1 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

S-108.199 OPTICAL COMMUNICATIONS AND INSTRUMENTS

SDH and WDM, 10.3.2004

Antti Pietiläinen

2 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Trend towards simplification of protocol stacks

WDM/Optical Networking LayerWDM/Optical Networking Layer

SDH TransportSDH Transport ATMATM IPIP Digital SignalDigital Signal(FR, FOTS, PDH)(FR, FOTS, PDH)

ATMATM IPIP

IPIPPDHPDH

FRFR

Transport/Application LayerTransport/Application Layer

TimeTime

CurrentSystems Current

R&DFuture

Deployment (3-6 yrs)

From this

Towards this

How the future of layering looked 4 years ago

3 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

PDHPDH

Trend towards simplification of protocol stacks

OTNOTN

SDH TransportSDH Transport EthernetEthernet IPIP

ATMATM IPIP

IPIP FRFR

Transport/Application LayerTransport/Application Layer

CurrentSystems Current

R&Dand future deplyment

From this

Towards this

How the future looks now

GFPGFP

GFPGFP

OTNOTN

4 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Acronyms of previous page

• IP = Internet protocol

• FR = frame relay

• PDH = plesiochronous digital hierarchy

• ATM = asynchronous transfer mode

• SDH = synchronous digital hierarchy

• GFP = generic framing procedure

• WDM = wavelength division multiplexing

• OTN = optical transport network

5 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Digital signal

• Analog telephone connection carries the frequencies between 300 Hz and 3400 Hz.

• The signal can be converted into a digital signal by sampling 8-bit samples at 8000 samples/s.

• Channels are multiplexed together using time domain multiplexing. Each channel gets one-byte timeslot in every frame. Frame rate is 8000 frames per second. 30 or 31 channels fit into 32 time slots where one or two time slots are used for frame alignment and signaling. The total bit rate of E1 frame is 2.048 Mbit/s.

• The ANSI frame T1 includes 24 64-kbit/s channels. A single frame has 24 x 8 =192 payload bits and one framing bit.

• The 64-kbit/s channels collected into one E1 or T1 are digitized using the same clock. Thus, the channels are synchronized with each other.Ramaswami has assumed the framing bit as a stuffing bit, which could accommodate bit rate differences, so p. 365 has an error.

• However, individual E1 and T1 signals are not necessarily synchronized with each other.

6 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Short history multiplexing hierarchy, PDH

• PDH – plesiochronous digital hierarchy. Multiplexing signals, which are running at almost the same speed.

• First standards in the second half of 1960s.• Tributaries and higher order bit streams are allowed to deviate from a

pre-defined bit rate by a specified amount, for example at 2 Mbit/s the value is 50 ppm.

• Justification (bit stuffing) process is therefore required, which brings all the tributaries up to the same bit rate before multiplexing takes place.

97728 Mbit/s139264 Mbit/s139264 Mbit/s432064 Mbit/s34368 Mbit/s44736 Mbit/s36312 Mbit/s8448 Mbit/s6312 Mbit/s2

1544 Mbit/s2048 Mbit/s1544 Mbit/s1

0.064 Mbit/s0.064 Mbit/s0.064 Mbit/s0

JapanEurope

E

North America

DS or T

Level

7 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

PDH multiplexer mountain

• When a signal is demultiplexed, the stuffed bits are removed. Each level knows how to demultiplex the next level.

• To extract a 2-Mbit/s signal from a high- bit rate stream, a “multiplexer mountain” is required.

34 -140 MUX

34 -140 MUX

8 -32

MUX

8 -32

MUX2 -8

MUX

2 -8

MUX

140 Mbit/s 140 Mbit/s

2 Mbit/s Drop/Add

34 Mbit/s

8 Mbit/s

2 Mbit/s

8 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Foundation of SDH/SONET

• Developed during late 1980s

• SDH - Synchronous digital hierarchy (Europe, Japan, Intercontinentalcables, ITU recommendation)

• SONET – Synchronous optical network (North America, ANSI standard)

• All clocks in a network are synchronized to a single master clock.

• All bit rates are integer multiples of the basic bit rates and no bit stuffing is required.

• A lower bit rate stream can be extracted from a multiplexed SONET/SDH stream in a single step.

9 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Other advantages of SONET/SDH

• Management• Incorporates extensive management information for managing the

network• Performance monitoring• Identification of connectivity and traffic type• Identification and reporting of failures• Data communication channel

• Interoperability• PDH standard did not specify standard format on the transmission link.

