Transcript SDH Principle

Fiber Optic Communication
By
Engr. Muhammad Ashraf Bhutta
Lecture Outlines
 SDH
Overview
 Frame structure and multiplex-ing methods
 Overheads and Pointers
SDH Overview
Background
of SDH
Disadvantages Advantages Disadvanof SDH tages of SDH
of PDH
Background about SDH emergence
What is SDH--Synchronous Digital Hierarchy. Similar to
PDH，they are all digital signal transmission system.
Why did SDH emerge?
1)What we need in info-society:
huge volume of info, and digital, integrated, personal.
2)What we want the transmission network to be:
Broadband---info-highway
Standard---universal interface all over the world
Disadvantages of PDH:
1 Interfaces
Electrical interfaces---only regional
standards, no universal standard.
3 rate hierarchies for PDH:European(2Mb/s)
Japanese, North American(1.5Mb/s).
Optical interfaces---no standards at all,
manufacturers develop at their will.
Multiplexing methods:
Asynchronous 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 put
the signals?
140Mb/s
140Mb/s
34Mb/s
34Mb/s
8Mb/s
8Mb/s
multiplexer
de-multiplexer
de-multiplexer
multiplexer
de-multiplexer
multiplexer
2Mb/s
Low-rate signals have to be separated from high-rate
signals level by level. Multiple levels of multiplexing/demultiplexing cause signals to deteriorate, it is not suitable
for huge-volume transmission.
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.
4 No universal network management interface
It is hard to set up an integrated network
management. No way to form a universal TMN.
PDH is inappropriate to transmit huge-volume signals, so
SDH came to play the part.
Advantages of SDH:
1 Interfaces
Electrical interfaces:standard rate
hierarchy(transmission speed level)
The basic rate level is called Synchronous Transfer
Module(STM-1), the other rate levels are the
multiple of STM-1.
Optical interfaces:only scramble the electrical signals.
SDH: optical code pattern is scrambled NRZ,
PDH: optical code pattern is scrambled mBnB.
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
SDH:high-rate signal is exactly 4 times that
of the next low-rate signal.
S
T
M
6
4
¡
4
Á
1
0
G
b
/
s
S
T
M
1
S
T
M
4
S
T
M
1
6
¡
Á
4
¡
4
Á
1
5
5
M
b
/
s
6
2
2
M
b
/
s
2
.
5
G
b
/
s
W
D
M
1
0
G
b
/
s
SDH:4×STM-1=STM-4 ；4×STM-4=STM-16
2 Multiplexing methods:
low-rate SDH→high-rate SDH(e.g.:4  STM-1→STM-4).
Uses byte interleaved multiplexing method.
STM-1
STM-1
Byte
interleaved
multiplexing
STM-1
STM-1
STM-4
A
1
A
2
C
1
C
2
C
3
A
3
B
3
B
2
B
1
Byte interleaved
multiplexing
C
2
A
1
B
1
C
1
A
2
B
2
A
3
B
3
C
3
Other signals→SDH:
Using pointers to align the low-rate signals in SDH frame
,so the receivers can directly drop low-rate signals.E.g.:
P
P
Packing
D
k
H
g
STM-1
Alignment
PK
Ga
PK
Gb
3 OAM
More bytes in SDH frame structure are used for
OAM purpose, about 5% of total bytes. SDH boasts
of high capability of OAM.
4 Compatibility
SDH is compatible with the existing PDH system.
SDH allows new types of equipment to be used,
allows broadband access, such as ATM.
SDH compatibility schematics
PDH, ATM
FDDI signals
packing
package
packing
SDH
network
STM-N
transmit
STM-N
transmit
Package
transmit
unpacking
PDH, ATM
FDDI signals
Disadvantages of SDH
1 low bandwidth utilization ratio--- contradiction
between efficiency and reliability.
632M
2M
34M
140M
334M=482M
STM-1
(155M)
1140M=642M
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.
Frame Structure and Multiplexing
methods
Multiplexing
Procedure
Components
and functions
140M
34M
2M
STM-N
STM-N Frame Structure
9×270 ×N bytes
Transmission 1
direction
SOH
3
4 AU-PTR
5
SOH
9
9×N
STM-N payload
(including POH)
261×N
270×N
columns
Transmit
left to right
up to down
1 Characteristics of SDH signals:
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.
2 Composition of SDH signals:
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.
If we should consider STM-N signal to be a truck, then
info 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.
STM-N
POH
Low-rate signals 1
Pkg
loading
packing
Low-rate signals n
Pkg
Pkg
Payload
Pkg
loading
packing
POH
Pkg
Pkg
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.
