PDH Plesiochronous Digital Hierarchy Plesiochronous – “Almost Synchronous” Multiplexing of 2Mbit/s signals into higher order multiplexed signals. Laying cable between switch sites is very expensive. Increasing traffic capacity of a cable by increasing bit rate. 4 lower order signals multiplexed into single higher order signal at each level.
PDH 140 565
140 34
34 8
8 2
140 565
140 34
34 8
2 8
PDH 140 565
140 34
34 2
140 565
140 34
34 2
PDH Limitations Synchronisation The data is transmitted at regular intervals. With timing derived from the transmitters oscillator.
TX
RX
1
1 0
1 0
1 0
1 0
1 0
1 0
1 0
0
The data is sampled at the same rate as it is being transmitted.
PDH Limitations Synchronisation These bits are missed at the receiver end.
The data is transmitted at regular intervals. With timing derived from the transmitters oscillator.
TX
RX
1
1 0
1 0
1 0
1 0
1 0
1 0
1 0
0
The data is sampled at a slower rate than the transmitter.
PDH Limitations Synchronisation The data is transmitted at regular intervals. With timing derived from the transmitters oscillator.
These bits are sampled twice at the receiver end.
TX
RX
1
1 0
1 0
1 0
1 0
1 0
1 0
1 0
0
The data is sampled at a faster rate than the transmitter.
Increased equipment requirements Increased space on site. Increased spares requirements.
PDH Limitations Lack Of Traffic Resilience
140 565
Traffic Lost
140 565
Traffic Lost
PDH Limitations Limited Network Management
! DCN
565 140
Traffic Lost
Alarm reported. No diagnosis tools available. Maintenance staff sent to site.
DCN
140 565
Traffic Lost
PDH Limitations No Mid-Fibre Meet
Vendor A
565 140
Vendor B 140 565
SDH
The Synchronous Digital Hierarchy
SDH – Global Networks x24
DS1
DS2
DS3
1.5Mb/s
x4
6Mb/s
x7
45Mb/s
North American bit rates 64Kb/s (PCM)
1st Order
2nd Order
3rd Order
4th Order
European bit rates x32
2Mb/s
x4
8Mb/s
x4
34Mb/s
x4
140Mb/s
E1
E2
E3
E4
X
Not supported in SDH.
x4
565Mb/s
X Non standard
SDH – Network Topologies Line Systems
Terminal
Terminal
SDH – Network Topologies Line Systems
Terminal
Regenerator
Terminal
SDH – Network Topologies Ring Systems
ADM
ADM
ADM
ADM
STM-1
Overheads Pointers Payload Overheads
STM-1 270 Bytes 9 Bytes
261 Bytes
Overheads Pointers 9 Bytes
Payload Overheads
STM-1 270 Bytes
1891
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2430
Overheads 1621
270
1351
2429
1081
269
Pointers 811
2428
6 5 4 3
541
Transmission time - 125 µseconds
268
12 11 10 9 8
2
271
Overheads 7
1
Payload 9 Bytes
261 Bytes 9 Bytes
STM-1 Overheads 9 Bytes
3 Bytes
Repeater Section Overheads
1 Byte
AU Pointers
5 Bytes
Multiplex Section Overheads
STM-1 Overheads
SDH
ADM
SDH
Regen
SDH
Regen
SDH
ADM
SDH
STM-1 Overheads
RS
SDH
ADM
SDH
RS
Regen
SDH
RS
Regen
SDH
ADM
SDH
STM-1 Overheads
MS
SDH
ADM
SDH
Regen
SDH
Regen
SDH
ADM
SDH
STM-1 Overheads
SDH
ADM
SDH
Regen
SDH POH
Regen
SDH
ADM
SDH
STM-1 Overheads
MS RS
SDH
ADM
SDH
RS
Regen
SDH POH
RS
Regen
SDH
ADM
SDH
STM-1 RS Overheads A1
A1
A1
A2
A2
B1
MD
MD
E1
D1
MD
MD
D2
A2
J0
X
X
MD
F1
X
X
MD
D3
AU Pointers
X – Reserved bytes MD – Media dependent
Multiplex Section Overheads
STM-1 RS Overheads A1
A1
A1
A2
A2
A2
J0
B1
E1
F1
D1
D2
D3
AU Pointers
The A1 & A2 bytes are used for frame alignment.
Multiplex Section Overheads
STM-1 RS Overheads A1
A1
A1
A2
A2
A2
J0
B1
E1
F1
D1
D2
D3
AU Pointers The J0 byte is used to carry the RS Path Trace. This is a repetitively transmitted string used to identify the transmitting node.
