Post on 15-Nov-2014
description
SDH Transport Systems
SYNCHRONIZATION OF DIGITAL SIGNAL :SYNCHRONIZATION OF DIGITAL SIGNAL :
In a set of Synchronous signals, the digital transitions in the signals occur at exactly the same rate. There may be a phase difference between the transitions of the two signals, and this would lie on specified limits.
SDH is a transmission protocol or it is a set of rules for transmitting the data from source to destination via optical fiber.
SYNCHRONOUS SIGNAL:
Requirement Of Synchronous Digital Hierarchy ( SDH )Requirement Of Synchronous Digital Hierarchy ( SDH )
Need for extensive network management capability within the hierarchy.
Standard interfaces between equipment.
Need for inter-working between north American and European systems.
Facilities to add or drop tributaries directly from a high speed signal.
Standardization of equipment management process.
Node View - TJ100MC1
Line Diagram
E1 Tributary Card - TET16/TET21/TET28
E3/DS3 Tributary Card - TE31
TP01
TP01FT
STM-1 Tributary Card - A011
STM-1e/E4 Tributary Card - A1E4
Node view - TJ100MC4
Line Diagram
Tributary Card E1- TET16/TET21/TET28Tributary Card E3/DS3 - TE313 E3/DS3 Tributary Card - TE33Ethernet Tributary Card – ETCEthernet Tributary Card – ETCFTTP01TP01FTSTM1 card Œ A011 or A012STM-1e/E4 Tributary Card - A1E4STM-1e Tributary Card - A012ESTM-4 Tributary Card - A041,A041VLRTR01
TJ100 MC-1 & TJ100 MC-4 can be configured as Regenerator (REG),
Terminal Multiplexers (TMUX),Add-Drop Multiplexers (ADM) and
Digital Cross-Connect (DXC)
SDH Network ElementsSDH Network Elements
The Network Elements of SDH Network :
Regenerator (Reg.)
Terminal Multiplexer (TM)
Add/Drop Multiplexer (ADM)
Digital Cross Connect (DXC)
STM-NSTM-N STM-NSTM-NRegeneratorRegenerator
Regenerator (Reg.)
It mainly performs 3R function:
1R – Reamplification
2R – Retiming
3R – Reshaping
It regenerates the clock and amplifies the incoming distorted and attenuated signal. It derive the clock signal from the incoming data stream.
Regenerator
Terminal Terminal MultiplexerMultiplexer
STM-NSTM-NPDHPDHSDHSDH
Terminal Multiplexer (TM)
It combines the Plesionchronous and synchronous input signals into higher bit rate STM-N Signal.
Terminal Multiplexer
Tributaries Line Interface (aggregate)
1 2 3 4
5 6 7
123..
1
(Optional)
Add/Drop Multiplexer (ADM)
STM-NSTM-NSTM-NSTM-N
PDHPDH SDHSDH
Add / Drop Add / Drop MultiplexerMultiplexer
Add/Drop Multiplexer
Tributaries
Add / Drop illustration:1 is dropped; 17 is added
1
2 1
17...
Synchronous Transport Module5 60
1
21 25 34 3
3
5 60
17
21 25 34 3
Drop
Add
Extraction from & insertion into high speed SDH bit streams of Plesiochronous and lower bit rate synchronous signal.
ADM makes possibilities of
Ring structure of network which provides the advantage of automatic back-up path switching in the event of fault.
STM-16STM-4STM-1
140 Mbit/s34 Mbit/s2 Mbit/s
STM-16STM-4STM-1
140 Mbit/s34 Mbit/s2 Mbit/s
Cross - Connect
Digital Cross Connect (DXC)
Digital Cross Connect (DXC)
Digital Cross Connect:
A digital cross connect is an equipment which has the capability of interconnecting tributaries
An Agg to Agg connection, a trib to aggregate connection and a tributary to tributary connection is also possible in case of a Digital Cross Connect
Types – Wideband VT/DS1 level
Broadband STS-n/DS3 level &
Narrowband DS0 level
SDH NE: Digital cross connect (DXC)
Ports
Ports
Ports
Ports
25
1
21
PDHATMIP
SDHSDHmultiplexermultiplexer
SDHSDH RegeneratorRegenerator
##Cross-Cross-
connectconnect
SDHSDHmultiplexermultiplexerSDH SDH SDH
PDHATMIP
Regenerator Section
Regenerator Section
Multiplex Section Multiplex Section
Path
TYPICAL LAYOUT OF SDH LAYER
General view of Path Section designations
TopologiesTopologies
Network Configurations
Point to Point
Point to Multipoint
Mesh Architecture
Ring Architecture
SDH Network TopologiesSDH Network Topologies
Point-to-Point NetworkPoint-to-Point Network
Chain NetworkChain Network
TerminalMultiplexer
(TM)
TerminalMultiplexer
(TM)Regenerator
Trib
utar
ies
Trib
utar
ies
TerminalMultiplexer
(TM)
TerminalMultiplexer
(TM)
Add DropMultiplexer
(ADM) Trib
utar
ies
Trib
utar
ies
Ring Network
Add DropMultiplexer
