SDH
SDH / SONET
1. Introduction to SDH/ SONET
• Applications / advantages/ disadvantages
2. Physical Configuration
3. SONET/ SDH Layers
4. Transmission Formats and Speed
5. Optical Interfaces Specifications
6. SONET/ SDH Rings
7. SONET/SDH Networks
Introduction to SDH / SONET
ITU-T standards is called the Synchronous Digital Hierarchy (SDH)
ANSI standards is called the Synchronous Optical Network (SONET)
Three Important concerns in designing SONET/ SDH*
1. It is a Synchronous network.
• A single clock is used to handle the timing of transmission and equipment across the entire network.
• Network wise synchronization adds a level of predictability to the system.
• This predictability , coupled with powerful frame design, enables individual channels to be multiplexed, thereby improving speed and reducing cost.
2. Standardization.
• SDH/SONET contains recommendations for the standardization of fiber optic transmission system equipment sold by different manufacturers.
3. Universal Connectivity.
•SDH/SONET physical specification and frame design include mechanism that allow it to carry signals from incompatible tributary systems. This flexibility gives SONET/ SDH a reputation for universal connectivity.
Applications:
1. Carrier for ISDN and B-ISDN.
2. Carrier for ATM cells.
3. Can support bandwidth on demand.
4. Can be used as the backbone or totally replace other networking protocols such as SMDS or FDDI.
5. Can replace PDH system,E1, E3 lines.
Introduction to SDH / SONET
Advantages of SDH
Flexible
Cost effective
Manageable
Standardized
International
New generation of multiplexers with directaccess to every single low-speed tributary(e.g. 2 Mbit/s/1.5 Mbit/s), sophisticated signal protection mechanisms
New generation of multiplexers with directaccess to every single low-speed tributary(e.g. 2 Mbit/s/1.5 Mbit/s), sophisticated signal protection mechanisms
Integration of multiplex, cross-connect andline terminal functions as part of a software-controlled network element
Integration of multiplex, cross-connect andline terminal functions as part of a software-controlled network element
Adequate and standardized signal overhead capacity for remote operation, administration and maintenance (OAM)
Adequate and standardized signal overhead capacity for remote operation, administration and maintenance (OAM)
Standardized line signal as a uniform interface for all manufacturers (multi-vendor policy)
Standardized line signal as a uniform interface for all manufacturers (multi-vendor policy)
Uniform multiplexing principle for both existing hierarchies (USA and Europe)Uniform multiplexing principle for both existing hierarchies (USA and Europe)
Introduction to SDH / SONET
Disdvantages of SDH
Abundant Overheads bits
low bandwidth utilization ratio, contradiction between efficiency and reliability
Mechanism of pointer adjustment is complex, it can cause pointer adjustment jitters
Software based Large-scale application of software makes SDH system vulnerable to viruses or mistakes.
Pointer adjustment
Physical Configuration*
MUX MUX
Add/drop
multiplexer
Regenerator Regenerator
Section Section Section Section
Line Line
Path
Multiplexer/ Demultiplexer: Multiplexer marks the beginning and end
points of a SDH link. They provide interface between a tributary network and SDH
and either multiplex signals from multiple sources into an STM signal or demultiplex
as STM signal into different destination Signals.
Regenerator: Regenerator extend the length of the links, it takes optical
signal and regenerates. SDH regenerator replaces some of the existing overhead
information with new information. These devices function at the data link layer.
Add/ drop multiplexer: It can add signals coming from different sources
into a given path or remove a desired signal from a path and redirect it without
demultiplexing the entire signal. Instead of relying on timing and bit position
add/drop multiplexer use header information such as addresses and pointers to
identify the individual steams.
Section: It is the optical link connecting two neighbor devices:
•Multiplexer to Multiplexer
•Multiplexer to Regenerator
•Regenerator to Regenerator
Line: It is the portion of the network between two multiplexers:
•STM Multiplexer to add/drop multiplexer
•Two add/drop multiplexers
•Two STM multiplexers
Paths: It is the end to end portion of the network between two STM multiplexers.
In a simple SDH of two multiplexers linked directly to each other, the section, line, and path are the same.
SONET/SDH Layers
Path layer
Section layer
Line layer
Photonic layer
Data link
Physical
SONET/SDH Layers
Photonic Layer: Corresponds to the physical layer of the OSI model. It includes physical specifications for the optical fiber channel, the sensitivity of the receiver, multiplexing functions, and so on. It uses NRZ encoding.
Section Layer: It is responsible for the movement of a signal across a physical section. It handles framing, scrambling and error control. Section layer overhead is added to the frame at this layer.
Line Layer: It is responsible for the movement of a signal across a physical line. Line overhead (Pointers, protection bytes, parity bytes etc) is added to the frame at this layers. STM multiplexer and add/drop multiplexers provide line layer functions.
Path Layer: It is responsible for the movement of a signal from its optical source to its optical destination. At the optical source, the signal is changed from an electronic form into an optical form, multiplexed with other signals, and encapsulated in a frame. Path layer overhead is added at this layer. STM multiplexer provide path layer functions.
Device Layer Relationship
MUX MUX
Add/drop
multiplexer
Regenerator Regenerator
Path
Section
Line
Photonic
Path
Section
Line
Photonic
Section
Line
Photonic
Section
Photonic
Section
Photonic
Commonly Used SONET and SDH Transmission Rates
Transmission Formats and speeds
QUIZ:
No of E1s in STM-1,STM-4,STM-16 and STM-64 ?
