JC
JC
JC
NJO PJO
RES
RES
RES
TCM5
TCM1
1 167 8 14 15
PSI
OTS OTS OTS OTS OTS OTS OTS
OMS OMS OMS OMS
OTM OADM/ROADM
Och OchOch
TCM1 (UNI to UNI)
OTN XC
OEO
OLA OLA OTM OTM OTMOLA
OTN boundaryOTN boundary
OTUk SMOTUk SM OTUk SM
PM
(NNI to NNI) TCM2(NNI to NNI)- TCM2
Electrical layer Optical layer
OTS, OMS, OCh are all optical layer trails and OTUk, ODUk, Client are all electrical layer trails.
OSC trail is independent, which is related to supervisory signal.
OTUK use SM section to send maintenance signals.
ODUK use PM and TCM to send maintenance signals.
OTS,OMS,OCh ,OSC send different optical layer maintenance signals.
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OTN Layer Network Trail
OTU OTU
OM OA OA OD
OTSOTSOTS
OMS
OCH
OTUk
ODUk
Client
OSC
OSC
OSC
OCh client trail sets the source/sink port at the client side of OTU. LQG, as an example, it is GE service trail of the client port.
OCh trail sets the source/sink port at the WDM side of OTU. LQG, as an example, it is the wavelength trail.
OMS trail sets the source/sink port at the OUT/IN port of MUX/DeMUX. It is a trail of the multiplex signal.
OTS trail is the fiber connection between adjacent OM/OD/OA in the main path.
OSC trail is independent, which is related to supervisory signals.
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Maintenance signals
FDI(forward defect indication)FDI is a signal sent downstream as an indication that an upstream defect has
been detected.
An FDI signal is detected in a trail termination sink function to suppress defects
or failures that would otherwise be detected as a consequence of the
interruption of the transport of the original signal at an upstream point..
AIS and FDI are similar signals. AIS is used as term when the signal is in the
digital domain. FDI is used as the term when the signal is in the optical domain.
FDI is transported as non associated overhead in the OTM overhead signal
(OOS).
The FDI is the signal sent to the downstream in OMS and OCh layers, to indicate the detected upstream defects. FDI-P indicates the payload forward defect, and FDI-O indicates the overhead forward defect.
OMS-FDI-P indicates the OMS servcie layer dfect of the OTS network layer.
OMS-FDI-O indicates that the transmission of the OMS overhead transmitted through the OOS is interrupted owing to the signal invalidity status of the OOS.
OCh-FDI-P indicates the OCh service layer defect in the OMS network layer. When the OTUk is terminated, OCh-FDI-P serves as the ODUk-AIS signal to continue.
OCh-FDI-O indicates that the transmission of the OCh overhead transmitted through the OOS is interrupted owing to the signal invalidity status of the OOS.
The FDI signal is generated in the adaptation sink function. In the trail terminal sink function, it is generated to suppress the downstream defects and invalidities detected owing to the transmission interruption of the upstream signals.
The FDI is similar to AIS. When the signal is in the optical domain, use the FDI. When the signal is in the digital domain, use the AIS. The FDI served as the non-associated overhead is transmitted in the OTM overhead signal (OOS)
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Maintenance signals
AIS(alarm indication signal)
AIS is a signal sent downstream as an indication that an upstream
defect has been detected. An AIS signal is generated in an
adaptation sink function
An AIS signal is detected in a trail termination sink function to
suppress defects or failures that would otherwise be detected as a
consequence of the interruption of the transport of the original
signal at an upstream point.
AIS is the electrical layer OTUk, ODUkP, ODUkT, and customer layer CBR sent to downstream to indicate the detected upstream defect, to suppress the downstream defects and invalidities detected due to the interruption of upstream signal transmission. The AIS of ODUkP and ODUkT layer uses the ASI with all-1 pattern.
Note:
OTUk-AIS supports the new service layer in future. At present, only the signal is required to be detected, instead of the generation of this signal. According to this recommendation, Huawei equipment only supports the detection of the OTUk-AIS, instead of inserting OTUk_AIS. CBR AIS is generated in the the ODUk/CBRx adaptation sink function. If the SDH receives this signal, it is detected as the LOF.
