Download - Transmission Principles
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Transport Physical Layer Overview
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Learnining Element Objectives• Describe the main characteristics of PDH and SDH
transmission• List the different transmission media: Copper, Fibre and
Radio• Understand the impact of different fault conditions (AIS
received from a leased line)
Transport Physical Layer Overview
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PCM and the PDH
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Plesiochronous Digital Hierarchy (PDH)
• It would be very wasteful of transmission resources if only 2Mbit/s signals were transmitted over the telecommunication network.
• Four 2Mbit/s signals interleave in multiplexed to produce a higher speed signal of approximately 8 Mbit/s.
• Then four of these 8 Mbit/s signals multiplexed together to form 34 Mbit/s signal• Four of 34 Mbit/s signals again multiplexed to make a 140 Mbit/s signal• The process of this types of Multiplexing is known as the Plesiochronous Digital
Hierarchy (PDH)• Plesiochronous - "almost synchronous”• Due to timing differences in the incoming 2 Mbit/s streams bits may be stuffed into
the frames as padding the TS location varies slightly in the higher layers (8,34,140Mbit/s) from frame to frame this is called “jitter” .
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Plesiochronous Digital Hierarchy (PDH)
• Few years ago the common way to build a backbone network that supplies broadband communication to the suppliers was a PDH network
• The topology of a PDH network is the Mesh topology where every multiplexer in each site worked with its own clock. In order to synchronize between two multiplexers that works together, usually the transmission was made according to the local clock and the reception was madeaccording to the recovered clock that was recovered from the received data
• The fact that each of the multiplexers transmits according to its own clock creates a problem when we need to multiplex several transmitted data streams, the problem is that we can't decide which clock to choose for the multiplexing. If we will choose a fast clock we will not have enough data to put in the frame from a slower incoming data stream (we will get empty spaces in the frame), from the other hand if we will choose a slow clock the data at the faster incoming stream will be lost
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PCM
There are two PCM systems recommended by the ITU:-• T1 (24 chan. in USA, Canada and Japan)• E1 (30 chan. in Europe and most of the world)
We will look at PCM 30.
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The conversion of analogue signals (speech) into a digital format is generally referred to as PCM.This is achieved by a number of processes:
SamplingQuantizingEncoding
Multiplexing
PCM30
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RA45355EN05GLA08 © Nokia Siemens Networks
Sampling
Analogue Signal
Sampling moments
(8000 per sec)
Samples
• This is where a “snapshot” of the analogue signal is taken.• Also the polarity and amplitude of the signal is determined (8000 times a
second or every 125 μsec)
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PAM Samples
PAM (Pulse Amplitude Modulation)
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-127
+127
0+1+2
-1-2
Quantizing
Levels
0
This is where the “snapshot” sample is assigned a quantizing level (one of 256).
Quantizing
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RA45355EN05GLA011 © Nokia Siemens Networks
16123
12316
16
123
3
16
Non-Linear Quantizing Table
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161514131211109876543210012345678910111213141516
1000101
100100010010101001100100110110011101001111
1000101
100100010010101001100100110110011101001111
Encoding (example)
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Chan 110011011
Chan 200011011
Chan 310011000
Chan 411111011
11111011 10011000 00011011 10011011
Multiplexing
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RA45355EN05GLA014 © Nokia Siemens Networks
The system bit rate can be calculated as follows:-
Sampling frequency X No of Time Slots X Bits per Time Slot
8000 X 32 X 8 =
= 2048 kbit/s
System bit rate
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PCM 30 Frame TS0
0 1 2 313015 16 17
Si 0 0 0 1 111
Si 1 A Sa6 Sa7 Sa8Sa5Sa4
125 μs
3.9 μs
0.49 μs