Therefore different vendors used different line coding, optical interfaces etc. In SDH standardization is more complete. However, there are still some problems in connecting equipment from different vendors

• Network availability• Incorporate specific network topologies and specific protection

techniques and associated protocols to provide high availability. Restoration time after failure can be less than 60 ms.

10 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Multiplexing

• The basic SONET bit rate is 51840 Mbit/s and the basic SDH bit rate is 155.420 Mbit/s. The highest bit rate standardized so far is 39813.120 Mbit/s.

STM-2561327.10438486.01639813.120STS-768OC-768

STM-64331.7769621.5049953.280STS-192OC-192

STM-1682.9442405.3762488.320STS-48OC-48

STM-420.736601.344622.080STS-12OC-12

STM-15.184150.336155.520STS-3OC-3

-1.72850.11251.840STS-1OC-1

SDH Equivalent

Overhead Rate (Mbps)

Payload Rate (Mbps)

Line Rate (Mbps)

Electrical Level

(ANSI)

Optical Level

(ANSI)

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SDH Multiplexing structure (ITU-T G.707)

STM-256

STM-64

STM-16

STM-4

STM-1

STM-0

AUG-256

AUG-64

AUG-16

AUG-4

AUG-1

AUG-4-256c

AUG-4-64c

AUG-4-16c

AUG-4-4c

AU-4

AU-3 VC-3

VC-4

VC-4-256c

VC-4-64c

VC-4-16c

VC-4-4c

C-4-256c

C-4-64c

C-4-16c

C-4-4c

C-4

C-3

C-2

C-12

C-11

VC-3

VC-2

VC-12

VC-11

TU-3

TU-2

TU-12

TU-11

TUG-2

TUG-3

Pointer processingMultiplexingAligningMapping

x 4

x 3

x 1x 7

x 7

x 3x 1

x 3

x 4

x 4

x 4

x 4

x 1

x 1

x 1

x 1

x 1

x 1 x 1

x 1

x 1

x 1

x 1

DS1 1.5M

E1 2M

DS2 6M

DS3 45ME3 34M

DS4 139ME4 139M

SONET

SONET

ETSI

ETSI

SONET

SONET

ETSISONET

SONETETSIETSI

ETSI

149.8M

599.04M

2396.16M

9584.64M

38338.56M

150.336M

12 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Procedures in SDH framing

• SDH mapping: A procedure by which tributaries are adapted into Virtual Containers at the boundary of an SDH network.

• SDH multiplexing: A procedure by which multiple lower order path layer signals are adapted into a higher order path or the multiple higher order path layer signals are adapted into a multiplex section.

• SDH aligning: A procedure by which the frame offset information is incorporated into the Tributary Unit or the Administrative Unit when adapting to the frame reference of the supporting layer.

13 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Cross-connecting VCs

• VCs arrive inside STMs into a cross connect. The VCs are recovered and cross-connected to another port and aligned into another STMs.

Connectionpoints

Connectionpoints

flexiblematrix

Out 1

Out 2

In 1

In 2

STM-1

STM-4 STM-1

STM-4

VC-4 pipes : continuous streamof virtual containers

1

4

1

32

1

31

2

4

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Aligning virtual containers into TU (transport unit) or AU (administrative unit)

• Virtual container is a frame (frame rate 8000 frames/s).

• The virtual containers are synchronous because the clock is derived from the master clock of the network.

• However, virtual containers may travel a long way and go through many links.

• Each link transmits frames between two nodes at a frame rate of 8000 frames/s. The bit rate of all consecutive links may be the same but the frame boundaries occur at different moments. Thus, VCs float inside the TUs or AUs and a pointer indicates where the starting point of a VC is within a TU or AU

TU-12 frame

TU-12 frame

VC-12 frame

Pointer

Pointer

15 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Justification bytes and pointer slip

• Sometimes the whole network is not synchronized and VCs may be running at a slightly faster or slower rate than the TU or AU.

• Therefore the pointer must slip one byte every now and then. Forallowing slightly faster rate there has to be an extra byte in the TU or AU that may take the last byte of a frame when there is a negative slip where the VC shifts to a location one byte earlier than before and would otherwise overwrite a byte. Correspondingly, in the case of positive split, one byte in the TU or AU is jumped over and left empty.

