SDH

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SDH
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SDH / SONET

• Introduction to SDH/ SONET
• Applications / advantages/ disadvantages
• Physical Configuration
• SONET/ SDH Layers
• Transmission Formats and Speed
• Optical Interfaces Specifications
• SONET/ SDH Rings
• SONET/SDH Networks

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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
• 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.
• Standardization.
• SDH/SONET contains recommendations for the
  standardization of fiber optic transmission
  system equipment sold by different manufacturers.

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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
• Carrier for ISDN and B-ISDN.
• Carrier for ATM cells.
• Can support bandwidth on demand.
• Can be used as the backbone or totally replace
  other networking protocols such as SMDS or FDDI.
• Can replace PDH system,E1, E3 lines.

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Advantages of SDH
Introduction to SDH / SONET
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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
Pointer adjustment
Large-scale application of software makes SDH
system vulnerable to viruses or mistakes.
Software based
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Physical Configuration
Add/drop multiplexer
Regenerator
Regenerator
MUX
MUX
Section
Section
Section
Section
Line
Line
Path
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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.
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• 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.
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SONET/SDH Layers
Path layer
Line layer
Section layer
Data link
Photonic layer
Physical
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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.
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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
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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
?
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Line rate calculation
Transmission Formats and speeds
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
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SDH components
Transmission Formats and seeds

• 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,OM
functions etc.
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SDH Frame
Transmission Formats and speeds
SDH
2
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140
270 x N Columns
1 Byte
261 Bytes
RSOH
Pointer
Payload
9 Rows
POH
MSOH
Actual Traffic
STM-1, STM-4, STM-16, STM-64, STM-256
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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
• There can be either two or four fibers running
  between the nodes on a ring.
• Operating signal signals can travel either
  clockwise only (unidirectional ring) or in both
  directions around the ring (which is called
  bidirectional ring).
• 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.

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SONET/ SDH Rings

• Following two architectures have become popular
  for SONET and SDH Networks
• Two fibers, unidirectional, path-switched ring
  (two-fiber UPSR)
• 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)

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SONET/ SDH Rings
Flow of primary and protection traffic from node
1 to node 3
Generic two fiber unidirectional path-switched
ring (UPSR) with counter rotating protection path.
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SONET/ SDH Rings
Architecture of a four-fiber bidirectional
line-switched ring (BLSR).
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SONET/ SDH Rings
Reconfiguration of a four-fiber BLSR under
transceiver or line failure.
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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
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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.
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SONET /SDH Networks
Functional concept of an add/drop multiplexer for
SONET/SDH applications.
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SONET /SDH Networks
Dense WDM deployment of n wavelengths in an
OC-192/ STM-64 trunk ring.
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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

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How 2 Mb signals are mappedinto an SDH stream?
Container
C-12
2 Mb/Sec
Path Overhead (POH)
Virtual Container
VC-12
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How 2 Mb signals are mappedinto an SDH stream?
VC-12
Starting address of Payload in VC.
Payload
Pointer
TU (Tributary Unit)
SOH
STM-1/4/16
SOH
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Formation of Synchronous Signal
Plesiochronous signal
Container (C)
Path overhead Additional information
forend-to-end monitoring
Virtual container (VC)
Pointer Phase relation between virtual container
(payload) and subordinate frame
Tributary unit (TU)
Synchronous Signal
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ITU-T recommendation G.707 and its realization
STM-N
n
1
VC4
AU4
C4
AUG
140 Mbit/s
1
3
TU3
TUG3
VC3
34 Mbit/s
C3
VC3
AU3
(45 Mbit/s)
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AU/G Administrative unit/group C Container STM
Synchronous transport module TU/G Tributary
unit/group VC Virtual container Pointer
processing Multiplexing Aligning Mapping C
ross-connect level
1
C2
VC2
TU2
TUG2
(6 Mbit/s)
3
C12
VC12
TU12
2 Mbit/s
VC11
C11
TU11
(1.5 Mbit/s)
Source TR BM TP 5
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Structure of a STM-1 frame
270 bytes
9
261
Payload
SOH
3
1 AU-4 pointer 3 TU-3 pointer
SOH
PTR
1
9 rows
VC-4
P
SOH
O
H
SOH
5
P
VC-3
e.g. 3 VC-3 in VC-4
O
H
Frame length 125 ?s
POH Path overhead PTR Pointer SOH Section overhead
SDH Basic information
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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
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SDH Multiplexing Structure
Mapping
1
AUG-64
STM-64
Aligning
4
Multiplexing
AUG-16
1
STM-16
Pointer processing
4
AUG-4
1
STM-4
4
1
1
AU-4
VC-4
C-4
AUG-1
STM-1
139264 kbit/s
3
TU-3
VC-3
C-3
1
TUG-3
34368 kbit/s
7
TUG-2
TU-12
VC-12
C-12
2048 kbit/s
3
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Intentionally Left Blank