Signalling information
Encoded signals 1 to 15 Encoded signals 16 to 30
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PCM 30 Frame TS 16 in Multiframe
0 1 16 31 0 1 16 31 0 1 16 31
No. 8 No. 152Mbit/s frame
No. 0
0 1 2 8 1514
0 0 0 0 YX XX a b c d ba dc a b c d ba dc
125 μs
Signalling frame 2 ms
MFAS NMFAS Chan 8 Chan 23 Chan 15 Chan 30
Signalling words Signalling words
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P mux1----30
64 kbit/sdatasignals
P mux1----30
P mux1----30
DigitalExchange
H/O Mux2 to 8
H/O Mux2 to 8
H/O Mux2 to 8
H/O Mux2 to 8
H/O Mux8 to 34
H/O Mux8 to 34
H/O Mux8 to 34
H/O Mux8 to 34
H/O Mux34 to 140
4 x 2048 kbit/s 4 x 8448 kbit/s 4 x 34368 kbit/s 139264 kbit/s
Hierarchy level0 1 2 3 4
Plesiochronous Digital Hiearcy
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Chan 12048 +50ppm
Chan 22048
Chan 32048 -50ppm
Chan 42048
Chan 4 bit Chan 3 bit Chan 2 bit Chan 1 bit
Justification
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1 to 10 1112 13 to 212 1 to 4 1 to 4 1 to 4 5 to 85 to 212 5 to 212 9 to 212
848 bits
SUBFRAME 1 SUBFRAME 2 SUBFRAME 3 SUBFRAME 4
FRAMEWORD
CB TD JC TD JC TD JC J/D TD
1 to 10 1112 13 to 384 1 to 4 1 to 4 1 to 4 5 to 85 to 384 5 to 384 9 to 384
1536 bits
SUBFRAME 1 SUBFRAME 2 SUBFRAME 3 SUBFRAME 4
FRAMEWORD CB TD JC TD JC TD JC J/D TD
1 to 12 13 14 17 to 488 1 to 4 1 to 4 1 to 4 5 to 85 to 488 5 to 488 9 to 488
2928 bits
SUBFRAME 1 SUBFRAME 2 SUBFRAME 3 TO 5 SUBFRAME 6
FRAMEWORD
CB TD JC TD JC TD JC J/D TD
15 16
REMOTE SERVICE
Higher Order Frame Structures
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Plesiochronous Digital Hierarchy (PDH)
Structure of E1 frame (2.048 Mbit/s)
32 TDM time slots (with 8 bits each / frame)
Time slots 1-31 carry digital signals (usually PCM speech) with a bitrateof 64 kbit/s.
Time slot 0 is used for frame synchronization:
0 1 2 3116
... ...received bit stream ... where does a new frame begin?
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2Mbit/s
DigitalExchange
Switch
DigitalExchange
Switch
2-8Mux2-8
Mux8-34Mux8-34
Mux34-140
Mux34-140Mux
140Mbit/s34Mbit/s8Mbit/s2Mbit/s
DigitalExchange
Switch
DigitalExchange
Switch
2-8Mux2-8
Mux8-34Mux8-34
Mux34-140
Mux34-140Mux
140Mbit/s34Mbit/s8Mbit/s
Plesiochronous Digital Hierarchy (PDH)
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TX ARX B
RX ATX B
RX ATX B
TX ARX B
CORRECT cabling ?
wrong cabling!
E1/T1/JT1 balanced interfaces cabling1/4
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TX ATX B
RX ARX B
RX ARX B
TX ATX B
CORRECT cabling ?
YES!
E1/T1/JT1 balanced interfaces cabling2/4
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RA45355EN05GLA024 © Nokia Siemens Networks
TX ARX B
RX ATX B
RX ATX B
TX ARX B
TX wires induce a signal into the RX wires
E1/T1/JT1 balanced interfaces cabling 3/4
When wrongly using the two wires of a twisted pair for different directions (TX and RX), the principle of balanced signals will NOT have it’s positive effect of elimination of common mode interfering signals.In opposite, both signal (TX+RX) will interfere with each other, the more, the longer the cable length is. Signal quality (bit errors) will be degraded.Also alarm management is affected: In case one end of the cable is disconnected from the terminal, the alarm “loss of signal” would be expected. But due to induction from the TX to the RX wire, there might be an incoming signal detected. No alarm at all or for instance “frame alignment lost” would be generated instead.
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E1 un-balanced signal
RX TX
electromagnetic interferences
time
PCM signal
disturbances can cause bit errors
0/1 information (pulse length)undefined
co-axial cable
signal is carried on center conductor, shield is grounded
When wrongly using the two wires of a twisted pair for different directions (TX and RX), the principle of balanced signals will NOT have it’s positive effect of elimination of common mode interfering signals.In opposite, both signal (TX+RX) will interfere with each other, the more, the longer the cable length is. Signal quality (bit errors) will be degraded.Also alarm management is affected: In case one end of the cable is disconnected from the terminal, the alarm “loss of signal” would be expected. But due to induction from the TX to the RX wire, there might be an incoming signal detected. No alarm at all or for instance “frame alignment lost” would be generated instead.
