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Department of: Technical programs
Transmission Junction network
Part 1
Transmission junction network
Sub - Sections
1 Telephone Network Pages (1-10)
Transmission
Junction Systems
2 Transmission Media Pages (1-17)
3 Transmission Systems Pages (1-27)
This document consists of pages 54
Chapter 1: Telephone Network
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1
Chapter 1 Telephone Network
Aim of study
This Chapter introduces an introduction to telecommunication networks and telephone
layer model.
Contents
1-1 Introduction to Telecommunication Networks 2
1-2 Telephone Layer Model 7
Chapter 1: Telephone Network
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2
Chapter 1
Telephone Network
The History of the Telephone
In the 1870s, two inventors Elisha Gray and Alexander Graham Bell both
independently designed devices that could transmit speech electrically (the
telephone). Both men rushed their respective designs to the patent office
within hours of each other; Alexander Graham Bell patented his telephone
first. Elisha Gray and Alexander Graham Bell entered into a famous legal
battle over the invention of the telephone, which Bell won.
The telegraph and telephone are both wire-based electrical systems, and
Alexander Graham Bell's success with the telephone came as a direct result of
his attempts to improve the telegraph.
1.1 Introduction to Telecommunication Networks
Telecommunications today is perhaps the fastest evolving field of study. It is
continuously offering new challenges and opportunities to
telecommunications network planners. The subscriber part of the
telecommunications network or the network connecting the subscribers to the
central office or the access network that has been traditionally simple twisted
copper pair based, point-to-point, and passive network is now becoming
increasingly complex. In the present scenario, it becomes imperative for the
access network planner to be familiar with both traditional and new
technologies, structures and methods as their plans would have a profound
long-term impact on how the network shapes up and meets the desired
objectives... The basic idea of telecommunication is the exchange of
information. The information may include voice, text, data, image and video.
A telecommunications network is therefore a system, which can provide these
Chapter 1: Telephone Network
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3
services to a number of end users. From the end users' perspective. The
network has some main tasks:
Make interconnection of end users possible.
Facilitate exchange of information in a form desired and suitable for their
terminals.
Send and receive signals to/from the end users to facilitate the
establishment, maintenance and dismantling of connections.
It is very important for network planners to pay attention to the technical
evolution of telecommunication systems. This would to enable proven new
technologies to provide high quality telephone service and meet demands of
new telecommunication services.
Demand and traffic patterns will change faster in the future than they do
today. To cope with this, one important property a network should have is
flexibility. Flexibility in simple term implies being able to provide bandwidth
on demand. If bandwidth can be provided on demand then the network
becomes capable of deploying and supporting a wide variety of services and
with greater ease and speed.
1.1.1 Local Exchange
Subscribers of a local area are connected to their respective telephone
exchange called local-exchange or local switch or terminal exchange. The
local area could be a single exchange local area in which case all the
subscribers are terminated on the same switch or a multi-exchange area when
the number of subscribers is large and one exchange cannot effectively and
economically serve the entire subscriber. In the case of multiexchange area,
each local exchange has its own area called exchange area and the envelope
of all exchange areas would be the local area.
Chapter 1: Telephone Network
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Calls among subscriber of the same exchange can be switched through
without the need of any other kind of links except the pairs linking
subscribers to this exchange.
Fig (1.1) Subscribers in a single exchange area
In a multi-exchange area, however, the subscribers connected to different
local exchanges can only communicate if the exchanges themselves are
linked. These links between the local exchanges are called junctions.
Fig (1.2) Subscribers in a multi-exchange area
Whereas each subscriber normally has one dedicated pair up to the exchange,
the junctions are dimensioned based on the traffic between exchanges and the
Local
Exchange
Chapter 1: Telephone Network
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5
grade-of-service required. Variations on this classical theme are coming and
we will see them as we proceed.
A multi-exchange local area may have another type of exchange called transit
or local transit. Transits, unlike a local exchange, does not have subscribers
connected to it and therefore does not act as a source or sink for traffic in the
network. It only collects and redirects the traffic among the local exchanges in
the local area. An example of such a network is shown below.
1.1.2 Transit Exchange (TR)
Here the diagram depicting the junction network also shows a new element
viz. a local transit exchange (TR). A transit would normally be used in bigger
sized network to ease traffic routing and cost optimizing the junction network.
In this example, the local area of the city is geographically divided into two
by a physical obstruction i.e. the river and the transit would make it easier and
less expensive to interconnect the local exchanges on both the sides to each
other as also the local exchanges on the other side to the national switch.
Fig (1.3) the Junction Network
NS
TR
TR NS
Local
Switch
National
Switch
Local Transit
Switch
Junctions
River
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1.1.3 National Exchange
What other links would be required if the subscribers of two different local
areas need to communicate? As we linked all the local exchanges of one local
area to each other, we could also directly link all the local exchanges of one
local area to all the exchanges of other local areas in the country. This, though
technically feasible, would be economically a disaster. Telecommunications
network therefore have another type of exchange called national switch or
trunk automatic exchange. All the local exchanges of one local area are
connected to at least one such switch. All the national switches of a country
are then connected to each other based on the switching plan. A national
switch is also a type of transit exchange as it collects and redistributes traffic.
Fig (1.4) Local Network
All the international calls are routed through international gateways to which
the national exchanges would be connected. International gateways of
different countries would be linked through terrestrial, submarine or satellite
links.
The links among national switches, among international switches and between
national and international switches are called trunks.
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Fig (1.5) Trunk Network
1.2 Telephone Layer Model
The telecommunication network can be described by a layered model
consisting of the following layers:
1. The Switching and Services layer consists of all the switching nodes,
local as well as transit. It also consists of any other equipment and like
computers and software used to provide services to the customers.
2. The Transport Layer represents the links among the nodes and
provides the medium and systems to carry the information from one node to
the other. These are junctions and trunks. Junctions are links between the
local switches and local and national switches. Trunks are the links between
the national switches, the national and international switches and between the
international switches i.e. the long distance network. The long distance or
trunk network is composed of multiplexed channels of varying capacity
connecting the National Switches and the International Switches. The trend
has been to move from point-to-point links using Plesiochronous Digital
Hierarchy (PDH) towards advanced networks with built in controllability
based on Synchronous Digital Hierarchy (SDH) technique. The two most
important trends in the long distance networks are digitization and
introduction of fiber-optic technologies. These developments have reduced
the transmission cost per channel-kilometer and improved the quality.
NS
NS
NS
NS
NS International
Switch
National
Switch
Trunks
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3. The Access Layer represents the access network that links the
customers to the local switch.
Fig (1.6)
Where:
MDF Main Distribution Frame
CCC Cross Connect Cabinet
DP Distribution Point.