Multiplex Section Overheads
SDH Path Trace London
SDH
Paris
SDH
SDH
ADM
SDH ADM
“London”
“Paris”
SDH Path Trace London
SDH
Paris
SDH
SDH
ADM
SDH ADM
“London”
“Paris”
“Paris”
“London”
SDH Path Trace London
Paris
“Paris”
SDH
SDH
“London”
SDH
ADM
SDH ADM
“London”
“Paris”
“Paris”
“London”
SDH Path Trace London
Paris
X
“London”
“Amsterdam”
SDH
SDH
!
SDH
ADM
SDH ADM
“London”
“Paris”
“Paris”
“London”
STM-1 RS Overheads A1
A1
A1
A2
A2
A2
J0
B1
E1
F1
D1
D2
D3
AU Pointers
The B1 byte is used for parity error checking. It carries the parity of the complete previous frame.
Multiplex Section Overheads
STM-1 RS Overheads A1
A1
A1
A2
A2
A2
J0
B1
E1
F1
D1
D2
D3
AU Pointers The E1 byte provides a 64Kbit/s channel that can be used to carry voice for engineering order wire use. As this is in the RS overhead this channel can be accessed at any node.
Multiplex Section Overheads
SDH EOW
SDH
ADM
SDH
Regen
SDH
Regen
SDH
ADM
SDH
STM-1 RS Overheads A1
A1
A1
A2
A2
A2
J0
B1
E1
F1
D1
D2
D3
AU Pointers
The F1 byte is reserved for user purposes.
Multiplex Section Overheads
STM-1 RS Overheads A1
A1
A1
A2
A2
A2
J0
B1
E1
F1
D1
D2
D3
AU Pointers The D1, D2, & D3 bytes provides a 192Kbit/s channel that is used as a data communications channel between nodes for management purposes.
Multiplex Section Overheads
SDH Management Network Management Centre
DCN Network DCN Connection
DCN Connection
DCC Channels
SDH
ADM Gateway Node
SDH
DCC Channels
Regen
SDH
DCC Channels
Regen
SDH
ADM Gateway Node
SDH
STM-1 MS Overheads A1
A1
A1
A2
A2
A2
J0
X – Reserved bytes
B1
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
STM-1 MS Overheads The B2 byte allows for parity error checking within the MS overhead. Parity is computed from the previous frame with the exception of the RS overheads.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
STM-1 MS Overheads The K1 & K2 bytes are for used for automatic protection switching. The are used to control the switches that occur on the network.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
SDH Network Resilience ADM
Standby path
ADM
ADM
Active path
ADM
SDH Network Resilience ADM
Active path
ADM
ADM
Standby path
ADM
SDH Network Resilience Network Management Centre
ADM
Switch
Active path
ADM
ADM
Standby path
ADM
STM-1 MS Overheads The Dx bytes are for used for a DCC channel within the MS overhead. 576Kbit/s are available for communication within this channel.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
STM-1 MS Overheads The S1 byte is used for synchronisation messaging. It denotes the quality level of the synchronisation that can be derived from this incoming signal.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
SDH Network Synchronisation Primary reference
ADM
ADM
Secondary reference
ADM
ADM
SDH Network Synchronisation Primary reference
ADM
ADM
Secondary reference
ADM
ADM
SDH Network Synchronisation Primary reference
ADM
ADM
Secondary reference
ADM
ADM
!
SDH Network Synchronisation Primary reference
ADM
ADM
Secondary reference
!
ADM
ADM
STM-1 MS Overheads The Z1 and Z2 bytes currently have no allocated function.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
STM-1 MS Overheads The M1 byte is used as a remote error indicator.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
Remote Error Indication B2 error detected
Multiplex section
SDH
ADM
SDH
Regen
SDH
Regen
Multiplex section
SDH
ADM
SDH
Remote Error Indication B2 error detected
Multiplex section
SDH
ADM
SDH
Regen
SDH
Regen
SDH
ADM
SDH
Multiplex section MS-REI received
MS-REI generated
STM-1 MS Overheads The E2 byte provides an EOW channel within the MS overhead.