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E1/T1/JT1 balanced signal
RX ARX B
TX ATX B
electromagnetic interferences
time
PCM signal
Differencial voltageTX A – TX B
Input stage is a differential amplifier that amplifies the difference voltage between signal A and B, but rejects the common mode disturbances
When wrongly using the two wires of a twisted pair for different directions (TX and RX), the principle of balanced signals will NOT have it’s positive effect of elimination of common mode interfering signals.In opposite, both signal (TX+RX) will interfere with each other, the more, the longer the cable length is. Signal quality (bit errors) will be degraded.Also alarm management is affected: In case one end of the cable is disconnected from the terminal, the alarm “loss of signal” would be expected. But due to induction from the TX to the RX wire, there might be an incoming signal detected. No alarm at all or for instance “frame alignment lost” would be generated instead.
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RA45355EN05GLA027 © Nokia Siemens Networks
Synchronous Digital Hierarchy (SDH)
SDH is a new multiplexing technique, which allows the insertion and Removal of an individual channel at any bit rate in the hierarchy.
The SDH has been designed to enable very effective monitoring and management of the telecommunications network to be carried out.
The SDH network works with a single central clock that synchronizes all the elements in the network
SDH is an internationally agreed standard. And developed to address following basic requirements.• Facilities to add or drop tributaries directly from a high speed signal• Need for extensive network management capability• Standardised interfaces between equipment• Need for inter-working between North American and European system• Standardisation of equipment management process
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RA45355EN05GLA028 © Nokia Siemens Networks
Synchronous Digital Hierarchy (SDH)
The SDH standards define the basic transmission bit rate and frame structuresThe frame are know as “Synchronous Transport Module” (STM) and the bit rates are as follows:-• STM-1 155.52 Mbit/s• STM-4 622.08 Mbit/s• STM-16 2.48832 Gbit/s (2.5 Gbit/s)• STM-64 9.95328 Gbit/s (10 Gbit/s)
The most common tributary bit rate to SDH is 2Mbit/s and a maximum of 63*2Mbit/s signal can be accommodated in an STM-1 (155.52Mbit/s)• In order to have the ability to connect a low rate PDH stream an improved
stuffing algorithm is used.• The SDH protocol enables transmitting any of the PDH bit rates directly by
mapping it to the STM-n frame, that gives the user the flexibility to transmit any configuration of tributary rates using only one multiplexing element, depicted bellow the difference between the SDH network element and the PDH
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Synchronous Digital Hierarchy (SDH)
SDH is based on byte interleaving and not bit interleaving , as PDH was based on.The bit rate increased from 64 Kbps in PDH to 2 Mbps in SDH.
PDH
155.52Mbit/s
34Mbit/s
2Mbit/s
6Mbit/s
1.5Mbit/s
45Mbit/s
64Kbit/s
140Mbit/s
SDHMultiplexer
STM-1 155.52 Mbit/s Optical or ElectricalSTM-4 6.22.08 Mbit/s OpticalSTM-16 2.48832 Gbit/s (2.5 Gbit/s) OpticalSTM-64 9.95328 Gbit/s (10 Gbit/s) Optical
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RA45355EN05GLA030 © Nokia Siemens Networks
STM-1 Basic Transport Level
SOH
9 columns
9 rows
261 columns
STM-1 VIRTUAL CONTAINER
(VC-4)
CAPACITY = 150.34 Mbit/s
SECTIONOVERHEAD
2430 bytes/frame x 8 bits/byte x 8000 frames/sec = 155.52 Mbit/s
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Overhead Location
MSOH
VC-4
9 columns
3 rows
5 rows
9rows
RSOH1 column
Payload
Pointer1 row
POH
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MSOH
RSOH
PointerPayload
POH
MSOH
RSOH
PointerPayload
POH
SDHRegenerator
Node
RSOH is stripped awayand checked on input
New RSOH is createdon output
Regenerator Node
The RSOH carries such information as frame alignment signal and management channels.In order to manage a SDH regenerator, for example, the management channel to the node must be placed in the RSOH as this is the only part of the signal that a regenerator can access. The rest of the STM-1 frame just passes through untouched.
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MSOH
RSOH
PointerPayload
POH
MSOH
RSOH
PointerPayload
POH
SDHMultiplexer
Node
RSOH and MSOH are both stripped awayand checked on input
New RSOH and MSOH are created on output
Multiplexer Node
There are three types of SDH multiplexer nodes:Terminal Multiplexer (TM) with only one SDH interfaceAdd-and-Drop Multiplexer (ADM) with two SDH interfacesDigital Cross-Connect (DXC) with three or more SDH interfaces
The part of the STM-1 signal that passes through the multiplexer is often referred to as the VC-4, but technically it is an AU-4 (Administrative Unit level-4). The payload plus Path Overhead (POH) make up a VC-4, while VC-4 plus pointer constitute an AU-4.