1.2.1 Main Distribution Frame (MDF)
Though located in the exchange building, MDF is as much a part of the
external network as it is of internal plant. It is the meeting point of internal
and external plant. It provides terminating space for the primary cable and the
cables from the exchange line terminating units. MDF provides the flexibility
of connecting any of the exchange side circuit to any of the external pairs by
jumper wires. The MDF has traditionally consisted of iron framework of
verticals and horizontals. The number verticals will depend on the size of the
exchange. The verticals are numbered' A, B, C... 'And are also known as bars.
There are ten horizontals resulting in ten cross points per vertical. On the line
side where the primary cables are terminated, each cross-point will have a
terminating block with a terminating capacity of 100 pairs.
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The exchange side (or the equipment side) of the MDF is not only reserved
for line circuit termination but it is also used as a termination point for
transmission circuits and other miscellaneous systems. The number of these
terminations per vertical will vary depending on the type of exchange and the
block used.
The MDF also gives a convenient place to put devices for over voltage and
over current protection. It also provides an isolation point for testing the line-
side and exchange side separately.
Fig (1.7)
1.2.2 Copper Conductor Cables
The primary cables are normally air-spaced, as they have to be pressurized.
The distribution cables are jelly filled.
The common conductor diameters are 0.4 mm, 0.5 mm, 0.63 mm and 0.9 mm.
The commonly used sizes are 5, 10, 20, 50, 100, 200, 600, 800, 1000, 1200,
1600 and 2000 pairs.
1.2.3 Cross Connect Cabinet
A cabinet has an arrayed arrangement of termination block. Cabinets are
available with varying termination capacity. An example could be a cabinet
with a total termination capacity of 1600 pairs including 800 for primary
Chapter 1: Telephone Network
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cable and 800 for distribution cable. A cabinet is provided in the network to
provide flexibility, separate primary side from distribution side, provide test
point for maintenance; cross connect primary pairs to distribution pairs.
1.2.4 Distribution Point DP
Secondary cable are distributed to DP each has a capacity 10 pair or 20 pair or
30 pair.
Chapter 2: Transmission Media
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Chapter 2 Transmission Media
Aim of study
This Chapter discusses the different types of transmission media.
Contents
2-1 Open Wire 2
2-2 Twisted Pair 2
2.3 Coaxial Cable 3
2.4 Microwave 5
2.5 Fiber Optics 6
Chapter 2: Transmission Media
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Chapter 2
Transmission Media
2.1 Open Wire
Open wire is traditionally used to describe the electrical wire strung along
power poles. There is a single wire strung between poles. No shielding or
protection from noise interference is used. We are going to extend the
traditional definition of open wire to include any data signal path without
shielding or protection from noise interference. This can include multi
conductor cables or single wires. This medium is susceptible to a large degree
of noise and interference and consequently is not acceptable for data
transmission except for short distances under 20 ft.
Fig (2.1)
2.2 Twisted Pair
Twisted pair is most widely used media for local data distribution.
They can carry digital or analog signals.
Bandwidth - 250 KHz
Data rate is several M bps.
They are used as local media, such as in a building, or a few rooms.
Open Wire
Chapter 2: Transmission Media
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Low cost.
Fig (2.2)
To connect between exchanges we prefer to use twisted pair with diameter 0.9
mm because it has low impedance and this enable to reach long distance.
2.3 Coaxial Cable
Coaxial cable consists of two conductors. The inner conductor is held inside
an insulator with the other conductor woven around it providing a shield. An
insulating protective coating called a jacket covers the outer conductor.
Bandwidth - 500 MHz
Fig (2.3)
Coaxial cable is a cable type used to carry radio signals, video signals,
measurement signals and data signals. Coaxial cable exists because we cannot
run open-wire line near metallic objects (such as ducting) or bury it. We trade
signal loss for convenience and flexibility. Coaxial cable consists of an
insulated center conductor that is covered with a shield. The signal is carried
between the cable shield and the center conductor. This arrangement give
Jacket Twisted Pair Bare wire
Jacket Shield Insulator Center
conductor
Chapter 2: Transmission Media
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4
quite good shielding against noise from outside cable, keeps the signal well
inside the cable and keeps cable characteristics stable.
Coaxial cables and systems connected to them are not ideal. There is always
some signal radiating from coaxial cable. Hence, the outer conductor also
functions as a shield to reduce coupling of the signal into adjacent wiring.
More shield coverage means less radiation of energy (but it does not
necessarily mean less signal attenuation).
Coaxial cables are typically characterized with the impedance and cable loss.
The length has nothing to do with coaxial cable impedance. Characteristic
impedance is determined by the size and spacing of the conductors and the
type of dielectric used between them. For ordinary coaxial cable used at
reasonable frequency.
2.3.1 Coaxial Cable Characteristic Impedance
The characteristic impedance depends on the dimensions of the inner and
outer conductors. The characteristic impedance of a cable (Zo) is determined
by the formula:
Zo = 138 log b/a
Where:
b the inside diameter of the outer conductor .
a the outside diameter of the inner conductor.
Here is a quick overview of common coaxial cable impedances and their main
uses:
1)50 ohms: 50 ohms coaxial cable is very widely used with radio transmitter
applications. It is used here because it matches nicely to many common
transmitter antenna types, can quite easily handle high transmitter power and
Chapter 2: Transmission Media
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is traditionally used in this type of applications (transmitters are generally
matched to 50 ohms impedance).
2)75 ohms: The characteristic impedance 75 ohms is an international
standard, based on optimizing the design of long distance coaxial cables. is
the coaxial cable type widely used in video and telecommunications
applications.
2.4 Microwave
- Requires no obstacles between transmitter and receiver
(Line Of Sight Link)
– Data rate - up to 300 Mbps
– Uses a parabolic dish antenna
Fig (2.4)
Direct line of sight transmission
between two ground stations
Microwave transmission
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2.5 Fiber Optics System
Low-loss glass fiber optic cable offers almost unlimited bandwidth and
unique advantages over all previously developed transmission media. The
basic point-to-point fiber optic transmission system consists of three basic
elements: the optical transmitter, the fiber optic cable and the optical receiver.
Fig (2.5)
The Optical Transmitter
The transmitter converts an electrical analog or digital signal into a
corresponding optical signal. The source of the optical signal can be either a
light emitting diode, or a solid-state laser diode. The most popular
wavelengths of operation for optical transmitters are 850, 1300, or 1550 nm .
The Fiber Optic Cable
The cable consists of one or more glass fibers, which act as waveguides for
the optical signal. Fiber optic cable is similar to electrical cable in its
construction, but provides special protection for the optical fiber within. For
systems requiring transmission over distances of many kilometers, or where
two or more fiber optic cables must be joined together, an optical splice is
commonly used .
