MOBILE COMMUNICATION THROUGH CDMA TECHNOLOGY

CDMA OVERVIEWCDMA OVERVIEW

Presentation by-Presentation by- Arunabh Kumar &Arunabh Kumar & Pravir Kumar withPravir Kumar with ECE Final Year,R.P.S.I.T Patna.ECE Final Year,R.P.S.I.T Patna.

SAHID MASWOODSAHID MASWOOD (HRD PATNA)(HRD PATNA)

SIGNATURESIGNATURE

COMMENTS:COMMENTS:

B.C.NAYAKB.C.NAYAK (CDMA LEAD)(CDMA LEAD)

SIGNATURESIGNATURE

COMMENTS:COMMENTS:

ContentsContents AcknowledgementAcknowledgement Mobile communication historyMobile communication history Multiple Access methodsMultiple Access methods GSM And CDMAGSM And CDMA Departments of CDMADepartments of CDMA R F OverviewR F Overview Switch OverviewSwitch Overview Call FlowCall Flow SignalingSignaling POIPOI NLD/ILDNLD/ILD Transportation OverviewTransportation Overview Fixed AccessFixed Access Out-side PlantOut-side Plant Advantages, DisadvantagesAdvantages, Disadvantages

AcknowledgementAcknowledgement

We got this great opportunity to present project on We got this great opportunity to present project on CDMA Overview prepared on the basis on four CDMA Overview prepared on the basis on four week training in Reliance Info COM Pvt. Ltd. Patna.week training in Reliance Info COM Pvt. Ltd. Patna.

We owe our sincere thanks toWe owe our sincere thanks to Shahid Maswood (HRD Patna)Shahid Maswood (HRD Patna) B. C. Nayak (CDMA LEAD)B. C. Nayak (CDMA LEAD) Manoj Sinha (MCN Cluster in charge)Manoj Sinha (MCN Cluster in charge)

We express sincere thanks to the management at We express sincere thanks to the management at RELIANCE INFOCOMM Pvt. Ltd. Mr. R.N.Rathore &RELIANCE INFOCOMM Pvt. Ltd. Mr. R.N.Rathore & MCN PatnaMCN Patna, in particular to , in particular to Mr. Saurav Chaurasiya,Mr. Mr. Saurav Chaurasiya,Mr. Amar Nath Prasad & Mr. Dhananjay Kumar, Amar Nath Prasad & Mr. Dhananjay Kumar, all are all are arranging and scheduling our training for 4 weeks. Without arranging and scheduling our training for 4 weeks. Without their generous support, We could not have completed our their generous support, We could not have completed our training so efficiently. At last, we are reallytraining so efficiently. At last, we are really thankful to Mr. thankful to Mr. Himanshu Shekhar & Miss. Priyanka PriyaHimanshu Shekhar & Miss. Priyanka Priya without there without there co-operation ,it couldn’t be possible.co-operation ,it couldn’t be possible.

MOBILE COMMUICATION HISTORYMOBILE COMMUICATION HISTORY

1st.Generation(1980s)

Analog

NMT CT0TACS CT1AMPS

2nd. Generation(1990s)

Digital

GSMDECTDCS1800 CT2PDCPHSIS-54IS-95IS-136UP-PCS

IMT-2000CDMA2000W-CDMA

3rd. Generation(2000s)

1946 Mobile communication Appeared St. Louis USA 1946to1970 Slow growth of mobile networks all over world.

1970 BELL LAB introduced Cellular Principle. 1979 AMPS System in US

Analogue technology used. Technologies incompatible. Modules cumbersome & heavy. 1980s TACS & NMT systems introduced by Europe

& Nordic countries. 1990s Digital Systems introduced.

1946- 1960s 1980s 1990s 2000s Appeared 1G 2G 3G

Analog Digital Digital

Multi Multi Unified Standard Standard Standard Terrestrial Terrestrial Terrestrial

& Satellite

Analog SystemsAnalog Systems (1st Generation) (1st Generation)

AMPS:AMPS: Advanced Mobile Phone Advanced Mobile Phone Service Service

(US, 800 MHz Band)(US, 800 MHz Band)

TACS: TACS: Total Access Communication Total Access Communication System System

(UK , 900 (UK , 900 MHz Band)MHz Band)

NMT450:NMT450: Nordic Mobile Telephone Service Nordic Mobile Telephone Service

(Scandinavian, 450 MHz & (Scandinavian, 450 MHz & 900 900 MHz Band)MHz Band)

Digital Systems Digital Systems ( 2nd Generation) 1990’s( 2nd Generation) 1990’s

DAMPS:DAMPS: Digital AMPS Digital AMPS

(US, 800 MHz Band, IS-54 (US, 800 MHz Band, IS-54 IS-136) IS-136)

CDMA:CDMA: Code Division Multiple Access System Code Division Multiple Access System

(US, 900 MHz Band, 1S-95)(US, 900 MHz Band, 1S-95)

GSM:GSM: Global System For Mobile Global System For Mobile Communication. Communication.

(Europe, 900 / 1800 MHz Band)(Europe, 900 / 1800 MHz Band)

Requirements for 3rd generation Mobile Requirements for 3rd generation Mobile SystemsSystems

High CapacityHigh Capacity Tolerance for interferenceTolerance for interference PrivacyPrivacy Tolerance for fadingTolerance for fading Ability to various data rate transmissionAbility to various data rate transmission Flexible Quality of Service (QoS)Flexible Quality of Service (QoS)

Multiple access methodMultiple access method

Multiple Accesses:Multiple Accesses:

*Multiple Accesses is the simultaneous use of a *Multiple Accesses is the simultaneous use of a communication system by one or more user.communication system by one or more user.

*Each user’s signal must be kept uniquely *Each user’s signal must be kept uniquely distinguishable from user’s signals todistinguishable from user’s signals to

allow private communications on demand. allow private communications on demand.