At an ADM or DXC node, cross-connections may not always be made at the AU-4 (VC-4) level, but rather at a lower (tributary) level within the payload (such as E1). In that case the payload must be terminated on input and opened up, in order to access the tributaries inside which are to be cross-connected. The pointer is used to access the payload and then discarded. Also the POH is stripped away and checked. On output, a new payload with new POH and new pointer are created. In effect, it is a whole new STM-1 signal.
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SDH SDHSDH
regen-erator
SDH SDH
Multiplexer
Regenerator section
Path section
Terminal multiplexer
Cross-connect
equipment
Multiplexer section
regen-erator
Terminal multiplexer
Regenerator
section
section
Section Overheads
To summarize:1. The Multiplexer section is added at the output of every multiplexer, and terminated and checked at the input of the following multiplexer.2. The Regenerator section is added at the output of every multiplexer or regenerator. It is terminated and checked at the input of every multiplexer and regenerator. Every node creates a Regenerator section.3. The Path section (POH) is created with the payload and contains information about the payload, such as its name, type and structure. The Path section stays with the payload between the multiplexing and demultiplexing stages, regardless of how many intermediate nodes the signal may pass through. The Path section provides for end-to-end monitoring of the signal path.
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9 columns
9 rows
A1
B1
D1
A1 A1 A2
E1
D2
A2 A2 J0
F1
D3
RSOH3 rows
RSOH
A1 & 2 Frame Alignment
J0 Trail Trace
B1 Error Monitoring
E1 Service Telephone
F1 User Byte
D1 - 3 Data Channel
Regenerator Section Overhead
The Regenerator section overhead consists of 3 rows and 9 columns (27 bytes).The first six bytes are designated as A1 & A2. These bytes contain the frame alignment signal, indicating where the frame begins and allowing the receiving node to synchronize to the incoming signal. J0 byte is reserved for trail trace identification. If we like, at every output we can give a name to the signal and check this name at the next input. Note that this ID is valid for only a single hop.(One byte only carries a single character, but at 8000 frames per second a string of successive frames can carry a longer ID.)FXC STM supports a trail trace identifier up to 15 characters long. (Unused characters should be filled in with spaces, to prevent any incompatibility with SDH equipment from different vendors – some use space characters as filler, others use null characters.)B1 is for error monitoring using 8-bit interleaved parity (BIP-8). E1 is reserved by ITU-T for service telephone use. It is a 64k channel.(At 8000 frames per second, each byte in the STM-1 frame represents a 64 kbit/s channel.)F1 is a user byte, reserved by ITU-T for the user to use in any way he wishes. The user byte is also a 64k auxiliary channel between stations. Bytes D1-D3 can be used for high-speed data or SDH network management information: 3 x 64k = 192 kbit/s channel. This channel is officially called DCCr, or Data Communic-ationsChannel in RSOH.Empty bytes are 64k channels which are not currently defined. These bytes can be used for any purpose (for example, to carry the Q1 channel for transmission management). However the ITU-T could reserve them in the future for some new functionality. So they can be used within a network, but should not be used when the signal passes from one network to another.
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B2
D4
D7
D10
S1
B2 B2 K1
D5
D8
D11
M1
K2
D6
D9
D12
E2
9 columns
9 rows
MSOH5 rows
MSOH
B2 Error Monitoring
K1 - K2 Network Backup
K2 (bits 6-8) RDI
S1 SSM
M1 REI
E2 Service Telephone
D4 - 12 Data Channel
Multiplexer Section Overhead
Similar to RSOH is the Multiplexer section overhead (45 bytes). Whereas RSOH can be decoded by both regenerators and multi-plexers, MSOH can only be decoded by multiplexers.The first three bytes are B2, used for error monitoring. Like B1 byte in RSOH, this is also interleaved bit-parity checking, but with 24 bits instead of 8.M1 byte is for Remote Error Indication (REI). If a parity error in the incoming signal is detected via the B2 bytes, REI is sent back through the M1 channel to the transmitting node.Bytes K1 & K2 are used for automatic protection switching. But FXC STM uses a simpler solution, which does not require protection information to be transmitted through these bytes.Bits 6-8 of K2 are for Remote Defect Indication (RDI). If the receiver detects a major fault in the incoming signal, it will send back RDI to the transmitting node. (This is similar to FEA – far end alarm – in PDH.)S1 byte is for SSM – Synchronisation Status Message. S1 carries information about the quality of the clock used to generate the signal. This information is useful in SDH network synchronization.E2 byte is reserved as a second service telephone channel.Bytes D4-D12 can be used for high-speed data or SDH network management information: 9 x 64k = 576 kbit/s channel. This channel is officially called DCCm, or Data Communications Channel in MSOH.
