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.
Introduction to SDH / SONET
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
New generation of multiplexers with direct
access to every single low-speed tributary
(e.g. 2 Mbit/s/1.5 Mbit/s), sophisticated signal protection mechanisms
Cost effective
Integration of multiplex, cross-connect andline terminal functions as part
of a software-controlled network element
Manageable
Adequate and standardized signal overhead capacity for remote operation,
administration and maintenance (OAM)
Standardized
Standardized line signal as a uniform interface for all manufacturers
(multi-vendor policy)
International
Uniform multiplexing principle for both existing hierarchies (USA and
Europe)
Disdvantages of SDH
Abundant
Overheads bits
low bandwidth utilization ratio,
contradiction between efficiency and
reliability
Pointer
adjustment
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.
Physical Configuration*
Add/drop
multiplexer
Regenerator
Regenerator
MUX
MUX
Section
Section
Line
Section
Section
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
Line layer
Data link
Section layer
Photonic layer
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
Path
Path
Line
Line
Line
Section
Section
Section
Section
Section
Photonic
Photonic
Photonic
Photonic
Photonic
Regenerator
Regenerator
MUX
MUX
Add/drop
multiplexer
Transmission Formats and speeds
Commonly Used SONET and SDH Transmission Rates
QUIZ:
No of E1s in STM-1,STM-4,STM-16 and STM-64 ?
Transmission Formats and speeds
Line rate calculation
9
270
Total Frame Capacity: 270 X 9 = 2430 Bytes
Total Number of Bits = 2430 X 8 = 19440 Bits
Time Period of One Frame = 125 microseconds
Bits/Second = 19440/125 X 10 -6 = 155.52 Mbits/Sec
= STM-1
4X STM-1 = STM-4
4XSTM-4 = STM-16
Transmission Formats and seeds
SDH components
 SDH Frame is made of the following
– SDH payload
– Pointer
– Path Over head
Overhead is fixed and is like a
Header. It contains all
– Section Overhead
» Multiplex section overhead
» Regenerator section overhead
information including
Monitoring,O&M functions etc.
Transmission Formats and speeds
SDH Frame
2
34
140
270 x N Columns
1 Byte
Pointer
POH
9 Rows
RSOH
MSOH
261 Bytes
Payload
Actual Traffic
STM-1, STM-4, STM-16, STM-64, STM-256
SDH
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 (twofiber 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
SONET/ SDH Rings
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 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
Where
OC-3 = STM-1
OC-12 = STM-4
OC-48 = STM-16
OC-192= STM-64
Generic configuration of a large SONET network consisting of linear
chains and various types of interconnected rings.
SONET /SDH Networks
Functional concept of an add/drop multiplexer for SONET/SDH applications.
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 mapped
into an SDH stream?
Container
2 Mb/Sec
C-12
Path Overhead (POH)
Virtual Container
VC-12
How 2 Mb signals are mapped
into an SDH stream?
Payload
Starting address of
Payload in VC.
VC-12
Pointer
TU
(Tributary Unit)
SOH
STM-1/4/16
9
270
SOH
Formation of Synchronous Signal
Plesiochronous signal
Container (C)
Path overhead
Additional information for
end-to-end monitoring
Virtual
container (VC)
Pointer
Phase relation between
virtual container (payload)
and subordinate frame
Tributary
unit (TU)
Synchronous Signal
ITU-T recommendation G.707 and its
realization
STM-N
×n
×1
AUG
AU4
VC4
×3
AU3
AU/G
C
STM
TU/G
VC
Administrative unit/group
Container
Synchronous transport module
Tributary unit/group
Virtual container
Pointer processing
Multiplexing
Aligning
Mapping
Cross-connect level
Source: TR BM TP 5
C4
140 Mbit/s
C3
34 Mbit/s
(45 Mbit/s)
×1
TUG3
TU3
VC3
VC3
×7
×1
TUG2
×3
TU2
VC2
C2
(6 Mbit/s)
TU12
VC12
C12
2 Mbit/s
TU11
VC11
C11
(1.5 Mbit/s)
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)
STM-1
SOH
SOH
POH
VC-4
SDH Multiplexing Structure
×1
AUG-64
×4
STM-64
STM-16
STM-4
×1
×1
×1
STM-1
Mapping
Aligning
Multiplexing
AUG-16
×4
Pointer processing
AUG-4
×4
×1
AU-4
AUG-1
VC-4
C-4
139264 kbit/s
×3
TUG-3
×1
TU-3
VC-3
C-3
34368 kbit/s
TU-12
VC-12
C-12
2048 kbit/s
×7
TUG-2
×3
Intentionally Left Blank