*Users can be separated many ways: *Users can be separated many ways: .Physically: on separated wires.Physically: on separated wires . By arbitrarily defined “channels” established in frequency, time, . By arbitrarily defined “channels” established in frequency, time, or any other variable imaginable. or any other variable imaginable.

Cellular Technologies

Data Rate VS

Mobility

Mobility

Data

Ra

te

W-LAN

High Data Rate up-to 54 Mbps. Little Mobility.

Fixed Wireless

Very High Data Rate up-to 155 Mbps. No Mobility.

155 Mbps

54 Mbps

2 Mbps

3 G

2 G

Satellite

Moderate Data Rates. Very long distances. very high Mobility.

Cellular

Moderate Data Rate. High Mobility.

In-door

Out-door

Vehicular.

MULTIPLEACCESSMETHOD

FDMA TDMA CDMA

MULTIPLE ACCESS METHODSMULTIPLE ACCESS METHODS

Mobile Station

Base Station

Mobile StationMobile Station

Mobile Station

Forward link

Reverse link

FDMAFDMA

Frequency Division Multiple AccessFrequency Division Multiple Access Oldest &most familiar method of radio Oldest &most familiar method of radio

communication communication Each user is assigned with unique channel of Each user is assigned with unique channel of

frequencyfrequency Acts as private freq. for its call durationActs as private freq. for its call duration As call terminates, the channel is released and As call terminates, the channel is released and

available for new call.available for new call. Number of users are lessNumber of users are less

TDMATDMA

Time Division Multiple AccessTime Division Multiple Access A user’s channel is a specific frequencyA user’s channel is a specific frequency But only allotted for a certain durationBut only allotted for a certain duration It belongs to the user for certain time slots in It belongs to the user for certain time slots in

repeating sequence.repeating sequence. Numbers of users are much greaterNumbers of users are much greater Groupe Special Mobile (GSM) uses this techniqueGroupe Special Mobile (GSM) uses this technique

CDMACDMA Code Division Multiple AccessCode Division Multiple Access Each user has specified frequency for all timeEach user has specified frequency for all time Each user has been given a unique code patternEach user has been given a unique code pattern From these codes connections are identifiedFrom these codes connections are identified. . This unique code is buried within a shared signal, mingled This unique code is buried within a shared signal, mingled

with other user’s code patterns. with other user’s code patterns. If a user’s code pattern is known, the presence or absence of If a user’s code pattern is known, the presence or absence of

their signal can be detected, thus conveying information.their signal can be detected, thus conveying information. Numbers of users are very largeNumbers of users are very large

In Technology CDMA Has Plus Point Over In Technology CDMA Has Plus Point Over GSM, Why?GSM, Why?

BecauseBecause CDMA is fasterCDMA is faster CDMA is more secureCDMA is more secure Connection on a CDMA network will never get Connection on a CDMA network will never get

dropped when moving from cell to celldropped when moving from cell to cell CDMA base stations cover a large areaCDMA base stations cover a large area

1 Billion GSM Subscriber’s To CDMA’s 1 Billion GSM Subscriber’s To CDMA’s 270 Million270 Million

GSM replaced archaic analogue systemGSM replaced archaic analogue system Late appearance of CDMALate appearance of CDMA Adopting CDMA means paying royalty to Adopting CDMA means paying royalty to

QUALCOMQUALCOM World standard for mobile communicationWorld standard for mobile communication Availability of international roaming Availability of international roaming

FUTURE’S TECHNOLOGYFUTURE’S TECHNOLOGY GSM & CDMA both are moving towards improved GSM & CDMA both are moving towards improved

technology based on CDMA techniquetechnology based on CDMA technique These techniques are Wideband-CDMA & CDMA These techniques are Wideband-CDMA & CDMA

2000.2000.

DEPARTMENTS OF CDMADEPARTMENTS OF CDMA

POI

NLD/ID

OSP FIXED ACCESS

TRANSPORT

MSC

R F

CDMA

R F OVERVIEWR F OVERVIEW What is cell?What is cell? A cell is a small area of service A cell is a small area of service

within a city, serviced by its own within a city, serviced by its own antenna.antenna.

Frequency Reuse In CDMA-Frequency Reuse In CDMA- All users use same frequencyAll users use same frequency Universal frequency reuse Universal frequency reuse

applies to the users in the same cell applies to the users in the same cell as well as to those in othersas well as to those in others

Complicated reuse pattern is not Complicated reuse pattern is not necessarynecessary

Spread Spectrum ConceptSpread Spectrum Concept

User 1

User 2

User 3

User n

Code 1

Code 2

Code 3

Code n

1800 1850 1910 1930 1990 2000MHz

mMobile TX Cell TX

Spread spectrum uses much larger slice(1.25MHz) of the available bandwidth. Same slice is used for all user with no time multiplexing but user is assigned with a different code of to uniquely identify them.

CDMA Cellular SpectrumCDMA Cellular Spectrum

824MHz 835MHz 845MHz 849MHz

825MHz 846.5MHz

A” A B A’ B’

A” A B A’ B’

869MHz 880MHz 890MHz 894MHz

870MHz 891.5MHz

REVERSE LINK

FORWARD LINK

Band Band OfOf CDMA CDMA The 850MHz CDMA band is most popularly used all over the worldThe 850MHz CDMA band is most popularly used all over the world

This band works betweenThis band works between 824-849MHz used for the Reverse link communication824-849MHz used for the Reverse link communication 869-894MHz used for the Forward link communication each of 25MHz.869-894MHz used for the Forward link communication each of 25MHz.

The total band of 25MHz is divided into small channels of 30KHzeach.An actual CDMA The total band of 25MHz is divided into small channels of 30KHzeach.An actual CDMA carrier will be using a multiple of the 30KHz channels.carrier will be using a multiple of the 30KHz channels.