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J1
B3
C2
G1
F2
H4
F3
K3
N1
1 column
9 rows
POH
POH
Trail Trace
Error Monitoring
Signal Label
Path User Channel
Path Status (Errors & Far End Equip.)
Path User Channel
Multiframe Pointer
Automatic Protection Control
Tandem Connection Monitoring
Path Overhead
The Path overhead (POH) is created with the payload and travels with the payload through the SDH network. It is only terminated when the payload itself is terminated (for example, when it is altered due to new cross-connections).J1 byte is for trail trace identification. It can contain a name which is given to the payload. When the payload is terminated, the name is checked to verify that the correct payload was received.Note that the trail trace in RSOH contains the name of the signal (which is valid for only one hop), while the trail trace in POH contains the name of the payload.B3 byte is for end-to-end error monitoring, using 8-bit parity.C2 byte contains the signal label. This identifies the type of signal carried in the payload, such as PDH, or ATM, or Frame Relay. It allows the receiver to verify that the incoming STM-1 signal is carrying the correct type of payload.The label “Unequipped” indicates that the signal is carrying an empty payload, one which does not contain any information.G1 byte is used to report the path status, such as REI and RDI.F2 and F3 bytes are reserved by the ITU-T as path-level end-to-end user channels. They could be used to send auxiliary information.H4 byte contains the multiframe pointer. The multiframe pointer is needed when 2 Mbit/ssignals are carried in the payload.K3 and N1 bytes are not used by FXC STM. The protection mechanism used, SNC-type protection (Sub-Network Connection protection), is both simpler and more flexible.
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RA45355EN05GLA038 © Nokia Siemens Networks
F F
SOH POH
F
155.52 Mbit/s
260 columns
TributaryUnits
Multiplexing Tributary Units to STM-1
The payload can carry tributary units, either 2 Mbit/s or 34 Mbit/s signals. Again, one STM-1 can hold up to 63 x 2M, 3 x 34M, 1 x 140M, or a combination of 2M and 34M signals.
A 2M frame is 32 bytes long (TS0-31). After path overhead and pointer information are added, it becomes a TU-12 (see following page).One TU-12 occupies 36 bytes, or 4 columns in the payload. There is room for 63 x TU-12’s in a STM-1 signal.
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AU-4 VC-4
C-4
TU-3 VC-3
TU-12 VC-12 C-12TUG-3
C-3
2 Mbit/s
34 Mbit/s
140 Mbit/s
STM-1
TU-12 VC-12 C-12
TU-12 VC-12 C-12
POH
POH
POH
POH
PTR
PTR
PTR
PTRSOH
TUG-2
TUG-2
TUG-2
TUG-2
TUG-2
TUG-2
TUG-2
TUG-3
TUG-3
Multiplexing
Mapping
Pointer proccessing
POHPTR
Áligning
STM-1 Multiplexing Structure
In SDH, each tributary signal is mapped into a “container” suitable for holding it. For example, a 2Mbit/s signal is mapped into a C-12 container.Why C-12? Because a European 2 Mbit/s E1 signal is a level “1” type “2” signal, while a North American 1.5 Mbit/s T1 signal is a level “1” type “1” signal. So actually the “12” in C-12 should not be pronounced as “twelve” but rather as “one-two”.When POH information is added to the C-12 container, it becomes a VC-12 “virtual container”. When a pointer is added, to indicate where in the container the tributary can be found, this becomes a TU-12 “tributary unit”.The STM-1 frame structure is based on multiplexing level-1 signals (2M) into level 2 (6M), level-2 signals into level 3 (45M), and level-3 signals into level 4 (150M).So three TU-12's are multiplexed into one TUG-2 “tributary unit group” level-2. Seven TUG-2's are multiplexed into one TUG-3, and three TUG-3's are multiplexed into one VC-4.3 x 7 x 3: This is how we get the number 63 x 2M which can be carried in one STM-1 signal.
