transmission principles

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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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• 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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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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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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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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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


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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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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


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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


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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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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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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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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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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

transmission principles

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