Optical Transport Network

1
Optical Transport Network Optical Transport
Module

• "Digital Wrapper"

Maarten Vissers Consulting Member of Technical
Staff Lucent Technologies email
mvissers_at_lucent.com
April 2002
2
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

3
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• OTN Characteristics
• Transitional Approaches
• Final Phase
• O/E/O processing objectives
• Digital processing objectives

4
OTN Characteristics

• New transport networking layer (carrier grade
  solution)
• Next step (after SDH/SONET) to support ever
  growing data driven needs for bandwidth and
  emergence of new broadband services
• Terrabit/second per fiber via DWDM lines
  (transport level)
• Gigabit/second paths at 2.5 Gb/s, 10 Gb/s, 40
  Gb/s (networking level)
• Service transparency for SDH/SONET, ETHERNET,
  ATM, IP, MPLS
• No change of SDH/SONET!
• One exception interpretation of STM-LOF alarm ?
  STM-AIS due to OTN fail
• Enhanced OAM networking functionality for all
  services
• Shortest physical layer stack for data services
  (IP ? OTN ? Fiber)

5
OTN Characteristics

• Gigabit level bandwidth granularity required to
  scale and manage multi-Terabit networks
• Wavelength level switching maximizes nodal
  switching capacity, the gating factor for
  reconfigurable network capacity
• Avoids very large numbers of fine granularity
  pipes that stress network planning,
  administration, survivability, and management

6
Transitional Approaches - Assessment

• Extended SDH (attempt at creating a new layer
  using SDH elements)
• Bandwidth multiplication by means of TDM ? more
  Gigabit/s on fiber (4x)
• Proprietary approaches attempting to carry lower
  rate STM-N including all overhead as a
  service within a higher rate STM-M (MgtN)
• strongly limited SDH multiplexing hierarchy not
  designed to carry the STM-N (i.e. itself) as a
  service
• No timing transparency
• 90 of STM-N/OC-N overhead bytes not passed
  through
• No STM-N/OC-N independent monitoring
• Multiple proprietary implementations created in
  industry
• no interworking

7
Transitional Approaches - Assessment

• Pre-OTN WDM (simple transport - vs. networking -
  solution)
• Bandwidth multiplication by means of WDM ?
  Terabit/s on fiber (100x)
• Client signal (e.g. STM-N, GbE) direct on
  wavelength
• simple transport, no monitoring
• or client specific non-intrusive monitoring
• per client type a monitor is needed
• additional client type implies additional monitor
  to be added
• alarm suppression signal (e.g. AIS) specific per
  client type
• additional client type implies additional alarm
  suppression signal to be added
• Point-to-point application that can transport
  STM-N/OC-N as a service

8
Final Phase

• OTN (networking solution)
• Management enabler of WDM network by means of
  addition of
• Overhead to "?" and "multi-?" signals
• "non-associated" or "out-of-channel" overhead
  e.g. preventing alarm storms
• Optical Channel (OCh) layer
• STM-N, IP, ATM and Ethernet signals mapped
  ("wrapped") into OCh frame (OCh Data Unit (ODUk))
• First transmission technology in which each
  stakeholder gets its own (ODUk) connection
  monitoring
• In addition ODUk supports/provides
• STM-N independent monitoring, becoming a service
  signal "itself", shortest physical layer stack
  for data services, TDM muxing, STM-N inverse
  multiplexing, client independent protection
  switching, plesiochronous timing (no sync network
  required)

9
O/E/O Objectives

• Minimise O/E/O processing in OTN
• O/E/O processing at edges of administrative/vendor
  (sub)domains
• Span engineering
• O/E/O processing at edges of protected or
  switched domain
• Span engineering (short/long route effects)
• Signal Fail Signal Degrade condition
  determination
• If more than 1 optical transparent subnetwork is
  included
• O/E/O processing at intermediate points
• Span engineering (long line sections)
• Losses in optical fabrics
• O/E E/O processing around electrical fabric

10
Digital Processing Objectives

• Digital processing at locations where O/E/O is
  already performed
• Fault and degradation detection
• Service Level Agreement (SLA) verification
• Signal Fail Signal Degrade condition
  determination for protection and restoration
  (e.g. if high accuracy is required)

11
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• Layer Networks
• Client Signals
• Optical Channel Structure
• Containment Relationships
• Example of Layer Network Trails
• OTN Interfaces
• Standardised and "Proprietary" Stacks