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TUG2 -1
TUG3 -2 TUG3 -3
TUG2 -2
TUG2 -3
TUG2 -4
TUG2 -5
TUG2 -6
TUG2 -7
TUG3 -1
VC12 VC12 VC12
1-1-1 1-1-2 1-1-3 2-1-1 2-1-2 2-1-3 3-1-1 3-1-2 3-1-3
1-2-1 1-2-2 1-2-3 2-2-1 2-2-2 2-2-3 3-2-1 3-2-2 3-2-3
1-3-1 1-3-2 1-3-3 2-3-1 2-3-2 2-3-3 3-3-1 3-3-2 3-3-3
1-4-1 1-4-2 1-4-3 2-4-1 2-4-2 2-4-3 3-4-1 3-4-2 3-4-3
1-5-1 1-5-2 1-5-3 2-5-1 2-5-2 2-5-3 3-5-1 3-5-2 3-5-3
1-6-1 1-6-2 1-6-3 2-6-1 2-6-2 2-6-3 3-6-1 3-6-2 3-6-3
1-7-1 1-7-2 1-7-3 2-7-1 2-7-2 2-7-3 3-7-1 3-7-2 3-7-3
2 31 2 31 2 31
K, L, M Numbering
So we can have up to 63 x 2M channels in an STM-1 signal. We could just number them from 1 to 63, but this limits the amount of information we get.Instead we can draw a diagram with 9 columns across and 7 rows down. We then divide this grid into 3 vertical slices.These three sections represent the TUG-3's, numbered 1,2,3 (across the top). Each can contain one 34M or 45M signal, or 21 x 2M signals.Then each TUG-3 can be divided horizontally into 7 TUG-2's. They can each hold one 6M signal or 3 x 2M signals.And every TUG-2 can be divided (across the bottom) into three VC-12's (or more accurately TU-12’s), which can each carry one 2M signal.So every box in the grid can be referenced according to its TUG-3 number (K), its TUG-2 number (L), and its VC-12 number (M). Each 2M channel in the STM-1 signal can be identified by its K-L-M index, from 1-1-1 to 3-7-3.
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• Asynchronous• Independent of bit stream format• No access to 64k or n x 64k signals• Accepts timing tolerance of +/-50 ppm
• Byte Synchronous• G.704 frame structure required• Direct access to 64k or n x 64k signals• Signal must be “SDH-synchronous”
2M Mapping Alternatives
Byte-synchronous mapping requires that the 2M signal be formatted according to the G.704 frame stucture (TS0-31).Asynchronous mapping does not require that the 2M signal have any particular format, and even allows the use of the 2M equipment’s internal clock.
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Transmission Media
A telecommunications network employs various types of transmission media• Copper• Microwave Radio• Optical Fibre Cable
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Copper Cables
• Most copper cables now only exist in the local access network between the customer premises and the local switch or access node. The major method of transmitting telecommunications information for many years but now being replaced by optical fibre cables
• There are many different types of copper cables in a network, some of the “twisted pair” Variety and some of the “ co-axial “ type
• Cooper cables are used where it is necessary to carry analogue information as it is difficult to transmit analogue signals over fibre cables
• Large existing operators have a vast investment in cooper cables in the local access network and new technologies are being developed to enable them to better use of these cables
• Digital signals can be coded in a special ways to enable them to be transmitted over copper more effectively providing fast internet access and other new services
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Microwave Radio1/3• Technically, Microwave are radio frequencies that lie between 300MHz
and 300GHz• These radio frequencies, when radiated from an antenna, can be focused
with aid of parabolic dish• This will cause the radio signal to be focused into narrow beam and then
can be used for “ line of sight “ transmission• In telecommunications the microwave frequencies between 1GHz and
38GHz are normally used• Microwaves radio antennae are normally spaced at maximum of about
48Km apart• As microwave are analogue, special microwave modems are used to
converts the digital signals to analogue and back to digital at far end of the microwave link
• Microwave radio system can provide rapid provision of new services and allow remote locations to be connected without the expense of laying cable across difficult terrain
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2-8 Mbit/sLess than 10 Km38 GHz
2-34 Mbit/s5-15 Km23 GHz
2-34 Mbit/s20-25 Km18 GHz
8 Mbit/s-140 Mbit/sMore than 30 Km7/8 GHzMain UsageTypical DistanceFrequency Band
The advantages of microwave transmission are:• Capital cost is usually low• Relatively quick and easy to install• Additional service can be provided cheaply• Irregular terrain difficulties can be overcomeThe disadvantages are:• Restricted to line of sight• Weather conditions affect the signal• Microwave repeaters must ha electrical power access
Microwave Radio2/3
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DigitalSignal
DigitalSignal
ModemModem
Analogue Microwave Radio Path
A typical digital Microwave System3/3
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Fibre Optic
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Standard fibre optics:
Fibre optics
FIBRE OPTICCore/cladding Æ
TRANSMISSION WAVELENGTH ATTENUATION BANDWAVELENGTH
62,5/125 m Multi-mode 1st window850 nm
4 dB/km 160 MHz/km
62,5/125 m Multi-mode 2nd window1310 nm
2 dB/km 200 MHz/km
50/125 m Multi-mode 1st window850 nm
3 dB/km 400 MHz/km
50/125 m Multi-mode 2nd window1310 nm
1 dB/km 800 MHz/km
9/125 m Single-mode 2nd window1310 nm
0,4 dB/km >20 GHz/km
9/125 m Single-mode 3rd window1550 nm
0,2 dB/km >200 GHz/km
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SM 9/125 MM 50/125
The principle applied to fibre optic is total internal reflection of light.