(ADM)
Add DropMultiplexer
(ADM)
Add
Drop
Mul
tiple
xer
(ADM
)
Add DropMultiplexer
(ADM)
Add DropMultiplexer
(ADM)
Add DropM
ultiplexer(ADM
)
Trib
utar
ies
Trib
utar
ies
Tributaries Tributaries
TributariesTributaries
TributariesExchange
STM-4 RingSTM-4 Ring
2Mbit/s
140Mbit/sSTM-1
Add DropMultiplexer
(ADM)
Add
Drop
Mul
tiple
xer
(ADM
)
Add DropMultiplexer
(ADM)
Add DropMultiplexer
(ADM)
Add DropM
ultiplexer(ADM
)
Exch
ange
Exch
ange
Add DropMultiplexer
(ADM)
STM-1
140Mbit/s
2Mbit/s
2Mbit/s
ADM linear route ( Bus )
ADM Ring
X XX
X X
X X X
Mesh Network
Trib
utar
ies
Trib
utar
ies
TributariesTributaries
Add D
rop&
Cross connect
Mux
Add
Dro
p&
Cro
ss c
onne
ctM
ux
STM-N Links
Add/Drop& Cross Connect
Mux
Add Drop& Cross connect
Mux
Optical Signals Electrical Signals MS Rate
DS0 64 Kb/s
DS1 1.544 Mb/s
VT1.5 1.728 Mb/s
VT2 2.304 Mb/s
DS3 44.736 Mb/s
OC-1 STS-1 51.84 Mb/s
OC-3 STS-3 155.52 Mb/s
OC-3c STS-3c 155.52 Mb/s
OC-12 STS-12 622.08 Mb/s
OC-48 STS-48 2488.32 Mb/s
OC-192 STS-192 9953.28 Mb/s
Standard MS Rates :
O C - 1O C - 3O C - 9O C - 1 2O C - 1 8O C - 2 4O C - 3 6O C - 4 8O C - 9 6O C - 1 9 2
S T S - 1S T S - 3S T S - 9S T S - 1 2S T S - 1 8S T S - 2 4S T S - 3 6S T S - 4 8S T S - 9 6S T S - 1 9 2
5 1 .8 4 01 5 5 .5 2 04 6 6 .5 6 06 2 2 .0 8 09 3 3 .1 2 01 2 4 4 .1 6 01 8 6 .2 4 02 4 8 8 .3 2 04 9 7 6 .6 4 09 9 5 3 .2 8 0
5 0 .11 21 5 0 .3 3 64 5 1 .0 0 86 0 1 .3 4 49 0 2 .0 1 61 2 0 2 .6 8 81 8 0 4 .0 3 22 4 0 5 .3 7 64 8 1 0 .7 5 29 6 2 1 .5 0 2
1 .7 2 85 .1 8 41 5 .5 5 22 0 .7 3 63 1 .1 0 44 1 .4 7 26 2 .2 0 88 2 .9 4 41 6 5 .8 8 83 3 1 .7 7 6
-S T M - 1
S T M - 4
S T M - 1 6
S T M - 6 4
O p tica l L ev e l
E lec tric a l L ev e l L in e R a te
P a y lo adra te( M B p s )
O v e rh e a dR a te( M b p s )
S D HE q u iv a le n t
Frame Structure
Transport Module
STM-n
(n >1)
STM-n
(n >1)
PayloadOne Section overheadSTM-4
STM-1 = 155 Mbit/s
STM-4 = 622 Mbit/s
STM-16 = 2.5Gbit/s
STM-64 = 10Gbit/s
• The STM – n signal is multiples of frames consisting of 9 rows with 270 bytes in each row
• The order of transmission of information is first from left to right and then from top to bottom
• The first 9 bytes in each row are for information and used by the SDH system itself.This area is divided into 3 parts
Regenerator Section Overhead(RSOH) Multiplex Section Overhead(MSOH) Pointers
STM-1 frame structure
Sdh22.exe
Data Rate Overall 9 rows*270
columns*8000frames/sec*8bits/byte = 155.52Mbps
9 rows*261 columns*8000frames/sec*8bits/byte =150.336MbpsUser Data/ Payload 9 rows*260 columns*8000frames/sec*8bits/byte =149.76Mbps
STM-1 frame structure
Check your learning section1
PAY LOAD
RSOH
MSOH
AU Pointer
261 Columns
270 Columns
9 Columns
1-3 rows
5-9 rows
4th row
STM-1 frame structureSTM-1 frame structure
Check your learning section2
SDH Multiplexing Process
STM-N Frame
• Is got by Byte Interleaved Multiplexing of
Lower Order Frame.
• For Example
STM-4 is got by Multiplexing 4 STM-1 Frames.
S D H
M U X
T rib u ta ryS ig n a lsS T M -1
L in e S ig n a l
S T M -3
Byte Interleaved multiplexing
STM - 4
TU Format
Columns Bytes/Frame
Bandwidth Payload
TU 11 3 27 1.728Mbps DS1
TU 12 4 36 2.304Mbps E-1
TU 2 12 108 6.912Mbps DS-2
SDH Over Heads
STM-1 Section Overhead
Y Y 1* 1*
Y- 1001 SS11 (S unspecified)
1*- All 1’s
A1 & A2 – Framing Bytes
• These two bytes indicate the beginning of the STM-N frame
J0 – Regenerator Section Trace
• It’s used to transmit a Section Access Point Identifier so that a section receiver can verify its continued connection to the intended transmitter
• Identifies by a number in the individual STM – 1s of a higher order STM - n
Regenerator Section OverheadRegenerator Section Overhead
• This is a parity code (even parity), used to check for transmission errors over a regenerator section
• Its value is calculated over all bits of the previous STM-N frame after scrambling, then placed in the B1 byte of STM-1 before scrambling E1 – Engineering Order wire • This byte is allocated to be used as a local order wire channel for voice communication between regenerators
• This byte functionality is available at both multiplexers and Regenerators
B1- Bit Interleaved parity (BIP-8)
RSOH (contd..)RSOH (contd..)
