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SONET/SDH Introduction – What is the Difference Between SONET and SDH?

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Why SDH/SONET?

• SDH (Synchronous Digital Hierarchy) and SONET (Synchronous Optical NETwork) are standards for interfacing optical networks.

• Simple multiplexing processes

• Easy access to various signals in a multiplexed high bit rate signal

• A flexible and efficient way of networking

– Network Distribution: Add/Drop capability

– Network survivability: APS (Automatic Protection Switching)

– Traffic Cross connection: capacity management, bandwidth management and protection route diversity

• Support advance Network Management System (OAM&P) – Overhead bits for Fault, Configuration, Performance Monitoring, Security and Accounting management

• Standardized interface can support multi vendor interworking, international connection and many different services; i.e. ATM, IP

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SONET/SDH Digital Hierarchy

OpticalLevel

SONETElectrical

Level

SDHEquivalent

Line Rate(Mbps)

PayloadRate

(Mbps)

OverheadRate

(Mbps)

SONETCapacity

SDHCapacity

OC-1 STS-1 – 51.840 50.112 1.728 28 DS-1s or 1 DS-3

21 E1s

OC-3 STS-3 STM-1 155.520 150.336 5.184 84 DS-1s or 3 DS-3s

63 E1s or1 E4

OC-12 STS-12 STM-4 622.080 601.344 20.736 336 DS-1s or 12 DS-3s

252 E1s or 4 E4s

OC-48 STS-48 STM-16 2488.320 2405.376 82.944 1,344 DS-1s or 192 DS-3s

1,008 E1s or 16 E4s

OC-192 STS-192 STM-64 9953.280 9621.504 331.776 5,376 DS-1s or 192 DS-3s

4,032 E1s or 64 E4s

Note: Although an SDH STM-1 has the same bit rate as the SONET STS-3, the two signals contain different frame structures. STM = Synchronous Transport Module (ITU-T)STS = Synchronous Transfer Signal (ANSI)OC = Optical Carrier (ANSI)

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SDH and SONET Bit Rate

SDHSDHSDHSDH Bit RateBit RateBit RateBit Rate SONETSONETSONETSONET

STM-1STM-1STM-1STM-1

STM-64STM-64STM-64STM-64 OC-192OC-192OC-192OC-192

OC-3OC-3OC-3OC-3

9.95Gb/s9.95Gb/s9.95Gb/s9.95Gb/s

155Mb/s155Mb/s155Mb/s155Mb/s

STM-4STM-4STM-4STM-4 OC-12OC-12OC-12OC-12622Mb/s622Mb/s622Mb/s622Mb/s

STM-16STM-16STM-16STM-16 OC-48OC-48OC-48OC-482.48Gb/s2.48Gb/s2.48Gb/s2.48Gb/s

STM-0STM-0STM-0STM-0 OC-1OC-1(STS-1)(STS-1)OC-1OC-1(STS-1)(STS-1)51Mb/s51Mb/s51Mb/s51Mb/s

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What is different about SDH vs. SONET?

• Together they are a set of global standards that interface equipment from different vendors. SDH is basically the international version of SONET, and SONET can be thought of as the North American version of SDH.

• There are some slight differences between SONET and SDH.

• The main differences are in the basic SDH and SONET frame formats, but SDH and SONET are essentially identical beyond the STS-3 signal level. The base signal for SONET is STS-1 and the base signal for SDH is STM-1. STS-3c is equivalent to STM-1 and the lower tributaries can be mapped interchangeably between the two formats from that point on.

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What is different about SDH vs. SONET? (Cont’)

• In SDH, both electrical and optical signals are referred to as STM signals.

• In SONET, however, electrical signals are called STS and optical signals are referred to as OC.

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SONET

• Defined by Bellcore and ANSI T1.X committees

Base rate (High Order) is 51.84Mbps (STS-1)

STS-1 Synchronous Payload Envelope (SPE) = 50.112M used for carrying tributaries or a DS3 signal

Tributaries (Low Order) used for SONET are:

VT1.5 (SPE Trib) = 1.728M for carrying DS1 (1.544)

VT2 (SPE Trib) = 2.304M for carrying CEPT (E1, 2.048)

VT6 (SPE Trib) = 6.912M, Never “formalized” same rate as VT Group

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SONET Hierarchy

x7

E1

DS1

x1

x3

x4

Tributaries of Base Signal (Low Order Payloads)

xN

Broadband STS-N Payloads (High Order Payloads)

VT 1.5

VT Group

VT 2

VT 6VT6 SPE

VT2 SPE

VT1.5 SPE

STS-N

STS-1SPE

STS-NSPE

x1

DS3x1

Data

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STS-1 Frame with VT Mapping

Section OHSection OH

Line OHLine OH

3 bytes

3

1

5

87 bytes

STS-1 SPESTS-1 SPE

STS-1 SPE PayloadSTS-1 SPE PayloadDS3 Mapped DS3 Mapped oror7x VTG Mapped7x VTG Mapped

