training report connect
TRANSCRIPT
Two Months industrial Training
At
CONNECT, Jalandhar
Submitted By : Pavitter Pal Kaur Submitted To : Er. Atul Mahajan
Roll Number : 6010404617
1
ABOUT HFCL INFOTEL
LTD.
HFCL Infotel Ltd. (Infotel) is part of the HFCL Group. Established in
the year 1987, Himachal Futuristic Communications Ltd. has developed a vast base
for manufacturing indigenous telecom equipment in India. It started with manufacturing
Transmission Equipment and soon expanded its product portfolio to manufacture Access
Equipment, Optical Fiber Cable, Accessories and Terminal Equipment. It also
provides turnkey solutions for setting up various types of telecom networks.
HFCL is a prominent supplier of Telecom Equipment to the state owned
Incombent Telecom Companies and Private Operators. It provides turnkey services to
various telecom operators and public enterprises such as the Indian Railways, Ministry
of Defence and other government departments. It has established a diverse customer
base. Infotel is a "Total Telecom Solutions Provider" offering Fixed Line telephony
(Telephone Services), Mobile telephony, Broadband Services, Customized Data Services
and Value Added Services.
Infotel was launched in Punjab in the year 2000 under the Connect brand
name. Infotel has set up state-of-the-art networks with coverage in over 136 towns of
Punjab with extensive optical fiber network coverage of over 3,500 km. Today, Infotel is
one of Punjab's leading private sector telecommunication service providers with an
aggregate customer base of 330,000(March 2007).
Infotel Broadband network supports interactive multi media services, and
can handle high quality content, high speed internet access and a large number of
interactive applications.
2
Infotel supports a wide Public Call Office (PCO) network across the state
of Punjab & Chandigarh. Now with over 45,000 PCOs, Infotel is deemed to have the
largest PCO network in India among all private fixedline services operator in a single
circle.
PRODUCTS AND SERVICES:
1. Voice Services: These include
Fixedline Telephony
Mobile Telephony
ISDN
Centrex (an alternative for EPABX)
Telemeet (audio conference service)
2. Data & Internet Services: These include
Mailing Solutions
Leased Line
Internet Leased Line
ISDN
Videomeet (Video conferencing)
Customized Solutions
3
HIGHLIGHTS:
October 2000 Launch of Telecom services in Punjab
January 2001 Launch of Internet services
February 2001 Launch of Limited mobility CDMA services
July 2004 Launch of Broadband data services
October 2005 Test Launch of Triple play services
September 2007 Launch of Ping Mobile
Technology Used:
CONNECT uses Optical Fiber Technology in the state of Punjab and
Chandigarh. Unlike conventional technologies, optical fiber supports Broadband
applications, which gives you the advantage of using a single line for all your
communication needs. HFCL, Lucent Technologies USA and Huawei Technologies
China also support it.
The PING Mobile Service:
HFCL launched their mobile service for Punjab and
Chandigarh under the brand name “Ping”. It offers call
charges of 1 paisa per second with the benefit of single second
4
billing. This means users will pay for exact usage time – in seconds rather than in
minutes.
It has also launched a new SIM-based color mobile handset on
which the ‘Ping’ mobile service will be made available. The service will be available on
the CDMA platform across 150 towns and 5,000 villages in Punjab and Chandigarh.
SUMMARY OF WORK
Connect is a leading telecommunications organization of Punjab. It
provides both wireline and wireless services in Punjab. For this there are various
departments including switching and O&M departments. The O&M deptt. further has
many sub deptts. like Transmission Deptt., corDECT Deptt., BSS Deptt., NE Deptt., ISP
Deptt., etc.
During our industrial training, we studied and worked in these different
departments.
A. Transmission Deptt.
This department basically controls all the transmission media for the
transfer of data and voice. The transmission media used is optical fiber. This is because,
there are minimum number of losses in this and is also not frequently damaged.
The data travels through E1s which is a 2Mbps PCM signal.
There are many transmission standards used:
a. PDH (Pleisochronous Digital Hierarchy)
b. SONET (Synchronous Optical Networking)
c. SDH (Synchronous Digital Hierarchy)
PDH was used earlier. It had limitations like insufficient capacity for network
management. Thus SONET and SDH were discovered.
5
SDH is the mostly used standard. Its basic structure level is Synchronous Transfer
Module (STM-1) having a bit rate of 155Mbps.
Bit Rate SDH SDH Capacity
155.5 Mbps STM-1 63 E1s
622 Mbps STM-4 252 E1s i.e. 4x63
2.5 Gbps STM-16 1008 E1s i.e. 16x63
Physically STM-4 is commonly used. It is a network device that converts optical
signal into electrical E1 and vice-versa.
The E1s from STM are terminated on an MDF (Main Distribution Frame). Here
E1s are cross-patched. Physically, each E1 has two wires – one for transmission and the
other for reception. While patching two E1s on a krone module of MDF, the trans of one
E1 is patched with receive of the other.
There are two types of alarms that may be shown in case an E1 goes down. They are as
follows:
LOS (Loss of Signal):
This is shown when patching is not done at the local terminal. Such a time
slot is deleted first. Then to re-establish the connection, cross-connection is made. Then a
protection is created for it. This is done to make it revertive, i.e., in case connection
breaks from one direction, it diverts to the other direction.
AIS (Alarm Indication Signal):
This signal is shown when the patching is not done at the remote terminal. The
multiplexer registers this alarm and then stops transmission of signal and transmits a
continuous sequence of 1s. This causes multiplexer at the other end to show an AIS
alarm.
Study of Different equipments used in transmission:
1.) EDFA (Erbium Doped Fiber Amplifier):
This is used to increase the power level of signal traveling through a medium.
6
2.) Power Meter:
This is used to measure the level of power through a medium such as optical fiber.
3.) Attenuator:
This is used to lower the level of power in order to avoid damage to equipments.
4.) OTDR (Optical Time Domain Reflectometer):
This is a device used to measure losses in an optical fiber of given length. It also
gives the approx. location where the loss has occurred.
5.) E1 Tester:
This is used to check if loop has been established and to see if there are any errors
in the connection.
6.) FDS (Fiber Distribution System):
Here individual nodes are connected to each other through spliced fibers using
connectors.
DSLAM (Digital Subscriber Line Access Multiplexer):
Earlier dial-up connections were used at homes i.e. a customer could
either use phone to make a call or connect it to the computer to access the internet. Also
the maximum speed that could be given was just around 56 kbps. Thus DSLAM came to
be used. These allow faster access to internet and user can use both phone and internet at
the same time.
The DSLAMs used earlier were based on ATM technology and now they
are IP based. ATM DSLAMs allowed lesser speeds and also lesser number of
subscribers. IP DSLAM supports more number of customers and also gives faster access
to internet (approx. 2Mbps).
DLC (Digital Local Circuit):
This is a network device used to provide internet access as well as wireline
services to customers. For this, it has many cards which control different functions.
7
To connect two branches of an organization, point-to-point connectivity
is required. This is provided by using radio modems.
B. BSS Controlling:
Erlang is the unit of traffic. Erlang is the resource (voice channel) which is
used continuously by one subscriber for one hour.
For wireless services, the main network devices are:
MSC (Mobile Switching Center)
BSC (Base Station Controller)
BTS (Base Transceiver Station)
Mobile Station
One MSC controls many BSCs which in turn control many BTSs. Each
BTS gives an alarm in case of any problem like increase in power, etc. These BTSs are
continuously monitored using iManager 2000 software. BSCs are connected to BTS
through two-layer switches, three-layer switches, STM and MDF. From MDF, E1s are
given to the BTS. BSCs may be E1 based or IP based. E1 based BSCs provide less speed
as compared to IP based BSCs.
One complete BSC has a capacity of 9600 erlangs.
All BSCs, BTSs have a number of cards to control different functions. For
example, CSPU card of BSC is used for signal processing, CBIE card is used for E1
interfacing in E1 based BSCs, etc.
A BTS acts as an interface to connect the mobile units to the BSC. The
BTS has the following main parts:
Duplexer
8
Amplifier
Transceiver
Clock
Rectifier
Power Supply Unit
Fans
Call Processor
These all parts are included in different cards of the BTS.
GSM (Global System for Mobile Communication):
It is a communication standard used for mobile communication.
Uplink Frequency – Mobile to BTS – 890 MHz to 915 MHz
Downlink Frequency – BTS to mobile – 935 MHz to 960 MHz
It consists of four main parts:
a. Mobile Station: It includes the SIM and the handset.
b. Base Station Subsystem (BSS): It consists of BSC and BTS.
c. Network Subsystem: It consists of MSC, HLR (Home Location Register), VLR
(Visitor Location Register), AUC (Authentication Center) and EIR.
d. OMC (Operation and Maintenance Center): It controls and maintains the
MSC, BSC and BTS.
The important features of GSM are roaming, handover, frequency hopping and frequency
reuse. Another standard of communication CDMA was also studied.
C. corDECT System:
The corDECT system is designed to provide a cost
effective wireless high quality voice and data connection in dense urban as well as sparse
rural areas. The system enables wireless subscriber to be connected to the PSTN in a cost
effective manner. Its different parts are as follows:
1. DECT interface unit (DIU)
9
2. Compact Base Station (CBS)
3. Relay Base Station (RBS)
4. Base Station Distributor (BSD)
5. Wallset
All these parts have been studied in detail.
ADSL (Asynchronous Digital Subscriber Line) is the main technology used in
HFCL to provide internet access to its customers. It is a high speed replacement for
modem or ISDN adapter that allows us to access the internet faster. It is a transmission
technique used on the line from modem to the service provider.
It is called “Asymmetrical” since the speed of transmission is not the same
in both directions. A small amount of data sent by the customer can result in the receipt
of a large amount of data from the internet. ADSL modems operate on a bit stream and
are intended for carrying digital information between digital equipment such as PCs.
Hence the word “Digital” is used. ADSL itself operates over the subscriber’s normal
telephone line to the local exchange. The telephone line can continue to be used for voice
calls through the use of devices called ‘Splitters’ that separate the data and voice on the
line. Thus the name- Asynchronous Digital Subscriber Line.
PC ADSL Local Loop Service Internet Modem Provider
Figure: Components of ADSL.