Light transmission in fibre optics
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Because of a non-uniform refraction index between the fibre optic core and cladding, under certain launching conditions a light ray enters the fibre optic guide and propagates along towards the fibre end, being guided by a successive reflection mechanism.
MM 50/125 SM 9/125
9 µm
125 µm125 µm
50 µm
CoreCladding
About fibre optics
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Single mode fibre optic distribution
• Made from a central core of a very pure glass surrounded by an outer layer of less dense glass
• Fibre are coated with plastic and stranded together to form multicore cables
• Very large bandwidth, Carry transmission digital signals in excess of 300Gbit/s
• Optical fibres very small & Light, easy to install in buildings & equipment racks
• Sophisticated methods needed to splice them together.• The light transmitted along optical fibre is in the infra red
range, hence invisible to human eye. This Light can damage the eye if exposed for long periods
• Safety arrangement must put in place when dealing with optical fiber installation and maintenance
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Opticalfibres
TubeContaining thefibres
Reinforcingmaterial
OuterCable sheath
Example of an optical fibre cable
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Single mode fibre optic distribution
• Extremely wide bandwidth, > 3 GHz• Transparent, no signal alteration• Negligible loss, 0,2 to 0,5 dB/km• Very good linearity• Low loss, both power supply and signal• Virtually avoids grounding problems, EMC proof• Standard, proven and reliable technology• Design and installation costs are significantly lower• Flexible, point to point or point to multi-point configuration
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General fiber handling rules
• Never touch the ferrules (or connector tips) with your fingers or let them make contact with any non specified surface or material after removing the protective caps of the LC connector plugs
• Do not put the fibre under permanent tensile stress• Be care full with bending optical fibres below a radius of
R=35mm
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REGEN. SECTION MULTIPLEXER SECTION HIGHER ORDER PATH
LOWER ORDER PATHLOS
LOFRS-TIMRS-BIP
MS-REI
MS-AIS
MS-AIS
AU4-AIS
VC4-AIS
TU12-AIS
VC12-AIS
HP-UNEQHP-TIMHP-BIPHP-REIHP-RDI
TU-AISTU-LOPTU-LOMHP-PLM
LP-UNEQLP-TIMLP-BIPLP-REILP-RDI
LP-PLM
J0
K2B2
AIS
B1
M1K2
A1
C2J1B3G1G1
H4C2V5J2V5V5V5
V5
MS-BIPMS-AIS
MS-RDIAU-AISAU-LOP
SDH Alarms
The SDH alarm hierarchy looks very forbidding, but SDH alarm routing and interpretation are not so confusing when the process is followed logically.Each higher-level alarm appears to generate a cascade of lower-level alarms, but these lower-level alarms are suppressed by the system so that only the original, highest-level alarm is indicated to the user.Down along the left-hand side are listed the overhead bytes (RSOH, MSOH, and POH) where the system detects the faults which produce these alarms.In ITN nodes, Higher-order Path refers to level-4 faults (which affect the entire payload), while Lower-order Path refers to level-1 faults (which only affect individual 2M tributaries). MS-level alarms signify that the entire STM-1 signal is faulty.PLM indicates that the type of payload received does not match the expected one. TIM indicates that the received signal “name” is incorrect.RDI signals the far-end that a fault has been detected in the incoming signal. REI merely reports that a parity error has been detected.