12
OTN Layer Networks Client Signals

• Three new layer networks
• one "Gbit/s" path layer
• OCh
• two section layers
• OMSn
• OTSn
• single channel section layer
• OPS0
• Client signals
• IP/MPLS
• ATM
• Ethernet
• STM-N

Optical Multiplex Section (OMSn) layer network
13
Optical Channel Structure

• Optical Channel layer network consists of 31
  structures
• Digital
• OCh Data Unit (ODUk)
• OCh Payload Unit (OPUk, k1,2,3)
• OCh Transport Unit (OTUk, OTUkV)
• Analogue OCh

14
OTN Containment Relationships
15
OTN Layer Network Trails

• Example of OTSn, OMSn, OCh, OTUk, ODUk, OPS0
  trails
• Transport of STM-N signal via OTM-0, OTM-n and
  STM-N lines

DXC
3R
3R
OCADM
LT
R
R
LT
3R
DXC
3R
OTM-0
Client
OTM-n
STM-N
Client
ODXC
LT Line Terminal w/ optical channel multiplexing
OCADM Optical Channel Add/Drop Multiplexer
ODXC ODU Cross-Connect
3R O/E/O w/ Reamplification, Reshaping Retiming
and monitoring
R Repeater
16
OTN Interfaces

• User to Network Interface (UNI)
• Network Node Interface (NNI)
• Inter Domain Interface (IrDI)
• Intra Domain Interface (IaDI)
• between equipment of different vendors (IrVI)
• within subnetwork of one vendor (IaVI)

Network Operator B
Network
USER
Operator
A
C
Vendor X
Vendor Y
17
Standardised "Proprietary" stacks

• Proprietary elements
• OTM-n.m
• optical parameters
• number of wavelengths
• bit rates of wavelengths
• supervisory channel
• OTUkV
• FEC
• frame format
• ODUk mapping

18
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• Application
• Nesting
• Overlapping

19
Multi-level Connection MonitoringApplications
Status of working protection connection is
monitored for SF and SD switch conditions
ODUk switched circuit UNI-UNI CM to initiate
"connection re-establishment"
QoS of client signal transport is monitored by
User
QoS of provided leased circuit is monitored by
Service Provider
QoS of provided leased circuit is monitored by
Network Operator
QoS provided by leased circuit is monitored by
User
Client Signal
USR2
NO A
NO B
NO C
USR1
Client Signal
20
Multi-level Connection MonitoringNesting
21
Multi-level Connection MonitoringNesting and
Overlapping
22
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• OTM Interface Signals
• OTM-16r.m
• OTM-0.m
• OTM-n.m
• OTM Signals versus OTN I/F
• OTM Overhead Signal
• Frame Formats
• OTUk, ODUk
• Overhead
• OTUk, ODUk
• OTUkV
• Overhead versus OTN I/F

23
OTM-16r.m Signal (m1,2,3,12,23,123)

• Up to 16 wavelengths carrying traffic, with fixed
  200 GHz grid independent of bit rate (2G5, 10G,
  40G)
• Optical parameters according to ITU-T
  Recommendation G.959.1
• Bit rate and format of the associated overhead
  according to ITU-T Recommendation G.709
• No Optical Supervisory Channel (OSC)
• non-associated overhead not required i.e. 3R
  points at each end, no repeaters

24
OTM-0.m Signal (m1,2,3)

• Single channel signal ("colourless" 1310 or 1550
  nm)
• Optical parameters according to ITU-T
  Recommendation G.959.1
• Bit rate and format of the associated overhead
  according to ITU-T Recommendation G.709
• No Optical Supervisory Channel (OSC)
• non-associated overhead not required i.e. 3R
  points at each end, no repeaters

25
OTM-n.m Signal (m1,2,3,12,23,123)

• Up to "n" wavelengths carrying traffic, with a
  grid dependent on bit rate
• 1 "out-of-band" Optical Supervisory Channel (OSC)
  transporting the OTM Overhead Signal (OOS)
• OTM Overhead Signal transports OTS, OMS, OCh
  (non-associated) overhead and General management
  communications

26
OTM Signals versus OTN Interfaces
27
OTM Overhead Signal (OOS)Non-associated
overhead

• OOS functions subject to standardization
• OOS bit rate format not standardized