ADSL exploits the unused analogue bandwidth that is potentially
available in the wires that run from the user premises to the local exchange.
The various components of ADSL are ADSL modem, DSLAM,
Broadband Access Server (BAS) and ISP.
D. ISP:
10
This department controls all the IP configurations for all the BTS. This includes
giving new IPs and using subnetting to configure different BTS. This also checks links
between various BTS from time to time to check for any losses. In case losses occur these
are reported to the BSS deptt. to take further actions. In case losses occur, it indicates that
the link between two sites is not correct. There may be some problem with the
transmission media.
TERMS OF REFERENCES
The major aim of the industrial training was to get to practically know the
working of the mobile phones and landline phones that have now become a basic
necessity for one and all. These systems otherwise seem to be very simple. But
practically doing all the controlling has given us a vast knowledge about the technologies
behind these systems.
We came to know about the media used for voice. E1s and optical fibers
are used for this purpose. The controlling of these media is done both through hardware
and software. Various equipments like E1 tester, OTDR, etc. are used for the testing of
transmission media.
We came to know how mobile calls originate and are carried on through
different network devices like BSC, BTS, etc. The working of landline phones is through
corDECT Wireless Access System. This uses the ADSL technology. Broadband services
are provided using DSLAMs. The DSLAMs may be based on IP technology or ATM
technology. Also the concept of IP addressing is used to configure new BTS.
11
ANALYSIS OF GENERAL FINDINGS
12
TRANSMISSION
Basic Definition: Transmission is an act of transfer of signal through a medium
using electrical or optical pulses.
Transmission Media:
There are four types of media that can be used in transmitting information in the
telecommunications world:
Copper wire
Coaxial cable
Optical fiber
Wireless
Earlier, copper wire was the only means of transmitting information. Technically
known as unshielded twisted pair (UTP), this consisted of a large number of pairs of
copper wire of varying size in a cable. The cable did not have a shield and therefore the
signal primarily the high-frequency part of the signal was able to leak out.
Coaxial cable consists of a single strand of copper running down the axis of the
cable. This strand is separated from the outer shielding by an insulator made of foam or
other dielectrics. A conductive shield covers the cable. Usually an outer insulating cover
is applied to the overall cable.
13
Fiber is the third transmission media. Whereas transmission over copper utilizes
frequencies in the megahertz range, transmission over fiber utilizes frequencies a million
times higher. This difference permits transmission speeds of immense magnitudes.
Transmission speeds of as high as 9.9Gbps have become common place in the industry
today. The tremendous capacity of fiber certainly makes for more efficient
communications; however, placing so much traffic on a single strand makes for greater
vulnerability. Most of the disruptions in the long-distance network are a result of physical
interruption of a fiber run.
Wireless communications is the final option as a transmission medium. This can
take several forms: microwave, synchronous satellites, low-earth-orbit satellites, cellular,
personal communications service (PCS), etc. In every case, however, a wireless system
obviates the need for a complex wired infrastructure. In the case of synchronous
satellites, transmission can take place across oceans or deserts. With microwave there is
no need to plant cable, and in mountainous territories this is a significant advantage.
Cellular and PCS afford mobility. There are advantages and disadvantages to each.
Transmission Standards:Certain standards are to be used for the transmission of signals from one place
to another. These are as follows:
PDH (Plesiochronous digital hierarchy)
SONET (Synchronous optical Network)
SDH (Synchronous digital hierarchy)
1) Plesiochronous Digital Hierarchy (PDH):
PDH stands for Plesiochronous Digital Hierarchy. PDH signals with a
high transmission rate are obtained by multiplexing several lower-rate signals. The input
signals of the tributaries are plesiochronous to each other, i.e. their clock rates have the
same nominal value, but there is, however, a slight amount of variation between the two.
14
The Plesiochronous Digital Hierarchy is a digital communication
technology. PDH is based on the fundamental concepts of Time Division Multiplexing
(TDM). Plesiochronous Digital Hierarchy is a technology used in telecommunication
networks to transport large quantities of data over digital transport equipment such as
fiber optic and microwave radio systems. The term plesiochronous is derived from Greek
plesio, meaning near, and chronous, time. Plesiochronous means nearly synchronous.
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 work together, usually the transmission was made according to the local
clock and the reception was made according to the recovered clock that was recovered
from the received data.
The plesiochronous digital hierarchy (PDH) has two primary
communication systems as its foundation. These are the T1 system based on 1544 kbit/s
that is recommended by ANSI and the E1 system based on 2048 kbit/s that is
recommended by ITU-T. The T1 system is used mainly in the USA, Canada and Japan.
European and certain non-European countries use the E1 system.
CONCEPT OF E1s:
An E1, logically, is a PCM signal that has been sampled, quantized and
encoded. Each E1 has got 30 channels, each sampled at 8 KHz, compressed according to
A-law. These 30 communications are byte interleaved. Each is of 8 bits. The frame has
two more channels; they are used for synchronization and signaling. The total bit rate is
2.048 Mbit/s.
FRAME SIGNALLING
ALLIGNMENT
(SYNCHRONIZATION)
15
0 1 ------------- 15 16 17 ------------- 31
256 bits, 125 µsec.
Figure: Frame structure of E1
This is also the basic principle of V5 protocol.
Physically, each E1 has two wires – one for transmission and the other for
reception. While patching two E1s on a krone module of MDF, the trans of one E1 is
patched with receive of the other.
Bit rates used for PDH:
Bit rates in accordance with ANSI: 1.5 Mbit/s, 6 Mbit/s and 45 Mbit/s.
Bit rates in accordance with CEPT: 2 Mbit/s, 8 Mbit/s, 34 Mbit/s and 140 Mbit/s.
Every signal has a separate frame structure and there is no frame synchronization of the
tributary signal inputs.
But PDH had many disadvantages.
1.) Interface:
a. There are only some regional provisions, instead of universal standards for electrical
interface. The present PDH digital signal hierarchy has three rate levels: European Series,
North American Series and Japanese Series. Each of them has different electrical
interface rate levels, frame structures and multiplexing methods. This makes it difficult
for international connections.
b. No universal standards for optical interfaces. All PDH equipment manufacturers use
their own line codes to monitor the transmission performance in the optical links.
2.) Multiplexing Method:
a. As PDH adopts asynchronous multiplexing method, the locations of the low rate
signals are neither regular nor fixed when they are multiplexed into higher-rate signals.
b. Since adding/dropping low-rate signals to high-rate ones must go through many
stages of multiplexing and de-multiplexing, impairment to the signals during
16
multiplexing/de-multiplexing processes will increase and transmission performance will
deteriorate. This is unbearable in large capacity transmission.
3.) No universal network management interface:
When buying a set of equipment from a vendor, you have to buy its network management
system. Different parts of the network may use different network management systems,
which are obstacles in forming an integrated telecommunication management system
(TMN).
Thus there came the reason for the invention of a new standard SDH
(Synchronous Digital Hierarchy). Synchronous Digital Hierarchy (SDH) and
Synchronous Digital Network (SONET) are new transmission systems that provide for
standardized high-speed optical transport. The goal of SDH and SONET is to provide
ease of networking, intervendor compatibility, standardized interfaces, and standardized
overhead for operations, administration, maintenance, and provisioning.
In HFCL, SDH is used.
2) Synchronous Digital Hierarchy (SDH):
SDH is a standard for telecommunication formulated by the International
Telecommunication Union (ITU). SDH was first introduced in telecommunications
network in 1992. SDH is based on overlaying a synchronous multiplexed signal onto a
light stream transmitted over optical fiber cable. SDH is also defined for use on radio
links, satellite links and at electrical interfaces between equipments.
SDH transmission network is composed by connecting different types of
NE (network elements) that are connected through optical fiber. The transmission
function of SDH is performed through different NEs.
Synchronous Digital Hierarchy allows multi-vendor interworking and
allows one SDH-compatible network element to communicate with another. Also, it is
synchronous hierarchy; therefore it allows single-stage multiplexing and de-multiplexing.
This eliminates hardware complexity, thus decreasing cost of equipment while improving
signal quality. It also provides network self-healing function. The so called self-healing
implies that when fault develops in the network, human intervention is not needed. The
network automatically restores transmission of service during the fault in an extremely
17
short time. The subscriber is practically unaware of the fact that a fault has occurred in
the network.
Synchronous Transport Module ( STM):
The basic structure level of SDH is Synchronous Transfer Module (STM-1) having a bit
rate of 155Mbps.
Bit Rate SDH SDH Capacity
155.5 Mbps STM-1 63 E1s
622 Mbps STM-4 252 E1s i.e. 4x63
2.5 Gbps STM-16 1008 E1s i.e. 16x63
STM is used to generate E1s that is it converts the electrical signal to
optical signal and optical signal to electrical signals. From STM E1s go to MDF (Main
Distribution Frame)
18
STM 1(155.5Mbps)
×4
STM 4(622 Mbps)
×4
STM 16(2.5 Gbps)DWDM
×4
100 Gbps STM 64(10 Gbps)
Figure: Synchronous Digital Hierarchy
As we know optical fiber is most widely used as the transmission medium for
transfer over long distances, therefore, STM has to be used at certain points. This is
because in mobile communication, the signal coming from one user is to be shifted to
other user for a communication to be established between them. This is done through a
Main Distribution Frame (MDF). An MDF can only receive electrical signals in the
form of E1s. An MDF is a platform where the E1s coming from different parts are
patched i.e., connected to each other. E1s physically have two terminals; one trans and
the other receive. To patch 2 E1s to one-another, trans of one is connected to receive of
other and vice versa. Thus STM is required to convert optical signal coming from far-off
distances to electrical or E1 form. An E1 is nothing but a 2Mbps PCM signal.
19
Figure: Structure of STM-1
AU-4
TU3-1
TU3-2
TU2-1
TU2-2
TU2-3
TU2-4
TU2-5
TU2-6
TU2-1
TU2-2
TU2-3
TU2-4
TU2-5
TU3-2
TU2-7
TU2-6
TU2-7
TU2-1
TU2-2
TU2-3
TU2-4
TU2-5
TU2-6
TU2-7
TU12-1
TU12-2
TU12-3
20
AU stands for Administrative Unit
TU12-1, TU12-2 and TU12-3 are the time slots.