Signal Input Signal Output
Fiber Optic Cable Optical
Transmitter
Optical
Receiver
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The Optical Receiver
The receiver converts the optical signal back into a replica of the original
electrical signal. The detector of the optical signal is either a PIN-type
photodiode or avalanche-type photodiode .
2.5.1 Advantages of Fiber Optic Systems and Application
Fiber optic transmission systems – a fiber optic transmitter and receiver,
connected by fiber optic cable – offer a wide range of benefits not offered by
traditional copper wire or coaxial cable. These include :
1- The ability to carry much more information and deliver it with greater
fidelity than either copper wire or coaxial cable .
2- Fiber optic cable can support much higher data rates, and at greater
distances, than coaxial cable, making it ideal for transmission of serial digital
data .
3- The fiber is immune to virtually all kinds of interference, including
lighting, and will not conduct electricity. It can therefore come in direct
contact with high voltage electrical equipment and power lines. It will also
not create ground loops of any kind .
4- As the basic fiber is made of glass, it will not corrode and is unaffected by
most chemicals. It can be buried directly in most kinds of soil or exposed to
most corrosive atmospheres in chemical plants without significant concern .
5- Since the only carrier in the fiber is light, there is no possibility of a Spark
from a broken fiber.
6- Fiber optic cables are virtually unaffected by outdoor atmospheric
conditions, allowing them to be lashed directly to telephone poles or existing
electrical cables without concern for extraneous signal pickup .
7- A fiber optic cable, even one that contains many fibers, is usually much
smaller and lighter in weight than a wire or coaxial cable with similar
Chapter 2: Transmission Media
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8
information carrying capacity. It is easier to handle and install, and uses less
duct space (It can frequently be installed without ducts).
8- Fiber optic cable is ideal for secure communications systems because it is
very difficult to tap but very easy to monitor. In addition, there is no electrical
radiation from a fiber .
Applications of Optical Fiber:
1- Computer Networks.
2- Trunks and Telephone Lines.
3- Medical Applications.
4- Submerged Communication.
5- Power Station.
6- Military Applications.
2.5.2 Light Basics
* Light rays propagate in different media with different velocities according
to the refractive index (n) of each medium.
* The refractive index is the ratio between the speed of light in both free
space and the medium respectively (n =c / ν)
* The speed of light in free space and air is (3x10 8 m / sec ) .
* When the light crosses the surface between two media, it is splitted into two
components one is reflected back in the first medium and the other is
refracted in the second medium according to the refractive indecies N1 & N2
obeying Snell's laws.
Chapter 2: Transmission Media
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Θ1 θ2
N1
N2
Θ2
Fig (2.6)
Note that:
The incidence angle (θ1): the angle between the incident ray and the plan
normal to the interface.
The incidence angle (θ2): the angle between the refracted ray and the plan
normal to the interface.
Snell's Law :
1- N1 Sin θ1 = N2 Sin θ2
2- The angle of incidence = the angle of reflection
Total Internal Reflection ( TIR ):
This occurs when: 1- (N1 > N2)
2- (θ1 > θc)
Critical Angle (θc) :
the incidence angle at which the refracted ray make refracted angle of 90
N1 Sin θc = N2 Sin θ1 = (N2/N1)
Chapter 2: Transmission Media
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When the (θ1 > θc) the refracted ray undergo total internal reflection in
the first medium.
In fiber optics the light is transmitted through the core of refractive index
N1 & the cladding has a refractive index N2 such that ( N1 >N2)
Fig (2.7)
Maximum Acceptance Angle( Φc ):
The maximum angle between the input ray & the axis of the fiber so that the
input ray can propagate along the fiber
By applying Snell's law of refraction at the (air-core) interface
Sin Φ1 =N1 Sin Φ2
At θ1 = θc Sin θ1 = Cos Φ2 = (N2/N1)
NA = Sin Φc =2
2
2
1 NN
This value is called numerical aperture (NA), is used to determine the
directions of accepted rays inside the optical fiber, and is considered a
characteristic property of the optical fiber.
CLADDING
CLADDING
CORE
θ1
Φ2
Φ1
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2.5.3 Fiber Structure
The basic structure of an optical fiber consists of three parts; the core, the
cladding, and the coating or buffer.
Fig (2.8)
CORE
1- The core is a cylindrical rod of dielectric material.
2- Dielectric material conducts no electricity.
3- Light propagates mainly along the core of the fiber.
4- The core is generally made of glass.
5- The core is described as having a radius of (a) and an index of
refraction n1.
CLADDING
1- The core is surrounded by a layer of material called the cladding.
2- Even though light will propagate along the fiber core without the layer
of cladding material, the cladding does perform some necessary
functions.
3- The cladding layer is made of a dielectric material with an index of
refraction n2.
Chapter 2: Transmission Media
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12
4- The index of refraction of the cladding material is less than that of the
core material.
5- The cladding is generally made of glass or plastic.
The cladding performs the following functions:
Reduces loss of light from the core into the surrounding air.
Reduces scattering loss at the surface of the core.
Protects the fiber from absorbing surface contaminants.
Adds mechanical strength.
COATING
1- Extra protection, the cladding is enclosed in an additional layer called
the coating or buffer.
2- The coating or buffer is a layer of material used to protect an optical
fiber from physical damage.
3- The material used for a buffer is a type of plastic.
4- The buffer is elastic in nature and prevents abrasions.
5- The buffer also prevents the optical fiber from scattering losses caused
by micro bends.
6- Micro bends occur when an optical fiber is placed on a rough and
distorted surface.
2.5.4 Optical Fiber Types
Fibers are classified according to the number of modes that they can
propagate.
* The first type is single mode fibers.
* The second type is multimode fibers.
The structure of the fiber can permit or restrict modes from propagating in a
fiber.
Chapter 2: Transmission Media
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2.5.4.1 Single Mode Fibers
The core size of single mode fibers is small.
The core size (diameter) is typically around 8 to 10 micrometers.
A fiber core of this size allows only the fundamental or lowest order mode
to propagate around a 1300 nanometer (nm) wavelength. Single mode fibers
propagate only one mode.
2.5.4.2 Multimode Fibers
As their name implies, multimode fibers propagate more than one mode.
Multimode fibers can propagate over 100 modes.
The number of modes propagated depends on the core size.
As the core, size the number of modes increases.
Another advantage is that multimode fibers permit the use of light-emitting
diodes (LEDs).
Multimode fibers also have some disadvantages.
As the number of modes increases, the effect of modal dispersion increases.
