Fiber Optic Communication By

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Fiber Optic CommunicationBy

• Engr. Muhammad Ashraf Bhutta

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Lecture Outlines

• SDH Overview
• Frame structure and multiplex-ing methods
• Overheads and Pointers

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SDH Overview
Background of SDH
Advantages of SDH
Disadvantages of PDH
Disadvan-tages of SDH
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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---universa
l interface all over the world
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Disadvantages of PDH 1 Interfaces Electrical
interfaces---only regional standards, no
universal standard. 3 rate hierarchies for
PDHEuropean(2Mb/s) Japanese, North
American(1.5Mb/s). Optical interfaces---no
standards at all, manufacturers develop at their
will.
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Where did I put the signals?
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Low-rate signals have to be separated from
high-rate signals level by level. Multiple levels
of multiplexing/de-multiplexing cause signals to
deteriorate, it is not suitable for huge-volume
transmission.
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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. 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.
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Advantages of SDH 1 Interfaces Electrical
interfacesstandard 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 interfacesonly scramble the electrical
signals. SDH optical code pattern is scrambled
NRZ, PDH optical code pattern is scrambled mBnB.
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SDHhigh-rate signal is exactly 4 times that of
the next low-rate signal.
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SDH4STM-1STM-4 4STM-4STM-16
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2 Multiplexing methods low-rate
SDH?high-rate SDH(e.g.4 ? STM-1?STM-4).
Uses byte interleaved multiplexing method.
Byte interleaved
multiplexing
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Byte interleaved multiplexing
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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.
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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.
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SDH compatibility schematics
PDH, ATM FDDI signals
packing
SDH network
Package
package
STM-N
STM-N
packing
transmit
transmit
transmit
unpacking
PDH, ATM FDDI signals
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Disadvantages of SDH 1 low bandwidth utilization
ratio--- contradiction between 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.
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Frame Structure and Multiplexing methods
Multiplexing Procedure
Components and functions
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STM-N Frame Structure
9270 N bytes
Transmission direction
1
Transmit left to right up to down
SOH
3
AU-PTR
4
STM-N payload (including POH)
5
SOH
9
9N
261N
270N columns
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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.
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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.
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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.
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Receiving According to the value of
AU-PTR, get the first info package, through the
regularity of byte interleaved multiplexing, get
the other packages
Sending AU-PTR indicates the first info
package
(SDH transmission 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.
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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.
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SDH Multiplexing Hierarchy
N
139264kbit/s
STM-N
AUG
VC-4
C-4
3
SDH signal
VC-3
TUG-3
7
34368kbit/s
C-3
Pointer processing
TUG-2
3
Align adjustment
2048kbit/s
VC-12
C-12
Mapping
Multiplexing
PDH signals
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140M multiplexing procedures(140M ?STM-N)
1
1
P O H
Rate Adaptation
POH
C4
VC4
To be continued
140M
9
9
1 260 1
261
125us
125us
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
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140M multiplexing procedures
AU-4
STM-1
1
1
(continue)
RSOH
payload
AU-PTR
1
270xN
alignment
SOH
AU-PTR
1
9
1
MSOH
9
9
10
270
1
270
STM-N
125us
125us
9
125us
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34M multiplexing procedures
C3
VC3
1
1
P O H
POH
Rate adaptation
To be continued
34M
9
9
1 84 1
85
125us
125us
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
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34M multiplexing procedures
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2M multiplexing procedures
POH
1
1
1
Primary Alignment
C12
Rate Adaptation
TU12
VC12
POH
To be continued
2M
9
PTR
9
9
1 4
1 4
1 4
125us
125us
125us
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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 12A standard info structure correspondi
ng to 2M, performs real-time monitoring. TU12---Tr
ibutary Unit 12 A standard info
structure corresponding to VC12, performs primary
pointer alignment forVC12.
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2M multiplexing procedures (2M ?VC4)
86
1
1
1
1
3
7
Byte Interleaved Multiplexing
TUG2
Byte Interleaved Multiplexing
TUG3
R R
(continue)
9
9
125us
125us
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Concept of multi-frame 4 C12 basic frames
make up 1 multi-frame. Both basic
frames and multi-frame carry the same
2M signal. One basic frame can hold the
info segment of 2M signal during 125us
period. One multi-frame holds the
info for 2M signal during 500us period.
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Relations between info structures
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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
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Overhead and Pointers
Overhead
Pointers
Path Overhead
Section Overhead
AU-PTR
TU-PTR
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Overhead
SOH
POH
RSOH
MSOH
VC4 POH
VC12 POH
(LPOH)
(HPOH)
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Layered monitoring
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SOH(take STM-1 as an example)
1 2 3 4 5 6
7 8 9
1 2 3 4 5 6 7 8 9
A1
A1
A1
A2
A2
A2
J0









B1
F1
E1
RSOH
D1
D3
D2
AU-PTR
B2
B2
B2
K1
K2
D4
D5
D6
D7
D8
D9
MSOH
D10
D11
D12
S1
M1
E2
Bytes reserved for domestic use

Marked bytes are not scrambled
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1) Framing bytesA1,A2 to locate the frame heads
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Frame Head?
N
Found A1,A2?
Give OOF
Y
Over 3ms
Generate LOF
Next process
Insert AIS
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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 byteB1 Performs
real-time monitoring over the signal stream
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Bit Interleaved parity
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B1 working mechanism
Detect B1
Insert B1
SDH Equipment Sending
SDH Equipment Receiving
STM-N
If error blocks occurred produce
RS-BBE performance event
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Detect B2
Insert B2
SDH Equipment Sending
SDH Equipment Receiving
STM-N
If error blocks occurred produce
MS-BBE performance event
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6) Multiplex section Remote Error Indication
byteM1 Sent from receiver to sender
Informs the sender the error blocks detected by
receiver through B2
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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.
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K2 Detection
Found K2(b6-b8)
110
111
Giving MS-AIS
Sending back MS-RDI
Producing MS-RDI
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Find K2(111) produce MS-AIS alarm event
Receive K2(110) produce MS-RDI alarm event
SDH Equipment Sender
SDH Equipment Receiver
STM-N
Sending back K2 (110)
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8) Synchronous Status byte S1(bit58)

• For synchronous status indication
• The smaller the value of S1, the higher the
  quality of synchronous clock!

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2 Path Overhead
Classification Lower-order POH--VC12
Higher-order POH---VC4 Difference VC-4
macro, VC-12 micro VC-4 includes VC-12
VC4 POH
VC12 POH
(LPOH)
(HPOH)