F1 – User Channel
• This byte is set aside for the user’s purposes
D1 to D3 – Data Communication Channel
• These three bytes form a 192 kbps DCC for Operation & management of the SDH System
• Network management system sends / receives provisioning, security, status / control alarm and performance monitoring command / response by way of DCC
RSOH (contd..)RSOH (contd..)
Regenerator Section Overhead :
• Performance monitoring (STM-n signal)
• Local orderwire
• Data communication channels to carry information for OAM&P
• Framing
STM Regenerator Section Overhead
• This is used to determine if a transmission error has occurred over a multiplex section. It is even parity, and is calculated over all bits of the MS Overhead and the STM-N frame (except the regenerator section) of the previous STM-N frame before scrambling
• The value is placed in the three B2 bytes of the MS Overhead before scrambling. These bytes are provided for all STM-1 signals in an STM-N signal
B2 – Bit Interleaved parity (BIP – 24)
MS OverheadMS Overhead
D4 to D12 – Data Communication Channel• These nine bytes form a 576 kbps DCC for Operation & management of the multiplexers on a SDH line
• Network management system sends / receives provisioning, security, status / control alarm and performance monitoring command / response by way of DCC
K1 & K2 – Multiplex Section Protn.
• These two bytes are used for MSP signaling between multiplex level entities for bi-directional automatic protection switching and for communicating Alarm Indication Signal (AIS) and Remote Defect Indication (RDI) conditions
MSOH (contd..)MSOH (contd..)
Automatic Protection SwitchingAutomatic Protection Switching
•APS is the capability of a transmission system to detect a failure on a working facility and to switch to a standby facility to recover the traffic.
•Only the Multiplex Section in SDH is protected in this automatic fashion.
•MS protection mechanism is coordinated by K1 and K2 bytes.
•Path protection is managed at a higher level by network management functions
Protection Switching is initiated due to :
• Signal failure
• Signal degradation
• In response to commands from a local craft terminal or a remote network manager.
APS (contd..)APS (contd..)
E2 – Engineering Order wire
• This byte is allocated to be used as a local order wire channel for voice communication between multiplexers• This byte is not accessible at the regenerators
M1 - Remote Error indication• It is used to indicate the MS layer remote error indication (MS-REI)
MSOH (contd..)MSOH (contd..)
S1 Synchronization status message byte (SSMB)
• Bits 5 to 8 of this S1 byte are used to carry the synchronization messages
0000 Quality unknown (existing sync. network)
0010 G.811 PRC (Primary Reference Clock)
0100 G.812 transit SSU-A (Synchronisation Supply Unit - A)
1000 G.812 local SSU-B (Synchronisation Supply Unit – B)
1011 G.813 Option 1 SEC (Synchronous Equipment Timing Clock)
1111 Do not use for synchronization.
MSOH (contd..)MSOH (contd..)
H1 Y Y H2 1 1 H3 H3 H3
H1 & H2 = VC payload pointer
H3 = Negative Justification
1 = All 1’s
Y = 1001SS11 (S bits unspecified)
SDH PointersSDH Pointers Use of Pointers• It indicates the starting position of VC• It is also used for justification• AU pointer is also used for concatenation• SDH provides payload pointers to permit differences in the phase and frequency of the Virtual Containers (VC-n) with respect to the STM-N frame
• Lower-order pointers are also provided to permit phase differences between VC-12/VC-2 and the higher-order VC-3/VC-4
To accomplish this, a process known as byte stuffing is used
• The value of the pointer has a range of 0 to 782
For example, • If the VC-4 Payload Pointer has a value of 0, then the VC-4 begins in the byte adjacent to the H3 byte of the Overhead;
• If the Payload Pointer has a value of 87 (since each row of the payload has 86 positions), then the VC-4 begins in the byte adjacent to the K2 byte of the overhead in the byte of the next row
• The pointer value, which is a binary number, is carried in bits 7 through 16 of the H1-H2 pointer word.
Pointers (contd..)Pointers (contd..)
pointer justification.exe
Positive Pointer Justification• When the data rate of the VC is too slow in relation to the rate of the STM-1 frame, positive stuffing must occur. An additional byte is stuffed in, allowing the alignment of the container to slip back in time. This is known as positive stuffingNegative Pointer Justification• Conversely, when the data rate of the VC is too fast in relation to the rate of the STM-1 frame, that negative stuffing must occur. Because the alignment of the container advances in time, the payload capacity must be moved forward. Thus, actual data is written in the H3 byte, the negative stuff opportunity within the Overhead; this is known as negative stuffing
Pointers (contd..)Pointers (contd..)
H1 Y Y H2 1 1
H2 1 1H1 Y Y
H1 Y Y H2 1 1
H3 H3 H3
H3 H3 H3
H3 H3 H3
Points outStart of VC-4 VC-4 Boundary
Points outStart of VC-4
Points outStart of VC-4 VC-4 Boundary
VC-4 Boundary
To next RowTo next Row
Positive justification opportunity
AU – 4 Positive Pointer AU – 4 Positive Pointer JustificationJustification
Points outStart of VC-4
Points outStart of VC-4 VC-4 Boundary
VC-4 Boundary
From next row
From next row
Negative justification opportunity
H1 Y Y H2 1 1
H2 1 1H1 Y Y
H1 Y Y H2 1 1
H3 H3 H3
H3 H3 H3
Points outStart of VC-4 VC-4 Boundary
AU – 4 Negative Pointer AU – 4 Negative Pointer JustificationJustification
MS Alarm indication signal
Performance Monitoring of individual STM-1’s
Protection Switching InformationMS Remote Defect Indication (RDI)
Data channels for OAM&P
Pointer to commencement of synchronous payload envelope
Express order-wire
Multiplexer Section Overhead
Multiplexer Section Overhead
Path OverHeadPath OverHead
TCM – Tandem Connection Monitoring
J1- Path trace
• Starting point of VC• It is used to transmit repetitively a path access
point identifier, similar to J0
B3 – Path Bit Interleaved Parity – BIP- 8
• Error Monitoring over the previous VC-4 frame.• Even parity is used to monitor path errors
Path OverheadPath Overhead
C2 – Signal Label• It is defined to indicate the composition or the maintenance of the VC-4
POH (contd..)POH (contd..)