Modal dispersion (inter modal dispersion) means that modes arrive at the
fiber end at slightly different times. This time difference causes the light pulse
to spread. Modal dispersion affects system bandwidth.
Fiber refractive index profiles classify single mode and multimode fibers as
follows:
Chapter 2: Transmission Media
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Fig (2.9)
Comparison between Single mode and Multimode fiber
Single mode fiber. Multimode fiber.
Only one mode propagates
Along the fiber.
Multimode propagates
Along the fiber.
Used in long distances,
High-speed communication.
Used in short distances, low Speed
communication.
Uses LD as an Optical Source. LED used as an optical source.
Table 1
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2.5.5 Optical Source Properties
Optical source converts electrical signal to optical signal
Comparison between optical sources
Light Emitting Diode
LED
Laser Diode
LD
More simple circuit More complex circuit.
More cheap Very expensive
Low output power High output power
Low temperature sensitivity High temperature sensitivity
Higher Radiance (wider output Beam
angle)
Lower Radiance (narrow output Beam
angle)
Used with multimode fiber Used with single mode fiber
In general LED is used in Short distance
and low Bandwidth Systems
In general LD is used in Long distance
and wide Bandwidth System
Table 2
2.5.6 Optical Detectors
Optical detectors coverts light signal to electrical signal.
Fig (2.10)
Photo diodes
P-I-N junction
Avalanche
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2.5.7 Fiber Optic Loses Curve
Wave length (nm)
Fig (2.11)
According to the previous curve, the most used wavelengths are 850 nm,
1310 nm and 1550 nm.
Att
enu
ati
on
(db
/km
)
0.1
0.2
0.5
1.0
2.0
5.0
10
20
100
200 400 600 800 1000 1200 1400 1600 1800
Visible light 850 nm
Window
Early 1970s Fiber
Modern Fiber
1310 nm
window 1550 nm
window
Chapter 2: Transmission Media
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2.5.8 Optical Fiber Connectors
Fig (2.12)
DEUTSH 1000 AMP OPIMATE SMA
D4 FC BICONIC
ST SC FDDI
ESCON SODC
3M Voition
LC MT-RJ OptUack
Duplex SC (for
corrpaision)
ST FDDI SC
Chapter 3: Transmission Systems
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Chapter 3 Transmission Systems
Aim of study
This Chapter discusses the analog, digital transmission and different multiplexing
techniques.
Contents
3-1 Analog and digital transmission in telecommunication 2
3-2 Pulse Code Modulation (PCM) 3
3.3 Plesiochronous Digital Hierarchy (PDH) 13
3.4 Synchronous Digital Hierarchy (SDH) 15
3.5 Concatenation 21
3.6 Ethernet Over SDH (EOS) 23
3.7 WDM (Wavelength Division Multiplexing) 25
3.8 Acronym 26
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Chapter 3
Transmission Systems
3.1 Analog and digital transmission in telecommunication
3.1.1 Analog Signal (AS)
That has a continuous nature rather than a pulsed or discrete nature.
Fig (3.1)
Disadvantages of analog signal:
1- Error cannot be detected and corrected.
2- Signal takes any values at any interval of time.
3- More exposed to noise.
4- Hard to separate noise.
5- High cost circuits.
3.1.2 Digital Signal (DS)
A digital signal is a discrete signal. It is depicted as discontinuous.
Fig (3.2)
(A) MODULATION
Digital signal
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Each pulse (on/off) is known as a bit. Bit is a contraction of the words binary
and digit a binary (two-level) signal (1 or 0) is the most common digit signal
in the telecommunication. The number of bits transmitted per second is the bit
rate of the signal.
Advantages of digital signal
1- Error often can be corrected.
2- Holds a fixed value for a specific length of time.
3- Has a sharp, abrupt change.
4- Present number of values allowed.
Applications of digital signal
Typical applications of digital signal processing are, for example, speech
compression and transmission in (digital) mobile phones, weather forecasting
and economic forecasting, analysis and control of industrial processes,
computer-generated animations in movies and image manipulation
3.2 Pulse Code Modulation (PCM)
When telephone communication began individual connecting paths were
used, i.e. a separate pair of wires was used for every telephone connection.
This was known as space-division multiplex (SDM) because of the fact that a
multitude of lines were arranged physically next to each other. Since a
particularly large proportion of capital is invested in the line plant, efforts
were made at an early stage to make multiple uses of at least those lines used
for long-range communications. This led to the introduction of frequency-
division multiplex (FDM). FDM is used in analog systems.
It is not the only way of making multiple uses of lines however, another
possibility is offered by time-division multiplex (TDM). Here, the transmitted
telephone signals are separated in time.
Chapter 3: Transmission Systems
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Sampling Theorem
The sampling theorem is used to determine the minimum rate at which an
analog signal can be sampled without information being lost when the
original signal is recovered.
The sampling frequency (f S) must be more than twice the highest frequency
contained in the analog signal (f A):
f S >= 2 f A
3.2.1 Analog-to-Digital Conversion
1) Sampling
A sampling frequency (f A) of 8000 Hz has been specified internationally for
the frequency band (300 Hz to 3400 Hz) used in telephone systems, i.e. the
telephone signal is sampled 8000 times per second. The interval between two
consecutive samples from the same telephone signal (sampling interval = TA)
is calculated as follows:
TA = = = 125μs
Figure (3.3) shows how the telephone signal is fed via a low-pass filter to an
electronic switch. The low-pass filter limits the frequency band to be
transmitted; it suppresses frequencies higher than half the sampling
frequency. The electronic switch - driven at the sampling frequency of 8000
Hz - takes samples from the telephone signal once every 125 μs. A pulse
amplitude modulated signal is thus obtained at the output of the electronic
switch: PAM signal.
1
F A
1
8000 Hz
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Fig (3.3)
2) Quantizing
The pulse amplitude modulated signals (PAM signal) still represents the
telephone signal in analog form. The samples can be transmitted and further
processed much more easily in digital form. The first stage in the conversion
to a digital signal - in this case a pulse code modulated signal (PCM signal) –
is quantizing. The whole range of possible amplitude values is divided into
quantizing intervals.
The quantizing principle is shown in Figure (3.4) .In order to simplify the
explanation only 16 equal quantizing intervals are numbered from +1 to +8 in
the positive range of the telephone signal and from -1 to -8 in the negative
range.
The appropriate quantizing interval is determined for each sample. Decision
values form the boundaries between adjacent quantizing intervals. On the
transmit side, therefore, several different analog values fall within the same
quantizing interval. On the receive side one signal value, corresponding to the
midpoint of the quantizing interval, is recovered for each quantizing interval.