J1J1

B3B3

C2C2

G1G1

F2F2

H4H4

F3F3

K3K3

Z3Z3

STS PointerSTS Pointer

VTVT

GroupGroup

VTVT

GroupGroup

VTVT

GroupGroup

VTVT

GroupGroup

VTVT

GroupGroup

VTVT

GroupGroup

VTVT

GroupGroup

VV

TT

11

55

VxVx

ptrptr

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Points to Remember in SONET

• The base layer is the STS-1 SPE

Single pointer to get to the STS-1 SPE (50MB level)

ALL tributary signals multiplex (via Pointer Processing) to the STS-1 SPE

Each STS-1 has it’s own path overhead

TOH is called Section and Line Overhead

SS bits (in H1) is set to 00

Bellcore (Telcordia) Alarming and GR-820 Performance Monitoring

Other Nuances:

Path Trace is 64bytes, Orderwire is Mu-Law, Z bytes not used, No J2, APS is different

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SDH

• Defined by ITU-T (previously CCITT) committees

Base rate (High Order) is 155.520 (STM-1)

Virtual Container 4 (VC-4) = 150.336M used for carrying tributaries or an E4 signal (or data)

Tributaries (Low Order) used for SDH are:

VC-11 = 1.728M for carrying DS1 (1.544) (rarely used in AU4)

VC-12 = 2.304M for carrying CEPT (E1)

Also a stuffing option for mapping VC11/1.5M to TU-12

VC-2 = 6.912M Just gaining acceptance (TU-2-Mc) for data

VC-3 = 50.112M (Same as STS-1 SPE) used for E3 AND DS3

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SDH Hierarchy

STM-16 AU-4-16c C-4-16cVC-4-16c

E1: 2.048Mb/s

E4: 139.264Mb/s

STM-4

STM-1

AU-4-4c

AU-4

AU-3

VC-4-4c

VC-4

C-4-4c

C-4

C-3

C-2

C-12

C-11

VC-3

VC-2

VC-12

VC-11

TUG-3

TUG-2

DS1:1.544Mb/s

E3: 34.368Mb/sDS3: 44.736Mb/s

DS2:6.312 Mb/s

VC-3

TU-3

TU-11

TU-12

TU-2

x4

x3

x1

x7x7

x3x3

564.992Mb/s

2259.968Mb/s

VC-n

AU-n

AUG

STM-n Synchronous Transport Module

Administrative Unit Group: One or more AU(s)

Administrative Unit: VC + pointers

Virtual Container: payload + path overhead

STM-64 AU-4-64c VC-4-64c C-4-64c

AUG

x16

x4

x4x64

x16

x4

9039.872Mb/s

Containers of Base Signal (Low Order Payloads)

High Order Payloads

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STM-1 Frame with AU-4 Mapping

Regenerator Regenerator Section OHSection OH

Multiplex Multiplex Section Section

OHOH

9 bytes

3

1

5

261 bytes

VC-4 Payload:VC-4 Payload:C4 or TUG-3 mappedC4 or TUG-3 mapped

J1J1

B3B3

C2C2

G1G1

F2F2

H4H4

F3F3

K3K3

N1N1

H1H1

H2H2

H3H3

H1H1

H2H2

H3H3

H1H1

H2H2

H3H3

C-3C-3

PayloadPayload

J1J1

B3B3

C2C2

G1G1

F2F2

H4H4

F3F3

K3K3

N1N15

bytes

Higher Order Higher Order Path OHPath OH

AU PointerAU Pointer

TUG-3TUG-3 TUG-2/VC12TUG-2/VC12

MuxedMuxed

C-3C-3

PayloadPayload

J1J1

B3B3

C2C2

G1G1

F2F2

H4H4

F3F3

K3K3

N1N1

VV

CC

11

22

VxVx

ptrptr

Low Order Low Order Path OHPath OH

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Points to Remember in SDH

• The base layer is the VC-4 ContainerSingle pointer to get to the VC-4

ALL Low Order (LO) Signals multiplex (via PP) to the VC-4

Additional pointer to get to VC-3, the STS-1 equivalent: A FUNDAMENTAL DIFFERENCE between SONET and SDH

TUG-3 is NOT the same as an STS-1

TOH is called Regenerator Section (RS) and Multiplex Section (MS) Overhead

SS bits (in H1) is set to 01

ITU-T Alarming and ITU-T Performance Monitoring

Other Nuances:

Path Trace (P-API) is 16 or 64 bytes, Orderwire is A-Law, Z (N1) bytes used for TCM, APS is different