The path is determined by the last digits. For example- 1-2-3-2, this is represented as:
AU4-1 TU3-2 TU2-3 TU12-2
The general method to connect two different areas:
First of all, optical fiber is laid underground in between the two areas.
Both the fibers are terminated on the FMS (Fiber Management System). From here the
fiber goes to the STM. STM converts optical signals into electrical E1s and vice-versa.
Electrical E1s go to the krone modules on the MDF (Main Distribution Frame). On the
MDF, E1s of all areas are connected to each other through patching.
Fiber Distribution System (FDS):
The Fiber Distribution System consists of a number of patch panels. A patch
panel is a panel in which adapters are arranged in such a way so that they are connected
to individual fibers spliced through connectors. These adapters could be connected to
patch cords or pig tails as per requirements. The ports through which these are connected
are called FCPC ports.
There are three types of ports:
1. FCPC ports – used on patch panels of FDS.
2. FCLC ports – used in STM-4 (layer switches).
3. FCSC ports – used in EDFA (Erbium Doped Fiber Amplifier).
Point of Interconnection (POI):
It is used to interconnect two different networks. For e.g., for connecting
Spice to BSNL, etc. These are of two types:
1. Backbone (BB): This is used to connect two cities to one another i.e.
intercity. For e.g., for connecting Chandigarh to Jalandhar, etc.
2. Backhaul (BH): This is used to connect various sites within a city i.e.
intracity. For e.g., connecting different nodes within a city.
In both the above cases, rings are used.
21
In case any E1 goes down, it is indicated by alarms:
1.) LOS (Loss of Signal): This is shown when patching is not done at the local
terminal. Such a time slot is deleted first. Then to re-establish the connection,
cross-connection is made. Then a protection is created for it. This is done to make
it revertive, i.e., in case connection breaks from one direction, it diverts to the
other direction.
2.) AIS (Alarm Indication Signal): This signal is shown when the patching is not
done at the remote terminal. The multiplexer registers this alarm and then stops
transmission of signal and transmits a continuous sequence of 1s. This causes
multiplexer at the other end to show an AIS alarm.
Advantages of SDH network:
o High speed
o Backup circuits
o Dynamic bandwidth utilization
o Compatibility
o Simple multiplexing
o Integration with PDH and SONET
OPTICAL FIBERS
Optical fibers are the most suitable medium for electrical communication nowadays since
they provide large bandwidth which is required for communication at long distances.
These work on the principle of Total Internal Reflection.
An optical fiber consists of three basic parts:
1. The core – where the actual propagation of light occurs.
2. The cladding – is present both to protect the core against external mechanical
forces and to limit the losses of energy due to some imperfections at the core
surface.
3. The jacket – protects and isolates cladding from the environment.
22
Optical fibers come in different standards as 6F, 12F, 24F, 36F and 48F. Each standard
fiber has the same number of tubes of optical fiber inside it. For e.g., a 6F fiber has 6
tubes of fibers inside it and so on. The color coding for a 6F is Blue, Orange, Green,
Brown, Grey and Natural. For a 12F fiber the color coding is Blue, Orange, Green,
Brown, Grey, White, Red, Black, Yellow, Violet, Pink and Natural.
TUBES
Figure: A 6F Optical Fiber with 6 tubes.
In the above diagram, B stands for Blue, O stands for Orange and W
stands for White. The first tube is always of blue color which indicates that this is the first
tube and eases the installation. Each tube further has got four optical fibers. These have
the color coding – Blue, Orange, Green and Natural.
For connecting two optical fibers, color coding has to be kept in mind. The
blue tube of one fiber is connected to blue of another fiber. This is the first tube, second is
orange and then cyclic order is followed.
For a wavelength of 1550 nm, the loss in an optical fiber is assumed to be
0.25 db/km, while for a wavelength of 1310 nm it is assumed to be 0.35 db/km. If losses
are found more than these values, then the route is changed onto some other fiber until
that fiber is repaired.
Different equipments used in transmission:
a. Power Meter: Power meter is used to measure the optical power. It consists of a
display unit and a calibrated sensor. In case the power is more, then an attenuator is
23
B1
O2
w3
w6
w5
w4
used to reduce the power and in case the power is low then optical fiber is changed in
order to increase the power.
b. Attenuator: In case the power measured inside an optical fiber comes high, then
it becomes necessary to reduce the level of power in order to avoid the various
equipments from getting damaged. This is because devices have a fixed value of
tolerance power.
c. E1 Tester: E1 tester is used to check the connection between the two points. It
consists of transmitter and receiver. Transmitter of the E1 is connected to the receiver
of the tester and receiver of E1 is connected to the transmitter of the tester. It gives ok
if there is no error. If it shows green light then it indicates that the loop has been
established. If it shows red light then it indicates that the loop has not been
recognized.
d. EDFA (Erbium Doped Fiber Amplifier): It is a fiber amplifier used to
increase the level of power going through an optical fiber so that it could cover large
distances. If the power level is positive, it increases power to around +17 db.
However if the power level is negative, it increases it to around +10 db.
Increase in power level is required since the acceptable power level
for most devices is -8 db to -28 db. If the level is less than this, then the power is not
detected by most of the devices. Also power more than -8 db damages the equipment.
Therefore EDFA is used only where distances involved are very large. If at the
receiver level power is still more, then attenuator is used. If power is less, then the
signal can be routed to another fiber. A power meter is used to measure optical
power.
EDFA optically amplifies signals without having to first convert them
into electrical form. Optical amplification usually produces less noise than electrical
amplification. An Erbium Doped Fiber Amplifier (EDFA) consists of a solid state
material (typically glass) which is drawn into a fiber. The core of the fiber is doped
with an ion (Er 3+) that emits at wavelength 1550 nm. The fiber is pumped by a
24
strong beam at a shorter wavelength (980 nm or 1480 nm), which excites the Erbium
ion to a higher energy level. During the transition state, the photons are emitted either
by spontaneous emission or by simulated emission. The long lifetime of the excited
state, approximately 10 ms, assures that instead of emitting noise by spontaneous
emission, stimulated emission (amplification) is dominant.
e. OTDR (Optical Time Domain Reflectometer):
An Optical Time Domain Reflectometer (OTDR) is used in fiber optics to
measure the time and intensity of the light reflected on an optical fiber. Basically, it is
used as a troubleshooting device to find faults, splices, and bends in fiber optic cables,
with an eye toward identifying light loss. Light loss is especially important in fiber optic
cables because it can interfere with the transmission of data. An OTDR can detect such
light loss and pinpoint trouble areas, making repairs easy.
An OTDR takes advantage of the scattering of light
in the optic fiber to make its measurements. The
OTDR emits a high-power pulse that hits the fiber
and bounces back. What comes back is measured,
factoring in time and distance, and the result is
"trouble spots," which radiate and can be targeted
for repair. In general, the data take the form of a
wave, with trouble spots clearly visible as
aberrations in the wave.
Thus it can create a display of the amount of backscattered light at any point in the fiber
as follows.
25
The slope of the fiber trace shows the attenuation coefficient of the fiber
and is calibrated in dB/km by the OTDR. In order to measure fiber attenuation, a fairly
long length of fiber with no distortions on either end from the OTDR resolution or
overloading due to large reflections. If the fiber looks nonlinear at either end, especially
near a reflective event like a connector, avoid that section when measuring loss.
26
DIGITAL LOCAL CARRIER (DLC)
Definition:
The local loop is the physical connection between the main distribution frame in
the user’s premises to the telecommunications network provider. Digital Loop Carrier
(DLC) technology makes use of digital techniques to bring a wide range of services to
users via twisted-pair copper phone lines.
Structure of DLC:
The DLC developed by UTStarcom is called the AN2000. The AN2000
uses a modular physical design with multiple racks integrated into full racks that form an
Access Node. Each AN2000 shelf consists of two common control slots & 16 universal
slots. One control shelf provides common control and distribution of services in a
multishelf Assembly. More than one control/Expansion shelf group may be housed in 1
Rack in order to increase E1 capacity or BRI (V5) capacity per rack.
AN2000 has got many shelves. These shelves have many cards which
perform all the functions. They are as follows:
Foreign Exchange & Subscriber Module(FXS)
Each FXS card contains 16 interface circuits i.e., serves 16 customers. These cards are
used to support voice. It also provides battery feed and ringing. It helps to detect on hook
and off hook subscribers using loop start signaling which is indicated by the LEDs on
these cards. A blinking LED shows that the subscriber is dialing other subscriber’s
number.
System Control Module (SCM)
The SCM card occupies a single “B” slot in the control shelf. It contains the system clock
and collects alarms and performance information and reports it to network management
system.
E1 Module
The E1 module monitors performance of each E1 lines and detects errors and alarms on
E1 lines. It provides LEDs for module and port status and alarms.
27
Synchronous Data Transfer (SDT) Module
The SDT module offers an East bound and West bound transmit receive pair. It supports
self healing ring capability.
Power Supply Module (PSM)
The PSM module uses a DC-DC converter to convert -48 V to +/-5V to provide power
needed by modules in shelf. It also provides failure alarm signals.
ISDN-BRI/IDSL Module ( BRI)
The BRI module contains 8 interface circuits. It is used for ISDN customers.
Power Supply Module with Ring Generator(PRM)
The PRM module provides the ringer tone.
Power Distribution & Alarm Panel(PDP)
The PDP module distributes –48 V DC from external supply to the system. It provides
system audible alarm.
Bus Adapter Modules(MBAM & EBAM)
The EBAM card provides connectivity of E1 with FXS cards.
Remote Testing Unit(RTU)
The RTU module is used to perform electrical tests of the subscriber loop and FXS line
circuitry.
28
The UTStarcom Data Circuit is used for point-to-point connectivity. For
e.g., consider an organization having two offices, one in Jalandhar and another in
Chandigarh. The organization wants a point-to-point connectivity between the two
offices. For this, a radio modem is used. The radio modem is of two types, one indoor
unit and one outdoor unit. The indoor unit has one output port and two LAN ports. The
output is connected to the input of the outdoor unit. The outdoor unit is connected to an
antenna. One such set-up is made at the node and another at the customer end. The
customer connects the two LAN ports of his indoor unit to his network of computers. But
the data in this case travels in form of E1s between Jalandhar and Chandigarh. The
computers can accept only digital data. Thus there is a need of E1 to Ethernet converter.