OCh OH extensions may be expected in future to
support e.g. OCh protection (e.g. OCh SPring)
28
OTUk and ODUk frame formats (k1,2,3)
ODUk bit rate 239/(239-k) "STM-N"
OTUk bit rate 255/(239-k) "STM-N"
29
OTUk and ODUk Overhead (k1,2,3)Associated
overhead
30
OTUkV (k1,2,3)

• Frame format is vendor specific
• Forward Error Correction code is vendor specific
• Minimum overhead set to support is
• Trail Trace Identifier
• Error Detection Code (e.g. BIP)
• Backward Defect Indicator
• Backward Error Indicator
• (Backward) Incoming Alignment Error
• Other overhead is vendor specific
• ODUk mapping into OTUkV is vendor specific

31
Overhead versus OTN Interfaces

• OTM Interface Ports on IP Router, ATM Switch,
  Ethernet Switch and SDH equipment should support
  the following minimum set of overhead
• OPUk Client Specific
• OPUk Payload Structure Identifier (PSI)
• ODUk Path Monitoring (PM)
• OTUk Section Monitoring (SM)
• Frame Alignment (FAS, MFAS)

32
Overhead versus OTN Interfaces

• Overhead passed through network
• OTM UNI to OTM UNI
• OTM NNI IrDI to OTM NNI IrDI

33
Overhead versus OTN Interfaces

• Overhead passed through network from OTM UNI to
  OTM UNI interface
• OPUk PSI, Client Specific
• ODUk PM, TCM ACT, TCM1..TCMn, TCM ACT, RES
• ODUk GCC1, GCC2 according contract
• ODUk APS/PCC definition is under study

34
Overhead versus OTN Interfaces

• Overhead passed through network from OTM NNI IrDI
  to OTM NNI IrDI interface
• OPUk PSI, Client Specific
• ODUk PM, TCM ACT, TCM1..TCMm, TCM ACT, FTFL, RES
• "m" in TCMm gt "n" in TCMn (UNI-UNI)
• ODUk GCC1, GCC2 according contract
• ODUk APS/PCC definition is under study

35
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• Forward Defect Indication (FDI, AIS)
• Backward Defect Error Indication (BDI, BEI)
• Open Connection Indication (OCI)
• Locked (LCK)
• Fault Type Fault Location (FTFL)

36
OTN Maintenance Signals Alarm Suppression
R
use of OTN maintenance signals FDI, AIS and PMI
will reduce number of alarms from 500k to 1 per
broken fiber
R
3R
R
37
OTN Maintenance Signals Alarm Suppression (FDI,
AIS)

• AIS/FDI at
• clients
• AIS at
• ODUk
• AIS at
• OTUk
• FDI at
• OCh
• FDI/PMI at
• OMSn
• PMI at
• OTSn

38
OTN Maintenance SignalsAlarm Suppression (FDI,
AIS)

• Generated at egress of OMSn, OCh and ODUk Link
  Connections
• Inserted on detection of Signal Fail
• OMSn-FDI and OCh-FDI
• is non-associated overhead
• ODUk-AIS
• is special ODUk signal pattern (0xFF)

39
Generic-AIS STM-AIS

• New maintenance signal _at_ STM-N level
• a continuous repeating 2047-bit PN-11 (1 x9
  x11) sequence
• Generated in OTN tributary ports
• ingress trib on detection of STM-N LOS
• egress trib on detection of ODUk signal fail
  type defect
• To be detected in SDH line/trib ports in addition
  to STM-LOF as "STM-AIS"
• ? In existing equipment detected as STM-LOF ?

40
OTN Maintenance Signals Backward Information
(BDI, BEI)

• RDI/REI at
• Clients
• BDI/BEI at
• ODUk
• OTUk
• No BI at
• OCh
• BDI at
• OTSn
• OMSn

41
OTN Maintenance SignalsOpen Connection
Indication (OCI)

• Generated in a Fabric
• Inserted when output port is not connected to
  input port
• OCh-OCI
• is non-associated overhead
• ODUk-OCI
• special ODUk signal pattern (0x66)

42
OTN Maintenance SignalsLocked (LCK)

• Generated in ODUk Tandem Connection endpoint
• Inserted when Administrative State is Locked
• to block a user to access the connection
• to prevent test patterns within the network
  entering a user domain
• ODUk-LCK
• special ODUk signal pattern (0x55)