16 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Building an STM-1 from E2s

C-122.048 Mbit/s tributary signal in

Add stuffing bits, 128 kbit/s

VC-12 Add VC-12 POH, 64 kbit/s(lower order VC POH)

Mapping

Alignment of VC-12 into TU-12 and add 2-byte TU pointer+justification byte + one empty byte for every 4 frames, 64 kbit/s

Multiplex x3

Multiplex x7

Multiplex x3 + add VC-4 POH, 576 kbit/s(higher order VC POH)

Alignment of VC-4 into AU-4and add AU pointer + 3 justification bytes

TU-12

TUG-2TUG-3

VC-4

AU-4

AUG-1 Multiplex x1

STM-1 Multiplex x1 + MSOH, 2.88 Mbit/s, and RSOH, 1.728 Mbit/s

STM = Synchronous transfer moduleMSOH = Multiplexer section overheadRSOH = Regenerator section overheadAUG = Administrative unit groupAU = Administrative unitTUG = Tributary unit groupTU = Tributary unitPOH = Path overheadVC = Virtual containerC = Container

17 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Moving pointer in a cross connect

TU-12 frame

TU-12 frame

VC-12 frame

Pointer

Multiplex section n

TU-12 frame

TU-12 frame

VC-12 frame

Pointer

Pointer

Multiplex section n + 1

18 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Recovering an E2 from an STM-1

C-122.048 Mbit/s tributary signal out

Remove stuffing bits

VC-12 Read VC-12 POH

Recovery of VC-12 from TU-12(read TU pointer + strip justification byte

Demultiplex ÷ 3

Demultiplex ÷7

Demultiplex ÷3 read VC-4 POH

Recovery of VC-4 from AU-4(read AU pointer + strip justification bytes)

TU-12

TUG-2TUG-3

VC-4

AU-4

AUG-1 Demultiplex ÷ 1

STM-1 Demultiplex ÷ 1, read MSOH and RSOH

STM = Synchronous transfer moduleMSOH = Multiplexer section overheadRSOH = Regenerator section overheadAUG = Administrative unit groupAU = Administrative unitTUG = Tributary unit groupTU = Tributary unitPOH = Path overheadVC = Virtual containerC = Container

19 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

SDH sublayers

Terminalmultiplexer

Terminalmultiplexer

Add/dropmultiplexerRegenerator

Regeneratorsection

Multiplexersection

(VC) path

Tributaries Tributaries

Section

Line

Path

SONET:

•Path, Multiplexer section and Regenerator section each carry management information, which is terminated at the endpoints of the path or section.

20 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

STM-1 frame• The resulting STM-1 frame

1

2

3

4

5

6

7

8

9

1 2 3 4 65 7 8 9 10

125 µs

AU pointers

Multiplex sectionoverhead

Regenerator sectionoverhead

270 bytes

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SDH physical interface example

• V-16.2

STM-16, 2.5 G1550 nm

• Fiber type G.652 standard single-mode fiber

• Loss 22-33 dB

• Allowed dispersion 2400 ps/nm

• Fiber has attenuation of <0.275 dB/km and dispersion 17 ps/nm/km

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Optical communications cumulative market size• The hype reached its peak in 2000• Current estimates indicate solid but lower growth

1990 1995 2000 2005 2010

CumulativeMarket

size

Core wave

Metro wave

Access wave

Estimate 2000

Estimate 2004

23 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Laboratory experiments conquering dispersion limits

• Chromatic dispersion limit using standard single-mode fiber: 2.5 Gbit/s -1000 km, 10 Gbit/s - 60 km. Most fiber laid in the ground is standard single mode fiber.

• 1 Terabit/s (100 × 10 Gbit/s) transmission over 7300 km non-zero dispersion shifted fiber, Electronics Lett. 35 (1999) p.2212.

• 1.28 Tbit/s (32 x 40 Gbit/s) over 1000 km non-dispersion-shifted fiber using dispersion compensation fiber, Electronics Lett. 37 (2001) p.43.

• DWDM 40 x 40G transmission over trans-Pacific distance (10,000 km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100 kmUltraWave™ fiber spans,” Technical Digest of OFC 2003, post-deadline paper, PD18, (2003).

24 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

WDM layer below SDH layer• WDM has introduced functionality, such as optical add/drop multiplexers

and optical regeneration below SDH in layered model.

• Optical transport network (OTN) layer serves SDH client layer.