A1 B1
A1
A1
A2
A2
A2
J0
F1 RepeaterE1 Section Overheads
D1
D2
D3
AU Pointers B2
K1
K2
D4
D5
D6
D7
D8
D9
D10
D11
D12
S1
B2
Z1
B2
Z1
Z2
Z2
M1
E2
X
X
SDH Pointers
Repeater Section Overheads
AU Pointers
Multiplex Section Overheads
SDH Pointers Payload area Repeater Section Overheads AU Pointers
Multiplex Section Overheads
Actual Payload Repeater Section Overheads AU Pointers
Multiplex Section Overheads Payload area
SDH Pointers Payload area Repeater Section Overheads AU Pointers
Multiplex Section Overheads
Actual Payload Repeater Section Overheads AU Pointers
Multiplex Section Overheads Payload area
SDH Pointers Payload area Repeater Section Overheads AU Pointers
Multiplex Section Overheads
Actual Payload Repeater Section Overheads AU Pointers
Multiplex Section Overheads Payload area
SDH Pointers Payload area Repeater Section Overheads AU Pointers
Multiplex Section Overheads
Actual Payload Repeater Section Overheads AU Pointers
Multiplex Section Overheads Payload area
SDH Pointers H1
H1
H1
H2
H2
9 Bytes
H2
H3
H3
H3
SDH Pointers H1
H1
H1
1 0 0 1 S S 1 1
H2
H2
H2
H3
H3
H3
1 0 0 1 S S 1 1
SDH Pointers H1
H1
H1
1 1 1 1 1 1 1 1
H2
H2
H2
H3
H3
H3
1 1 1 1 1 1 1 1
SDH Pointers H1
H1
NDF NDF NDF NDF S
H1
S
H2
I
D
H2
I
H2
D
I
H3
D
Pointer value
H3
I
D
H3
I
D
SDH Pointers H1
H1
H1
H2
H2
H2
H3
Payload
H3
H3
Past STM-1 STM16 Frame 4320 Bytes 144 Bytes
4176 Bytes
Overheads Pointers Payload
9 Bytes
Overheads
Past STM-1 Signal
Medium
Bit rate
E1
Electrical
2Mit/s
E3
Electrical
34Mit/s
E4
Electrical
140Mit/s
STM-1
Electrical / Optical 155Mbit/s
STM-4
Optical
622Mbit/s
STM-16
Optical
2.5Gbit/s
STM-64
Optical
10Gbit/s
STM-256 (future)
Optical
40Gbit/s
SDH Hierarchy STM-N
xN
AUG
AU-4
C-4 140M
VC-4 x3
x3
AU-3
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7 x7
TUG-2
x1
x3
Mapping
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
Aligning Multiplexing
x4
SDH Hierarchy C-4 140M
The Container isx3 the basic element of SDH. PayloadAU-3 signals that are to be transported across the SDH layer are mapped into the appropriate container. 1.5M maps into a C-11 2M maps into a C-12 6M maps into a C-2 34M maps into a C-3 45M maps into a C-3 140M maps into a C-4
C-3 45M 34M C-2 6M
C-12 2M
C-11 1.5M
SDH Hierarchy C-4 140M
VC-4 VC-3 x3
AU-3
Overhead bytes collectively known as the Lower Order Path Overhead are added to the container to form a Virtual Container.
C-3 45M 34M
VC-3
VC-2
C-2 6M
VC-12
C-12 2M
VC-11
C-11 1.5M
SDH Hierarchy C-4 140M
VC-4 VC-3 x3
The VC-11/12/2 POHAU-3 is comprised of : V5 - Indication and error monitoring. J2 - Path indication N2 - Tandem connection monitoring K4 - Automatic protection switching
VC-4 TU-3 A Pointer is added x3 to the Virtual Container to create a AU-3 Tributary Unit. This pointer functions in the same way as the pointer within the section overheads but is applied at a lower level and should not be confused with the higher level pointer. This lower level pointer is known as the TU Pointer
VC-3 C-3 45M 34M
VC-3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
SDH Hierarchy C-4 140M
VC-4 TU-3 x3
AU-3
Four of the TU-11 Tributary Units can be multiplexed together to create A Tributary Unit Group-2 (TUG-2)
VC-3 C-3 45M 34M
VC-3
TUG-2
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy C-4 140M
VC-4 TU-3 x3
AU-3
Alternatively three of the TU-12s can be multiplexed together to form the TUG-2
VC-3 C-3 45M 34M
VC-3
TUG-2
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy C-4 140M
VC-4 TU-3 x3
AU-3
Or the last way to construct the TUG-2 is to use a single TU-2.
VC-3 C-3 45M 34M
VC-3
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy C-4 140M
VC-4 TUG-3 x3
AU-3
TU-3
VC-3 C-3 45M 34M
VC-3 x7
In a typical lower order SDH network carrying 2M traffic 7 TUG-2s will be multiplexed together to create a TUG-3.