This means for an actually utilized bw of 1.23MH will need 41*30KHz channels.This means for an actually utilized bw of 1.23MH will need 41*30KHz channels. Relationship between the channel numbers and actual freq.Relationship between the channel numbers and actual freq. Reverse link frequency =(825+N0.03)MHzReverse link frequency =(825+N0.03)MHz Forward link frequency=(870+N0.03)MHzForward link frequency=(870+N0.03)MHz N=CDMA Channel NumberN=CDMA Channel Number

Spread Spectrum ConceptSpread Spectrum Concept Spread spectrum uses much larger slice (1.25 MHz) of the available Spread spectrum uses much larger slice (1.25 MHz) of the available

bandwidth. Same slice is used for all users with no time multiplexing but each bandwidth. Same slice is used for all users with no time multiplexing but each user is assigns with a different code to uniquely identify them.user is assigns with a different code to uniquely identify them.

CDMA uses a modulation technique called “Spread Spectrum” to transport a CDMA uses a modulation technique called “Spread Spectrum” to transport a narrow band voice signal over a wide bandwidth channel .The wide bandwidth narrow band voice signal over a wide bandwidth channel .The wide bandwidth for IS-2000 is 1.23 MHz .for IS-2000 is 1.23 MHz .

The CDMA modulation technique uses three methods for spectrum spreading:The CDMA modulation technique uses three methods for spectrum spreading: . frequency hopping (FH). frequency hopping (FH) . time hopping (TH) . time hopping (TH) . direct sequence (DS). direct sequence (DS)

While FH is more popular in CDMA system used for military purpose in While FH is more popular in CDMA system used for military purpose in commercial CDMA system DSSS is popularly used. commercial CDMA system DSSS is popularly used.

Direct Sequence-Spread Spectrum (DSSS) Direct Sequence-Spread Spectrum (DSSS) TechniquesTechniques

CDMA is a scheme in which multiple users are assigned radio CDMA is a scheme in which multiple users are assigned radio resources using the DSSS techniques.resources using the DSSS techniques.

Although all users are transmitting in the same RF band, all users’ Although all users are transmitting in the same RF band, all users’ arte separated from each other via the use of orthogonal codes (Walsh arte separated from each other via the use of orthogonal codes (Walsh Code).Code).

Each user has full time use of the entire spectral allocations.Each user has full time use of the entire spectral allocations.

Each user’s signal is spread over the entire bandwidth and codes so as Each user’s signal is spread over the entire bandwidth and codes so as to appear like broadband noise to every other user.to appear like broadband noise to every other user.

CDMA SPREADINGCDMA SPREADING(Time Domain)(Time Domain)

Spreading SystemSpreading SystemIn a spread system the data information signal, b(t),

is multiplied by a wideband signal, c(t), which is the output signal of the Direct Sequence (DS) generator – a pseudorandom noise (PN) output signal. The signal

which will eventually be transmitted, y(t) = b(t) c(t), will occupy bandwidth far in excess of the minimum m

bandwidth to transmit the data information.

Spreading Gain or Processing Gain (G) = Tb/Tc,

Where, Tb is the bit interval of the Information steam & Tc is the bit interval of the DS stream. Tc is also called

Chip Time .

CDMA SPREADINGCDMA SPREADING(Frequency Domain)(Frequency Domain)

The Processing Gain & Capacity RelationThe Processing Gain & Capacity Relation CDMA spreading gain consider a user with a 9600 bps Vocoder CDMA spreading gain consider a user with a 9600 bps Vocoder talking on a CDMA signal 1,228,800 Hz wide. talking on a CDMA signal 1,228,800 Hz wide. The processing gain is 1228800/9600 = 128, which is 21 db. The processing gain is 1228800/9600 = 128, which is 21 db.

.. Shannon’s work suggests that a certain bit rate of information deserves a certain bandwidth .If Shannon’s work suggests that a certain bit rate of information deserves a certain bandwidth .If one CDMA user is carried alone by a CDMA signal, the processing gain is large (roughly 21 one CDMA user is carried alone by a CDMA signal, the processing gain is large (roughly 21 db for an 8k vocoder).db for an 8k vocoder).

. . Each doubling of the number of users consumes 3 db of the processing gain. Each doubling of the number of users consumes 3 db of the processing gain. . . Somewhere above 32 users, the signal-to-noise ratio becomes undesirable and the ultimate Somewhere above 32 users, the signal-to-noise ratio becomes undesirable and the ultimate

capacity of the sector is reached. capacity of the sector is reached.

.. Practical CDMA systems restrict the number of users per sector to ensure processing gain Practical CDMA systems restrict the number of users per sector to ensure processing gain remains at usable levelsremains at usable levels..

WALSH CODESWALSH CODES

64 are available64 are available 64 Chips long – lasts 1/19200 sec 64 Chips long – lasts 1/19200 sec mutually orthogonal mutually orthogonal The user signal (or control channel) is multiplied by The user signal (or control channel) is multiplied by

the Walsh code. the Walsh code. The Walsh code provides each user or channel with an The Walsh code provides each user or channel with an

unique identifier and, in DS spreading, spreads the frame unique identifier and, in DS spreading, spreads the frame across the entire 1.23MHz bandwidth.across the entire 1.23MHz bandwidth.

PN SHORT CODESPN SHORT CODES one pair is used (I & Q)one pair is used (I & Q) 32 K long –lasts 26-2/3 ms, repeats 75x in 2sec. 32 K long –lasts 26-2/3 ms, repeats 75x in 2sec. Generated in 15 – bit tapped shift register. Generated in 15 – bit tapped shift register. Nearly self – orthogonal if compare out of sync Nearly self – orthogonal if compare out of sync On the Reverse link it is used only for quadrature spreading On the Reverse link it is used only for quadrature spreading

without any offset orwithout any offset or The PN Short Code is used only for tracking the The PN Short Code is used only for tracking the

mobile that means to calculate the round trip delay or path mobile that means to calculate the round trip delay or path delay for the mobile. delay for the mobile.