Path LAYER

Multiplex Section LAYER

Regenerator Section LAYER

Optical Channel LAYER

Optical Multiplex Section LAYER

Optical Transmission Section LAYER

Fibre LAYER

TDMElectricalLayers

WDMOpticalLayers

25 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Optical sections within a single SDH regeneration section

OPTICAL MULTIPLEX

SECTION

OPTICAL MULTIPLEX

SECTION

OPTICAL TRANSMISSION

SECTION

TRIBUTARYSIGNALS

WDMMULTI-

PLEXER

WDMDEMULTI-PLEXER

OPTICAL CROSS-CONNECT

OPTICALAMPLIFIER

OPTICALAMPLIFIER

TRIBUTARYSIGNALS

Optical Channel

SDH REGENERATOR SECTION

OPTICAL TRANSMISSION

SECTION

OPTICAL TRANSMISSION

SECTION

26 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Optical channel frame• STM-16 + FEC = OTU1, STM-64 + FEC = OTU2, STM-256 + FEC = OTU3

• Other payload mappings available, for example Generic framing procedure.

OTU type OTU nominal bit rate OTU bit rate tolerance

OTU1 255/238 × 2 488 320 kbit/s

±20 ppmOTU2 255/237 × 9 953 280

kbit/s

OTU3 255/236 × 39 813 120 kbit/s

NOTE – The nominal OTUk rates are approximately: 2 666 057.143 kbit/s (OTU1), 10 709 225.316 kbit/s (OTU2) and 43 018 413.559 kbit/s (OTU3).

OTU = Optical channel transport unit, FEC = Forward error correction

Source ITU-T G.709 (03/2003)

27 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Optical transport network functionality

• Service provisioning

• Protection

• Performance monitoring

• Wavelength conversion

• Multiplexing and grooming

• Bit rate transparency (with provisions)• High bit rate more sensitive to dispersion and attenuation• Very high bit rate consumes more optical bandwidth

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WDM network elements

• Optical add/drop multiplexers (OADM)

Ring network Linear network

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WDM network elements

• Optical crossconnects (OXC)

Mesh

OADM

OADM

OADM

OXC

OXC

30 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Protection at different optical layers

Trail Protection Subnetwork Protection

1 + 1 1 : 1 m : n 1 + 1 1 : 1 m : n

Optical Channel Layer (end-to-endtrail, ffs) (section)

Optical MultiplexSection Layer

(meshednetworks)

(ringprotection)

(ringprotection)

(meshednetworks)

(ringprotection)

(ringprotection)

Optical TransmissionSection Layer

OADMOADM

OADM

OXC

OXC

• Optical channel protection• A backup route is planned for a path

• Optical multiplex section protection• A link between two OXCs has a backup

route.

31 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

OADM architectures

• Parallel where all the wavelengths are separated and multiplexed back

λ1, λ2, …, λw

λ1, λ2, …, λw

λ1

λ2

λw

λ1

λ2

Drop Add

32 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

OADM architectures

• Modular version of parallel architecture

λ1, λ2, …, λw

λ1, λ2, …, λw

λ1 λ2

Band 4

Band 3

Band 2

Band 1

Drop Add

33 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

OADM architectures

• Serial

λ1, λ2, …, λw λ1, λ2, …, λw

λ1Drop Add λ2 λ3

Drop Addλ1, λ2, λ3

λ1, λ2, …, λw λ1, λ2, …, λw

• Band drop

34 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

OADM architectures

• Reconfigurable parallel architecture

λ1, λ2, …, λN

λ1λ2λN

λ1, λ2, …, λN

Optical switch

35 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Optical crossconnect (OXC)

OXC

OLT (optical line terminal)

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Different scenarios for OXC deployment

Opticalcore

OLT (optical line terminal)• Electrical switch core

O E OO E O

O E OO E O

OO

OO

EE

EE

OO

OO

E OE O

E OE O

EE

EE

OO

OO

O E OO E O

O E OO E O

OO

OO

EE

EE

OO

OO

E OE O

E OE O

EE

EE

OO

OO

OO

OO

OO

OO

• Optical switch core surrounded by O/E/O converters

Electrical core

37 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Different scenarios for OXC deployment

OLT

• Optical switch core connected directly to transponders in OLT

O E OO E O

O E OO E O

OO

OO

EE

EE

OO

OO

• Optical switch core directly connected to multiplexer in OLT

Optical core

Optical core

OLT

38 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Optical core wavelength plane OXC

Local add

λ1, λ2, λ3

λ1, λ2, λ3

λ1, λ2, λ3λ1, λ2, λ3

λ1

λ2

λ3λ1 λ1λ3λ2 λ2

Local drop

39 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi

Reading instructions

• SDH, pp. 364-381. SDH multiplexing hierarchy instead of SONET multiplexing hierarchy.

• WDM, pp. 403-430 and optical network layering and the principle of optical protection.