Sections and
Paths
Low-rate signal 1
Low-rate signal 2
.
SDH
Section signal
(SOH)
Low-rate signal n
low-rate path
signal(POH)
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.
According to the value of AU, the receiver can directly
drop low-rate signals from STM-N frame. That is to
say we can get the “goods” directly from the “carriage”
if we know the label of the “goods”.
Because the “goods” are placed regularly in the
“carriage”, we only need to know the first piece of
“goods”.
Receiving:
Sending:
AU-PTR indicates the first
info package
According to the value of
AU-PTR, get the first info
package, through the
regularity of byte interleaved
multiplexing, get the other
packages
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(SDH transmission
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network)
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For low-rate signals such as 2M, 34M. We need two-levels
of 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.
AU-PTR
Secondary alignment
2M
34M
TU-PTR
Primary alignment
Multiplexing procedures of SDH
low-rate SDH→high-rate SDH:
byte interleaved multiplexing, 4 into 1.
PDH signals→STM-N: synchronous multiplexing:
140M→STM-N
34M→ STM-N
2M→STM-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.
SDH Multiplexing Hierarchy
×N
STM-N
AUG
139264kbit/s
AU-4
SDH signal
C-4
VC-4
×3
TU-3
TUG-3
VC-3
×7
C-3
Pointer
processing
Align
adjustment
Multiplexing
34368kbit/s
TUG-2
×3
TU-12
VC-12
C-12
2048kbit/s
Mapping
PDH signals
140M multiplexing procedures(140M →STM-N)
1
Rate
Adaptation
1
POH
C4
140M 9
1
260
125us
9
P
O
H
1
VC4
125us
To be continued
261
C4---Container 4: A standard info structure corresponding to 140M,
performs bit rate justification.
VC4---Virtual Container 4: A standard info structure corresponding
toC4, performs real-time performance monitoring of 140M
140M multiplexing procedures
AU-4
(continue)
1
STM-1
1
RSOH
AU-PTR
alignment
AU-PTR
1
SOH
125us
1
270xN
1
9
10
payload
MSOH
9
270
9
1
125us
270
AU-4---Administrative Unit 4, a info structure
corresponding toVC4, performs pointer alignment.
140M—VC4—AU-4—STM-1,
One STM-1 can only incorporate one 140M signal.
STM-N
9
125us
34M multiplexing procedures
C3
VC3
1
1
POH
Rate adaptation
34M
9
1
84
125us
P
O
H
9 1
To be continued
125us
85
C3---Container 3: A standard info structure corresponding to 34M,
performs bit rate justification.
VC3---Virtual Container 3: A standard info structure corresponding
to C4, performs real-time performance monitoring of 140M
34M multiplexing procedures
1 TUG-3 86
1
(continue) 1 TU-3 86
H1
1
1 H1
1
H2
H2
×3
P
TU- H3
H3
Fill
BIM
PTR
O
Gap
R
H
125us
9
9
125us
9
VC4
261
RR
125us
TU3---Tributary Unit 3: A standard info structure corresponding to
VC3, performs primary alignment.
TUG3---Tributary Unit Group 3: A standard info structure
corresponding toTU3.
34M—VC3—TU3—TUG3；3 TUG3—VC4—STM-1；
One STM-1 can hold 3 34M.
2M multiplexing procedures
POH
1
1
C12
Rate
Adaptation
1
VC12
POH
Primary
Alignment
TU12
To be continued
2M
9
1
4
125us
9
1
125us
4
9
1
PTR
125us
4
2M multiplexing procedures (2M →VC4)
C12--Container 12: A standard info structure
corresponding to 2M, performs bit rate justification
for 2M signals, 4 basic frames constitute a multi-frame.
VC12---Virtual Container 12:A standard info structure
corresponding to 2M, performs real-time monitoring.
TU12---Tributary Unit 12: A standard info structure
corresponding to VC12, performs primary pointer
alignment forVC12.
2M multiplexing procedures (2M →VC4)
×3
1
×7
Byte Interleaved
Multiplexing
(continue)
1
1
TUG2
86
1
Byte
Interleaved
Multiplexing
R R TUG3
9
9
125us
125us
2M Multiplexing procedures(2M →VC4)
TUG2---Tributary Unit Group 2
TUG3---Tributary Unit Group 3
2M—C12—VC12—TU12；3TU12—TUG2；
7 TUG2—TUG3；3TUG3—VC4—STM-1。
One STM-1 is able to hold 3×7×3= 63 2M.
Multiplexing structure for 2M is 3-7-3.