The E1s coming from a place reach the MDF from where they are given to the E1 to
Ethernet converter. The E1 to Ethernet Converter converts E1s to Ethernet and vice
versa.
There is another DLC made by Huawei which is called the F02A shelf. It
has got A32 cards in place of FXS cards. Each A32 card serves 24 customers. Instead of
BRI card, it uses the DSL card for ISDN. There is also an ASU card where the fiber is
terminated. This card is also responsible for formation of rings so that in case the fiber
communication breaks in one direction it can be reverted onto the other direction.
DSLAM is used for internet connection. ICM (Integrated Controller Module) Card is
used to store the configuration of DSLAM.
The DSLAM has 16 cards each of which serves 24 customers. The front
card is called the IPDSL card. It is the basic internet card. At the back of DSLAM, there
is a splitter card which splits voice and data. A splitter card basically performs
multiplexing.
In case a user wants to use both voice telephony and internet connection,
then the voice coming from the A32 card is sent to simple voice modules and then to the
DSLAM which splits the voice and data and then through the data modules sends them to
the customer through the MDF.
But if a customer wants to use only vice, then voice coming from FXS or
A32 card is sent to the simple voice modules from where it is sent to the customer
through the MDF.
29
DIGITAL SUBSCRIBER LINE ACCESS
MUTIPLEXER (DSLAM)
Introduction:
A Digital Subscriber Line Access Multiplexer (DSLAM) allows
telephone lines to make faster connections to the Internet. It is a network device, located
near the customer's location that connects multiple customer Digital Subscriber Lines
(DSLs) to a high-speed Internet backbone line using multiplexing techniques. By locating
DSLAMs at locations remote to the telephone company central office (CO), telephone
companies are now providing DSL service to consumers who previously did not live
close enough for the technology to work
Path taken by data to DSLAM Residential/commercial source: DSL modem plugged into the customer's
computer.
Local loop: The telephone company wires from a customer to the telephone
company's central office, often called the "last mile".
DSLAM: a device for DSL service. Sending on the customer or downstream
side, it intermixes voice traffic and VDSL traffic onto the customer's DSL line.
Receiving on that side, it accepts and separates outgoing phone and data signals
from the customer. It directs the data signals upstream towards the appropriate
carrier's network, and the phone signals towards the voice switch.
Main Distribution Frame (MDF): a wiring rack that connects outside subscriber
lines with internal lines. It is used to connect public or private lines coming into
the building to internal networks. At the telco, the MDF is generally in proximity
to the cable vault and not far from the telephone switch.
Hardware details
Customers connect to the DSLAM through ADSL modems or DSL
routers, which are connected to the PSTN network via typical unshielded twisted pair
telephone lines. Each DSLAM has multiple aggregation cards, and each such card can
30
have multiple ports to which the customer lines are connected. Typically a single
DSLAM aggregation card has 24 ports, but this number can vary with each manufacturer.
The most common DSLAMs are housed in a telco-grade chassis, which are supplied with
(nominal) 48 volts DC. Hence a typical DSLAM setup may contain power converters,
DSLAM chassis, aggregation cards, cabling, and upstream links. The most common
upstream links in these DSLAMs use gigabit ethernet or multi-gigabit fiber optic links.
Ustarcom AN20001B DSLAM
Earlier dial-up connections were used. These provided speeds of not more
than 56 kbps and also narrow bandwidth. Thus these were narrowband services. DSLAM
allows telephone lines to make faster connections to the internet.
HFCL uses UStarcom AN20001B DSLAM. It contains 16 aggregation
cards and each card serves 24 customers. Each card creates its own VLAN (Virtual Local
Area Network). The advantage of using VLANs is in case of broadcasts. As we all know
31
viruses spread through broadcasts. In case a virus broadcasts in DSLAM, the 24
customers in one particular VLAN are only affected.
There is one controller card ICM which contains two giganet ethernet
ports and two straight cable ports.
VLAN :- Virtual LAN, commonly known as a VLAN, is a group of hosts with a
common set of requirements that communicate as if they were attached to the same wire,
regardless of their physical location. A VLAN has the same attributes as a physical LAN,
but it allows for end stations to be grouped together even if they are not located on the
same LAN segment. Network reconfiguration can be done through software instead of
physically relocating devices.
VLANs are created to provide the segmentation services traditionally
provided by routers in LAN configurations. VLANs address issues such as scalability,
security, and network management. Routers in VLAN topologies provide broadcast
filtering, security, address summarization, and traffic flow management. By definition,
switches may not bridge IP traffic between VLANs as it would violate the integrity of the
VLAN broadcast domain.
VLAN IC
M
VLAN
VLAN
32
ISP Router
The earlier DSLAMs used ATM technology. But such DSLAMs used four
E1 ports instead of Gigabit Ethernet ports. Thus they could serve limited number of
subscribers and that too with limited speeds. Gigabit ports can provide speeds of upto
1000Mbps.
The internet connection is provided through modems at the customer side.
These modems also contain RAS (Remote Access Server). This is responsible for
authentication of the user through password and then the speed is assigned according to
the policies configured in the DSLAM.
33
The V5 ProtocolDefinition:
V5 is an Access Network Technology. The V5 standard specifies
interfaces between the access network and the Local Exchange. Two interfaces to support
narrowband services have been specified, V5.1 and V5.2, both based on 64 Kbit/s
channels and 2.048 Mbit/s links.
V5.1 is a 2.048 Mbit/s interface intended for access networks which
support PSTN and ISDN BRI user ports and provide for managed flexibility of bearer
channel allocation but which do not perform a traffic concentration function.
V5.2 is a multi-2.048 Mbit/s interface for access networks which
additionally may support ISDN PRA user ports and which have traffic concentration
capability.
The major differences between the V5.1 and V5.2 interfaces are:
• V5.1 uses only one 2.048 Mbit/s link whereas V5.2 may use up to sixteen 2.048 Mbit/s
links on one interface.
•V5.1 does not support concentration whereas V5.2 is inherently designed to support it.
•V5.1 does not support ISDN primary rate access user ports whereas V5.2 does.
Physical (timeslots):
The 2.048 Mbit/s interfaces utilise the usual 32 time-slot frame structure defined in
G.703/G.704. Time slot 0 is used for frame alignment and timeslot 16 of the first 2.048
Mbit/s link is utilised by the V5 ‘control protocol’ which performs a number of
housekeeping functions.
V5 Characteristics:
Facility: A V5 interface connection consists of full digital, 2,048 kbit/s facility or E1s (1
for V5.1 up to 16 for V5.2). Each facility has 32 64-kbps channels.
Exchange: The exchange provide switching and call processing functionality, including,
for example, supplementary services, charging announcements and DTMF decoding
34
Access Network: The access network is responsible for maintenance of the access
network and subscriber lines. Access network deals with the physical connection (or
termination) of the subscriber lines. It is also responsible for testing of digital lines and
transport of subscriber speech data and subscriber line signals.
OPTICAL NETWORKING UNIT (ONU)
HFCL uses HONET 160B ONU. It is one type of transmission unit. It is used to
provide landline services to the customers.
It has following cards:-
1. ASU: In ONU, 5 ASU cards are used. Each card has 8 E1 ports. These convert
optical signal to electrical signal.
2. EMU: 1 EMU card is used. It stands for Environment Monitoring Unit.
3. SDH card: This card serves 15 customers.
4. AC TO DC: It converts 220V AC to - 48 DC.
5. DC TO DC: It converts -48V to +12V or +5V DC.
6. RSP card: It serves up to 5 customers. It convert optical signal to electrical signal.
35
OPTIXMetro 1000 optix
Overview:
The OptiX 155/622H system developed by Huawei is a new generation of
STM-1/STM-4 compatible multi-service transmission equipment. It supports
STM-1/STM-4 optical synchronous transmission and on-line upgrade from STM-1 to
STM-4. The OptiX 155/622H system provides abundant interfaces and powerful cross-
connect capability.
Via its SDH interface, the OptiX 155/622H system can build a
transmission network with Optix 155/622, OptiX 2500+(metro3000) and OptiX 10G
systems. Via its PDH, ATM or Ethernet interfaces, it can interwork with access network
equipment, GSM base station, ETS base station, exchange and router to form a
communication network.
Through OptiX iManager T2000, a subnetwork-level integration NMS for
transmission network, a user can configure, maintain and monitor the equipment and the
network. An authorized user can use the OptiX iManager T2000 system to maintain the
whole network at any NE or remote NMS center of transmission network.
36
Features:
1.) Interface
The OptiX 155/622H system provides abundant service interfaces and auxiliary
interfaces.
SDH interface
A single OptiX 155/622H supports STM-1 SDH optical interfaces, or STM-1 SDH
electrical interfaces, or STM-4 SDH optical interfaces, or combination of the
STM-1/STM-4 SDH interface.
PDH interfaces
The OptiX 155/622H provides PDH interfaces operating at E1 and T1 rates. A single
OptiX 155/622H can provide a maximum of 80 E1 interfaces, or 64 T1 interfaces, or
combination of the above PDH interfaces.
ATM service interface
The OptiX 155/622H provides the STM-1 optical interfaces that can access ATM service.
Ethernet service interfaces
The OptiX 155/622H provides 10M/100M self-adaptive Ethernet electrical interfaces
with VC-12 or VC-3 as the mapping unit, or 100M Ethernet optical interfaces with VC-
12 as the mapping unit.
Environment monitoring unit interfaces
37
The OptiX155/622 provides primary power voltage monitoring, environment temperature
monitoring, Boolean value signal input, Boolean value signal output, and RS-232 or RS-
422 serial communication interface
Clock input/output interfaces
The OptiX 155/622H provides clock input interfaces and clock output interfaces, which
can be set to 2MHz or 2Mbit/s mode.
Power input interfaces
The OptiX 155/622H provides two -48V DC or +24V DC power input interfaces.
Abundant auxiliary interfaces
The OptiX 155/622H provides several data interfaces for the user with its powerful
overhead processing capability:
RJ-45 Ethernet interface
user-defined asynchronous RS-232 data interfaces
Modem interface with X.25 characteristics
For two networks not connected together via optical fiber, inter-network DCC
communication can be established by interconnecting the Ethernet interfaces.