Binary Hex Mapping
0000 0000 00 Unequipped
0000 0001 01 Equipped,non specific
0000 0010 02 TUG structure
0000 0011 03 Locked TU
0000 0100 04 34 / 45 Mbps into C3 (async)
0001 0010 12 140 Mbps into C4 (async)
0001 0011 13 ATM
0001 0100 14 MAN (DQDB)
0001 0101 15 FDDI
G1- Path status
• It is defined to send back the path status and performance to where the path is generated
F2,F3 – Path User Channels
• It is assigned for user communication purposes between path elements by the network operator
H4 – Multi frame Indicator
• H4 byte provides the multiframe information
POH (contd..)POH (contd..)FEBE FERF UNUSED
K3 – Automatic protection switching(APS) channel
• (b1-b4) are assigned for APS signaling for protection at the VC-4/3 path labels
N1 – Network operator Byte
• The tandem connection monitoring function is currently not used
POH (contd..)POH (contd..)
VC12 path overhead
BIP-2 (Bits 1 and 2). The Bit Interleaved Parity (BIP) bits are used to provide an error monitoring function for the VC-12 path.
REI (Bit 3). The Remote Error Indication (REI) bit is used to communicate detected BIP-2 errors back to the VC-12 path originator.
RFI (Bit 4). Remote Fail Indicator (RFI). Not used in present applications.
Signal label (Bits 5 to 7). These bits are used to indicate the payload mapping and equipped status.
RDI (Bit 8). The Remote Defect Indicator (RDI) bit is used to indicate certain detected TU path alarms to the VC-12 path originator.
Performance Monitoring of STM SPE
Path Status
Path Trace
Signal Label (Unequipped or Equipped)
STM Path OverheadSTM Path Overhead
STM-4 Section OverHeadSTM-4 Section OverHead
MAPPING
Elements of SDHElements of SDH
• Container (C) • Virtual Container (VC)
• Tributary Unit (TU)
• Tributary Unit Group (TUG)
• Administrative Unit (AU)
• Administrative Unit Group (AUG)
• Synchronous Transport Module - N (STM – N)
• Input signals are placed into the containers
• It adds stuffing bytes for PDH signals,which compensates for the permitted frequency deviation between the SDH system and the PDH signal
• C12 (2 Mbps – G.703)• C11 (1.5 Mbps)• C2 (6 Mbps)• C3 (34 / 45 Mbps)• C4 (140 Mbps)
ContainerContainer
Virtual Container
=+POH PAYLOAD PAYLOADPOH
ANALOGY:
Packing C2 carton box with some more packing material and labeled as VC2 box
MAPPING : It is a process from Containers to Virtual containers.
• It adds overheads to a container or groups of tributary units, that provides facilities for supervision and maintenance of the end to end paths
• VCs carry information end to end between two path access points through the SDH system
• VCs are designed for transport and switching sub-SDH payloads• VC12 (C12 + POH)• VC11 (C11 + POH)• VC2 (C2 + POH)• VC3 (C3 + POH)• VC4 (C4 + POH)
Virtual ContainerVirtual Container
Virtual Container (contd..)• At each level, subdivisions of capacity can float individually between the payload areas of adjacent frames. Each subdivision can be readily located by its own pointer that is embedded in the overheads. • The pointer is used to find the floating part of the AU or TU, which is called a virtual container (VC).
• The AU pointer locates a higher-order VC, and the TU pointer locates a lower-order VC. For example, an AU–3 contains a VC–3 plus a pointer, and a TU–2 contains a VC–2 plus a pointer.
• A VC is the payload entity that travels across the network, being created and dismantled at or near the service termination point.
• It adds pointers to the VCs
• This pointer permits the SDH system to compensate for phase differences within the SDH network and also for the frequency deviations between the SDH networks
• TUs acts as a bridge between the lower order path layer and higher order path layer
• TU12 (VC12 + pointer)
• TU2 (VC2 + pointer)
• TU3 (VC3 + pointer)
Tributary UnitTributary Unit
• It defines a group of tributary units that are multiplexed together
• As a result, a TU group could contain one of the following combinations
• Three TU-12s (TUG – 2)
• Seven TUG-2s (TUG – 3)
Tributary Unit GroupTributary Unit Group
• It adds pointer to the HO Virtual containers(similar to the tributary unit) • AU - 3 (VC-3 + pointer)• AU - 4 (VC-4 + pointer)
Administrative Unit GroupAdministrative Unit Group• It defines a group of administrative units that are multiplexed together to form higher order STM signal
Administrative UnitAdministrative Unit
Synchronous Transport Module – nSynchronous Transport Module – n
• It adds section overhead (RSOH & MSOH) to a number of AUGs that adds facilities for supervision & maintenance of the multiplexer & regenerator sections
• This is the signal that is transmitted on the SDH line
• The digit “n” defines the order of the STM signal
SDH Generalised Multiplexing SDH Generalised Multiplexing StructureStructure
Mapping of 2Mbps into STM – N signalMapping of 2Mbps into STM – N signal
A corresponding arrangement is used for demultiplexing
2.048 Mbps(E1)
1 2 3 32
32 Bytes
1 2 3 32VC-1235 Bytes
POH (Lower Order)
1 2 3 32C-1234 Bytes
Stuffing Bytes
Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N
TU-12
36 Bytes
Pointer
9 Rows
4 Columns
TU 12 is arranged Into Matrix of 9 X 4
Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N
TUG-2 9 Rows
12 Columns
9 Rows
4 Columns 4 Columns 4 Columns
TU-12 TU-12 TU-12
Multiplexing
Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N
7 TUG-2s
Stuffing Bytes
86 Columns 84 Columns
TUG 3
X 7 TUG-2 TUG-3(multiplexing)
Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N
HOPOH
VC - 4
258 Columns
Stuffing Bytes
261 Columns
TUG - 3 TUG - 3 TUG - 3
86 Columns
X 3 TUG–3
Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N
261 Columns
AU – 4 (Adding Pointer)
PO
H
Pay LoadAU Pointer
9 Columns
4 th Row
Pay LoadPO
H
VC - 4
261 Columns
9 rows
Mapping of 2Mbps into STM – NMapping of 2Mbps into STM – N
SYNCHRONIZATION
Synchronization is the means of keeping all of the digital equipment in your network operating at the same rate.