PN LONG CODEPN LONG CODE

only one is used only one is used (2)42 – 1 chips long – lasts 40+ days! (2)42 – 1 chips long – lasts 40+ days! generated in 42 – bit shift register. generated in 42 – bit shift register. Any short sample is nearly orthogonal with any other short sample. Any short sample is nearly orthogonal with any other short sample.

Information about the long code is broadcast to the mobile station by the sync Information about the long code is broadcast to the mobile station by the sync channel to help the mobile lock onto the base station and helps provide separation channel to help the mobile lock onto the base station and helps provide separation from other station. from other station.

It is used to scrambled the interleaved signal and provide additional security against It is used to scrambled the interleaved signal and provide additional security against

interception and interference. interception and interference. An additional advantage of the long code is that it allows the transmitter to use less An additional advantage of the long code is that it allows the transmitter to use less

power ,maintaining control over the ambient RF environment and increasing the power ,maintaining control over the ambient RF environment and increasing the overall capacity of the cell.overall capacity of the cell.

Steps evolved for signal transmissionSteps evolved for signal transmission

1. A pseudo random code is generated, different for 1. A pseudo random code is generated, different for each channel& successive connections.each channel& successive connections.

2. The information data modulates the pseudo 2. The information data modulates the pseudo random codes.random codes.

3. The resulting signal modulates the carrier.3. The resulting signal modulates the carrier. 4. The modulated carrier is amplified and broadcast.4. The modulated carrier is amplified and broadcast.

Steps evolved for receiving the signalsSteps evolved for receiving the signals

1.The carrier is received and amplified.1.The carrier is received and amplified. 2.The received signal is now demodulated by 2.The received signal is now demodulated by

receiving the codes.receiving the codes. 3.The receiver acquires the received code and phase 3.The receiver acquires the received code and phase

locks its own code to it.locks its own code to it. 4.The received signal is correlated with the generated 4.The received signal is correlated with the generated

code, extracting the information code, extracting the information data.data.

CDMA Switch OverviewCDMA Switch Overview

CDMA Network Architecture

MS(Mobile Switch)MS(Mobile Switch) This consists of the mobile telephone, fax machine etc. This is the part of the This consists of the mobile telephone, fax machine etc. This is the part of the

network that the subscriber will see.network that the subscriber will see.

The MS consists of two parts, the Mobile Equipment (ME) and an electronic The MS consists of two parts, the Mobile Equipment (ME) and an electronic ‘smart card’ called a Universal Identity module (UIM).‘smart card’ called a Universal Identity module (UIM).

The ME(Mobile Equipment) is the hardware used by the subscriber to access the The ME(Mobile Equipment) is the hardware used by the subscriber to access the network. The hardware has an identity number associated with this identity number network. The hardware has an identity number associated with this identity number is called the International Mobile Equipment Identity (IMEI). is called the International Mobile Equipment Identity (IMEI).

The UIM is a card which plugs into the ME or programmed into it. This identifies The UIM is a card which plugs into the ME or programmed into it. This identifies thethe MS subscriber. The subscriber is identified by an identity number called the MS subscriber. The subscriber is identified by an identity number called the International Mobile Subscriber Identity (IMSI).International Mobile Subscriber Identity (IMSI).

Mobile Equipment may be purchased from any store but the UIM must be obtained Mobile Equipment may be purchased from any store but the UIM must be obtained from the CDMA network provider. Without the it, the ME will only be able to make from the CDMA network provider. Without the it, the ME will only be able to make emergency calls.emergency calls.

BTS(Base Tranciever Station)BTS(Base Tranciever Station) This is a part of the CDMA network which communicates with MS .This is a part of the CDMA network which communicates with MS .

The BTS contains the RF components that provide the air interface for a particular The BTS contains the RF components that provide the air interface for a particular cell.The antenna is included as part of the BTS.cell.The antenna is included as part of the BTS.

The BTS comprises the radio equipment such as transreceivers and antennas which are The BTS comprises the radio equipment such as transreceivers and antennas which are needed to serve each cell in the network .needed to serve each cell in the network .

A group of BTSs are controlled by a BSC. A group of BTSs are controlled by a BSC. BTS in BTS in Trans-directionTrans-direction does: does:

Channel Coding Channel Coding Interleaving Interleaving Frame Building Frame Building Modulation Up-ConversionModulation Up-Conversion Amplification.Amplification.

Continued...Continued... BTS inBTS in Receive-directionReceive-direction does:does:

Down-Conversion Down-Conversion Demodulation Demodulation De-Scrambling De-Scrambling Decoding Decoding Digital to Analog (D/A) conversion.Digital to Analog (D/A) conversion.

BTS is usually located in the center of the cell.BTS is usually located in the center of the cell. BTS has 1 to 16 RF channels. These channels are to be different BTS has 1 to 16 RF channels. These channels are to be different

from those of the adjacent cellsfrom those of the adjacent cells It It acts as mobile interfaceacts as mobile interface to the cellular network. to the cellular network.

•.

BSC(Base Station Controler)BSC(Base Station Controler) The BSC manages all the radio-related functions of a CDMA network.The BSC manages all the radio-related functions of a CDMA network.

It is a high capacity switch that provides functions such as MS handover,radio channel It is a high capacity switch that provides functions such as MS handover,radio channel assignment and the collection of cell configuration data.A number of BSCs may be assignment and the collection of cell configuration data.A number of BSCs may be controlled by each MSC. controlled by each MSC.

Performs radio resource managementPerforms radio resource management Assigns and releases frequencies and time slots for all the MS’s in its areaAssigns and releases frequencies and time slots for all the MS’s in its area Reallocation of frequencies among cellsReallocation of frequencies among cells Hand over protocol is executed here. Hand over protocol is executed here. Time and Frequency Synchronization signals to BTS’s.Time and Frequency Synchronization signals to BTS’s. Time Delay Measurement and notification of an MS to BTSTime Delay Measurement and notification of an MS to BTS Power Management of BTS and MS.Power Management of BTS and MS.