2.) Services
The OptiX 155/622H supports the access of PDH signals, SDH signals, ATM service and
Ethernet service which supports V.35/X.21protocol. In addition, it supports the hybrid
transmission of PDH signals, SDH signals, and ATM services within the same
equipment.
3.) Networking and Protection
Flexible networking capability
38
With a large-capacity cross-connect matrix, the OptiX 155/622H can provide powerful
networking capability. It supports multiple network topologies such as point-to-point,
chain, ring, hub, and mesh networks.
Ideal protection mechanism
The OptiX 155/622H provides network protection, including ring Path Protection (PP),
Subnetwork Connection Protection (SNCP),shared fiber virtual trail protection, and VP-
Ring protection of an ATM ring network.
4 EFS board
Provides 10M/100M self-adaptive Ethernet electrical interfaces
Supports GFP (General Frame Processor) /LAPS (Link Access Processor
SDH) /HDLC(High-level Data Link Control) mapping protocol. The mapping
protocol is optional
Supports LCAS (Link Capacity Adjustment Scheme) protocol
Supports CAR (Committed Access Rate)
39
Base Station Subsystem (BSS)
The main technologies used are GSM and CDMA. These have been explained below:
Global System for Mobiles
Introduction:
In this day and age, many folks need to be accessible everywhere, whether
they're at work or play, in the office or at home. To meet this demand, the GSM standard
(Global System for Mobile Communications) for mobile telephony was introduced in
the mid-1980s. Today, GSM is the most popular mobile radio standard in the world.
Before GSM networks there were public mobile radio networks (cellular).
They normally used analog technologies, which varied from country to country and from
manufacturer to another. These analog networks did not comply with any uniform
standard. There was no way to use a single mobile phone from one country to another.
The speech quality in most networks was not satisfactory. GSM became popular very
quickly because it provided improved speech quality and, through a uniform international
standard, made it possible to use a single telephone number and mobile unit around the
world.
Benefits of GSM:
1. Support for international roaming
2. Distinction between user and device identification
3. Excellent speech quality
4. Wide range of services
5. Interworking (e.g. with ISDN, DECT)
40
6. Extensive security features
GSM also stands out from other technologies with its wide range of services:
1. Telephony
2. Asynchronous and synchronous data services (2.4/4.8/9.6 kbit/s)
3. Access to packet data network (X.25)
4. Telematic services (SMS, fax, videotext, etc.)
5. Many value-added features (call forwarding, caller ID and voice mailbox)
6. E-mail and Internet connections.
Frequency Ranges for GSM:
GSM-900 Standard:
Uplink Frequency: 890 MHz – 915 MHz
Downlink Frequency: 935 MHz – 960MHz
GSM-1800 Standard:
Uplink Frequency: 1710 MHz – 1785 MHz
Downlink Frequency: 1805 MHz – 1880 MHz
Uplink: Signal flow from Mobile Station (MS) to Base Transceiver Station (BTS).
Downlink: Signal flow from Base Transceiver Station (BTS) to Mobile Station (MS).
The simultaneous use of separate uplink and downlink frequencies enables
communication in both the transmit (TX) and receive (RX) directions. The radio carrier
frequencies are arranged in pairs and the difference between these two frequencies
(uplink-downlink) is called the Duplex Frequency. In GSM 900 the duplex frequency
(the difference between uplink and downlink frequencies) is 45 MHz. In GSM 1800 it is
95 MHz. The lowest and highest channels are not used to avoid interference with services
using neighbouring frequencies, both in GSM 900 and GSM 1800. Modulation used is
41
GMSK. It also uses linear predictive coding (LPC). The purpose of LPC is to reduce the
bit rate.
The total number of carriers in GSM 900 is 124, whereas in GSM 1800 the number of
carriers is 374. The devices in the Base Transceiver Station (BTS) that transmit and
receive the radio signals in each of the GSM channels (uplink and downlink together) are
known as Transceivers (TRX).
GSM System Architecture:
A GSM network can be divided into three groups: The mobile station (MS), the base
station subsystem (BSS) and the network subsystem. They are characterized as follows:
a. The mobile station (MS):
A mobile station may be referred to as a handset, a mobile, a portable
terminal or mobile equipment (ME). It also includes a subscriber identity module (SIM).
Each SIM card has a unique identification number called IMSI (International Mobile
Subscriber Identity). The SIM card contains the identification numbers of the user, a list
of the services that the user has subscribed to and a list of available networks. In addition,
the SIM card contains tools needed for authentication and ciphering and, depending on
the type of the card, there is also storage space for messages such as phone numbers, etc.
42
In addition, each MS is assigned a unique hardware identification called IMEI
(international mobile equipment identity). Besides providing a transceiver (TRX) for
transmission and reception of voice and data, the mobile also performs a number of very
demanding tasks such as authentication, handover, encoding and channel encoding.
b. The base station subsystem (BSS):
The base station subsystem (BSS) is made up of the base station controller
(BSC) and the base transceiver station (BTS). GSM uses a series of radio transmitters
called BTSs to connect the mobiles to a cellular network. Their tasks include channel
coding/decoding and encryption/decryption. A BTS is comprised of radio transmitters
and receivers, antennas, the interface to the PCM facility, etc. The BTS may contain one
or more transceivers to provide the required call handling capacity. A cell site may be
omni directional or split into typically three directional cells. A group of BTSs are
connected to a particular BSC which manages the radio resources for them. Today's new
and intelligent BTSs have taken over many tasks that were previously handled by the
BSCs. The primary function of the BSC is call maintenance. The mobile stations
normally send a report of their received signal strength to the BSC every 480 ms. With
this information the BSC decides to initiate handovers to other cells, change the BTS
transmitter power, etc.
c. The network subsystem.
The mobile switching center (MSC): It acts like a standard exchange in a fixed network
and additionally provides all the functionality needed to handle a mobile subscriber. The
main functions are registration, authentication, location updating, handovers and call-
routing to a roaming subscriber. The signaling between functional entities (registers) in
the network subsystem uses Signaling System 7 (SS7). If the MSC also has a gateway
function for communicating with other networks, it is called Gateway MSC (GMSC).
The home location register (HLR): It is a database used for management of mobile
subscribers. It stores the international mobile subscriber identity (IMSI), mobile station
43
ISDN number (MSISDN) and current visitor location register (VLR) address. The main
information stored there concerns the location of each mobile station in order to be able
to route calls to the mobile subscribers managed by each HLR. The HLR also maintains
the services associated with each MS. One HLR can serve several MSCs.
The visitor location register (VLR): It contains the current location of the MS and
selected administrative information from the HLR, necessary for call control and
provision of the subscribed services, for each mobile currently located in the
geographical area controlled by the VLR. A VLR is connected to one MSC and is
normally integrated into the MSC's hardware.
The authentication center (AUC): It is a protected database that holds a copy of the
secret key stored in each subscriber's SIM card, which is used for authentication and
encryption over the radio channel. The AUC provides additional security against fraud. It
is normally located close to each HLR within a GSM network.
The equipment identity register (EIR): The EIR is a database that contains a list of all
valid mobile station equipment within the network, where each mobile station is
identified by its international mobile equipment identity (IMEI). The EIR has three
databases:
White list: approved, error-free IMEIs, without restrictions.
Black list: Unapproved or bad/stolen handsets.
Grey list: for handsets/IMEIs that are uncertain.
Operation and Maintenance Center (OMC):
The OMC is a management system that oversees the GSM functional blocks. The OMC
assists the network operator in maintaining satisfactory operation of the GSM network.
Hardware redundancy and intelligent error detection mechanisms help prevent network
down-time. The OMC is responsible for controlling and maintaining the MSC, BSC and
BTS. It can be in charge of an entire public land mobile network (PLMN) or just some
parts of the PLMN.
44
COMMONCHANNELSCOMMON
CHANNELS
BROADCASTCHANNELS
BROADCASTCHANNELS
COMMONCONTROL
CHANNELS
COMMONCONTROL
CHANNELS
DEDICATEDCONTROL
CHANNELS
DEDICATEDCONTROL
CHANNELS
TRAFFICCHANNELSTRAFFIC
CHANNELS
FCCHFCCH SCHSCH BCCHBCCH SDCCHSDCCH SACCHSACCH FACCHFACCH
PCHPCH RACHRACH AGCHAGCH TCH/FTCH/F TCH/HTCH/H TCH/EFRTCH/EFR
DEDICATEDCHANNELS
DEDICATEDCHANNELS
LOGICALCHANNELSLOGICAL
CHANNELS
Physical Channels and Logical Channels:
Time Division Multiple Access (TDMA) divides one radio frequency channel into
consecutive periods of time, each one called a "TDMA Frame". Each TDMA Frame
contains eight shorter periods of time known as "Timeslots". The TDMA timeslots are
called "Physical Channels" as they are used to physically move information from one
place to another.
In GSM the logical channels can be divided into two types:
Dedicated Channels
Common Channels
Logical Channels:
There are twelve different types of Logical Channels, which are mapped into Physical
Channels in the radio path. Logical channels comprise of Common Channels and
Dedicated Channels. Common Channels are those, which are used for broadcasting
different information to mobile stations and setting up of signaling channels between the
MSC/VLR and the mobile station.
Logical Channels
45
Over the radio path, different type of signaling channels is used to facilitate the
discussions between the mobile station and the BTS, BSC and MSC/VLR. All these
signaling channels are called Dedicated Control Channels.
Traffic channels are also Dedicated Channels as each channel is dedicated to only one
user to carry speech or data.
Broadcast Channels
Base Stations can use several TRXs but there is always only one TRX, which can carry
Common Channels. They contain general information about the network and the
broadcasting cell.
There are three types of broadcast channels:
1. Frequency Correction Channel (FCCH)
FCCH bursts consist of all "0"s which are transmitted as a pure sine wave. This acts like
a flag for the mobile stations, which enables them to find the TRX among several TRXs,
which contains the Broadcast transmission. The MS scans for this signal after it has been
switched on since it has no information as to which frequency to use.