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SONET Vs. SDH

• SONET UPSR = SDH SNCP (Sub-Network Connection Protection)

WTR is up to 12 minutes in 1 minute increments

“Hold-off” timer for SDH – 0-10S in 100mS increments

• SONET BLSR = SDH MS-SPRing (Multiplex Section – Shared Protection Ring), SDH does not specify MS-SPRing @ STM-4 (but we allow it)

• SONET APS = SDH MSP (Multiplex Section Protection)

• SONET Mesh/ Virtual Ring = SDH Same as/Extension of SNCP (and this has been around a while in SDH Networks)

• SONET Path Trace = SDH Path Access Point Identifier (P-API, or API)

• SONET Alarms: CR, MJ, MN = SDH Alarms PMA (Prompt Maintenance Activity), DMA (Deferred Maintenance Activity): We kept the CR/MJ/MN and added the “-PMA/DMA as a suffix

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SONET Vs. SDH (cont…)

• SDH Collects Errored Block Seconds, Errored Second “Ratios”

• SDH is beginning to use Tandem Connection Monitoring – “Path within a path”

Adds additional Path Trace, BIP, FEBE and RDI to a high or low-order path

• SONET, STS-SPE (50.112M) is the base-rate payload – SDH, the base is 155M and the VC-3 (STS equivalent) is a “tributary” to the VC-4

• It’s not a central office, it’s an “Exchange”

• It’s not a Class 5/ Class 4, it’s a Local Switch and a Transit Switch

• It’s not a DCS, it’s a DXC

SONET uses 3/3s and 3/1s, SDH uses 4/4s and 4/3/1s

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Terminology Summary

SDH SONET

STM-1 OC-3

STM-4 OC-12

STM-16 OC-48

STM-64 OC-192

STM-256 OC-768

Optical I/O Board

SDH SONET

Not applicable STS-1

VC4 STS-3c

VC4-4c STS-12c

VC4-8c STS-24c

VC4-16c STS-48c

VC4-64c STS-192c

Path Type

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Terminology Summary

SDH SONET

MSP APS/FFP

MS-SPRing BLSR

SNCP PPMN/UPSR

Protection Type Overhead Naming

SDH SONET

RS - Regenerator Section

Section

MS - Multiplex Section

Line

HP - High Order Path

Path

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Terminology Summary

SDH SONET

AU-LOP LOP-P

AU-AIS AIS-P

HP-UNEQ UNEQ-P

HP-TIM TIM-P

HP-SLM SLM-P

HP-RDI RDI-P/RFI-P

HP-DEG SD-P

HP-EXC SF-P

HP-REI REI-P

Alarms

SDH SONET

LOS LOS

LOF LOF

RS-TIM TIM-S

MS-AIS AIS-L

MS-RDI RDI-L/RFI-L

MS-DEG SD-L

MS-EXC SF-L

MS-REI REI-L

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Terminology Summary

PM Monitored Types

SDH SONETNot defined CV – Code Violation

EB – Errored Block Not defined

BBE – Background Block Error Not defined

ES – Errored second ES – Errored second

Not defined SEFS - Severely Errored Framing Seconds

SES - Severely Errored Second SES - Severely Errored Second

Not defined FC- Failure Count

UAS - Unavailable Second UAS - Unavailable Second

BBER - Background Block Errored Ratio Not defined

ESR – Errored second Ratio Not defined

SESR - Severely Errored Second Ratio Not defined

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Terminology Summary

SDH SONETNot defined CV-S

RS-EB Not defined

RS-BBE Not defined

RS-ES ES-S

Not defined CV-LNE

Not defined CV-LFE

MS-EB-NE Not defined

MS-EB-FE Not defined

MS-BBE-NE Not defined

MS-BBE-FE Not defined

MS-ES-NE ES-LNE

MS-ES-FE ES-LFE

PM Monitored EntitiesSDH SONET

Not defined FC-LNE

Not defined FC-LFE

MS-UAS-NE UAS-LNE

MS-UAS-FE UAS-LFE

Not defined CV-PNE

Not defined CV-PFE

HP-EB-NE Not defined

HP-EB-FE Not defined

HP-BBE-NE Not defined

HP-BBE-FE Not defined

HP-ES-NE ES-PNE

HP-ES-FE ES-PFE

HP-SES-NE SES-PNE

HP-SES-FE SES-PFE

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Terminology Summary

PM Monitored Entities (Cont.)

SDH SONETNot defined FC-PNE

Not defined FC-PFE

HP-UAS-NE UAS-PNE

HP-UAS-FE UAS-PFE

HP-BBER-NE Not defined

HP-BBER-FE Not defined

HP-ESR-NE Not defined

HP-ESR-FE Not defined

HP-SESR-NE Not defined

HP-SESR-FE Not defined

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