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Synchronous
Average frequency of all
clocks in the system is the
same.
No multiplexing stages are
needed, any lower order
signal can be added to a
higher order signal easily.
No bit stuffing.
Asynchronous.
Eachterminal on thenetwork running on its own
clock. Uses multiple stages for
multiplexing, lower order(e.g. E1-2Mbs) signals areneeded to bring up to arange of higher order(e.g.E3-34Mbs) signal formultiplexing.
Bit stuffing technique is
use.
Introduction to
Synchronization
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PDH
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Older Networks were developed for point to point
transmission.
Supported manual approach to network management
& maintenance.
In PDH signal structures, no place for network
management & maintenance functions(i.e.no spare
signal capacity for improvement in signal transmission.
PDH cont
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Development caused interconnection, difficult &
unreliable
(Result:Existing standards for point to point
communication became unsuitable)
PDH is stage by stage multiplexing based
on 64 Kb/s voice channels with different hierarchies in theworld & approved specs; covered up to 140 Mb/s (1920voice channels).
PDH cont
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Lower order signal could not be accessed directlywithout de-multiplexing & multiplexing again (addedcost)
No common standards available above 140 Mb/s(Result:Vendor Dependency)
Customer circuits, Speed & B.W. limited.
No proper response to new customer services (Lessefficient, not cost effective, B.W control notpossible)
PDH cont
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(HIERARCHIES)
PDH Hierarchies
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1. InterfacesElectrical interfaces---only regional standards,
no universal standard.
2. Three rate hierarchies for PDH:European(2Mb/s) .
Japanese (1.5 Mb/s)
North American(1.5Mb/s).
3. Optical interfaces---no standards at all,
manufacturers develop at their will.
Difficult to inter-connect
Disadvantage of PDH
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Multiplexing for PDH:
The location of low-rate signals in high-rate signals is not
regular nor predictable. So it is impossible to directly
add/drop low-rate signals from high-rate signals.
Where
did I putthe signals?
Disadvantage of PDH cont..
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140Mb/s34Mb/s 34Mb/s
8Mb/s 8Mb/s
2Mb/s
140Mb/s
de-multiplexerde-multiplexer
de-multiplexer multiplexer
multiplexer
multiplexer
Low-rate signals have to be separated from high-rate signals
level by level. Multiple levels of multiplexing/de-multiplexingcause signals to deteriorate, it is not suitable for huge-volume
transmission.
Disadvantage of PDH cont..
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OAM OAM function affects the maintenance cost.It is determined
by the number of overhead bytes(redundant bytes);
There are VERY few redundant byes available in PDH
signals which can be used as OAM purpose, so OAM in PDH
is very poor, it is unreliable either.
No universal network management interface.
It is hard to set up an integrated network management.
No way to form a universalTMN. PDH is inappropriate to transmit huge-volume signals, so
SDH came to play the part.
Disadvantage of PDH cont..
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It's based on overlaying a synchronousmultiplexed signal onto a light stream
transmitted over fiber-optic cable.
SDH is also defined for use on radio relay links,satellite links, and at electrical interfacesbetween equipment.
Introduction to Synchronous Digital
Hierarchy cont
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SDH
Asynchronous
E0 64 kbit/s One 64 kbit/sE1 2.048 Mbit/s 32 E0E2 8.448 Mbit/s 128 E0E3 34.368 Mbit/s 16 E1E4 139.264 Mbit/s 64 E1
Synchronous
STM-0 51 Mbit/s 21 E1STM-1 155 Mbit/s 63 E1 or 1 E4STM-4 622 Mbit/s 252 E1 or 4 E4STM-16 2.4 Gbit/s 1008 E1 or 16 E4STM-64 10 Gbit/s 4032 E1 or 64 E4
Transmission Hierarchies
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All these factors & deficiencies
led to the birth of
S.D.H
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Overheads
and Pointers
SDH
Overview
Frame
structure
and
multiplex-
ing
methods
Logical parts
of SDH
equipment
SDH Principle1
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The principle is divided into 4 parts:
1- SDH OverviewTo have the basic concept of SDH
What is SDH? What are the differences?
Advantages and disadvantages of SDH system.