2. Synchronization Channel (SCH)
The SCH contains the Base Station Identity Code (BSIC) and a reduced TDMA frame
number. The BSIC is needed to identify that the frequency strength being measured by
the mobile station is coming from a particular base station.
3. Broadcast Control Channel (BCCH)
The BCCH contains detailed network and cell specific information such as: frequencies
used in the particular cell and neighbouring cells, channel combination, paging groups,
etc.
Common Control Channels
Common Control Channels comprise the second set of logical channels. They are used to
set up a point-to-point connection.
There are three types of common control channels:
1. Paging Channel (PCH)
46
The PCH is a downlink channel, which is broadcast by all the BTSs of a Location Area in
the case of a mobile terminated call.
2. Random Access Channel (RACH)
The RACH is the only uplink and the first point-to-point channel in the common control
channels. It is used by the mobile station in order to initiate a transaction, or as a response
to a PCH.
3. Access Grant Channel (AGCH)
The AGCH is the answer to the RACH. It is used to assign a mobile a Stand-alone
Dedicated Control Channel (SDCCH). Additional information in the AGCH is the
frequency hopping sequence. It is a downlink, point-to-point channel.
Dedicated Control Channels
Dedicated Control Channels compose the third group of channels. There are three
dedicated channels. They are used for call set-up, sending measurement reports and
handover. They are all bi-directional and point-to-point channels.
1. Stand-alone Dedicated Control Channel (SDCCH)
The SDCCH is used for system signaling: call set-up, authentication, location update, and
assignment of traffic channels and transmission of short messages.
2. Slow Associated Control Channel (SACCH)
An SACCH is associated with each SDCCH and Traffic Channel (TCH). It transmits
measurement reports and is also used for power control, time alignment and in some
cases to transmit short messages.
3. Fast Associated Control Channel (FACCH)
The FACCH is used when a handover is required.
Traffic Channels (TCH)
Traffic Channels are logical channels that transfer user speech or data, which can be
either in the form of Half rate traffic (5.6 kbits/s) or Full rate traffic (13 kbits/s). Another
form of traffic channel is the Enhanced Full Rate (EFR) Traffic Channel. The speech
coding in EFR is still done at 13Kbits/s, but the coding mechanism is different than that
47
used for normal full rate traffic. EFR coding gives better speech quality at the same bit
rate than normal full rate. Traffic channels can transmit both speech and data and are bi-
directional channels.
Services provided by GSM:
GSM is a multiservice system that allows various types of communication
that can be distinguished by the nature of the transmitted information. Generally, based
on the nature of the transmitted information, services can be grouped as speech services,
where the transmitted data is speech and data services which cover the rest of the
information types such as text, facsimile, etc.
Also there are the following services:
Basic Services, which are individual functions and may be automatically available and
included in the basic rights of the subscriber as soon as he registers.
Supplementary Services, which are extra services, those are not included as basic
features, but are associated with the basic services by enhancing and/or adding extra
features to the basic services.
Teleservices:
Speech (Telephony): The most important service for mobile systems, normal speech
service, including emergency calls.
Speech, Emergency calls: Emergency calls are possible automatically.
Short message Service: For the reception and sending of Short messages.
Group 3 Facsimile transmission (with alternate speech)
Bearer Services:
Bearer Services come into the picture when data transmission services are needed and
there are a number of different types of data services available. The distinctions between
these data services are based on the users (which can be connected to the PSTN, ISDN or
48
a PSPDN network) and the mode of transmission (packet or circuit switched, whether
end-to-end digital or not, synchronous or asynchronous).
The bearer services are used for data communication in a similar fashion as
in the PSTN and are essentially used for data communication between GSM networks
and PSTN. Since the PSTN network is designed for voice communication with a
bandwidth of 3.1Khz, digital data has to be modulated with an audio frequency carrier in
order to enable transmission via the PSTN. Thus it is necessary for the GSM users to be
able to use this function while communicating with the PSTN.
However, this is not easily realized in GSM networks because of the radio
characteristics of the Air Interface. This interface is based on a special speech-coding
algorithm that ensures the best quality with the lowest possible bit rate e.g. 13 kbits/s,
which makes it incompatible for modem signals. Thus a GSM user will never need a
modem for data communication. The connection between the mobile station and the
GSM network is fully digital.
Supplementary services:
Supplementary services enhance or supplement the basic
telecommunication services. The same supplementary services may or may not be
employed by a number of different basic services such as basic telephony or T62
automatic facsimile service. The following list covers most of the common services, as
well as the essential supplementary services.
Barring of all incoming calls
Barring of all Incoming calls when roaming
Barring of Incoming Calls when abroad
Barring of outgoing calls
Barring of outgoing International Calls
Call forwarding on mobile subscriber busy
Call forwarding on no answer
49
Call Hold
Call Waiting
Conference call
System features
This section provides a brief description of the GSM network features.
1. Roaming: The roaming feature allows a user to make and receive calls in any GSM
network and to use the same user-specific services worldwide.
2. Handover: In a cellular network, the radio and fixed voice connections are not
permanently allocated for the duration of a call. Handover, or handoff as it is called in
North America, means switching an ongoing call to a different channel or cell. The
execution and measurements required for handover are a basic function of the RR
protocol layer. There are four different types of handovers in GSM, which involve
transferring a connection between:
a. Channels (timeslots) in the same cell (intra-BTS handover)
b. Cells under the control of the same BSC (inter-BTS handover).
c. Cells under the control of different BSCs, but belonging to the same MSC (inter-
BSC handover)
d. Cells under the control of different MSCs (inter-MSC handover)
Handovers can be initiated by either the BSC or the MSC (as a means of traffic load
balancing). During its idle timeslots, the mobile scans the broadcast control channel of up
to 16 neighboring cells, and forms a list of the six best candidates for possible handover,
based on the received signal strength. This information is passed to the BSC and MSC, at
least once per second, and is used by the handover algorithm.
The decision on when to initiate a handover is a function of the following parameters:
receive quality,
receive level.
Successful handovers in GSM can take place at propagation speeds of up to 250 km/h.
50
3. Frequency hopping: The mobile station has to be frequency-agile, meaning it can
move between different frequencies in order to transmit and receive data, etc. A normal
handset is able to switch frequencies 217 times per second. GSM makes use of this
frequency agility to implement slow frequency hopping, where the mobile and the BTS
transmit each TDMA frame on a different carrier frequency. The frequency hopping
algorithm is broadcast on the broadcast control channel. Since multipath fading is
dependent on the carrier frequency, slow frequency hopping helps alleviate the problem.
In addition, co-channel interference is in effect randomized. The broadcast and common
control channels are not subject to frequency hopping and are always transmitted on the
same frequency.
4. Authentication: Authentication normally takes place when the MS is turned on with
each incoming call and outgoing call. A verification that the »Ki« (security code) stored
in the AuC matches the »Ki« stored in SIM card of the MS completes this process.
The user must key in a PIN code on the handset in order to activate the hardware before
this automatic procedure can start.
5. Frequency Reuse:
There are a limited number of frequencies available to each Base Station
Subsystem and they must be distributed between the cells to ensure a balanced coverage
throughout the BSS.
The frequencies have to be reused. If you do not distribute the
frequencies properly throughout the network the result will be a high level of interference
caused by overlapping frequencies. To avoid this, the GSM network includes a
specification of the Frequency reuse patterns, one of which is presented in figure below.
51
1 23
4 5
7 8
9
6
•
1 23
4 5
7 8
9
6
•
1 23
4 5
7 8
9
6
•
1 23
4 5
7 8
9
6
•
1 23
4 5
7 8
9
6
• 1 23
4 5
7 8
9
6
•
• •
•
•
•
•
•
• •
•
Figure: Frequency reuse pattern example
The next step involves the dimensioning of the Location Areas. This is carried out
according to the traffic characteristics of each area. The final phase is the dimensioning
of the Fixed Network on the basis of the traffic requirements and dimensioning of the
entire radio network.
52
CODE DIVISION MULTIPLE ACCESS
Introduction:
CDMA is a driving technology behind the rapidly advancing personal
communications industry. Because of its greater bandwidth, efficiency, and multiple
access capabilities, CDMA is becoming a leading technology for relieving the spectrum
congestion caused by the explosion in popularity of cellular mobile phones, fixed
wireless telephones, and wireless data terminals. Since becoming an officially recognized
digital cellular protocol, CDMA is being rapidly implemented in the wireless
communications networks of many large communications corporations.
CDMA stands for "Code Division Multiple Access". It is a form of
spread-spectrum, an advanced digital wireless transmission technique. Instead of using
frequencies or time slots, it uses mathematical codes to transmit and distinguish between
multiple wireless conversations. Its bandwidth is much wider than that required for
simple point-to-point communications at the same data rate because it uses noise-like
carrier waves to spread the information contained in a signal of interest over a much
greater bandwidth. However, because the conversations taking place are distinguished by
digital codes, many users can share the same bandwidth simultaneously.
CDMA CHANNELS:
53
CDMA logical channels:
Many users share a common CDMA carrier. Each physical channel
supports approximately 20 users with current technology. Each physical channel is
divided into several logical channels by the Walsh functions (downlink) or the unique
long code (uplink).
Theoretically, on the downlink each physical channel can be divided into
64 logical channels using every Walsh function. However, interference begins to degrade
user signals when more that 20 users share one IS-95 carrier.
The logical channels can be broken down into two groups:
Control Channels used for transmission of control and system setup information
such as timing or synchronization and to pass control messages between the base
station and mobile unit when the mobile unit is not on a traffic channel.
Traffic Channels used for transmission of user data (speech) once the mobile
unit is in an active talking state. The traffic channel also passes associated
signaling over the uplink and downlink once it is setup for a call.
IS-95 defines four control channels for CDMA. They are as follows:
Pilot Channel (downlink) - The pilot channel helps mobile units to acquire the
timing of the downlink traffic channel. One pilot channel is transmitted on each
individual RF carrier. It uses the short code and Walsh code 0 to continuously
transmit an all zeros (0's) signal for mobiles to lock onto. It provides a phase
reference for coherent demodulation and provides a means for signal strength
comparisons between base stations for determining handoff.
Sync Channel (downlink) - The sync channel is used by the mobile unit to
acquire synchronization to the frames of information sent on the traffic channels.