HANDOVERHANDOVER

Handover occurs when a call has to be passed from one cell Handover occurs when a call has to be passed from one cell to another as the user moves between cells. In a traditional to another as the user moves between cells. In a traditional "hard" handover"hard" handover, the connection to the current cell is broken, , the connection to the current cell is broken, and then the connection to the new cell is made. This is and then the connection to the new cell is made. This is known as a "break-before-make" handover. Since all cells in known as a "break-before-make" handover. Since all cells in CDMA use the same frequency, it is possible to make the CDMA use the same frequency, it is possible to make the connection to the new cell before leaving the current cell. connection to the new cell before leaving the current cell. This is known as a "make-before-break" or This is known as a "make-before-break" or "soft" handover"soft" handover. . Soft handovers require less power, which reduces Soft handovers require less power, which reduces interference and increases capacity. interference and increases capacity.

MSC(Mobile ServicesSwitching Centers)MSC(Mobile ServicesSwitching Centers) The MSC is included in the CDMA system for call-switching. The MSC is included in the CDMA system for call-switching.

Its overall purpose is the same as that of any telephone Its overall purpose is the same as that of any telephone exchange.exchange.

Each MSC provides service to MSs located within a defined Each MSC provides service to MSs located within a defined geographic coverage area.geographic coverage area.

One MSC is capable of supporting a regional capital with One MSC is capable of supporting a regional capital with approximately one million inhabitants. An MSC of this size will be approximately one million inhabitants. An MSC of this size will be

contained in about half a dozen racks.contained in about half a dozen racks.

GMSC(Gateway Mobile Services Switches GMSC(Gateway Mobile Services Switches Centers)Centers)

Connects mobile network to a fixed network.Connects mobile network to a fixed network. Entry point to aEntry point to a PLMN. PLMN. Usually one per Usually one per PLMN.PLMN. Request Request routing informationrouting information from the HLR from the HLR

and routes the connection to the local MSCand routes the connection to the local MSC

MSC(Mobile ServicesSwitching Centers)MSC(Mobile ServicesSwitching Centers)

The functions carried out by the MSC are listed below: The functions carried out by the MSC are listed below: a. Call Processinga. Call Processing b. Operations and Maintenance Supportb. Operations and Maintenance Support c. Billing c. Billing Signaling protocol with BSC.Signaling protocol with BSC. Paging and Short Message Services.Paging and Short Message Services. Routing of traffic and signaling.Routing of traffic and signaling. It undertakes Radio Resource Management. It undertakes Radio Resource Management. Verifying IMSI, Authentication, Interrogation of HLR.Verifying IMSI, Authentication, Interrogation of HLR.

HLR(Home Location Register)HLR(Home Location Register) n/w database that stores and manages all mobile subscriptions belonging to n/w database that stores and manages all mobile subscriptions belonging to

a specific operator.a specific operator.

The information stores includes:The information stores includes: . Subscriber identity.. Subscriber identity. . Subscriber supplementary services. . Subscriber supplementary services. . Subscriber location information.. Subscriber location information. . Subscriber authentication information.. Subscriber authentication information. The HLR is a centralizedThe HLR is a centralized

VLR(Visitor Location Register)VLR(Visitor Location Register) The VLR database contains information’s about all mobile subscribers The VLR database contains information’s about all mobile subscribers

currently located in an MSC service area. currently located in an MSC service area.

There is one VLR for each MSC in a network.There is one VLR for each MSC in a network.

When a subscriber roams into new MSC service area, the VLR connected to When a subscriber roams into new MSC service area, the VLR connected to that MSC requests information about the subscriber from the subscriber’s that MSC requests information about the subscriber from the subscriber’s HLR.HLR.

The HLR sends the copy of the information to the VLR and updates its own The HLR sends the copy of the information to the VLR and updates its own location information.location information.

When subscriber makes a call,the VLR will already have the information When subscriber makes a call,the VLR will already have the information required for call set up.required for call set up.

EIR & AuCEIR & AuC Equipment Identity Register (EIR):Equipment Identity Register (EIR):

Contains three lists for IMEI check:Contains three lists for IMEI check: White listWhite list – – contains mobile equipmentcontains mobile equipment approvedapproved without without

restriction.restriction. Grey listGrey list – – contains the equipment to becontains the equipment to be observed.observed. Black listBlack list – – contains thecontains the unapprovedunapproved equipment.equipment. EIR checks whether the IMEI fits into one of these lists and passes EIR checks whether the IMEI fits into one of these lists and passes

result to MSC. For example, if mobile fits into the black list, it result to MSC. For example, if mobile fits into the black list, it cannot participate in the call setup.cannot participate in the call setup.

Authentication Center (AuC):Authentication Center (AuC): Security related functions.Security related functions. Verifies individual parameters assigned to each mobile subscriber.Verifies individual parameters assigned to each mobile subscriber.

CALL FLOWCALL FLOW Mobile Subscriber ISDN (MSISDN):Mobile Subscriber ISDN (MSISDN):

Country Code (CC)Country Code (CC) (Up-to 3 decimal places) (Up-to 3 decimal places)National Destination Code (NDC)National Destination Code (NDC) (2 to 3 digits). (2 to 3 digits).Subscriber Number (SN)Subscriber Number (SN) (Max up-to 10 digits). (Max up-to 10 digits).