2- Frame structure and multiplexing method of SDH signalsThe functions of each part in SDH signal frame structure
Multiplexing the commonly encountered PDH signals
(2Mb/s, 34Mb/s,140Mb/s) into SDH signals?
SDH Principle
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3- Overhead and Pointers
Layered monitoring mechanism of SDHOverheads
Directly add/drop lower-rate signals in SDHPointers
4- Logical composition of SDH equipment
Common network elements of SDH network
Logical function blocks of SDH equipment
SDH Principle Curriculum
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Where it can be
usedDisadvantages
of SDH
Background
of SDHAdvantages
of SDH
SDH Overview
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1. What is SDH.
2. What are the differences.
3. Where it can be used.
4. Advantages & Disadvantages of SDH
Background of SDH
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New Digital Hierarchy
155.52 Mb/s, 622.08 Mb/s, 2488.32 Mb/s etc.
Existing PDH and future ATM signals are
carried over the SDH system
Very basic functions are same as PDH.
Multiplex low bit rate digital signals to
higher bit rate and transmit large informationefficiently.
What is SDH ?
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SDH is a STANDARD for high speed
High capacity telecommunication networks
More specifically it is a SYNCHRONOUS DIGITAL
TRANSPORT SYSTEM designed for providing a more
simple, economic & Flexible telecommunication network
infrastructure.
What is SDH ? cont
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What are differences?Synchronous Network All network elements work on the same clock.
Abundant Overhead Bits
To carry large information for Network
Management
Unified Interface and Multiplexing specifications Common to Europe, North America and Japan
digital hierarchies.
Standard optical interfaces.
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What are differences? cont.. Simple multiplexing process
Easy access to tributary signals in a multiplexed
high bit rate signal.
ADD/DROP ----------------- distribution
RING ---------------------- survivability
CROSS CONNECT --------- capacity management
band width management protection route
diversity.
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In all traditional N/W application areas, providing
interconnection between three major
telecommunication networks.
Where S.D.H is used?
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Multi-vender Environment
International Connection
Realization of highly advanced Network Management System.
Fault management.
Configuration management. Performance management.
Security management.
Accounting management.
What are benefits ?
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Interfaces
Electrical interfaces:standard rate hierarchy
(transmission speed level).
Optical interfaces:only scramble the electrical
signals.
Advantages of SDH
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SDH Signals Bit rate(Mb/s)
STM-1 155.520 or 155M
STM-4 622.080 or 622M
STM-16 2488.320 or 2.5G
STM-64 9953.280 or 10G
The basic rate level is called Synchronous
Transfer Module(STM-1), the other rate
levels are the multiple of STM-1.
Advantages of SDH cont
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STM-1155Mb/s
STM-4622Mb/s
STM-162.5Gb/s
STM-6410Gb/s
10Gb/s
4 4
4
WDM
SDH:4STM-1=STM-44STM-4=STM-16
Advantages of SDH cont
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Multiplexing methods:
low-rate SDHhigh-rate SDH(e.g.:4 STM-1STM-4).
Uses byte interleaved multiplexing method.
STM-1
STM-1
STM-1
STM-1
STM-4
Byte
interleaved
multiplexing
Advantages of SDH cont
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Other signalsSDH:Using pointers to align the low-rate signals in SDH frame
,so the receivers can directly drop low-rate signals.E.g.:
P
D
H
Packing P
kg
Alignment
PKG
a
PKG
b
STM-1
Advantages of SDH cont
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OAM More bytes in SDH frame structure are used for
OAM purpose, about 5% of total bytes. SDH boasts
of high capability of OAM.
Compatibility SDH is compatible with the existing PDH system.
SDH allows new types of equipment to be used,
allows broadband access, such as ATM.
Advantages of SDH cont
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STM-N STM-N
PDH, ATM
FDDI signals
packing
packagePackage
packing transmit
SDH
network
unpacking
PDH, ATM
FDDI signalsSDH compatibility schematics
transmit transmit
Advantages of SDH cont
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1. Low bandwidth utilization ratio--- contradictionbetween efficiency and reliability.
2. Mechanism of pointer adjustment is complex, it can
cause pointer adjustment jitters
3. Large-scale application of software makes SDH system
vulnerable to viruses or mistakes.