It also broadcasts important overhead information that all mobiles need to know
54
to successfully access the base station. Up to one sync channel is transmitted on
each individual RF carrier using Walsh code 32.
Page Channel (downlink) - The page channel is used for the transmission of
control information from the base station to the mobile if the mobile is not
currently using a traffic channel. For example, if the mobile has an incoming call,
the base station will send the mobile a page message on an assigned page channel.
Access Channel (uplink) - The access channel is used by the mobile to send
control messages and information to the base station if it is not currently using a
traffic channel. It is used to gain access or register.
The Traffic Channels are used to send user data (speech) between the base station and the
mobiles, along with signaling traffic. Four different rates are possible: Rate 1, Rate 1/2,
Rate 1/4, and Rate 1/8. The downlink traffic channel is referred to as the forward traffic
channel. On uplink it is called the reverse traffic channel.
There are three types of associated signaling sent over the traffic channels:
Blank-and Burst - all of the user speech or data in a frame is replaced by
signaling or control information.
55
Dim-and-Burst - only part of the user speech or data in a frame is replaced by
signaling or control information.
Power Control (downlink) - Every 1.25 milliseconds (or 800 times a second) two
bits are inserted which allows the mobile to adjust its transmitted power ± 1 dB.
How CDMA works
CDMA uses codes to convert between analog voice signals and digital signals. CDMA
also uses codes to separate (or divide) voice and control data into data streams called
"channels."
Generating a CDMA signal:
There are five steps in generating a CDMA signal.
analog to digital conversion
vocoding
encoding and interleaving
channelizing the signals
conversion of the digital signal to a Radio Frequency (RF) signal
Analog to digital conversion
The first step of CDMA signal generation is analog to digital conversion, sometimes
called A/D conversion. CDMA uses a technique called Pulse Code Modulation (PCM) to
accomplish A/D conversion.
Voice Compression
The second step of CDMA signal generation is voice compression. CDMA uses a device
called a vocoder to accomplish voice compression.
The term "vocoder" is a contraction of the words "voice" and "code."
56
Vocoders are located at the BSC and in the phone.
How compression works
People pause between syllables and words when they talk. CDMA takes advantage of
these pauses in speech activity by using a variable rate vocoder.
Variable Rate Vocoder
57
A CDMA vocoder varies compression of the voice signal into one of four data rates
based on the rate of the user's speech activity. The four rates are: Full, 1/2, 1/4 and 1/8.
The vocoder uses its full rate when a person is talking very fast. It uses the 1/8 rate when
the person is silent or nearly so.
Vocoder types
CDMA systems can use either an 8 kbps (kilobytes per second) or a 13 kbps vocoder.
The earliest CDMA systems used the 8kbps vocoder to maximize capacity.
The 13 kbps vocoder was later developed to provide a more land-line quality voice
signal. The great improvement in quality was worth the slight reduction in capacity.
Recently the CDMA community adopted a new 8 kbps vocoder. This new vocoder is
usually referred to as the EVRC (Extended Variable Rate Coding). It combines the
quality of 13 kbps vocoding with the capacity of the 8kbps data rate.
Encoding and interleaving
Encoders and interleavers are built into the BTS and the phones.
The purpose of the encoding and interleaving is to build redundancy into the signal so
that information lost in transmission can be recovered.
How encoding works
The type of encoding done at this stage is called "convolutional encoding." A simplified
encoding scheme is shown here.
58
A digital message consists of four bits (A, B, C, D) of vocoded data. Each bit is repeated
three times. These encoded bits are called symbols.
The decoder at the receiver uses a majority logic rule. Thus, if an error occurs, the
redundancy can help recover the lost information.
Burst errors
A burst error is a type of error in received digital telephone signals. Burst errors occur in
clumps of adjacent symbols. These errors are caused by fading and interference.
Encoding and interleaving reduce the effects of burst errors.
How interleaving works
Interleaving is a simple but powerful method of reducing the effects of burst errors and
recovering lost bits. In the example shown here the symbols from each group are
interleaved (or scrambled) in a pattern that the receiver knows.
De-interleaving at the receiver unscrambles the bits, spreading any burst errors that occur
during transmission.
59
Two kinds of codes
CDMA uses two important types of codes to channelize users. Walsh codes channelize
users on the forward link (BTS to mobile). Pseudorandom Noise (PN) codes channelize
users on the reverse link (mobile to BTS).
Walsh codes
Walsh codes provide a means to uniquely identify each user on the forward link. Walsh
codes have a unique mathematical property--they are "orthogonal."
In other words, Walsh codes are unique enough that the voice data can only be recovered
by a receiver applying the same Walsh code. All other signals are discarded as
background noise
PN codes
60
Pseudorandom Noise (PN) codes uniquely identify users on the reverse link.
A PN code is one that appears to be random, but isn't. The PN codes used in CDMA yield
about 4.4 trillion combinations of code. This is a key reason why CDMA is so secure.
Digital to Radio Frequency (RF) conversion
The BTS combines channelized data from all calls into one signal. It then converts the
digital signal to a Radio Frequency (RF) signal for transmission.
Digital to analog conversion
After the CDMA signal is transmitted, the receiver must reverse the signal generation
process to recover the voice, as follows:
1. Conversion of RF signal to digital signal
2. Despreading the signal
3. Deinterleaving and decoding
4. Voice decompression
5. Digital to analog voice recovery
POWER CONTROL IN CDMA:
THE NEAR-FAR PROBLEM:
Let's assume there are two users, one near the base and one far from the
base. The propagation path loss difference between these extreme users may be many
tens of dB. In general, the strongest received mobile signal will capture the demodulator
at the base station. In CDMA, stronger received signal levels raise the noise floor at the
base station demodulators for the weaker signals, thereby decreasing the probability that
weaker signals will be received.
To help eliminate the "Near-Far Problem", CDMA uses power control.
The base station rapidly samples the radio signal strength indicator levels of each mobile
and then sends a power change command over the forward radio link. The purpose of this
is so that the received powers from all users are roughly equal. This solves the problem of
a nearby subscriber overpowering the base station receiver and drowning out the signals
of far away subscribers. An extra benefit is extended battery life. That is, when a mobile
unit is close to a base station, its power output is lower. In other words, the mobile unit
transmits only at the power necessary to maintain connection.
61
Handoffs in CDMA
The act of transferring support of a mobile from one base station to
another is termed handoff. In other words, Handoff occurs when a call has to be handed
off from one cell to another as the user moves between cells. In a traditional "hard"
handoff, the connection to the current cell is broken, and then the connection to the new
cell is made. This is known as a "break-before-make" handoff. Since all cells in CDMA
use the same frequency, it is possible to make the connection to the new cell before
leaving the current cell. This is known as a "make-before-break" or "soft" handoff. Soft
handoffs require less power, which reduces interference and increases capacity. The
implementation of handoff is different between the narrowband standards and the CDMA
standards.
corDECT Wireless Access System
Introduction:
corDECT Wireless in Local Loop System is based on Digital Enhanced
Cordless Telecommunications (DECT) standard of European Telecommunications
standards Institute (ETSI) which was initially designed for the use of cordless telephones.
corDECT wireless access system provides telephone and internet service to the
subscriber. The distance between the subscriber unit and the base station is rated at 2 to 3
km. A relay base station can be used to extend the distance further.
62
The CBS is connected to DIU normally using three twisted pair wires
which carry signal as well as power from DIU to CBS. Alternatively it can be connected
to DIU through BSD (base station distributor). BSD is connected to DIU through
standard E1 interface.
For long range communication a WS-IP or WS can also be connected to
CBS using a two hop DECT wireless link, one between WS-IP and Relay Base Station
and other one between Relay Base Station (RBS) and Compact Base Station (CBS).
The range supported between a CBS and RBS is 25 km.
System Architecture:
The CorDECT system is designed to provide a cost effective wireless high
quality voice and data connection in dense urban as well as sparse rural areas. The system
enables wireless subscriber to be connected to the PSTN in a cost effective manner.
The following are the basic parts of corDECT system:
Dect Interface Unit (DIU)
Compact Base Station (CBS)
Relay Base Station (RBS)
Base Station Distributor (BSD)
1. DECT INTERFACE UNIT (DIU):
The DIU is a DECT exchange for Wireless subscriber and provides an
interface to a public Switched Telephone Network (PSTN). Its important functions are
such as call processing, CBS powering and PCM transcoding. System operation and
Maintenance (O&M) and remote fault monitoring can be performed from the DIU or
alternatively from a remote location using the Network Management System. The DIU is
the heart of the system and supports upto 1000 subscribers through 20 bases stations and
is a fully redundant switch.
63
The interface to the PSTN is via E1 digital links. Interface for connecting
upto 6 E1 lines are provided. With 4 E1 lines, the system can typically cater to about
1000 subscribers with 0.1 Erlang per subscriber and a Grade of Service of 1%.
An optional subscriber MUX (SMUC) unit in the DIU converts the E1
interface to 30 junction lines, which can be connected to two-wire subscriber lines of an
exchange.
The DIU consists of between three to six standard sub-racks in one or two
cabinets depending on the corDECT system configuration. All critical cards have a
standby so that system availability is ensured in case of failure. The system is powered by
48V power supply.
E1 link(s)
The DIU has got many cards to perform various functions. Each DIU has 5 BIMC cards.
Each BIMC card controls 1 site. Each BSD is controlled by a BIMC card. Each DIU has
20 BUIC (Base Station U-Interface Controller) cards. Each BUIC card controls 1 CBS.
64
-48V Power Supply
Alarm Panel
BSNL
PWRF is the Power Supply Card. There are three PWRF cards in load sharing
mode. Maximum of two cards can supply required power under full load. They
have -48 V Input & 5V Output.
SWCH (SWitCH or Central Switching and Control Card) Card is the heart of
DIU. It communicates/co-ordinates the cards through PCM Streams.
Clock Card: It generates common clock pulses (20 MHz Crystal Oscillator).
BUIC - Base Station (U Interface) Controller provides power to the base-station
as well as links CBS through 3 twisted pair copper wires.
Alarm Panel: It operates on -48V and displays critical and major alarms.
OMC PCs: There are two OMC PCs to provide redundancy. They work on
operating platform of Linux. They support tape drive for taking backup of billing
files, log files and also support online diagnosis of the status of all the cards.
