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

2. 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

3. SONET/SDH Digital Hierarchy
Optical
Level
SONET
Electrical
SDH
Equivalent
Line Rate
(Mbps)
Payload
Rate
Overhead
Capacity
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
5.184
84 DS-1s or
3 DS-3s
63 E1s or
1 E4
OC-12
STS-12
STM-4
20.736
336 DS-1s or
12 DS-3s
252 E1s or
4 E4s
OC-48
STS-48
STM-16
82.944
1,344 DS-1s or
192 DS-3s
1,008 E1s or
16 E4s
OC-192
STS-192
STM-64
5,376 DS-1s or
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)

4. SDH and SONET Bit Rate SDH Bit Rate SONET OC-1 (STS-1) STM-0 51Mb/s
2.48Gb/s
OC-48
STM-64
9.95Gb/s
OC-192

5. 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.

6. 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.

7. SONET Defined by Bellcore and ANSI T1.X committees
Base rate (High Order) is 51.84Mbps (STS-1)
STS-1 Synchronous Payload Envelope (SPE) = M 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

8. SONET Hierarchy STS-N STS-N SPE Data STS-1 SPE DS3 VT Group VT6 SPEx7 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 6
VT6 SPE
VT2 SPE
VT1.5 SPE
STS-N
STS-1 SPE
STS-N SPE
DS3
Data

9. STS-1 Frame with VT Mapping
3 bytes
87 bytes
STS-1 SPE
Section OH 3 1 5 J1 B3 C2 G1 F2 H4 F3 K3 Z3
STS-1 SPE Payload DS3 Mapped or 7x VTG Mapped
STS Pointer
Line OH VT
Group
ptr VT
Group VT
Group VT
Group VT
Group VT
Group VT
Group Vx V T 1 5

10. 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

11. SDH Defined by ITU-T (previously CCITT) committees
Base rate (High Order) is (STM-1)
Virtual Container 4 (VC-4) = M 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 = M (Same as STS-1 SPE) used for E3 AND DS3

12. SDH Hierarchy High Order Payloads Containers of Base Signal
C-4-64c
STM-64
AU-4-64c
VC-4-64c
AUG
x16 x4
x64
Mb/s
STM-16
AU-4-16c
VC-4-16c
C-4-16c
Mb/s
STM-4
VC-4-4c
C-4-4c
AU-4-4c
Mb/s
STM-1
AU-4
VC-4
C-4
E4: Mb/s x3 x3
AU-3
TUG-3
TU-3
VC-3
High Order Payloads
Containers of Base Signal
(Low Order Payloads)
C-3
E3: Mb/s
DS3: Mb/s
VC-3 x7 x7 x1
TU-2
VC-2
C-2
STM-n
Synchronous Transport Module
Administrative Unit Group: One or more AU(s)
Administrative Unit: VC + pointers
Virtual Container: payload + path overhead
TUG-2
DS2:6.312 Mb/s x3
AUG
TU-12
VC-12
C-12
E1: 2.048Mb/s
AU-n x4
TU-11
VC-11
C-11
DS1:1.544Mb/s
VC-n

13. STM-1 Frame with AU-4 Mapping
9 bytes
261 bytes
Regenerator Section OH 3 1 5 J1 B3 C2 G1 F2 H4 F3 K3 N1
VC-4 Payload: C4 or TUG-3 mapped
AU Pointer
Multiplex Section OH H1 H2 H3 H1 H2 H3 H1 H2 H3 J1 B3 C2 G1 F2 H4 F3 K3 N1
C-3
Payload J1 B3 C2 G1 F2 H4 F3 K3 N1
C-3
Payload
ptr
TUG-3
TUG-2/VC12
Muxed
Higher Order Path OH V C 1 2 Vx
5 bytes
Low Order Path OH

14. Points to Remember in SDH
The base layer is the VC-4 Container
Single 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

15. 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 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

16. 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

17. Terminology Summary SDH SONET SDH SONET Optical I/O Board Path Type
STM-1
OC-3
STM-4
OC-12
STM-16
OC-48
STM-64
OC-192
STM-256
OC-768
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

18. RS - Regenerator Section
Terminology Summary
Protection Type
Overhead Naming
SDH
SONET
MSP
APS/FFP
MS-SPRing
BLSR
SNCP
PPMN/UPSR
SDH
SONET
RS - Regenerator Section
Section
MS - Multiplex Section
Line
HP - High Order Path
Path

19. Terminology Summary SDH SONET SDH SONET Alarms LOS 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
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

20. Terminology Summary SDH SONET PM Monitored Types Not defined
CV – Code Violation
EB – Errored Block
BBE – Background Block Error
ES – Errored second
SEFS - Severely Errored Framing Seconds
SES - Severely Errored Second
FC- Failure Count
UAS - Unavailable Second
BBER - Background Block Errored Ratio
ESR – Errored second Ratio
SESR - Severely Errored Second Ratio

21. Terminology Summary SDH SONET SDH SONET PM Monitored Entities
Not defined
FC-LNE
FC-LFE
MS-UAS-NE
UAS-LNE
MS-UAS-FE
UAS-LFE
CV-PNE
CV-PFE
HP-EB-NE
HP-EB-FE
HP-BBE-NE
HP-BBE-FE
HP-ES-NE
ES-PNE
HP-ES-FE
ES-PFE
HP-SES-NE
SES-PNE
HP-SES-FE
SES-PFE
SDH
SONET
Not defined
CV-S
RS-EB
RS-BBE
RS-ES
ES-S
CV-LNE
CV-LFE
MS-EB-NE
MS-EB-FE
MS-BBE-NE
MS-BBE-FE
MS-ES-NE
ES-LNE
MS-ES-FE
ES-LFE

22. Terminology Summary SDH SONET PM Monitored Entities (Cont.)
Not defined
FC-PNE
FC-PFE
HP-UAS-NE
UAS-PNE
HP-UAS-FE
UAS-PFE
HP-BBER-NE
HP-BBER-FE
HP-ESR-NE
HP-ESR-FE
HP-SESR-NE
HP-SESR-FE

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