Line rate calculation
9
270
Total Frame Capacity: 270 X 9 = 2430 BytesTotal Number of Bits = 2430 X 8 = 19440 BitsTime Period of One Frame = 125 microsecondsBits/Second = 19440/125 X 10 -6 = 155.52 Mbits/Sec = STM-1
4X STM-1 = STM-44XSTM-4 = STM-16
Transmission Formats and speeds
SDH components
SDH Frame is made of the following
– SDH payload
– Pointer
– Path Over head
– Section Overhead» Multiplex section overhead» Regenerator section overhead
Overhead is fixed and is like a
Header. It contains all
information including
Monitoring,O&M functions etc.
Transmission Formats and seeds
SDH Frame
SDH2 34 140
STM-1, STM-4, STM-16, STM-64, STM-256
270 x N Columns
PO
H
MSOH
Pointer Payload
RSOH
9 Rows
Actual Traffic
261 Bytes1 Byte
Transmission Formats and speeds
SONET/ SDH Rings
•SONET and SDH are configured as either ring or mesh architecture.
•So Loop diversity is achieved in case of link or equipment failure.
•SONET/SDH rings are commonly called self-healing rings. Means automatic switching to standby link on failure or degradation of the link.
Three main features of SONET/SDH rings:
1. There can be either two or four fibers running between the nodes on a ring.
2. Operating signal signals can travel either clockwise only (unidirectional ring) or in both directions around the ring (which is called bidirectional ring).
3. Protection switching can be performed either via line-switching or a path switching scheme.
• Line switching moves all signal channels of an entire STM-N channel to a protection fiber.
• Path switching can move individual payload channels within a STM-N channel to another path.
SONET/ SDH Rings
Following two architectures have become popular for SONET and SDH Networks:
1. Two fibers, unidirectional, path-switched ring (two-fiber UPSR)
2. Two fiber or four fiber, bidirectional, line switched ring( two fiber or four fiber BLSR)\
(They are also referred to as unidirectional or
bidirectional self healing ring , USHRs or BSHRs)
SONET/ SDH Rings
Generic two fiber unidirectional path-switched ring (UPSR) with counter rotating protection path.
Flow of primary and protection traffic from node 1 to node 3
Architecture of a four-fiber bidirectional line-switched ring (BLSR).
SONET/ SDH Rings
Reconfiguration of a four-fiber BLSR under transceiver or line failure.
SONET/ SDH Rings
SONET /SDH Networks
SONET/SDH equipment allows the configuration of a variety of network architectures, as shown in next slide. For example
•Point-to-point links•Linear chains•UPSRs•BLSRs•Interconnected rings
Each of the individual rings has its own failure recovery mechanisms and SONET/SDH network management procedures.
An important SONET/SDH network element is the add/drop multiplexer(ADM). This piece of equipment is a fully synchronous, byte-oriented multiplexer that is used to add and drop subchannels within an OC-N signal.
The SONET/SDH architectures also can be implemented with multiple wavelengths. For example, Fig in next slide, will show a dense WDM deployment on an OC-192 trunk ring for n wavelengths
SONET /SDH Networks
Generic configuration of a large SONET network consisting of linear chains and various types of interconnected rings.
Where
OC-3 = STM-1
OC-12 = STM-4
OC-48 = STM-16
OC-192= STM-64
Functional concept of an add/drop multiplexer for SONET/SDH applications.
SONET /SDH Networks
SONET /SDH Networks
Dense WDM deployment of n wavelengths in an OC-192/ STM-64 trunk ring.
Mapping
Is the procedure through which signals are packed inside an SDH frame
PDH signal passes through the following steps before emerging as an SDH Signal
Container (C-X) Virtual Container (VC-X) Tributary Unit (TU-X) Tributary Unit Group (TUG-X) Administrative Unit (AU-4) STM Signal
How 2 Mb signals are mappedinto an SDH stream?
C-12
VC-12
2 Mb/Sec
Container
Virtual Container
Path Overhead (POH)
How 2 Mb signals are mappedinto an SDH stream?
VC-12
STM-1/4/16
Payload
Pointer
SOHSOH
270
9
TU (Tributary Unit)
Starting address of Payload in VC.
Formation of Synchronous Signal
PointerPhase relation between virtual container (payload) and subordinate frame
Plesiochronous signal
Path overheadAdditional information forend-to-end monitoring
Tributary unit (TU)
Virtualcontainer (VC)
Container (C)
Synchronous Signal
VC11
ITU-T recommendation G.707 and its realization
× n
× 1× 3
× 7
× 1
C2
C11
× 3VC12
× 1
VC4
VC3
C3
VC2
VC3
C12TU12
TU2
TU3TUG3
TUG2
140 Mbit/s
34 Mbit/s(45 Mbit/s)
(6 Mbit/s)
2 Mbit/s
(1.5 Mbit/s)
AU4STM-N
AU3
TU11
C4AUG
Source: TR BM TP 5
AU/G Administrative unit/groupC ContainerSTM Synchronous transport moduleTU/G Tributary unit/groupVC Virtual container
Pointer processing
MultiplexingAligningMapping
Cross-connect level
SDH Overheads
• An overhead is like a delivery notice with the parcel which contains information about the contents, Condition, type, address, postal date, weight etc. of the parcel.
• In the SDH a distinction is made between Section Overhead (SOH) and Path Overhead (POH)
SOH
SOHPOH
STM-1
VC-4
SDH Multiplexing Structure
STM-1 AU-4
TU-3
AUG-1
TUG-3 VC-3 C-3
VC-4 C-4
TU-12 VC-12 C-12
TUG-2
×1 ×1
×3
×1
×7
×3
139264 kbit/s
34368 kbit/s
2048 kbit/s
Pointer processing
Multiplexing
Mapping
Aligning
AUG-4
AUG-16
AUG-64
STM-4
STM-16
STM-64
×1
×1
×1
×4
×4
×4
Intentionally Left Blank