There are two PCs, one is active and the other is passive. The active controls the
current calls while the passive takes data from the active on a daily basis. If active goes
down, then the work is shifted to passive. The active is then rescued using Linux Rescue
using the linux commands.
Expansion Sub-rack 0
PIBIBU
BU BU BUBIBU
BU BU BU BUBUBUBIBU
CLCK
CLCK
SWCH
SWCH
TOCN
TOCN
PI PI PI PI
PWRF
PWRF
PWRF
Main Sub-rack
Expansion Sub-rack 1
PIBIBU
BU BU BUBIBU
BU BU BU
65
2. COMPACT BASE STATION (CBS):
It provides wireless access in an area and supports twelve simultaneous
full duplex channels. The CBS is a small unobtrusive pole mounted or wall mounted
unit. Each CBS serves one cell providing upto 12 simultaneous speech channel gain of
the handset. Typically it ranges from 150m-5kms.
The CBS has two antennas for diversity. A direction antenna with
significant gain can be used when coverage required is either confined to certain
directions, or the coverage area is divided into sector covered by different CBSs.
Otherwise an omni-directional antenna could be used.
The CBS is interfaced to the DIU using 3 standard subscriber pair from
the existing loop plant. The pairs also supply power to the CBS from the DIU. The
maximum distance between CBS and DIU is 4kms. with 0.4 mm dia copper twisted pairs.
Alternatively the CBSs are interfaced the DIU through the base station
distributor (BSD) unit. In this case, the BSD is connected to DIU with an E1 link using
radio or fiber and CBS are connected to the BSD using three pairs of twisted pair copper
able each of which carries both the power as well as signal to the CBS. The maximum
distance between CBSW and BSD is 1km when 0.6mm twisted pair copper cable is used.
3. RELAY BASE STATION (RBS):
For coverage in large areas, two wireless links are used. An RBS is
mounted between CBS and Wallset-IP. Thus one wireless link is between WS-IP and
RBS and the other between RBS and CBS.
An RBS can handle 11 calls simultaneously. It has two units:
RBS Air Unit (mounted on a tower and has baseband and RF subsystems).
RBS Ground Unit (supplies power and provides maintenance support and
is mounted at the bottom of the tower.
An RBS Air Unit has three antennas:
o Directional Antenna with high gain (towards the serving CBS).
o Two antennas for diversity (for communication with subscriber units).
66
4. BASE STATION DISTRIBUTOR (BSD):
The base station distributor is an optional unit used when a cluster of the
CBSs are to be located some distance away from the DIU. The BSD is connected to the
DIU on E1 lines & each E1 line carries signals for four CBSs. The BSD demultiplexes
the signal on the E1 line and fides it to the four CBS. The four CBS are connected to the
BSD each using 3 pairs of 0.6mm twisted pair copper wires. The maximum distance
supported is 1km. The copper wires carry both power and signals from BSD to CBS.
The health of the BSD as well as the CBSs can be upgraded from the DIU.
One base station distributor can support upto 4 CBS. Interface between the DIU and BSD
is E1 interface which can be copper fiber or radio.BSD is designed to extend CORDECT
coverage to the subscribers away from DIU.
Asynchronous Digital Subscriber
Line (ADSL)It is a high speed replacement for modem or ISDN adapter that allows us to access the
internet faster. It is a transmission technique used on the line from modem to the service
provider.
67
It is called Asymmetrical since the speed of transmission is not the same in both
directions. A small amount of data sent by the customer can result in the receipt of a large
amount of data from the internet. ADSL modems operate on a bit stream and are intended
for carrying digital information between digital equipment such as PCs. Hence the word
Digital is used. ADSL itself operates over the subscriber’s normal telephone line to the
local exchange. The telephone line can continue to be used for voice calls through the use
of devices called ‘Splitters’ that separate the data and voice on the line. Thus the name-
Asynchronous Digital Subscriber Line.
How does ADSL work?
ADSL exploits the unused analogue bandwidth that is potentially available in the wires
that run from the user premises to the local exchange. This wiring was designed to carry
that portion of the frequency spectrum that is occupied by normal speech. The wires can,
however, carry frequencies above this rather limited spectrum. This is the portion that
ADSL uses.
68
A comparison of ADSL with PSTN & ISDN:
1. PSTN and ISDN are dial-up technologies.
•ADSL is 'always-on'.
•ADSL is un-metered and charged at a flat-rate.
2. PSTN and ISDN allow you to use fax, data, voice, data to the Internet, data to other
devices.
•ADSL is just about data to the Internet.
3. PSTN and ISDN allow you to choose the Internet Service Provider you want to use.
•ADSL connects you to a pre-defined ISP.
4. ISDN runs at 64kbps or 128kbps.
•ADSL can potentially download at 8Mbps.
•Many home ADSL services are provided at around 512kbps.
5. PSTN stops you using your phone.
•ADSL allows you to surf and phone at the same time.
ADSL Components:
PC ADSL Local Loop Service Internet
Modem Provider
Figure: Components of ADSL.
69
1. ADSL Modem: ADSL modem is connected to the telephone wiring (called the 'local
loop') that connects you to the local exchange equipment. The ADSL modem uses a
combination of several advanced signal processing techniques in order to achieve the
required throughput speeds on ordinary telephone wiring at distances up to several miles
from the local exchange.
ADSL works by implementing many modems in parallel, each of which
uses its own slice of the available bandwidth. ADSL uses many individual
modems working in parallel to exploit maximum bandwidth and deliver very high
speed.
‘Local Loop’ is the term applied to the ordinary telephone wires that go from a user's
premises to the telephone company. It is only on the local loop that ADSL
communications actually take place.
2. Service Provider: The service provider has three important components:
•DSLAM - DSL Access Multiplexer
•BAS - Broadband Access Server
•ISP - Internet Service Provider
1. The DSLAM is the piece of equipment at your local exchange that is at the other end
of your ADSL connection. It houses a bank of ADSL modems on one side and has a
single fibre-optic data connection on the other.
The DSLAM consolidates a number of ADSL user connections onto a single fibre
connection. This fibre will normally be connected to a Broadband Access Server or BAS.
2. The Broadband Access Server (BAS) is the piece of equipment that sits between the
DSLAM at the telephone exchange and the ISP that connects you to the Internet. A single
BAS will probably handle connections from several DSLAMs. The purpose of the BAS
is to unwrap the various protocols inside which your data travels over the ADSL
connection.
3. The Broadband Access Servers are connected to an Internet Service Provider or ISP.
This is the place where your connection to the Internet is made. The ISP usually provides
other services like mail and news servers, and may cache frequently-used pages from the
Internet so that you can access them more quickly.
70
How do voice and data co-exist in ADSL?
If you are surfing the Internet using an ADSL modem, then a telephone call can still be
made on the same line. Splitters that separate the high frequencies used by ADSL from
the low frequencies used by voice are situated at each end of the local loop. At your end
of the connection, the low frequencies go to your phone and the high frequencies go to
your ADSL modem. At the local exchange, the low frequencies go to the normal
telephone network while the high frequencies go to the service provider.
IP Addressing
An IP address is a numeric identifier assigned to each machine on an IP
network. It designates the specific location of a device on the network. An IP address can
be private - for use on a local area network (LAN) - or public - for use on the Internet or
other wide area network (WAN). IP addresses can be determined statically (assigned to a
71
computer by a system administrator) or dynamically (assigned by another device on the
network on demand). An IP address consists of 32 bits of information. These bits are
divided into four sections, referred to as octets or bytes, each containing 1 byte (8 bits).
Octets can take any value between 0 and 255.
An IP address is considered private if the IP number falls within one of the
IP address ranges reserved for private uses by Internet standards groups.
These private IP address ranges exist:
1. 10.0.0.0 through 10.255.255.255
2. 169.254.0.0 through 169.254.255.255
3. 172.16.0.0 through 172.31.255.255
4. 192.168.0.0 through 192.168.255.255
Private IP addresses are typically used on local networks including home,
school and business LANs including airports and hotels.
Devices with private IP addresses cannot connect directly to the Internet.
Likewise, computers outside the local network cannot connect directly to a device with a
private IP. Instead, access to such devices must be brokered by a router or similar device
that supports Network Address Translation (NAT). NAT allows an Internet Protocol (IP)
network to maintain public IP addresses separately from private IP addresses.
NAT allows computers on the home LAN to share a single Internet
connection. Additionally, it enhances home network security by limiting the access of
external computers into the home IP network space.
Classes of Network Address:
The IPv4 address space can be subdivided into 5 classes - Class A, B, C,
D and E. Each class consists of a contiguous subset of the overall IPv4 address range.
Class Leftmost bits Start Address Finish Address
A 0xxx 0.0.0.0 127.255.255.255
72
B 10xx 128.0.0.0 191.255.255.255
C 110x 192.0.0.0 223.255.255.255
D 1110 224.0.0.0 239.255.255.255
E 1111 240.0.0.0 255.255.255.255
Ranges of different classes:
Class A: If the first octet of the IP address is in the range 0 to 127, both inclusive.
Class B: If the first octet of the IP address is in the range 128 to 191, both inclusive.
Class C: If the first octet of the IP address is in the range 192 to 223, both inclusive.
Classes D and E: The addresses between 224 and 255 are reserved for Class D and E
networks. Class D (224-239) is used for multicast addresses and Class E (240-255) for
scientific purposes.
8 bits 8 bits 8 bits 8 bits
Class A
Class B
Class C
Class D MULTICAST
Class E RESEARCH
RECOMMENDATIONS
It is recommended that the following changes be made on the basis of the studies:
Since more and more customers are using internet nowadays, so it becomes
necessary to provide good internet services to them. The services must be reliable
and at good speeds.
73
NETWORK HOST HOST HOST
NETWORK NETWORK HOST HOST
NETWORK NETWORK NETWORK HOST
The systems used for wireless telephony like BSC, BTS must be reliable. They
must be checked for faults frequently.
The network of wireless services should be good.
The wireline services provided must also be reliable.
REFERENCES
Technical Manuals of network devices’ manufacturers - Huawei, UTStarcom, Dellcron.
www.wikipedia.org
www.huawei.com
74
www.dellcron.com
www.google.com
75