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Maintenance signals
AIS(alarm indication signal)
ODUk-AIS is specified as all "1"s in the entire ODUk signal, excluding
the frame alignment overhead (FA OH), OTUk overhead (OTUk OH)
and ODUk FTFL
The presence of ODUk-AIS is detected by monitoring the ODUk STAT
bits in the PM and TCMi overhead fields
1
2
3
4
1 17 3824
All-1s pattern
87 14
FTFL
FA OH OTUk OH
STA
T
STA
T
STA
T
STA
T
STA
T
STA
T
STA
T
The AIS of ODUkP and ODUkT level uses the all-1 pattern, as shown in the figure.
When we introduce the PM and TCMi overhead, we have learnt that the value 111 of STAT field of PM or TCMi indicates the detected ODUk_AIS signals. When ODUkP or ODUkT detects the AIS, it only concerns about the value of the STAT of the corresponding level. For example, to detect the AIS of the TCM1, check whether the STAT corresponding bit of the TCM1 is 111; To check the AIS of the PM, check whether the STAT corresponding bit of the PM is 111.
To insert the AIS, the ODUkP or ODUkT is not distinguished. For either of them, insert to PM or 6-level PCM overhead area or all payloads (excluding FTFL byte). Therefore, it is called the insertion of ODUk-AIS signals. The ODUk_AIS may be generated in the adaptation sink function from OTU to ODU or in the ODUkT termination sink function. For the adaptation sink function from OTU to ODT, insert the ODUk_AIS owing to the invalidity of the service layer. For the ODUkT termination sink function, when the TCM is in the operation mode, insert ODUk_AIS owing to the detection of the LCK, OCI, and TIM. Whether the TIM is inserted with the AIS can be set.
When the AIS is cleared, 111 of the STAT of the local area is cleared also. For example, for the TCM1 source function, change the STAT of the TCM1 from 111 to 001.
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Maintenance signals
BDI (Backward Defect Indication)
Backward Defect Indication Payload defect (dBDI-P) is
monitored at the OTS and OMS layers. The purpose of
monitoring this parameter is to allow for single ended
supervision of the trail
During signal fail conditions of the overhead signal, dBDI-P
shall be set to false
The Backward Defect Indication (BDI) includes the OTS of the optical layer, the BDI of the OMS layer, OTUk and ODUkP of the electrical layer, and the BDI of the ODUkT layer.
The BDI-P indicates the payload backward defect. The BDI-O indicates the overhead backward defect. If the remote defect of the BDI inserting the OOS detected consecutively in X ms, the BDI is generated. If the BDI-P upstream defect inserted by OOS detected within the consecutive Y ms is cleared, clear the BDI-P. The values of X and Y needs the further study.
For the electrical layer OTUk, ODUkP and ODUkT layer’s BDI, we have learnt the electrical layer overhead part. If the BDI bit of the SM/PM/TCMi overhead domain of the consecutive five frames (bit 5 of byte 3) is 1, generate the dBDI. If the BDI bit of the SM/PM/TCMi overhead domain of the consecutive five frames (bit 5 of byte 3) is 0, clear the dBDI.
If the signal is invalid, the BDI should be cleared.
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Maintenance signals
OCI (open connection indication)
A signal sent downstream as an indication that upstream the signal is not
connected to a trail termination source
The presence of ODUk-OCI is detected by monitoring the ODUk STAT bits
in the PM and TCMi overhead fields.
The repeating "0110 0110" pattern is the default pattern; other patterns
are also allowed as long as the STAT bits in the PM and TCMi overhead
fields are set to "110".
1
2
3
4
1 17 382487 14
FTFL
FA OH OTUk OH
STA
T
STA
T
STA
T
STA
T
STA
T
STA
T
STA
T Repeating “0110 0110” pattern
The Open connection indication (OCI) is used for the optical layer OCh, electrical layer ODUkP, and ODUkT to indicate that the upstream signal does not connect to the trail terminal source signals. The OCI signal is generated in the connection function. Through the connection function, output at any output connection point that is not connected to any input connection point. The OCI signals are detected in the trail terminal sink function.
For the OCh layer, if the input and output is detected in the consecutive X ms, generate the OCI. If the input and output connection is normal or the overhead signal is invalid in the consecutive Y ms, clear OCI. The values of X and Y are still under the research.