In terms of synchronous networks (SDH/SONET), this means that all network elements must be oriented towards a single clock. In SDH and SONET, higher bit rates and synchronization are the major Advances compared to older transmission technologies. This is the only way to assure uniform standardization at all hierarchy levels and represents a major challenge for system manufacturers and network operators.
Synchronization
Primary Reference Clock ( PRC )
Stratum 1
DIGITAL EXCHANGEStratum 1
TRANSMISSION NETWORK
Digital ExchangeStratum 2
Digital ExchangeStratum 2
Digital ExchangeStratum 2
Transmission Network
Digital ExchangeStratum 3
Digital ExchangeStratum 3
Digital ExchangeStratum 3
Digital ExchangeStratum 3
Digital ExchangeStratum 3
SYNCHRONIZATION HIERARCHY
The network illustrates the digital network synchronization hierarchy,with all clocks normally operating at the same frequency as the reference source. A large network can comprise the interconnection of many such clusters of nodes, each operating plesiochronous.
Clock Hierarchies
CLOCK SUPPLY HIERARCHYCLOCK SUPPLY HIERARCHY STRUCTURESTRUCTURE
• S1 Clk : Cesium / Rubidium atomic clk.
Accurate upto 0.00001ppm.
Loses 1sec every 3000yrs.• S2 Clk : Accurate to 0.016ppm.
<255 slips in 1st 86 days after loosing S1 link.
1st slip can’t occur within first 7 days.• S3 Clk : Accurate upto 4.6ppm.
<255 slips in 1st 24hrs after loss of reference.
1st slip can’t occur <6mins after reference loss.• S4 Clk : No guarantee.
Stratum Accuracy Skip Rate Notes
1 10*10-112.523/Year PRC
2 1.6*10-811.06/Day Electronic Switch Sys
3 4.6*10-6 132.48/Hour DCS
4 3.2*10-5 15.36/Min PBX, CPE
All network elements are synchronised to a central clock
The central clock is generated by a high precision primary clock(prc)-G.811 (10x10-11 )
Clock is distributed throughout the network,this signal is passed on to the Sub-ordinate Synchronization units (ssu) and synchronous equipment clock (sec)
SYNCHRONIZATIONSYNCHRONIZATION
SelectorInternal Clock
Auotmatic Switch
Timing Signal Generator (TSG)
Primary Secondary
Internal Diagram of BITS
S1 Synchronization status message byte (SSMB)
• Synchronization Status Messaging is the transmission of synchronization quality messages between NEs.•Bits 5 to 8 of this S1 byte are used to carry the synchronization messages
0000 Quality unknown (existing sync. network)
0010 G.811 PRC (Primary Reference Clock)
0100 G.812 transit SSU-A (Synchronisation Supply Unit - A)
1000 G.812 local SSU-B (Synchronisation Supply Unit – B)
1011 G.813 Option 1 SEC (Synchronous Equipment Timing Clock)
1111 Do not use for synchronization.
QL settings for use with SSM
Example: Ring synchronization
Figs. A,B,C give a simple example of ring synchronization using four network elements and
a PRC clock source:
. Configuration of network elements for clock distribution
. Clock distribution behavior when a fault occurs
During normal operation, the complete ring is clocked by the PRC, which is directly connected to NE 1 (clock input T3). This NE cannot derive a clock from the data inputs and is not configured initially as a clock port. This prevents possible clock loops.
The other three network elements derive the clock from the incoming data signals. The best clock source is always used (here, PRC). The output signals have this clock quality, so PRC is indicated in the S1 byte. To avoid clock loops, ªDon't Use for Synchronizationº (DNU) is indicated in the S1 byte in the opposite direction.
At NE 4, PRCs are present at both data ports. In this case according to the clock derivation table determining the priority in case of identical clock priority, the clock from NE 3 is used.
What happens to the ring in case of a fault ?
In this case, NE 3 no longer receives a valid synchronization signal from NE 2, so it operates in holdover mode (Fig. B) since an alternative clock source is not yet available. This is also indicated in the S1 byte (SEC) towards NE 4.
NE 4 now receives a signal with PRC quality from NE 1 in the reverse direction. According to the clock derivation table, NE 4 takes the synchronization clock from the reverse direction (NE 1).
The same applies to NE 3, which uses the clock from NE 4 from the reverse direction (Fig. C).
Despite the disruption, all of network elements still use the PRC clock.