140M
34M
2M
1140M=642M
334M=482M
632M
STM-1(155M)
Disadvantages of SDH
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Components
and functions
Multiplexing
Procedure
Frame Structure and Multiplexing
methods
140M
34M
2M
STM-N
2
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1. Components &Functions
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I must
understand the functions
of different parts
of SDH frame
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9270N bytes
SOH
SOH
AU-PTR
1
345
9
STM-Npayload
(including POH)
9N 261N
270N
columns
Transmission
direction Transmit
left to rightup to down
STM-N frame structure
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Block frame in units of bytes(8bit),
Transmission---from left to right, from top to bottom,
Frame frequency constant---8000 frames/s,
frame period 125us.
Characteristics of SDH signals
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1. Payload
It is where we put all the information in STM-N
frame structure. All kinds of effective info, such
as 2M, 34M ,140M are first packed before
being stored here. Then they are carried by STM-
N signals over the SDH network.
Composition of SDH signals
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If we should consider STM-N signal to be a truck, theninfo payload would be the carriage of the truck. In order to
monitor the transmission status of the goods during
transportation, POH are added to each information package.
Pkg
Pkg Pkg
PkgPkg
Payload
PkgLow-rate signals 1
Low-rate signalsn
loading
POH
POH
packing
packing
STM-N
loading
Composition of SDH signals cont
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2. Section Overhead Accomplishes monitoring of STM-N signal streams. To check
whether the goods in STM-N carriage is damaged or not.
Regenerator Section Overhead(RSOH): monitor the overall
STM-N signals.
Multiplex Section Overhead(MSOH): monitor each STM-1
in STM-N signal.
RSOH, MSOH and POH set up SDH layered monitoring
mechanism.
Composition of SDH signals cont
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. SDH
Section signal(SOH)
Low-rate signal 1
Low-rate signal 2
Low-rate signal n
low-rate path signal(POH)
Sections and Paths
Composition of SDH signals cont
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3. Administrative Unit Pointer(AU-PTR)
Indicates the location of low-rate signals in STM-N
frame(payload), makes the location of low-rate
signals in high-rate signals predictable.
Composition of SDH signals cont
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Sending:AU-PTR indicates the first
info package
Receiving:According to the value ofAU-PTR, get the first info
package, through the
regularity of byte interleaved
multiplexing, get the other
packages
(SDH transmission
network)
Composition of SDH signals cont
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2M
34MTU-PTR
Primary alignment
AU-PTRSecondary alignment
For low-rate signals such as 2M, 34M. We need two-levelsof pointers to align.
First, small information goods is packed into middle information
goods. Tributary unit pointer(TU-PTR) is used to align the
location of small goods in middle goods.
Then these middle goods are packed into big goods, AU-PTR is
to align the location of middle info package.
Composition of SDH signals cont
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low-rate SDHhigh-rate SDH:
byte interleaved multiplexing, 4 into 1.
PDH signalsSTM-N: synchronous multiplexing:140MSTM-N
34M STM-N
2MSTM-N
Multiplexing is based on the multiplexing route diagram.
ITU-T defines several different multiplexing routes, but for
any country or region, the method is unique.
2. Multiplexing Procedure of SDH
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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-4-64cC-4-64c
AUG
x16
x4
x4x64
x16
x4
9039.872Mb/s
Containers of Base Signal(Low Order Payloads)
High Order Payloads
Multiplexing Procedure of SDH cont...
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Regenerator
Section OH
Multiplex
Section OH
9 bytes
3
1
5
261 bytes
VC-4 Payload:
C4 or TUG-3 mapped
J1
B3
C2
G1
F2
H4
F3
K3
N1
H1
H2H3
H1
H2H3
H1
H2H3
C-3
Payload
J1
B3
C2
G1
F2
H4
F3
K3
N15 bytes
Higher Order
Path OH
AU Pointer
TUG-3
TUG-2/VC12
Muxed
C-3
Payload
J1
B3
C2
G1
F2
H4
F3
K3
N1
V
C
1
2
Vx
ptr
Low Order Path
OH
Multiplexing /Mapping of Signals cont...