As shown in the figure, it is the OCI pattern of the ODUkP and ODUkT layer. Detect the OCI, which is similar to the detection of the AIS. Check whether the corresponding bit of the STAT is 110. For example, check the OCI of the TCM1 to check whether the STAT corresponding bit of the TCM1 is 110. Detect the OCI of the PM, to check whether the STAT corresponding bit of the PM is 110.
Insert the OCI, and insert to PM and 6-level TCM area and all payloads. Clear the OCI to clear 110 of this area STAT. For example, for TCM1, it means to change the STAT of the TCM1 from 110 to 001. If the data signal is invalid, the OCI should be cleared.
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Maintenance signals
LCK (locked)
A signal sent downstream as an indication that upstream the connection is
"locked", and no signal is passed through.
The presence of ODUk-LCK is detected by monitoring the ODUk STAT bits in
the PM and TCMi overhead fields.
dLCK shall be declared if the accepted STAT information (AcSTAT) is “101”.
dLCK shall be cleared if the accepted STAT information is not equal to “101”.
During signal fail conditions of the data signal, dLCK shall be set to false.
1
2
3
4
1 17 382487 14
FTFL
FA OH OTUk OH
STA
T
STA
T
STA
T
STA
T
STA
T
STA
T
STA
T Repeating “0101 0101”pattern
To support the operator's requirement of locking the user access point signal, ODUkP and PDUkT layer provide the LCK maintenance signals to indicate the upstream connection is the locked signal, without signals passing.
When the operator performs sets up the test, the customer signals are replaced by the locked (LCK) fixed digital signals. It is generated through the service layer adaptation sink and source function, and is sent to the downstream. The downstream termination sink function allows the report of the LCK alarm, indicating that the upstream connection is locked and no signals pass.
As shown in the figure, it is the LCK pattern of the ODUkP and ODUkT layer. Detect the LCK, and check whether the corresponding bit of the STAT is 101. For example, check the LCK of the TCM1 to check whether the STAT corresponding bit of the TCM1 is 101. Detect the LCK of the PM, to check whether the STAT corresponding bit of the PM is 101.
Insert the LCK, and insert to PM and 6-level TCM area and all payloads. Clear the LCK to clear 101 of this area STAT. For example, for TCM1 source function, change the STAT of the TCM1 from 101 to 001.
The priority of inserting the LCK is higher than that of the AIS. That is, if a user sets the insertion of the LCK and meets the condition of automatic insertion of the ASI, the result is insertion of the LCK.
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Maintenance signals
IAE (Incoming Alignment Error)
IAE at the OTUk layer: dIAE shall be declared/cleared if the IAE bit in the SM
overhead field (byte 3, bit 6) is “1”/ “0” for X consecutive frames. X shall be 5.
IAE at the ODUkT layer: dIAE shall be declared/cleared if the accepted STAT
information (AcSTAT) is/is not “010”.
During signal fail conditions of the data signal, dIAE shall be set to false .
BIAE (Backward Incoming Alignment Error)
dBIAE shall be declared/cleared if the BEI/BIAE bits in the SM/TCM overhead
field (byte 3, bit 1 to 4) are/are not “1011” for X consecutive frames. X shall
be 3.
During signal fail conditions of the data signal, dBIAE shall be set to false .
Incoming Alignment Error (IAE) and Backward Incoming Alignment Error (BIAE). The electrical layer OTUk and ODUkT provide the maintenance signals of IAE and BIAE. IAE and BIAE are not the fault reasons. The IAE is used to suppress the near end performance of the OTUk and ODUkT (EBC and DS). The BIAE is used to suppress the remote performance of the OTUk and ODUkT.
For the IAE of the OTUk, if the IAE bit in the consecutive 5-frame SM overhead domain (bit 6 of byte 3) is 1, generate the dIAE. If the IAE bit in the consecutive 5-frame SM overhead domain (bit 6 of byte 3) is 0, clear the dIAE. For the IAE of the ODUkT, if the received STAT information is 010, generate the dIAE. If the received STAT information is not 010, clear the dIAE.
If the signal is invalid, the dIAE and dBIAE should be cleared.