Errors & Alarms
PDHATMIP
SDHSDHmultiplexermultiplexer
SDHSDH RegeneratorRegenerator
##Cross-Cross-
connectconnect
SDHSDHmultiplexermultiplexerSDH SDH SDH
PDHATMIP
Regenerator Section
Regenerator Section
Multiplex Section Multiplex Section
Path
TYPICAL LAYOUT OF SDH LAYER
General view of Path Section designations
The advantage of the alarms monitoring are illustrated as follows :
Complete failure of a connection results, for example, in a LOS alarm (loss of signal) in the receiving network element.
This alarm triggers a complete chain of subsequent messages in the form of AIS.
The transmitting side is informed of the failure by the return of an RDI alarm (remote defect indication).
The alarm messages are transmitted in defined bytes in the TOH or POH.
Numerous alarm and error messages are built into SDH. They are known as defects and anomalies, respectively. They are coupled to network sections and the corresponding overhead information.
Types of Alarms
Equipment Alarms
Facility Alarms
What is difference between a Defect and a Failure?
A defect is a detection of an alarm such as loss of signals, loss of frames. AIS loss of excessive errors.
A failure is a defect that persists beyond a maximum time allocated. It is used to access to integrate Automatic Protection Switching ( APS ).
Equipment Alarms
• Card Failure• Card Mismatch• Card Missing• DCN Failure• Fan Failed• Disk 90% full• Derived Voltage high/low• I/p Voltage on PSU high/low• LAN port down• Memory usage exceeded• SW download failed• Temperature too high
Facility Alarms
• AIS E1/MS/P/STM• LOS• LOF• OOF• LOM• LFD• RDI MS/P• REI MS/P• RFI P• LOP MS/P• TIM RS/MS/P• PLM P
Cont..
• Signal Degrade• Signal Fail• Timing Reference Failed• Forced Switch Active• Forced Switch to channel• Manual Switch Active• Manual Switch to channel• Laser Bias Voltage high/low• Derived I/p voltage high/low
LOS
Signal Degrade
Signal Fail
Loss Of Signals ( LOS ) :Loss Of Signals ( LOS ) :
It could be due to cut cable, excessive attenuation of the signal or an equipment fault.
The LOS state will clear when 2 consecutive framing patterns are received and no LOS condition is detected.
OOF
LOF
TIM(J0)
DCC Fail
@ RSOH
Out of Frame (OOF ) :Out of Frame (OOF ) :
This situation occurs when 4, or in some This situation occurs when 4, or in some implementations, 5 consecutive SDH frames are implementations, 5 consecutive SDH frames are received with invalid framing patterns(A1 and A2 received with invalid framing patterns(A1 and A2 bytes) bytes)
The maximum time to detect OOF is therefore 625MsThe maximum time to detect OOF is therefore 625Ms
The OOF clears when consecutive SDH frames are The OOF clears when consecutive SDH frames are received with valid framing patterns received with valid framing patterns
Loss Of Frame ( LOF ) :Loss Of Frame ( LOF ) :
The LOF occurs when the OOF state exists for a specified time in msecs
If OOFs are intermittent,the timer is not reset to zero until an “in frame” state persists continuously for specified time in msecs
As the framing bytes are there in Regenerator section overhead(RSOH) this alarm is sometimes known as RS-LOF
@ MSOH
AIS/RDI(K1,K2)
DCC Fail
Timing Reference Signal Fail(S1)
REI(M1)
MS-AIS :
This alarm is sent by a Regenerator Section Terminating equipment(RSTE) to alert the downstream Multiplex section Terminating Equipment(MSTE) of detected LOS or LOF state
It is indicated by an STM-N signal containing valid RSOH and a scrambled all 1’s pattern in the rest of the frame
The MS-AIS is detected by the MSTE when bits 6 to 8 of the received k2 byte are set to “111” for 3 consecutive frames
Removal is detected by the MSTE when bits 6 to 8 of the received k2 byte are set with a pattern other than “111” in bits 6 to 8 of k2
AU-4 AIS :
This is sent by MSTE(Multiplex Section Terminating This is sent by MSTE(Multiplex Section Terminating Equipment) to alert the downstream higher order path Equipment) to alert the downstream higher order path terminating equipment (HOPTE) of a detected LOP state or terminating equipment (HOPTE) of a detected LOP state or a received AU path AIS a received AU path AIS
The AU-4 path AIS is indicated by transmitting an all 1’s The AU-4 path AIS is indicated by transmitting an all 1’s pattern in the entire AU-4(I.e an all 1‘s pattern in H1,H2 pattern in the entire AU-4(I.e an all 1‘s pattern in H1,H2 and H3 bytes pointer bytes plus all bytes of associated VC-and H3 bytes pointer bytes plus all bytes of associated VC-4) 4)
Removal of AU-4 path AIS is detected when three Removal of AU-4 path AIS is detected when three consecutive valid AU pointers are received with normal consecutive valid AU pointers are received with normal NDF’sNDF’s
TU-12 AIS :
This is sent downstream to alert the Lower Order Path This is sent downstream to alert the Lower Order Path Terminating Equipment(LOPTE) of a detected TU-12 LOP Terminating Equipment(LOPTE) of a detected TU-12 LOP state or a received TU-12 path AISstate or a received TU-12 path AIS
TU-12 path AIS is indicated by transmitting an all 1’s pattern TU-12 path AIS is indicated by transmitting an all 1’s pattern in the entire TU-12 (I.e all 1’s in pointer bytes v1,v2,v3and in the entire TU-12 (I.e all 1’s in pointer bytes v1,v2,v3and v4 plus all bytes of associated VC) v4 plus all bytes of associated VC)
The TU-12 AIS detected by the LOPTE when all 1’s pattern The TU-12 AIS detected by the LOPTE when all 1’s pattern is received in bytes v1 and v2 or three consecutive multi-is received in bytes v1 and v2 or three consecutive multi-frames.frames.