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy C-4 140M
VC-4 TUG-3 x3
AU-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7
Alternatively if the network is carrying 34M or 45m traffic the TUG-3 can be created from a single TU-3
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy C-4 140M
VC-4 x3 x3
AU-3
3 TUG-3s can be multiplexed together to create a VC-4. When this is created another layer of path overhead is added. This is known as the High Order Path Overhead.
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy AU-4
C-4 140M
VC-4 x3
x3
AU-3
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7
A single VC-4 will have a pointer added to create an Administrative Unit, known as an AU-4
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy AUG
AU-4
C-4 140M
VC-4 x3
x3
AU-3
The Administrative Unit Group is created when multiplexing several Administrative Units. Using this route through the hierarchy only one AU-4 is needed to create the AUG, no processing is performed or overhead added.
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy STM-N
xN
AUG
AU-4
C-4 140M
VC-4 x3
x3
AU-3 To create the SDH signal several AUGs are multiplexed together with the section overheads added to create the STM-N signal. For example, one AUG would be used in an STM-1, whereas sixteen AUGs would be used to create an STM-16 signal
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7
TUG-2
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy STM-N
xN
AUG
AU-4
C-4 140M
VC-4 x3
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7
TUG-2 There is an alternative way to create the signal, although the one shown here is typically used. The alternative route is mainly used when interconnecting with SONET networks or for SDH radio applications where lower bit rate STM-0 / OC-1s are used as the building block instead of STM-1
x1
x3
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy STM-N
xN
AUG
AU-4
C-4 140M
VC-4 x3
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7 x7
TUG-2
x1
x3 Seven TUG-2s are multiplexed together to form a VC-3. This stage also adds a High Order Path Overhead.
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy STM-N
xN
AUG
AU-4
C-4 140M
VC-4 x3
AU-3
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7 x7
TUG-2
x1
x3 A pointer is added to the VC-3 to create an AU-3. This pointer is know as an AU Pointer.
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
SDH Hierarchy STM-N
xN
AUG
AU-4
C-4 140M
VC-4 x3
x3
AU-3
TUG-3
x1
TU-3
VC-3 C-3 45M 34M
VC-3 x7 x7
TUG-2
x1
x3 Three AU-3s can be multiplexed together to form an AUG if an STM-1 or higher is going to be created. The AUG then has the section overheads added.
TU-2
VC-2
C-2 6M
TU-12
VC-12
C-12 2M
TU-11
VC-11
C-11 1.5M
x4
DWDM Within The Network Site A
ADM
ADM
ADM
Site D
Site C
Site B
ADM
DWDM Within The Network Site A
ADM
Network 1
Site D
ADM
ADM
Network 2
ADM
Site F
ADM
Site E
ADM
ADM
Site C
Site B
ADM
DWDM Within The Network Site A
Site C
Site B
Site D
M M
D
D
A
M
A
A
M
M
Network 2
D
D
D
A
D
M
Network 1
A
A
M
D
A
D
M
A
Site E
Site F
Protocol Independent DWDM networks are protocol independent. They transport wavelengths of light and do not operate at the protocol layer.
SDH SONET Ethernet Digital Video ….
DWDM Amplifiers Red direction
λ1 λ2 λ3 λ4 λ1 λ2 λ3 λ4
DWDM Coupler
Blue direction
Blue Amplifier
Red Amplifier
Blue Amplifier
Red Amplifier
DWDM Coupler
λ5 λ6 λ7 λ8 λ5 λ6 λ7 λ8
DWDM Equalisation
This wavelength has not been equalised
DWDM Equalisation λ5 TX
RX
High Order
ADM
RX
TX
TX
RX
High Order
ADM Low Order
RX
TX
Fibre Management Frame
Fibre Management Frame
λ8
DWDM Coupler
Red Amplifier
Low Order
λ4 λ7 Electrical/Fibre Management Frame
λ6
λ3 Fibre Management Frame
λ1 Electrical/Fibre Management Frame
Variable Output Transmitter
λ2
Variable Optical Attenuator
Optical Dispersion
Chromatic Dispersion
Polarisation Mode Dispersion While a light pulse is not itself polarised, it consists of two perpendicularly polarised components.
Polarisation Mode Dispersion
An imperfectly shaped core can affect one of the components of the pulse
Impurities within the core can delay the arrival of one of the components.
Four Wave Mixing With two wavelength within the fibre, two additional wavelengths are generated.