Chapter 3: Transmission Systems
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This causes small discrepancies to occur between the original telephone signal
samples on the transmit side and the recovered values. The discrepancy for
each sample can be up to half a quantizing interval. The quantizing distortion
which may arise on the receive side as a result of this manifests itself as noise
superimposed on the useful signal. Quantizing distortion decreases as the
number of quantizing intervals are increased. If the quantizing intervals are
made sufficiently small the distortion will be minimal and the noise
imperceptible.
Fig (3.4)
If equally large quantizing intervals are used over the whole amplitude range,
relatively large discrepancies will occur in the case of small signal amplitudes
(uniform quantizing). These discrepancies might be of the same order of
magnitude as the input signals themselves and the signal-to-quantizing noise
ratio would not be large enough. For this reason, 256 unequal quantizing
intervals are used in the practice (non-uniform quantizing):
- Small quantizing intervals for lower signal values
+8
+7
+6
+5
+4
+3 +2
+1
-1
-2
-3
-4
-5
-6
-7
-8
Decision
Values
PAM signal Quantizing intervals
Sampling instants
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- Larger quantizing intervals for higher signal values
a) The "13 segment characteristic"
(A-law, e.g. for the PCM30 transmission system in Europe)
b) The "15 segment characteristic"
(μ-law, e.g. for the PCM24 transmission system in the USA)
We will focus on A-law
Fig (3.5)
3) Encoding
In this case, each sample is represented in 8 bit so we have 28
= 256 level and
the 8 bit is formatted as follow:
8-bit word
1- Bit (8) used for sign.
1 2 3 4 5 6 7 8
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1 Positive Side 0 Negative Side
2- Bits (5), (6) and (7) used for segment number.
3- Bits (1), (2), (3) and (4) used to determine the level number inside the
segment.
We have 8000 sample each second and each sample is encoded in 8 bit so we
have:
Bit rate = 8000 × 8 = 64 Kbps
3.2.2 Structure of the 2 Mbit/s Frame (Europe)
In the direction of transmission, the primary multiplexer PCM30 transforms
up to 30 signals with different features into 64-kbit/s-digital signals and then
combines them by the time division multiplexing procedure to a 2048-kbit/s
(2-Mbit/s)-signal. The individual signals can be either speech signals
converted by pulse code modulation, or digital signals (e.g. data).
In the receive direction a demultiplexer isolates the individual signals out of
the 2 Mbit/s signal. The 64-kbit/s-digital signals are then converted again into
analog signals.
The 2-Mbit/s pulse frame accord. To CCITT-recommendation G.704 consists
of 32 time intervals with 8 bits each. In the intervals, 1 to 15 and 17 to 31
speech or digital signals are transmitted. Interval 16 contains the channel-
associated signaling information (CAS) combined in one multi-frame,
optionally, an additional device specific data channel. In the Interval 0
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Fig (3.6) The Multi-frame in case of using CAS
There is an alternate transmission of a frame alignment signal (FAS) or a
service word (SW).
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Fig (3.7)
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PCM30 bit rate calculation:
Bit rate = 32 × 8 × 8000 = 2.048 Mbps
This is called E1.
PCM24 (American)
There is American standard PCM24 for digital transmission
Fig (3.8)
PCM24 bit rate calculation:
Bit rate = [1+ (24×8)] × 8000 = 1.544 Mbps
This is called T1.
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Comparison between PCM30 and PCM 24
Common characteristics
8 KHz Sampling frequency 1
8000 /s No. of samples per telephone
signal 2
Pulse frame period 3
8 bits No. of bits in a PCM word 4
b.d = 8000 /s ×8 bits =64 kbit /s Bit rate of a telephone channel 5
PCM 24 PCM 30 System– specific characteristics
Law- µ
15
A-law
13
Encoding / Decoding
No. of segments in characteristic 1
24 32 Number of channel time slots per
pulse frame 2
d.g+1*=(8bit×24) +1*
= 193 bits.
d.g = 8bit × 32 =
256 bits
Number of bits per pulse frame
(* = additional bit) 3
Period of an 8-bit channel time
slot 4
b.h =
8000/s×193bits= 1544
kbit /s
b.h =
8000/s×256bits=
2048 kbit /s
Bit rate of time division multiplex
signal 5
Table 1
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3.3 Plesiochronous Digital Hierarchies (PDH)
Digital multiplexers are applied wherever a high transmission capacity with
effective use of transmission paths to be realized.
The basic idea of multiplexing is the time interleaving of digital signals of
different sources in order to form a common signal with a bit rate, which is
correspondingly higher (multiplex process). On the system's receiving side
the appropriate separate signals are reobtained from the sum signal (de-
multiplex process). This means that the original digital signals of the
multiplexed signal sources are available again at the output of such a system.
The European plesiochronous digital hierarchy (CEPT-standard) is based on a
2048 kbit/s digital signal (stage 1) which may come for example from a
PCM30 system, a digital exchange or from any other device.
Starting from this signal, the next higher hierarchies are formed, each having
a transmission capacity, which is four times the previous one.
Bit-by-bit interleaving
This method is used for all systems beyond the 2 Mbit/s hierarchy. Here a
cyclic transmission sequence is applied, where only one bit of each separate
signal is transmitted. This means that the signal of a certain multiplexer input
appears only in every fourth bit of the sum signal.
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Fig (3.9)
For Europe system PDH Hierarchy is:
E2 = 4 X E1 = 8448 Kbps
E3 = 4 x E2 = 34368 Kbps
E4 = 4 x E3 = 139264 Kbps
E5 = 4 x E4 = 564992 Kbps
The Signals 2 Mbps, 34 Mbps, 140 Mbps are called PDH signals.
Primary rate
2. Order
Japanese standard
North American
Standard
European
Standard
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3.4 Synchronous Digital Hierarchy (SDH)
SDH (Synchronous Digital Hierarchy) is an international standard for high-
speed telecommunication over optical/electrical networks, which can
transport digital signals in variable capacities. It is a synchronous system,
which intends to provide a more flexible, yet simple network infrastructure.
Why using SDH?
Although PDH was a breakthrough in the digital transmission systems, it has
many weaknesses:
No world standard for optical interfaces. Networking is impossible at the
optical level.
Rigid asynchronous multiplexing structure.
Limited management capability.
Because of PDH disadvantages, it was obvious that a new multiplexing
method is needed. The new method was called SDH.
3.4.1 SDH Advantages
First world standard in digital format.
First optical Interfaces.
Transversal compatibility reduces networking cost. Multivendor
environment drives price down
Flexible synchronous multiplexing structure.
Easy and cost-efficient traffic add-and-drop and cross connect capability.