A subscriber can hold several ISDN’s for selection of different services.A subscriber can hold several ISDN’s for selection of different services. International Mobile Subscriber Identity (IMSI):International Mobile Subscriber Identity (IMSI):

Mobile Country Code (MCC)Mobile Country Code (MCC) Mobile Network Code (MNC)Mobile Network Code (MNC) Mobile Subscriber Identification No. (MSIN)Mobile Subscriber Identification No. (MSIN) IMSI is stored in the SIM. Mobile Station can be operated if SIM with the valid IMSI is stored in the SIM. Mobile Station can be operated if SIM with the valid

IMSI is inserted in the equipment.IMSI is inserted in the equipment. The Equipment should have valid IMEI.The Equipment should have valid IMEI.

Types Of Call

On Net Call Off Net Call

Local STD Local STD

onOn Net Call-call in same networkOff Net Call-call in other network

Call Initiation, Setup and TerminationCall Initiation, Setup and Termination

• The mobile user when decides to make a call, enters the desired phone The mobile user when decides to make a call, enters the desired phone number. This initiates an access probe. The mobile uses the access number. This initiates an access probe. The mobile uses the access channel and attempts to contact the serving base station.channel and attempts to contact the serving base station.

• Since no traffic channel has been established, the mobile uses open Since no traffic channel has been established, the mobile uses open loop power control. Multiple tries are allowed at random times to loop power control. Multiple tries are allowed at random times to avoid collisions that can occur on the access channel. Each successive avoid collisions that can occur on the access channel. Each successive attempt is made at a higher power level. After each attempt, the mobile attempt is made at a higher power level. After each attempt, the mobile listens to the paging channel for a response from the base stations. listens to the paging channel for a response from the base stations.

Call Initiation, Setup and TerminationCall Initiation, Setup and Termination

Once the access request has been received by the base station, Once the access request has been received by the base station, the base station responds with an assignment to a traffic the base station responds with an assignment to a traffic channel (Walsh code). The base station initiates the land channel (Walsh code). The base station initiates the land link, and conversation takes place.link, and conversation takes place.

Call termination can be initiated either from the mobile or Call termination can be initiated either from the mobile or the land side. In either case the transmissions are stopped, the land side. In either case the transmissions are stopped, the Walsh code is freed, and the land line connection is the Walsh code is freed, and the land line connection is broken. The mobile unit resumes monitoring the page broken. The mobile unit resumes monitoring the page channel of the current serving cell.channel of the current serving cell.

Outgoing CallOutgoing Call

Receiving Incoming CallReceiving Incoming Call

CALL FLOW SCENARIO FOR 93……MOBILE CALL FLOW SCENARIO FOR 93……MOBILE NO.S..NO.S..

Call from 9334….to local 9334….Call from 9334….to local 9334….

MSCPatna

A B

•Call from 9334….to STD Delhi No.093.MSCPatna

GMSCPatna

GMSCDelhi

MSCDelhiA B

93 Local to B.S.N.L Local

GMSCPatna

MSCPatnaA B (through BSNL tax POI)

93 Local to B.S.N.L. STD

MSCPatna

ILT Switch

Patna

ILTSwitchDelhi

A B (thr’bsnl NLD POI)

Ending CallEnding Call

WHAT IS E1? WHAT IS E1? E1 is a signal in which voice as well as data flow through it.E1 is a signal in which voice as well as data flow through it. On It consists of 32 channels which can carry the data up to 2.04 mbps.On It consists of 32 channels which can carry the data up to 2.04 mbps. Multiplying 64kbps of data with the 32 channels it will be 2.04mbps of information Multiplying 64kbps of data with the 32 channels it will be 2.04mbps of information

which is carried by 1E1.which is carried by 1E1. THEREFORE,THEREFORE, E2=2E1=2 * 2.048 =4.096mpbs of data E2=2E1=2 * 2.048 =4.096mpbs of data As we go further,As we go further, E3=2E2=2*4.096=81.96mbps of data & so on.E3=2E2=2*4.096=81.96mbps of data & so on. The above mentioned hierarchy is called plieo digital hierarchy The above mentioned hierarchy is called plieo digital hierarchy (PDH).(PDH). These are These are

electrical transmission hierarchy.electrical transmission hierarchy. If there is need to have more active channels we can add E1’s according to subscriber If there is need to have more active channels we can add E1’s according to subscriber

and traffic needs, for having more active channels there is a hierarchy called and traffic needs, for having more active channels there is a hierarchy called synchronous digital hierarchy i.e. SDH(STM).synchronous digital hierarchy i.e. SDH(STM).

1 STM = 63 E1.1 STM = 63 E1. 1 STM = 63 * 2.048 +(Extra padding bits + dummy for synchronization) = 155.5mbps of 1 STM = 63 * 2.048 +(Extra padding bits + dummy for synchronization) = 155.5mbps of

data is being carried.data is being carried.

SIGNALINGSIGNALINGINTRODUCTIONINTRODUCTION

Terminal

Transmission Links

SwitchingCentre

MANUAL EXCHANGEMANUAL EXCHANGE

Calling party off, hook lamp onCalling party off, hook lamp on Verification of eligibility-query for called party informationVerification of eligibility-query for called party information Called party information-analysis by the operatorCalled party information-analysis by the operator Ring to called party if trueRing to called party if true Called party answer- connectionCalled party answer- connection Either party on hook lamp offEither party on hook lamp off Recapitulation of the link-disconnectionRecapitulation of the link-disconnection

Exchange ModelExchange Model Compared to manual exchange, we can sayCompared to manual exchange, we can say Hardware = Chords, Lamps Eyes ,Hands e.t.c.Hardware = Chords, Lamps Eyes ,Hands e.t.c. Software = Brain ,Reasoning ,JudgmentSoftware = Brain ,Reasoning ,Judgment

ELEMENT OF ANELEMENT OF ANEXCHANGEEXCHANGE

SubscriberInterface Switch

Control System

SubscriberInterfaceM.S.

M.S.