Concept of multiframe:
4 C12 basic frames make up
1 multi-frame.
Both basic frames and
multi-frame carry the same
2M signal.
SDH
One basic frame can hold
the info segment of 2M
signal during 125us period.
C12
One multi-frame holds the
C12
info for 2M signal during
500us period.
C12
C12
1#
STM-1
2#
STM-1
3#
STM-1
4#
STM-1
Multiplexer
1#
2#
3#
4#
63 2M
Relations between info structures
E1
C12
VC12
TU12
E3
C3
VC3
TU3
E4
C4
VC4
Summary
STM-N frame structure and functions of
different parts of the frame
Methods for multiplexing PDH into STM-N frames
140M multiplexed into STM-N frames
34M multiplexed into STM-N frames
2M multiplexed into STM-N frames
Overhead and Pointers
Overhead
Section
Overhead
Path
Overhead
Pointers
AU-PTR
TU-PTR
Overhead
SOH
RSOH
POH
MSOH
VC4
PO
H
(HPOH)
VC12
POH
(LPOH)
Layered monitoring
VC12
LO-POH
VC4
HO-POH
STM-1
MSOH
STM-N
RSOH
SOH(take STM-1 as an example)
1
1
2
3
4
5
6
7
8
9
2
3
4
A1* A1* A1* A2 *
B1
E1
D1
D2
5
6
7
8
A2 * A2 * J0 * *
F1
D3
9
*
RSOH
AU-PTR
B2 B2
D4
D7
D10
S1
B2
K1
D5
D8
D11
K2
D6
D9
M1
MSOH
D12
E2
Bytes reserved for domestic use
Marked * bytes are not scrambled
1) Framing bytes:A1,A2 to locate the
frame heads
Signal stream
STM-N STM-N STM-N STM-N STM-N STM-N
Frame
Head?
Found
A1,A2?
N
Give OOF
Y
Over 3ms
Generate LOF
Next
process
Insert AIS
2) DCC Data Communication Channel bytes:D1—D12
An info channel for OAM between NE-NE
D1-D3 is in Regenerator section(DCCR),
D4-D12 is in Multiplex section(DCCM),
NM
UTP
DCC channel
OAM info includes: performance monitoring, alarms
inquiry, command issue,etc.
3) Order wire bytes: E1,E2
Each provides a 64kb/s order wire digital telephone.
E1is for RS order wire
E2 is for MS order wire
E2can not be used by a REGs
4) Bit interleaved parity byte:B1
Performs real-time monitoring over the signal stream
Bit Interleaved parity
BIP-8
A1
A2
A3
A4
00110011
11001100
10101010
00001111
B
01011010
B1 working mechanism:
Insert B1
SDH
Equipment
Sending
Detect B1
STM-N
If error blocks occurred
produce: RS-BBE
performance event
SDH
Equipment
Receiving
5) Bit interleaved Parity B2 byte
monitor the error blocks of MS
Insert B2
SDH
Equipment
Sending
Detect B2
STM-N
If error blocks occurred
produce: MS-BBE
performance event
SDH
Equipment
Receiving
6) Multiplex section Remote Error Indication byte:M1
Sent from receiver to sender
Informs the sender: the error blocks detected by receiver
through B2
M1 received
produce: MS-REI
performance event
SDH
Equipment
Sender
Error blocks found
produce: MS-BBE
performance event
STM-N
Send M1
byte
SDH
Equipment
Receiver
7) Automatic Protection Switching(APS) bytes---K1,K2
Carries APS protocol for MSP switching
MS Remote Defect Indication byte:
K2(b6-b8)=111, indicates that all “1” signals have
been received, receiver will give MS-AIS alarm
K2(b6-b8)=110, indicates that MS-RDI has been
received, which means the counter-part has received
signal deterioration, such as MS-AIS, RLOF etc.
K2 Detection
Found
110
K2(b6-b8)
111
Giving
MS-AIS
Sending back
MS-RDI
Producing
MS-RDI
Receive K2(110)
produce: MS-RDI
alarm event
SDH
Equipment
Sender
Find K2(111)
produce: MS-AIS
alarm event
STM-N
Sending back K2
(110)
SDH
Equipment
Receiver
8)
Synchronous Status byte S1(bit5~8)
 For
synchronous status indication
 The smaller the value of S1, the higher
the quality of synchronous clock!
Classification:
2 Path Overhead
Lower-order POH--VC12
Higher-order POH---VC4
Difference:
VC-4 macro, VC-12 micro
VC4
VC-4 includes VC-12
POH
(HPOH)
VC12
POH
(LPOH)