Reduced number of back-to-back interfaces improves network reliability
and serviceability.
Powerful management capability.
New network architecture. Highly flexible and survivable self-healing
rings available.
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Backward and forward compatibility: Backward compatibility to existing PDH.
Byte-by-Byte interleaving
SDH uses byte-by-byte interleaving to generate multiplex sum signal.
3.4.2 SDH Hierarchy
The following diagram shows these multiplexing paths:
Fig (3.10)
Container ( Cn )
To transmit PDH signal along SDH network it putted first in frame called
container.
Each PDH signal has a specific container, for example:
C12 2 Mbps
C3 34 Mbps
C4 140 Mbps
STM-1 AUG AU-4 VC-4 C-4 139264
Kb/s
HO
P
44736 Kb/s
(DS3)
34388 Kb/s
C-3
VC-3 TU-3 TUG-3
VC-3 AU-3
TUG-2 TU-2
TU-12
TU-11
VC-2
VC-12
VC-11
C-2
C-12
C-11
6312 Kb/s
(DS2)
2048 Kb/s
1544 Kb/s
(DS1)
LOP
xN
x1
x3
x3
x1
x3
x1
x4
x7
x7
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Virtual Containers ( VCn )
Once a container has been created, path overhead byte is added to create a
virtual container. Path overheads contain alarm, performance and other
management information.
Vcn = Cn + POH
Ex:
VC12 = C12 + POH
Tributary Unit ( TUn )
Tun = VCn + Pointer
We put pointer to define the beginning of VCn signal so overcome the change
in the clock difference in the network.
Ex:
TU12 = VC12 + Pointer
Tributary unit group ( TUGn )
It is multiplexing between homogenous signals.
Administrative Unit ( AU4 )
AU4 = VC4 + Section overhead (SOH)
3.4.3 SDH basic frame
A frame with a bit rate of 155.52 Mbit/s is defined in ITU-T Recommendation
G.707. This frame is called the synchronous transport module (STM). Since
the frame is the first level of the synchronous digital hierarchy, it is known as
STM-1. It is made up from a byte matrix of 9 rows and 270 columns.
Transmission is row by row, starting with the byte in the upper left corner and
ending with the byte in the lower right corner. The frame repetition rate is 125
ms. each byte in the payload represents a 64 kbit/s channel.
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Fig (3.11)
Section overhead (SOH)
The first 9 bytes in each of the 9 rows are called the overhead. G.707 makes a
distinction between the regenerator section overhead (RSOH) and the
multiplex section overhead (MSOH). The reason for this is to be able to
couple the functions of certain overhead bytes to the network architecture.
The table below describes the individual functions of the bytes.
AU Pointer
It is first 9 bytes, which located in the fourth row and it is used mainly to
define the beginning of VC4 frame.
Payload
It is used to carry the traffic. It can carry 63 E1 or 3 E3 or 1 E4 or mixing
of E1s and E3s
STM-1 bit rate calculation :
Bit rate = 270 x 9 x 8 x 8000 = 155.52 Mbps
270 columns (Bytes)
270
9
1
1
3
4
5
9
RSOH
AU pointer
MSOH
Payload
(Transport capacity)
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SDH Rates
SDH is a transport hierarchy based on multiples of 155.52 Mbit/s
The basic unit of SDH is STM-1:
STM-1 = 155.52 Mbit/s STM-4 = 622.08 Mbit/s
STM-16 = 2588.32 Mbit/s STM-64 = 9953.28 Mbit/s
Fig (3.12)
3.4.4 SDH Network Topology
Traditional networks make use of Point-to-Point, Mesh and Hub (i.e. star)
arrangements.
Fig (3.13)
STM-N = N x STM-1
Section
Overhead
Section
Overhead
Section
Overhead
STM-1
STM-4
STM-16
Each Frame is sent in 125µs!
9/ Rows
9/ Rows
9/ Rows
9 Col
36 Col
144 Col 4.176 Col
261 Col
1.044 Col
2488.32 Mbps
622.08 Mbps
155.52 Mbps
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However, SDH allows these to be used in a much more comprehensive way:
Fig (3.14)
3.4.5 SDH Network Protection
1) 1+1 Protection
Fig (3.15)
2) 1+N Protection
Fig (3.16)
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3) Ring Protection
Fig (3.17)
3.5 Concatenation
This mechanism is provided to allow bit rates in excess of the excess of the
capacity of C-4 container to be transmitted; the AU-4-4c is intended for
Ethernet. The advantage of this method is that the payload must not be split
up, since a virtually container is formed within STM-4. The payloads of
several consecutive AU-4s are linked by setting all pointers to a fixed value,
the concatenation indicator (CI), with the exception of the pointer for the first
AU-4.
ADM
ADM
ADM
ADM
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The first pointer indicates J1
All other pointers are set to concatenation indication (CI)
Fig (3.18)
Fig (3.19)
Fig (3.20)
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3.6 Ethernet Over SDH (EOS)
Refers to a set of protocols, which allow Ethernet traffic to be carried over
synchronous digital hierarchy networks in an efficient and flexible way.
Ethernet frames which are to be sent on the SDH link are sent through an
"encapsulation" block (typically Generic Framing Procedure or GFP) to
create a synchronous stream of data from the asynchronous Ethernet packets.
The synchronous stream of encapsulated data is then passed through a
mapping block, which typically uses virtual concatenation (VCAT) to route
the stream of bits over one or more SDH paths. As this is byte interleaved this
provides better level of security compared to other mechanism for Ethernet
transport.
After traversing SDH paths, the traffic is processed in the reverse fashion:
virtual concatenation path processing to recreate the original synchronous
byte stream, followed by decapsulation to converting the synchronous data
stream to an asynchronous stream of Ethernet frames.
The SDH paths may be VC-4, VC-3, and VC-12 paths. Up to 64 VC-12 paths
can be concatenated together to form a single larger virtually concatenated
group. Up to 256 VC-3 or VC-4 paths can be concatenated together to form a
single larger virtually concatenated group. The paths within a group are
referred to as "members". A virtually concatenated group is typically referred
to by the notation:
<Path Type>-<X>v
Where:
<Path Type> VC-4, VC-3, VC-12 or VC-11
X the number of members in the group.
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A 10-Mbit/s Ethernet link is often transported over a VC-12-5v, which
allows the full bandwidth to be carried for all packet sizes.
A 100-Mbit/s Ethernet link is often transported over a VC-3-2v, which
allows the full bandwidth to be carried when smaller packets are used (< 250
bytes) and Ethernet flow control restricts the rate of traffic for larger packets.
A 1000-Mbit/s (or 1G) Ethernet link is often transported over a VC-3-21v
or a VC-4-7v which allows the full bandwidth to be carried for all packets.