43
Fault Type Fault Location (FTFL)

• Helps Service Provider to automatically locate
  fault/degradation to specific Network Operator
  domain
• No need to call around any longer
• Section and Tandem Connection endpoints insert
  FTFL in forward direction on detection of SF or
  SD condition
• Specific FTFL function at UNI
• extracts forward info and sends it in opposite
  direction as backward info
• filters outgoing and incoming FTFL information
  (security issue)
• Specific FTFL extraction function
• reads FTFL forward and backward information at
  intermediate point along connection

44
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• CBR (e.g. STM-N)
• IP, ETHERNET
• ATM
• Test Signals
• Bit stream with/without octet timing
• Bit Rate Agnostic CBR

45
Mapping STM-N (N16,64,256)

• G.709 provides two mappings for STM-N signals
• bit synchronous
• asynchronous
• G.709 defines interworking between both mappings
• common demapper, and
• bit synchronous mapping has fixed Justification
  Control (JC)

STM-16
STM-64
STM-256
D Data, FS Fixed Stuff, JC Justification
Control, N/PJO Negative/Positive Justification
Opportunity
46
Mapping IP and Ethernet

• G.709 provides an encapsulation for packet based
  client signals
• There is no need for SDH or 10G-Ethernet to
  encapsulate IP
• A new protocol is being defined Generic Framing
  Procedure
• a generic mechanism to carry any packet signal
  over fixed rate channels (e.g. SDH, SONET and
  OTN's ODUk) - ITU-T Rec. G.gfp

Bandwidth for GFP stream in ODU1 2 488 320
kbit/s ODU2 9 995 276 kbit/s ODU3 40 150 519
kbit/s
47
Generic Framing Procedure G.7041
48
Mapping ATM

• G.709 provides a mapping for cell based client
  signals
• Mapping ATM into ODUk is similar to mapping into
  SDH

Bandwidth for ATM stream in ODU1 2 488 320
kbit/s ODU2 9 995 276 kbit/s ODU3 40 150 519
kbit/s
49
Mapping Test Signals

• G.709 provides a mapping for test signals
• Two test signals are defined
• NULL sequence (all-0's)

50
Mapping Test Signals

• Two test signals are defined (continued)
• 2 147 483 647-bit Pseudo Random Binary Sequence
  (PRBS) 1 x28 x31
• groups of 8 successive PRBS bits are mapped into
  a data byte

51
Mapping bit stream without octet timing

• G.709 provides a generic mapping for client
  signals encapsulated into a bit stream, with or
  without octet timing
• A regional standards organisation or an industry
  forum may deploy this mapping for a new client
  signal
• It must also define the OPUk Client Specific (CS)
  overhead

52
Bit Rate Agnostic CBR Mapping

• New mapping method which maps a CBR signal of any
  rate (within a range up to OPUk payload capacity)
• Bit rate is a fixed bit rate with a small
  tolerance in the ppm range.
• For inclusion in G.709 version 2
• Description in G.709 Living List
• Further development in 2001/2002 timeframe

53
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• Wavelength Division Multiplex (WDM)
• Time Division Multiplex (TDM)
• TDM Tributary Slots
• TDM Overhead
• TDM Mapping

54
Wavelength Division Multiplex

• OTM-16r.m signal
• 16 channels
• fixed 200 GHz grid independent of bit rate of OCh
  signal
• designed for interworking purposes
• OTM-n.m signal
• no predefined number of channels
• no predefined grid
• grid may depend on bit rate of OCh signal
• e.g. 25, 50, 100 GHz for OTU1, OTU2, OTU3 resp.
• developments in technology are driving
  capabilities

55
Wavelength Division Multiplex - Structure
56
Time Division Multiplex

• TDM muxing in the OTN will be applied for
• lower rate service signal transport
• in long distance line systems and/or sub-networks
  optimised for single (higher) bit rate
• increased throughput
• in optical fabrics and/or sub-networks
• reduced administrative complexity
• in large networks
• lower cost networks
• TDM muxing introduces additional complexity when
  tributary signal must be routed
• requires demux and mux stages around switch fabric

57
Time Division Multiplex

• TDM muxing is muxing of ODUk signals into higher
  order ODUk signals
• ODU1 into ODU2
• ODU1 and/or ODU2 into ODU3
• ODU1 into ODU2 into ODU3 is possible, but not the
  recommended method when ODU1s are the service
  signals that are to be switched/cross connected
  within an "ODU3 network"
• if ODU1s enter such ODU3 network via ODU2, the
  ODU2 is terminated at the edge and the ODU1s are
  remultiplexed into an ODU3
• if ODU2 is service signal, of course no
  demuxing/remuxing will occur at edges
• Multiplexing via byte interleaving