For the signals sent to the upstream by the BIAE, if the BEI/BIAE bit of the consecutive 3-frame SM/TCMi overhead domain (bit1-bit4 of byte 3) is 1011, generate dBIAE. If the BEI/BIAE bit of the consecutive 3-frame SM/TCMi overhead domain (bit1-bit4 of byte 3) is 1011, clear dBIAE.
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Maintenance and management signal
Y––LTC
YYYBEI
Maintenance
Signal
YYYBIP-8Signal quality
Y–YIAE/BIAE
YYYBDI
YY–LCK
YY–OCI
YYYAIS
YYYTTIConnectivity
–YYLOF/LOMAlignment
ODUkTODUkPOTUk
Network layerssignal
Management
function
For the framing and monitoring, the OTUk and ODUkP support to obtaining the LOF and LOM through the detection of the FAS and MFAS. The ODUkP is applicable to the scenario from the low-level ODU multiplexing to the high-level ODU signals.
For the continuity monitoring, three layers support the TTI signals of the corresponding level.
For the information maintenance, three layers support AIS, BDI, and BEI signals. The ASI of the OTUk layer is the generic AIS signal. In ODUkP and ODUkT, there are all-1 AIS signals.
ODUkP and ODUkT layers support OCI and LCK signals.
The ODUkT layer supports the LTC signals. Note: LTC indicates there is no TCM source.
OTUk and ODUkT support the IAE/BIAE signals.
For the monitoring of the signal quality, three layers support the performance detection based on the BIP-8 calculation. That is, check the OPUk frames. But the check location and layers are different.
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Contents
1. Optical transport hierarchy
2. OTN interface structure
3. Multiplexing/mapping principles and bit rates
4. Overhead description
5. Maintenance signals and function for different layers
6. Alarms and performance events
Objectives for this chapter:
Classify the alarms into the corresponding layer;
Outline the suppression mechanism of alarms.
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Alarms
OPUk_PLM,OPU2_MSIM,OPU3_MSIMOPUk
ODUk_TCMi_TIM,ODUk_TCMi_DEG ,ODUk_TCMi_EXC ,ODUk_TCMi_BDI,
ODUk_TCMi_LCK,ODUk_TCMi_OCI, ODUk_TCMi_AIS,ODUk_TCMi_LTC
ODUk_TCMi
ODUk_PM_TIM,ODUk_PM_DEG,ODUk_PM_EXC,
ODUk_PM_BDI,ODUk_PM_LCK,ODUk_PM_OCI,ODUk_PM_AIS,ODUk_L
OFLOM
ODUk_PM
OTUk_LOF,OTUk_AIS,OTUk_LOM,OTUk_TIM,OTUk_DEG,
OTUk_EXC,OTUk_BDI,BEFFEC_EXC
OTUk
Alarms Layer
Remark: k=1,2,3,5G, i=1~6.
Firstly,about the OTN alarm of each electrical layer, for the alarms of OTUk layer, except the BEFFEC_EXC alarm related to the FEC, other alarm names start with “OTUk”. For the ODUkP layer, except ODUk_LOFLOM, other alarms start with “ODUk_PM”. For ODUkT layer alarms, the name starts with “ODUk_TCMi”. The OPUk layer alarm starts with “OPUk”.
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Performance events
ODUk_TCMi_BBE,ODUk_TCMi_BBER,ODUk_TCMi_BIAES,ODUk_TCMi_ES,ODUk_TCMi_F
EBBE,ODUk_TCMi_FEBBER,ODUk_TCMi_FEES,ODUk_TCMi_FESES,ODUk_TCMi_FESESR,
ODUk_TCMi_FEUAS,ODUk_TCMi_IAES,ODUk_TCMi_SES,ODUk_TCMi_SESR,ODUk_TCMi
_UAS
ODUk_TCMi
ODUk_PM_BBE,ODUk_PM_BBER,ODUk_PM_ES,ODUk_PM_FEBBE,ODUk_PM_FEBBER,O
DUk_PM_FEES,ODUk_PM_FESES,ODUk_PM_FESESR,ODUk_PM_FEUAS,ODUk_PM_SES,
ODUk_PM_SESR,ODUk_PM_UAS
ODUk_PM
OTUk_BBE ,OTUk_BBER,OTUk_BIAES,OTUk_ES,OTUk_FEBBE,OTUk_FEBBER,OTUk_FEES,
OTUk_FESES,OTUk_FESESR,OTUk_FEUAS,OTUk_IAES,OTUk_SES,OTUk_SESR,OTUk_UAS,
FEC_AFT_COR_ER
OTUk
Performance eventslayer
K=1,2,3,5G i=1~6.