Link Capacity Adjustment Scheme (LCAS), which dynamically changes the
amount a bandwidth used for a virtual concatenated channel. Using Link
Capacity Adjustment Scheme (LCAS), signaling messages are exchanged
within the SDH overhead in order to change the number of tributaries being
used by a Virtually Concatenated Group (VCG). The number of tributaries
may be either reduced or increased, and the resulting bandwidth change may
be applied without loss of data in the absence of network errors.
Fig (3.21)
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3.7 WDM (Wavelength Division Multiplexing)
Until the late 1980s, optical fiber communications was mainly confined to
transmitting a single optical channel. Because fiber attenuation was involved,
this channel required periodic regeneration, which included detection,
electronic processing, and optical retransmission. Such regeneration causes a
high-speed optoelectronic bottleneck and can handle only a single
wavelength. After the new generation amplifiers were developed, it enabled
us to accomplish high-speed repeater less single-channel transmission. We
can think of single ~ Gbps channel as a single high-speed lane in a highway in
which the cars are packets of optical data and the highway is the optical fiber.
However, the ~25 THz optical fiber can accommodate much more bandwidth
than the traffic from a single lane. To increase the system capacity we can
transmit several different independent wavelengths simultaneously down a
fiber to fully utilize this enormous fiber bandwidth. Therefore, the intent was
to develop a multiple-lane highway, with each lane representing data traveling
on a different wavelength. Thus, a WDM system enables the fiber to carry
more throughputs. By using wavelength-selective devices, independent signal
routing also can be accomplished.
WDM (wavelength division multiplexing), in which several baseband-
modulated channels are transmitted along a single fiber but with each channel
located at a different wavelength. Each of N different wavelength lasers is
operating at the slower Gbps speeds, but the aggregate system is transmitting
at N times the individual laser speed, providing a significant capacity
enhancement. The WDM channels are separated in wavelength to avoid cross
talk when they are (de)multiplexed by a non-ideal optical fiber. The
wavelengths can be individually routed through a network or individually
recovered by wavelength-selective components. WDM allows us to use much
of the fiber bandwidth, although various device, system, and network issues
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will limit the utilization of the full fiber bandwidth. Note that each WDM
channel may contain a set of even slower time-multiplexed channels.
Fig (3.22)
3.8 Acronym
Add Drop Multiplexer ADM
Analog Signal AS
Administrative Unit AU4
Cross Connect Cabinet CCC
Channel-associated signaling CAS
Concatenation Indicator CI
Container Cn
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Distribution Point. DP
Digital signal DS
Ethernet Over SDH EOS
Frame Alignment Signal FAS
Frequency-Division Multiplex FDM
Generic Framing Procedure GFP
Link Capacity Adjustment Scheme LCAS
Light Emitting Diode LED
Laser Diode LD
Main Distribution Frame MDF
Pulse Amplitude Modulated PAM
Pulse Code Modulation PCM
Plesiochronous Digital Hierarchy PDH
Path Overhead POH
Space-Division Multiplex SDM
Synchronous Digital Hierarchy SDH
Section Overhead SOH
Synchronous Transport Module STM
Service Word SVW
Time-Division Multiplex TDM
Total Internal Reflection TIR
Tributary Unit TUn
Virtual Container VCn
Virtually Concatenated Group VCG
Wavelength Division Multiplexing WDM
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Part 2
SS7
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SS7 Overview
Training SectorChapter2 : SS7 Overview
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1 Introduction
2 Signaling Network
2.1 Components of a Signaling Network
2.2 Modes of Signaling
2. Signaling Network Structure
Introduction of Signaling
Contents
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1 Introduction
Why do we need signaling?
Communication networks connect terminal equipments by using nodes (exchanges) to
communicate speech, data, text, images etc.
The nodes have to exchange some information in order to control the setup and clear
down of these connections and also to maintain the network itself, this information is
called signaling.
Basically we have two kinds of signaling information:
Signaling between the terminal equipment and the nodes.
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Signaling between two nodes.
Signaling between two nodes is divided into Two different types.
Type 1: Channel-associated signaling (CAS)
In such a system the 32 channels are divided as follows:
30 channels available for up to 30 voice calls and also can carry Register signals.
Channel (0) dedicated to carrying frame synchronization information.
Channel (16)dedicated to carrying signaling information (Line signals).
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All 30-speech channels have to share the capacity of this one signaling channel.
Time slot 16 of any one frame is always assigned to two different speech channels
simultaneously, with each speech channel being allocated 4 bits respectively.
Channel-associated signaling systems re used mainly in networks employing
preferably analog exchanges.
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Exchange A Exchange B
Speech channel
Common channel
Figure 1.Channel-Associated signaling
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E xc h a n ge
A
E xc h an g e
B
C h .1C h .0 C h .2 C h.1 6 C h .3 1C h .3 0
P C M 1
S yn c h ro n iza t io n
U s e rIn fo .+R e gi s te r
S i gn a ls
L i ne S i gn a ls
C h .1C h .0 C h .2 C h.1 6 C h .3 1C h .3 0
P C M n
S yn c h ro n iza t io n
U s e rIn fo .+R e gi s te r
S i gn a ls
L i ne S i gn a ls
Figure 2.Connection between two exchanges using CAS signaling
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FAS TS 1 TS 2 TS 30TS 16Fram e 0
FA S SW
SW TS 1 TS 2 TS 31TS 30F ram e 1
T S 1 T S 17
TS 16 TS 17
TS 31
TS 31
TS 17
Figure 3.a Frames of one of the PCMs in case of using CAS signaling
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F AS TS 1 TS 2 T S 3 1T S 3 0F ra m e 2
T S 2 T S 1 8
TS 1 6 T S 3 1TS 1 8T S 1 7
SW TS 1 T S 3 1F ra m e 1 5
T S 1 5 T S 3 1
TS 1 6 T S 3 1TS 1 8T S 1 7T S 1 5
Figure 3.b Frames of one of the PCMs in case of using CAS signaling
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Type 2: Common channel signaling (CCS)
In such a system one common signaling channel is provided for a number of speech
channels.
Thus, the capacity of the signaling channel is available as a common pool and is
used by the speech channels according to the dynamic demand, i.e. there is no
permanent assignment of signaling channel to speech channel.
The common signaling channel (often referred to as signaling link) carries out the
signaling information transport for a number of speech channels.
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The signaling link can be viewed as a tunnel, which connects two exchanges,
possesses a typical transmission rate of 64 kbit/s and accepts and conveys all
signaling information.
Signaling information transfer is made possible by sending messages. A message is
an information block whose structure and meaning of the single elements in the block
are defined by specifications.