A SWITCHA SWITCH

Subscriber Services

Operation & MaintenanceFunction

Signaling Function

Call Handling Function

Processors

NETWORK CONCEPTNETWORK CONCEPT

Processor (Call handling

Function)

Processor (Call handling

Function)

PN

O&MN/W

SignalingN/W

Access NetworkAccess Network

RSS

Subscriber MultiplexP

P

P

P

P

P P

Subscriber Switch

GroupSwitch

Local Exchange

RLL

Remote Subscriber Switch

Tower

Switching in telecom networkSwitching in telecom network

ServiceSubscriber

-voice-data

-video

ServiceSubscriber

-voice-data

-video

The ITU-T defines switching as : “the establishing ,on demand, of an individual connection from a desire inlet to a desired outlet within a set of inlets &outlets for as long as is required for the transfer of information”. Today the word ‘information’ not only denotes the speech we hear in our telephone receiver, but also incorporate all types of information from several telephone services

INTER EXCHANGE SIGNALINGINTER EXCHANGE SIGNALING

CASChannel Associated

Signalinge.g. R1,R2,system no.5

CCSCommon Channel

Signalinge.g. system no. 7

Muscles and Nerve’s of a N/WMuscles and Nerve’s of a N/W A digital telecom n/w conist of a n/w of bearer channels (Muscles).A digital telecom n/w conist of a n/w of bearer channels (Muscles). An overlaping n/w of signaling channels (Nerves).An overlaping n/w of signaling channels (Nerves).

Switch

Switch

Switch

Switch

Switch

= Signal = Speech

Speech & Signaling ConceptsSpeech & Signaling Concepts This signaling is message based signaling.It is widely used signaling in ckt This signaling is message based signaling.It is widely used signaling in ckt

switched n/w.switched n/w. Signling is separated from speech.It can now travel on separate n/w.Signling is separated from speech.It can now travel on separate n/w. CAS CAS CCSCCS

SignalingSignaling

SignalingSignaling

SignalingSignaling

Speech

Why a common channel signaling standard?Why a common channel signaling standard? Obtimized for operation in digital telecommunication network in conjunction Obtimized for operation in digital telecommunication network in conjunction

with stored program controlled exchanges.with stored program controlled exchanges.

It can meet present and future requirements of information transfer for inter-It can meet present and future requirements of information transfer for inter-processor transactions within telecom network for call control, remote control & processor transactions within telecom network for call control, remote control & management and maintenance signaling.management and maintenance signaling.

It provides a reliable means for transfer of information in correct sequence and It provides a reliable means for transfer of information in correct sequence and without loss or duplication.without loss or duplication.

The signaling system meets requirements of call control signaling for telephone, The signaling system meets requirements of call control signaling for telephone, ISDN & ckt switched data transmission services that can also be used as a ISDN & ckt switched data transmission services that can also be used as a reliable transport system for other types of information transfer between reliable transport system for other types of information transfer between exchanges & specialized centers in telecom network (e.g. for management & exchanges & specialized centers in telecom network (e.g. for management & maintenance purpose).maintenance purpose).

CCS#7 NETWORK : BASIC ELEMENTSCCS#7 NETWORK : BASIC ELEMENTS

Signaling Point Code (SPC)Signaling Point Code (SPC) It is the identity of an exchange.It is the identity of an exchange. It is addresed by a 14 bits code (OPC,DPC).It is addresed by a 14 bits code (OPC,DPC). A signaling point handles the signaling information.A signaling point handles the signaling information. One exchange may have more than one point code.One exchange may have more than one point code. SPC can be 14 bits or 24 bits long.SPC can be 14 bits or 24 bits long. Formats for its representation will depend on signaling network where it is used Formats for its representation will depend on signaling network where it is used Signaling End Point (SEP)Signaling End Point (SEP) It’s a source or a sink of signaling traffic.It’s a source or a sink of signaling traffic.

CCS#7 NETWORK : BASIC ELEMENTSCCS#7 NETWORK : BASIC ELEMENTS

STP

SP SP

LS

SL LS

SP-Signaling point signalingSTP- Signaling transfer point speechOWNSP-Own signaling point

Signaling points are connected with signaling data links.

Architecture OF CCS#7Architecture OF CCS#7

TUPTCAP

SCCP

TSUP

MTP LEVEL 3

MTP LEVEL 2

MTP LEVEL 1

Architecture OF CCS#7Architecture OF CCS#7 The message transfer part consists of three levels.The message transfer part consists of three levels. The lowest level MTP 1 is equivalent to the OSI Physical The lowest level MTP 1 is equivalent to the OSI Physical

layer. It defines the physical, electrical and functional layer. It defines the physical, electrical and functional characteristics of the digital signaling.characteristics of the digital signaling.

The middle level MTP level 2 is equivalent to the OSI Data The middle level MTP level 2 is equivalent to the OSI Data link layer. It assures accurate end-to-end transmission of a link layer. It assures accurate end-to-end transmission of a message across a signaling link. It implements flow control message across a signaling link. It implements flow control message sequence validation and error checking. When an message sequence validation and error checking. When an error occurs on a signaling link, the message (or set of error occurs on a signaling link, the message (or set of messages) is retransmitted. messages) is retransmitted.

Architecture OF CCS#7Architecture OF CCS#7 MTP level 3 is equivalent to MTP level 3 is equivalent to OSIOSI Network layer. It Network layer. It

provides message routing between signaling points provides message routing between signaling points in the in the SS7SS7 network.MTP level 3 re-routes traffic network.MTP level 3 re-routes traffic away from failed links and signaling points and away from failed links and signaling points and controls traffic when congestion occurs. controls traffic when congestion occurs.

SCCPSCCP provides connectionless and connection provides connectionless and connection oriented network services and global title translation oriented network services and global title translation (GTT) capabilities above MTP level 3. (GTT) capabilities above MTP level 3.