Removal of TU-12 is detected when three consecutive valid Removal of TU-12 is detected when three consecutive valid TU-12 pointers are received with normal NDF’sTU-12 pointers are received with normal NDF’s
If the received signal contains bit errors, the receiving network element detects and reports BIP errors. Since this is not the same as a complete failure of the connection, the alarm here is referred to as an anomaly that is indicated back in the direction of transmission. The return message is called a REI (Remote Error Indication).
REI & RDI:
If network is failed due to fault in network connection itself, breakup in path or fault in terminal equipment then RDI (Remote Defect Indication) alarm will appear.
@ HOPOH
TIM(J1)
PLM(C2)
REI,RDI,PLM,TIM,AIS,LOP(G1)
LOM(H4)
IEC,TC-REI/OEI/API/RDI/ODI(N1)
Loss Of Pointer (LOP )Loss Of Pointer (LOP )
The LOP state occurs when ‘n’ consecutive invalid pointers are received or ‘n’ New Data Flags(NDF) are received(other than in a concatenation indicator)
The LOP state is cleared when 3 equal valid pointers or 3 consecutive AIS indications are received.This alarm is very rare in steady state because the pointer is either valid or is all 1s
An AIS indication is all 1’s pattern in the pointer bytes.Concatenation is indicated when the pointer bytes are set to “1001XX1111111111” I.e NDF enabled(H1 and H2 bytes for AU LOP; v1 and v2 bytes for TU LOP)
Loss Of Multiframe (LOM )Loss Of Multiframe (LOM )
The LOM state occurs on SDH LOVCs & SONET VTs.
LOM is detected by checking the 7 & 8 bit of H4 Byte.
LOM is recovered when an error free H4 sequence is found in 4 consecutive VC – n frames.
@LOPOH
REI,RDI,RFI,PLM,AIS,LOP(V5)
AIS,TC-REI/OEI/API/RDI/ODI(N2)
TIM/PLM(J2)
RFI
Lossof
FrameMS-REI
Lossof
Signal
MS-AISLossof Signal
RFI Z
SDHREGEN
SDHREGEN
SDHREGEN
SDHMUX
SDHMUX
SDHMUX
SDHMUX
SDHMUX
SDHMUX
STM-1STM-1
STM-1 STM-1
STM-1STM-1
Cable Cut
Cable Cut
Excessive Errors
Some SDH alarms :
PROTECTION SCHEMES
Failure Events
According to ATIS Causes
1) Fiber cable dig-ups 2) Fiber cable non-dig-ups 3) Digital cross-connects 4) Synchronization timing 5) Internal power components
Protection Schemes
Linear Protection (1+1,1:1,1:N)
Ring protection:
Unidirectional (UPSR/SNCP, MSP) Bi-directional (2FMSSP,
4FMSSP)
In 1+1 protection, for each of the working unit(Which can be either unit or path)there will be a corresponding protection unit
Both the units will be carrying data all the time ,the receiving end will select the better of the two signals
In case of failure,there will be a switching from working to protection
Even if the fault in the working unit is rectified ,there will be no automatic switching from protection unit back to working unit
This is called Non-Revertive type(because there is no automatic reversion from working to protection even when the working unit is functioning properly)
1+1 Protection1+1 Protection
Protection Section
Working Section
Multiplex SectionSDH Multiplexer SDH Multiplexer
Protection Section
Working SectionSDH Multiplexer SDH Multiplexer
Fault
1+1 Protection1+1 Protection
1+1 Card Protection
1+1 Protected Linear Link
Even in 1:1 protection, for each of the working unit(Which can be either unit or path)there will be a corresponding protection unit
Only working unit will be carrying data all the time,in case of the failure in the protection unit there will be a switching to the protection unit
Once the fault in the working unit is rectified there will be a switching from protection unit back to the working unit
This is called Reversion type(because there is an automatic reversion from protection back to the working once the working unit is restored)
1:1 Protection(Dedicated Protection)1:1 Protection(Dedicated Protection)
1:N protection is very similar to 1:1 protection,except the fact that for N working units there will be one protection unit
This is also called revertive protection,because as soon as the fault in the working unit is rectified there will be an automatic reversion from working to protection
1: N Protection1: N Protection
1:N Card Protection
1:N Protected Linear Network
Path Protection
A
B C
D E
path protectionswitching
within 30 ms
VC-n
working path
protection path
VC-n
Unidirectional Operation
Bidirectional Operation
Unidirectional Path Switched Ring/SNCP
UPSR/SNCP
In Uni-directional rings,signal is being carried in only one direction that is either clockwise or anti-clockwise
Only in case of failure there will be a switching in the other direction also
In the above example let us assume that there is an interruption in the circuit between A and B.Direction y is unaffected by this fault , an alternative path must however,be found for direction X
The connection is therefore switched to the alternative path in the Network elements A and B
The other network elements(C and D) switch through the back up path
A simpler method is to use the so-called path switched ring
Traffic is transmitted simultaneously over both the working line and the protection line
If there is an interruption, the receiver (in this case A)switches to the protection line and immediately takes up the connection
UPSR/SNCP
Advantages of UPSR/SNCP
• Unidirectional protection switching is a simple scheme to implement and does not require a protocol.
• Unidirectional protection switching can be faster than bidirectional protection switching because it does not require a protocol.