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Section
Overhead
Overhead
Overhead and Pointers
Pointers
Path
OverheadAU-PTR TU-PTR
3
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Overhead
SOH
RSOH MSOH
POH
VC4
POH
VC12
POH
(HPOH)(LPOH)
OVERHEAD
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STM-N
RSOH
STM-1
MSOH
VC4
HO-POHVC12
LO-POH
Layered Monitoring
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A1 A1 A1 A2 A2 A2 J0
B1
D1
B2
D4
D7
D10S1
B2 B2 K1
D5
D8
D11M1 E2
D12
D9
D6
K2
F1
D3
E1
D2
AU-PTR
* *
*
RSOH
MSOH
Bytes reserved for domestic use
Marked bytes are not scrambled
1 2 3 4 5 6 7 8 9
1
2
3
45
6
7
89
* * * ****
SOH (Section Over Head)
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SDH Networking
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I want to masterthe common NEs
and the functions
of logical blocks
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TM: Terminal Multiplexer
ADM: Add/Drop Multiplexer
REG: Regenerator
DXC: Digital Cross Connect
Network Element
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Common NEs in SDH Network
TM ADM REG DXC
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TMSTM-N
2M 34M 140M STM-M Note: (M
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ADMSTM-N
2M 34M 140M
(Optical interface)
(Tributary Interface)
Application ofADM in chain network
TMTM ADM
STM-N ew
Multiplexing, cross-connection
(Optical interface)
STM-M Note: (M
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REGSTM-N
TMTM REG
STM-N ew
ADMADM
Regeneration, amplification and relaying
(Optical interface)(Optical interface)
Application ofREG in chain network
REG (Regenerator)
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DXC
Core function is cross-connection
Used at hub station
(Optical interface)(Optical interface)
DXC (Digital Cross Connect)
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Chain Network
Star Network
Ring Network
Basic Networks
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A B C D E
All the nodes are connected one after another
Both ends open
Not easy to provide protection
Chain Network
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A
A special node connected directly with
other nodes
No direct connection with other nodes
Easy and flexible to manage
E
DC
B
Star Network
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A
Connect the end nodes of chain network
Easy to provide protection
Widely used network
C
B
E
D
Ring Network
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Protection
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SDH need to be highly reliable.
Down-time should be minimal (less than 50 msec)
So systems must repair themselves (no time for manual intervention)
Upon detection of a failure (dLOS, dLOF, high BER)
the network must reroute traffic (protection switching)from working channel to protection channel
The Network Element that detects the failure (tail-end NE)initiates the protection switching
The head-end NE must change forwarding or to send duplicate traffic
Protection switching is unidirectionalProtection switching may be revertive (automatically revert to working channel)
head-end NE tail-end NE
working channel
protection channel
What is Protection?
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Head-end and tail-end NEs have bridges (muxes)
Head-end and tail-end NEs maintain bidirectional signaling channel
Signaling is contained in K1 and K2 bytes ofprotection channel
K1 tail-end status and requests
K2 head-end status
head-end bridge tail-end bridge
working channel
protection channel signaling channel
How Does it works ?
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Types of Protection? Linear 1+1 Protection (SNCP)
Linear 1+N Protection
Two Fiber or Four Fiber Protection
Unidirectional & Bidirectional Protection
UPSR & BLSR (MS-SPRing)
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Simplest form of protection
Can be at STM-n level (different physical fibers) or at STM/VC
level (called Sub Network Connection Protection)
working channel
protection channel
extra traffic
Linear 1+1 Protection
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In order to save BW
we allocate 1 protection channel for every N
working channels
working channels
protection channel
Linear 1+N Protection
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1 + 1 protection
1 : n protection
Bridge Switching
XWorking Line/PathProtection Line/Path
Working Line/Path
Protection Line/PathX
Line : STM-N line, Path : VCn path
1+1 & 1+ N Protection
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Unidirectional routing
working channel B-A same direction (e.g. clockwise) as A-Bmanagement simplicity: A-B and B-A can occupy same timeslotsInefficient: waste in ring BW and excessive delay in one direction