This table lists OTN performance events in the OTUk, ODUk_PM, and ODUk_TCMi layers. For definitions related to the performances, see ITU-T G.8201.ES: Errored Second: When one or more bit error blocks are found in one second, it is called ES. FEES: far end ES.SES: Severely Errored Second: In one second period, include ≥ 15% bit error blocks, or, there is at least one defect (OCI/AIS/LCK/IAE/LTC/TIM/PLM). FESES: far end severely errored second.SESR: Severely Eroded Second Ratio: It indicates the ratio between the SES and total seconds in the available time within the fixed test interval. FESESR: far end Severely Eroded Second Ratio.BBE: Background Block Error: It indicates the bit error block beyond the severely eroded second. FEBBE: far end background block error.BBER: Background block error ratio. It indicates the ratio between the BBE and total blocks in the available time within the fixed test interval. The total number of the blocks excludes the number of the blocks in the SES. FEBBER: far end background block error ratio.UAS: Unavailable second: It starts from 10 consecutive SES events. The 10 seconds are considered as a part of the unavailable second. The new available time period starts from 10 consecutive non-SES events. Ten seconds can be considered as one part of the available time. FEUAS: Far end unavailable second.IAES: Incoming Alignment Error Second: When the IAE error exists in one second, the second is the incoming alignment error second. BIAES: backward Incoming Alignment Error Second.After the FEC is used, the definitions of all performance events are after the FEC. That is, the detection of the performance event (for example, BBE and SES) is after all error corrections.
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Questions
Which kinds of the components does the OTM-n.m have?
What’s the difference between SM and PM?
Which kinds of the components does the OTM-n.m have?
OTSn, OMSn, OCh, OTUk/OTUkV, ODUk, OPUk
What’s the difference between SM and PM?
SM is in the OTUk OH,PM is in the ODUk OH.
SM contains TTI/BIP-8/BEI/BIAE/BDI/IAE/RES,PM contains TTI/BIP-8/BEI/BDI/STAT.
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Summary
Optical transport hierarchy
OTN interface structure
Multiplexing/mapping principles and bit rates
Overhead description
Maintenance signals and function for different layers
Alarms and performance events
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Abbreviations and AcronymsAIS 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
CMEP Connection Monitoring End Point
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
IAE Incoming Alignment Error
IrDI Inter-Domain Interface
JOH Justification Overhead
MFI Multi-frame Indicator
MSI Multiplex Structure Identifier
NNI Network Node Interface
OCC Optical Channel Carrier
OCG Optical Carrier Group
OCGr Optical Carrier Group with reduced functionality
OCh Optical channel with full functionality
OChr Optical channel with reduced functionality
OCI Open Connection Indication
ODTUG Optical channel Data Tributary Unit Group
ODTUjk Optical channel Data Tributary Unit j into k
ODU Optical Channel Data Unit
ODUk Optical Channel Data Unit-k
OMS Optical Multiplex Section
OMU Optical Multiplex Unit
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Abbreviations and AcronymsONNI Optical Network Node Interface
OOS OTM Overhead Signal
OPS Optical Physical Section
OPU Optical Channel Payload Unit
OPUk Optical Channel Payload Unit-k
OSC Optical Supervisory Channel
OTH Optical Transport Hierarchy
OTM Optical Transport Module
OTN Optical Transport Network
OTS Optical Transmission Section
OTU Optical Channel Transport Unit
OTUk completely standardized Optical Channel Transport Unit-k
OTUkV functionally standardized Optical Channel Transport Unit-k
PCC Protection Communication Channel
PLD Payload
PMI Payload Missing Indication
PRBS Pseudo Random Binary Sequence
PSI Payload Structure Identifier
PT Payload Type
RES Reserved for future international standardization
SAPI Source Access Point Identifier
Sk Sink
SM Section Monitoring
So Source
TCM Tandem Connection Monitoring
TS Time Slot
TxTI Transmitted Trace Identifier
UNI User-to-Network Interface
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