58
Time Division Multiplex - Structure
59
Time Division Multiplex - artist impression

• 4x ODU1 into ODU2 payload
• ODU1 adapted to ODU2 clock via justification
• adapted ODU1 signals byte interleaved into OPU2
• ODU2 and OTU2 overhead added
• ODU1 floats in ¼ of the OPU2
• ODU1 frame will cross an ODU2 frame boundary

60
Time Division Multiplex -ODU2 Tributary Slot
Allocation
61
Time Division Multiplex -ODU3 Tributary Slot
Allocation
62
Time Division Multiplex - OverheadMSI, JC, PJO1,
PJO2
63
Time Division Multiplex - Mapping

• Asynchronous mapping of ODU information bytes
• -1, 0, 1, 2 byte justification control
• ODU1 into ODU3 mapping includes Fixed Stuff
  column
• ODU1 into ODU2 and ODU2 into ODU3 mapping is
  without fixed stuff

64
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

• ODUk-Xv
• OPUk-Xv Overhead
• Mapping Client signals

65
Virtual Concatenation

• Virtual Concatenated ODUk's
• ODUk-Xv, with X1..256
• Provide
• Ability to transport STM-64 and STM-256 signals
  via fibers not supporting 10G and/or 40G
  wavelengths
• STM-64 into ODU1-4v
• STM-256 into ODU2-4v or ODU1-16v
• Finer granularity bandwidth for data signals
• X 2G5 10G 40G via ODU1-Xv ODU2-Xv
  ODU3-Xv
• Application of Link Capacity Adjustment Scheme
  (LCAS, Rec. G.7042) offers
• Hitless bandwidth modification
• Build in resilience when signal components routed
  via two or more diverse routes

66
Virtual Concatenation - Inverse muxing

• Mapping of client signal into OPUk-X
• Inverse muxing of OPUk-X signal into X OPUk
  signals
• ODUk overhead is added to each of the X OPUk
  signals
• ODUk signals are transported

67
Virtual Concatenation - Overhead

• PSI
• vcPT
• VCOH
• MFI1, MFI2
• SQ
• LCAS
• CTRL
• GID
• RSA
• MST
• CRC8
• Res

68
Virtual Concatenation - Mapping

• STM-N
• asynchronous
• bitsynchronous
• ATM
• GFP (IP, ETH, MPLS)
• Test signals

STM-64 into OPU1-4v
STM-256 into OPU2-4v
STM-256 into OPU1-16v
69
Contents

• OTN Rationale
• OTN Layer Networks
• Multi level Connection Monitoring
• OTM Signals
• Maintenance Signals
• Mapping Client Signals
• Multiplexing
• Virtual Concatenation
• OTN Standards

70
OTN Standards in ITU-T - Transport Plane

• Framework
• Network Architecture
• Structures and bit rates
• Equipment
• Equipment Management Function
• Protection
• Data Communication Network
• Jitter Wander Performance
• Error Performance
• Physical
• Information Model
• Optical Safety
• Generic Framing Procedure
• Link Capacity Adjustment Scheme
• Bringing into Service Maintenance
• Q factor measurement

• G.871 (10/00)
• G.872 (10/01)
• G.709 (02/01), G.709 am.1 (10/01)
• G.798 (10/01)
• G.874 (10/01), G.7710 (11/01)
• G.gps (2002), G.otnprot (2002)
• G.7712 (10/01)
• G.8251 (2002)
• G.optperf (2002)
• G.959.1 (02/01), G.693, G.dsn (2003)
• G.874.1 (10/01), G.875 (2002)
• G.664 (06/99)
• G.7041 (10/01)
• G.7042 (10/01)
• M.24otn (2003)
• O.qfm (?)

71
OTN Standards in ITU-T - Control Plane

• Automatic Switched Transport Network
• Automatic Switched Optical Network
• Distributed Connection Management
• Automatic Discovery Techniques
• Routing
• Signalling Communication Network
• Link Resource Manager

• G.807 (05/01)
• G.8080 (10/01)
• G.7713 (10/01)
• G.7714 (10/01)
• G.7715 (2002)
• G.7712 (10/01)
• G.7716 (2002?)

72
OTN Standards in ITU-T
73
OTN Standards in ITU-T
74

• THANK YOU