• Under multiple failure conditions there is a greater chance of restoring traffic by protection
Unidir. MS Dedicated Protection Ring - normal State
Unidir. MS Dedicated Protection Ring - failed State
MSSP
• In this type bandwidth is segregated in to three ways
• Working Traffic
• Extra Traffic
• Non Pre-emptible unprotected Traffic (NUT)
2F Multiplexer Section Shared Protection
2 Fiber MSSP – Normal condition2 Fiber MSSP – Normal condition
A F
B
C D
E
ADM
TributaryTributary
One Fiber
2 Fiber MSSP - Fault2 Fiber MSSP - Fault
A F
B
C D
E
ADM
TributaryTributary
Node A
Node D
Node B Node C
Node ENode F
workingprotection
Fiber 1
Fiber 2
2F MSSP2F MSSP
Node A
Node D
Node B Node C
Node ENode F
MS ProtectionSwitching
within 50 ms
Fiber 1
Fiber 2
2F MSSP2F MSSP
In this network connection between network elements are bi-directional.the overall capacity of the network can be split up for several paths each with one bi-directional working line
While for unidirectional rings,an entire virtual ring is required for each path
If a fault occurs between neighboring elements A and B,network element B triggers protection switching and controls network element A by means of the k1 and k2 bytes in the SOH
2F MSSP (Multiplexer Section Shared Protection)2F MSSP (Multiplexer Section Shared Protection)
4F MSSP
4 Fiber MSSP - Normal4 Fiber MSSP - Normal
A F
B
C D
E
ADM
TributaryTributary
4 Fiber MSSP (Span Switch) - Fault4 Fiber MSSP (Span Switch) - Fault
A F
B
C D
ETributary
Tributary
Protection Fiber 3+4Working Fiber 1+2
4 Fiber MSSP (Ring Switch) - Fault4 Fiber MSSP (Ring Switch) - Fault
A F
B
C D
ETributary
Tributary
Protection Fiber 3+4Working Fiber 1+2
NODE A NODE B
NODE D NODE E NODE F
NODE C
NODE A NODE B
NODE D NODE E NODE F
NODE C
STS-n
STS-n
NODE A NODE B
NODE D NODE E NODE F
NODE C
NODE A NODE B
NODE D NODE E NODE F
NODE C
NODE A NODE B
NODE D NODE E NODE F
NODE C
NODE A NODE B
NODE D NODE E NODE F
NODE C
Even greater protection is provided by bi-directional rings with 4 fibers
Each pair of fibers transports working and protection channels
This results in 1:1 protection, i.e.100% redundancy This improved protection is coupled with relatively high
costs
4F MSSP4F MSSP
Advantages of MSSP
• With bidirectional protection switching operation, the same equipment is used for both directions of transmission after a failure.
• With bidirectional protection switching, if there is a fault in one path of the network, transmission of both paths between the affected nodes is switched to the alternative direction around the network. No traffic is then transmitted over the faulty section of the network and so it can be repaired without further protection switching.
• Bidirectional protection switching is easier to manage because both directions of transmission use the same equipments along the full length of the trail.
Protected Add/ Drop With MSP on 1 Pair of Tribs
COMBINATIONS PROTECTIONS
Dual trib to aggreagate with MSPon aggregates and MSP on 2 tribs
Protected Add/Drop with Card Protection on 1 Trib
Unprotcted Trib to Trib with Card Protection on 2 Tribs
Protected Trib to Trib with cp on 1 trib and MSP on 2 tribs
Node Element Ring
Types of Traffic Matrix
Advantage of SDH :
The SDH is based on global international standard.
Faster provision of services by remoter control.
In service performance monitoring of signals.
Possibility of control of circuit routing by customers.
Easier management of bandwidth.
Remote test access and maintenance from a central location.
Optical Transmission interfaces.
It will allow existing PDH hierarchies to be transported in the SDH.
Reduced amount of equipment in the network and hence savings on accommodation and power consumption.
Greater equipment reliability due to advanced electronic circuitry and 1+1 protection.
Improved protection facilities for transmission failures.
Advance network management features.
Single stage multiplexing into the higher bit rates.
Cross connect functionality can be distributed around the network.
Advantage of SDH (Contd.):
Software and configuration information can be downloaded to network elements.
Reliability of ring networks using path protection.
Implementation of new broadband services such as ATM is made easier.
There are cost saving and increased revenue to the network operation.
Equipment from different manufacturer can be connected together in the same network.
Advantage of SDH (Contd.):
COMPARISION OF SDH / PDH
PDH SDH
The reference clock is not synchronized throughout the network
The reference clock is synchronized throughout the network.
Multiplexing / Demultiplexing operations have to be performed from one level to the next level step by step.
The synchronous multiplexing results in simple access to SDH system has consistent frame structures throughout the hierarchy.
PDH system has different frame structures at different hierarchy levels.
SDH system has consistent frame structures throughout thehierarchy.
Physical cross-connections on the same level on DDF are forced if any
Digital cross- connections are provided at different signal levels and in different ways on NMS
PDH SDH
G.702 specifies maximum 45Mpbs & 140Mpbs & no higher order (faster) signal structure is not specified
G.707 specified the first level of SDH.That is, STM-1, Synchronous Transport Module 1st Order & higher. (STM-1,STM-4,STM-16,STM-64)
PDH system does not bear capacity to transport B-ISDN signals.
SDH network is designed to be a transport medium for B-ISDN, namely ATM structured signal.
Limited amount of extra capacity for user / management
It will transport service bandwidths Sufficient number of OHBs is available
Bit - by - bit stuff multiplexing Byte interleaved synchronous multiplexing.
Comparison (Contd.)