RS = Regenerator Section AU = Administrative UnitMS = Multiplexer Section TU = Tributary UnitHP = Higher-order Path VC = Virtual ContainerLP = Lower-order PathAIS = Alarm Indication Signal PLM = PayLoad MismatchBIP = Bit Interleaved Parity RDI = Remote Defect IndicationLOF = Loss Of Frame REI = Remote Error IndicationLOM = Loss Of Multiframe TIM = Trace Identifier MismatchLOP = Loss Of Pointer UNEQ = UnequippedLOS = Loss Of Signal
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SDH Alarms
• LOS Loss of signal Drop in incoming optical power level causes high bit error rate
• OOF Out of frame A1, A2 errored for ≥ 625 μs• LOF Loss of frame If OOF persists for ≥ 3 ms• RS BIP Error Regenerator Section Mismatch of the
recovered• BIP Error (B1) and computed BIP-8 Covers the whole STM-N
frame• RS-TIM Regenerator Section Mismatch of the accepted Trace
Identifier Mismatch and expected Trace Identifier in byte J0• MS BIP Error Multiplex Section BIP Mismatch of the
recovered Error (B2) and computed N x BIP-24 Covers the whole frame except RSOH
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• MS-AIS Multiplex Section K2 (bits 6, 7, 8) = 111 Alarm Indication Signal for ≥ 3 frames
• MS-REI Multiplex Section Number of detected B2 Remote Error Indication errors in the sink side encoded in byte M1 of the source side
• MS-RDI Multiplex Section K2 (bits 6, 7 8) = 111 for Remote Defect Indication ≥ z frames (z = 3 to 5)
• AU-AIS Administrative Unit All ones in the AU pointer Alarm Indication Signal bytes H1 and H2
• AU-LOP Administrative Unit 8 to 10 NDF enable 8 to 10 Loss of Pointer invalid pointers
• HP BIP Error HO Path BIP Error (B3) Mismatch of the recovered and computed BIP-8 Covers entire VC-n
• HP-UNEQ HO Path Unequipped C2 = 0 for ≥ 5 frames
SDH Alarms
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Anomalies/Defects Detection criteria• LP BIP Error LO Path BIP Error Mismatch of the recovered and computed BIP-8
(B3) or BIP-2 (V5 bits 1, 2) Covers entire VC-n• LP-UNEQ LO Path Unequipped VC-3: C2 = 0 for ≥ 5 frames frames VC-m (m = 2,
11, 12): V5 (bits 5, 6, 7) = 000 for ≥ 5 multiframes• LP-TIM LO Path Trace Mismatch of the accepted Identifier Mismatch and
expected Trace Identifier in byte J1 (VC-3) or J2
SDH Alarms
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Anomalies/Defects Detection criteria• LP-REI LO Path VC-3: Number of detected Remote Error Indication B3 errors in
the sink side encoded in byte G1 (bits 1, 2, 3, 4) of the source side VC-m (m = 2, 11, 12): If one or more BIP-2 errorsdetected in the sink side, byte V5 (bits 3) = 1 on the source side
• LP-RDI LO Path VC-3: G1 (bit 5) = 1 for ≥ z Remote Defect Indication frames VC-m (m = 2, 11, 12): V5 (bit 8) = 1 for ≥ z multiframes (z = 3, 5 or 10)
• LP-PLM LO Path Mismatch of the accepted Payload Label Mismatch and expected Payload Label in byte C2 or V5 (bits 5, 6, 7)
SDH Alarms
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Anomalies/Defects Detection criteria• HP-TIM HO Path Trace Identifier Mismatch of the accepted Mismatch and
expected Trace Identifier in byte J1• HP-REI HO Path Number of detected B3• Remote Error Indication errors in the sink side encoded in byte G1 (bits 1,2, 3, 4)
of the source side• HP-RDI HO Path G1 (bit 5) = 1 for ≥ z• Remote Defect Indication frames (z = 3, 5 or 10)• HP-PLM HO Path Mismatch of the accepted• Payload Label Mismatch and expected Payload Label in byte C2• TU-LOM Loss of Multiframe H4 (bits 7, 8) multiframe X = 1 to 5 ms not recovered
for X ms• TU-AIS Tributary Unit All ones in the TU pointer• Alarm Indication Signal bytes V1 and V2• TU-LOS Tributary Unit 8 to 10 NDF enable 8 to 10• Loss of Pointer invalid pointers
SDH Alarms