The control of signaling information transfer is separated from the control of speech-
channel through-connection.
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Exchange A Exchange B
Speech channel
Common channel
Figure 4.Common channel signaling
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E x c h a n g e
A
E x c h a n g e
B
C h . 1C h . 0 C h . 2 C h . 3 1C h . 3 0
P C M 1
S y n c h ro n i z a t i o n U s e r I n f o .
S i g n a l i n gC h a n e l
C h . 1C h . 0 C h . 2 C h . 3 1C h . 3 0
P C M n
S y n c h ro n i z a t i o n U s e r I n f o .
C h . n
Figure 5.Connection between two exchanges using CCS signaling
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What are the advantages of common channel signaling
systems?
• The separation between speech channel network and signaling network is the key to
the more flexible communications networks of the future (ISDN).
•The creation of common signaling channels allows unrestricted communication and
flexible data transfer between two exchanges and/or their processors. This
data transfer can also be used for network
management, operating and administration functions.
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• The common signaling channels can also be used
to exchange non-circuit-related control information between exchanges (e.g.
CCBS, CCNR, IN applications, etc.).
• Signaling information can be exchanged without
regard to the speech channel or circuit status, and
without disturbing the calling or called party.
• Reduced call setup times thanks to the high
transmission capacity (normally 64 kbit/s) and the
usage of message structures (one message can
include all called party digits).
• Processor-friendly message structure (multiples of 8 bits).
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• Common channel signaling also supports services
such as
User-to-user signaling
Messages are exchanged directly between
two terminals and pass through the network
in transparent mode.
End-to-end signaling
Messages are exchanged between the
originating and destination exchange without
being evaluated in the transit exchanges.
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• Reliability is high because error detection and
correction measures provide for error-free message
transmission. If one signaling link fails, Rerouting
guarantees that the signaling information will still be
transferred.
• Like most modern protocols, the SS7 protocol is layered. The layered structure of the
system gives us the ability to change a level without affecting the other levels. This
means future services and applications can be implemented fast and cost-effectively.
The first two common channel signaling systems
specified internationally by ITU-T were
ITU-T signaling system No. 6 (CCS6) and
ITU-T signaling system No. 7 (SS7)
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Exchange A Exchange B
Speech channels
Com m on channel signaling links
Exchange C
Figure 6.Alternative paths through the signaling network
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2 Signaling Network
2.1 Components of a SS7 Signaling Network
Basic concepts
A telecommunications network served by common channel signalling is composed of a
number of switching and processing nodes interconnected by transmission links. To
communicate using SS7, each of these nodes requires to implement the necessary
“within node” features of SS7 making that node a signalling point within the SS7
network. In addition, there will be a need to interconnect these signalling points such
that SS7 signalling information (data) may be conveyed between them. These data
links are the signalling links of SS7 signalling network.
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The combination of signalling points and their interconnecting signalling links form the
SS No. 7 signalling network.
Signaling network components
Signaling points
A distinction is made between:
• Signaling points (SP) and
• Signaling transfer points (STP).
The signaling points are the sources (origination points) and sinks (destination points) of the
signaling traffic. In a communications network both these points are usually exchanges.
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The signaling transfer points forward received signaling messages to another signaling
points.
No call processing of the message takes place in a signaling transfer point. A signaling
transfer point may be integrated in a signaling point (e.g. an exchange) or may be a
separate node in the signaling network.
All signaling points in a SS No. 7 network are identified by a unique code known as a point
code (Signaling Point Code (SPC)) defined by a corresponding numbering scheme and can
therefore be addressed specifically in a signaling message.
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Signaling link
The common channel signalling system uses signalling links (time slots belonging to an
existing transmission route [e.g. a PCM30 link] ) to convey the signalling messages
between two signalling points.
For redundancy purposes, more than one signaling link generally exists between two
signaling points. If one signaling link fails the SS7 functions cause the signaling traffic to be
diverted to functioning alternative links.
A number of signalling links that directly interconnect two signalling points forms what is
called a signalling link-set.
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Two signaling points that are directly interconnected by a signaling link are, from a signaling
network structure point of view, referred to as adjacent signaling points.
Switching
network
Control
Signaling linkterminal
Signaling linkterminal
Switching
network
Control
Signaling link
Circuits
Figure 7.Signaling and circuit network
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2.2 Modes of signaling
Two different signaling modes can be used in the signaling network.
If the associated mode of signaling is used, the signaling link is routed together with the
associated circuit group.
That is to say, the signaling link is connected with those signaling points, which are also
the end points of the circuit group. This signaling mode is recommended in cases
where the traffic relation between the signaling points A and B carries high traffic loads.
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In the quasi-associated mode of signaling the signaling links and the circuit group
follow different routes. Although the circuit group connects the signaling points A and B
directly, one or more signaling transfer points handle the signaling for the circuit group.
This mode is advantageous for less busy traffic relations as it allows one signaling link
to be used for several destinations simultaneously.
Signaling point A S ignaling point B
C ircu it group
S ignaling link
Figure 8.Associated mode of signaling
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Signaling point A Signaling point B
Circuit group
Signaling links
Signaling point C/
signaling transfer point
Figure 9.Quasi-associated mode of signaling
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Signaling point modes
A signaling point, at which a message is generated, is the originating point of that
message.
A signaling point to which a message is destined, is the destination point of that
message.
A signalling point at which a message is received on one signalling link and is
transferred
to another link, is a Signal Transfer Point (STP).
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Signaling routes
The path determined for the signaling between an origination point and a destination
point is termed the signaling route.
Between these two signaling points the signaling traffic can be distributed over several
different signaling routes.
All the signalling routes that may be used between an originating point and a
destination point by a message traversing the signalling network is the signalling route
set for that signalling relation.
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O r i g in a t in g
p o in t AD e s t in a t io n
p o in t BL S E T 2T 2 T 4
T 1 T 5
T 3
L S E T 3
L S E T 1
T x : S ig n a l in g t r a n s fe r p o in t
Figure 10.Signaling route set
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In Figure 10 the signaling routes from A to B are LSET1, LSET2 and LSET3.
These routes comprise the signaling route set for B.
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2.3 Signaling Network structure
The definition of two different modes of signaling allows various signaling network designs.
A network can be structured with a uniform mode of signaling (associated or quasi-
associated) or else with a mixed mode (associated and quasi-associated).
The worldwide signaling network is categorized by two functionally independent levels, the
first one is the international level and the second one is the national level. Each network has
a separate numbering scheme for its own signaling points.
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The circuits between two adjacent signaling points are combined to form a circuit
group.
Figure 11. Network Structure
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