Bidirectional routingA-B and B-1 are opposite in direction
both using shortest routespatial reuse: timeslots can be reused in other sections
A
BA-B
B-A
A
B
B-A
A-B
C
B-C
C-B
Unidirectional & Bidirectional Protection
UPSR & BLSR (MS SPRi )
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Of all the possible combinations, only a few are in use
Unidirectional Path Switched Ringsprotects tributariesextension of 1+1 to ring topology
Bidirectional Line Switched Rings (two-fiber and four-fiber versions)
called Multiplex Section Shared Protection Ring in SDHsimultaneously protects all tributaries in STMextension of 1:1 to ring topology
Path switchingLine switching
Two-fiberFour-fiber
UnidirectionalBidirectional
UPSR
BLSR
UPSR & BLSR (MS-SPRing)
UPSR
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SDH/SONET Optical Ring
Working Ring(WR)
Fiber Cut
ProtectionRing(PR)
X 2:1 Switch1:2 Bridge
UPSR
BLSR (MS SP Ring)
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BLSR/2F: Bidirectional Line Switched Ring /N-Fiber
SDH/SONET Optical Ring
Working Channel
Fiber Cut
Protection Channel
Node 4
Node 3
Node 1T2,1
Node 2
T2,1 T1,4
XLooping
Looping
BLSR (MS-SP Ring)
UPSR & BLSR (MS SPRing) cont
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Working channel is in one direction
protection channel in the opposite direction
Two-fiber versionhalf of OC-N capacity devoted to protectiononly half capacity available for traffic
Four-fiber versionfull redundant OC-N devoted to protectiontwice as many NEs as compared to two-fiber
Example
recovery from unidirectional fiber cut
UPSR & BLSR (MS-SPRing) cont
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NGSDH(Next Generation SDH)
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SDH legacy technology is improving and adopting
data-friendly features.
Three technologies are central to Next-Generation
SDH.
Virtual Concatenation: VCAT
Link Capacity Adjustment Scheme: LCAS
Generic Framing Procedure: GFP
Next Generation SDH
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Purpose of GFP
New ITU-T standard, G.7041 describes a
Generic Framing Procedure (GFP) which may beused for efficiently mapping client signals into
and transporting them over SONET/SDH or
G.709 links.
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Generic Framing Procedure (GFP) Overview
GFP defines a mapping of client data signals into SDH
payloads in order to allow SDH to transport non-TDM traffic
more efficiently. GFP defines two types of client signals:
Frame-mapped GFP for PDU-oriented signals such as IP/ PPPor Ethernet MAC.
Transparent-mapped GFP for block-oriented signals such as
Fiber Channel.
Benefits of GFP
GFP provides major benefits. It gives one uniform mechanism
to transport any data type over SDH.
Purpose of GFP
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VCAT
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Payloads that dont fit into standard VT/VC sizes can be accommodated
by concatenating of several VTs / VCs
For example, 10 Mbps doesnt fit into any VT or VC
so w/o concatenation we need to put it into an STS-1 (48.384 Mbps)
the remaining 38.384 Mbps can not be used
We would like to be able to divide the 10 Mbps among7 VT1.5/VC-11 s = 7 * 1.600 = 11.20 Mbps or
5 VT2/VC-12 s = 5 * 2.176 = 10.88 Mbps
Concatenation
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Virtual Concatenation (VCAT G.707)
payload split over multiple STSs / STMs
fragments may follow different routes
requires support only at path terminations
requires buffering and differential delay alignment
Virtual Concatenation
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VCAT is an inverse multiplexing mechanism (round-robin)
VCAT members may travel along different routes in SONET/SDH network
Intermediate network elements dont need to know about VCAT
(unlike contiguous concatenation that is handled by all intermediate nodes)
H4
Virtual Concatenation
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Using VCAT increases efficiency to close to100% !
Rate Mb/s w/o VCAT efficiency with VCAT efficiency
10 STS-1 21% VT2-5v
VC-12-5v
92%
100 STS-3c
VC-4
67% STS-1-2v
VC-3-2v
100%
1000 STS-48c
VC-4-16c
42% STS-3c-7v
VC-4-7v
95%
Efficiency Comparison
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Link Capacity AdjustmentScheme
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LCAS is defined in G.7042
LCAS extends VCAT by allowing dynamic BW changes.
Benefits of LCAS
The use of LCAS provides an effective way for the Service Provider to change
the bandwidth
allocated. Provisioning quickly the right bandwidth at any time is a major
operations management goal of Service Providers.
LCAS
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THANKS
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Any Question?