POIPOI(Point of Interconnection)(Point of Interconnection)

Point of Interconnection (POI) is a sort of Point of Interconnection (POI) is a sort of interconnection established between two service interconnection established between two service providers when communication to be made between providers when communication to be made between their subscribers. There are various types of POI, their subscribers. There are various types of POI, such as NLD POI, ILD POI, SDC POI, etc. These such as NLD POI, ILD POI, SDC POI, etc. These help to route an inter-network call at different help to route an inter-network call at different locations following different procedures and locations following different procedures and different taxes such as: L1 tax, L2 tax, etc. different taxes such as: L1 tax, L2 tax, etc.

NLD/ILDNLD/ILD ((National Long Distance / International Long National Long Distance / International Long Distance)Distance)

When a subscriber makes a call, the signal is received by BTS and is When a subscriber makes a call, the signal is received by BTS and is transmitted to MSC by transport equipments. MSC, after receiving the transmitted to MSC by transport equipments. MSC, after receiving the signal, verifies the validity of the subscriber and then sends the signal signal, verifies the validity of the subscriber and then sends the signal to to ILTILT (Integrated Local Trunk) switch. The call now is routed (Integrated Local Trunk) switch. The call now is routed according to its destination code; such as 0 for national call, 00 for according to its destination code; such as 0 for national call, 00 for international call, 2 for calls going to BSNL subscribers, 3 for calls international call, 2 for calls going to BSNL subscribers, 3 for calls going to Reliance subscribers, etc. The ILT switch then sends the going to Reliance subscribers, etc. The ILT switch then sends the signal to its destination based on the destination code through proper signal to its destination based on the destination code through proper routing. The routing. The STDSTD calls are routed through the calls are routed through the NLDNLD route. The route. The ISDISD calls are routed through calls are routed through ILDILD route. route.

TRANSPORT and I&CTRANSPORT and I&C Transport provides the communication paths that carry user and Transport provides the communication paths that carry user and

network control information between nodes in a network. In general, network control information between nodes in a network. In general, transmission facilities consist of a medium (e.g., free space, the transmission facilities consist of a medium (e.g., free space, the atmosphere, copper or fiber optic cable) and electronic equipment atmosphere, copper or fiber optic cable) and electronic equipment located at points along the medium. This equipment amplifies (analog located at points along the medium. This equipment amplifies (analog systems) or regenerates (digital systems) signals, provides termination systems) or regenerates (digital systems) signals, provides termination functions at points where transmission facilities connect to switching functions at points where transmission facilities connect to switching systems, and may provide the means to combine many separate sets of systems, and may provide the means to combine many separate sets of call information into a single "multiplexed" signal to enhance the call information into a single "multiplexed" signal to enhance the transmission efficiency .The Transport network consists of the SDH. transmission efficiency .The Transport network consists of the SDH. The SDH has various advantages in the respect that it can be used to The SDH has various advantages in the respect that it can be used to provide higher bandwidth that is so much in demand nowadays for provide higher bandwidth that is so much in demand nowadays for providing services such as internet, video on demand, etc.providing services such as internet, video on demand, etc.

Synchronous Digital Hierarchy (SDH)Synchronous Digital Hierarchy (SDH) Synchronous digital hierarchy (SDH) refers to a group of fiber-optic Synchronous digital hierarchy (SDH) refers to a group of fiber-optic

transmission rates that can transport digital signals with different capacities.transmission rates that can transport digital signals with different capacities.

SDH Overview-SDH Overview- As semiconductor circuits appears and demand for telephone capacity As semiconductor circuits appears and demand for telephone capacity

increased, PCM (transmission method, in 1960) developed.increased, PCM (transmission method, in 1960) developed. With PCM (multiple use of a single line by digital time domain multiplexing), With PCM (multiple use of a single line by digital time domain multiplexing),

the analog telephone signal is first sampled at a bandwidth of 3.1 kHz, quantized the analog telephone signal is first sampled at a bandwidth of 3.1 kHz, quantized and encoded then transmitted at a bit rate of 64 kbps. and encoded then transmitted at a bit rate of 64 kbps.

SDH overview contd…SDH overview contd… When 30 such coded channels are collected together in a frame along When 30 such coded channels are collected together in a frame along

with the necessary signaling information, a transmission rate of 2048 with the necessary signaling information, a transmission rate of 2048 kbps is achieved. This so-called primary rate is used throughout the kbps is achieved. This so-called primary rate is used throughout the world. world.

Only the USA, Canada and Japan use a primary rate of 1544 kbit/s, Only the USA, Canada and Japan use a primary rate of 1544 kbit/s, formed by combining 24 channels instead of 30.formed by combining 24 channels instead of 30.

The growing demand for more bandwidth meant that more stages of The growing demand for more bandwidth meant that more stages of multiplexing were needed throughout the world. A practically multiplexing were needed throughout the world. A practically synchronous (or, to give it its proper name: plesiochronous) digital synchronous (or, to give it its proper name: plesiochronous) digital hierarchy is the resulthierarchy is the result

Towards the end of the 1980s, the so-called synchronous digital Towards the end of the 1980s, the so-called synchronous digital hierarchy (SDH) was introducedhierarchy (SDH) was introduced

SDH overview contd…SDH overview contd… This paved the way for a unified network structure This paved the way for a unified network structure

on a worldwide scale, resulting in a means of on a worldwide scale, resulting in a means of efficient and economical network management for efficient and economical network management for network providers. network providers.

The networks can easily be adapted to meet the ever-The networks can easily be adapted to meet the ever-growing demand for bandwidth-hungry applications growing demand for bandwidth-hungry applications and services.and services.

SDH overview contd…SDH overview contd…Japanese Standard North American Standard European Standard

OSP (OSP (Out-Side PlantOut-Side Plant))The OSP department in any telecom service provider looks after the The OSP department in any telecom service provider looks after the

various utility items such as:various utility items such as: the batteriesthe batteries the DG set at the Switchthe DG set at the Switch the BTSthe BTS the Repeater stationsthe Repeater stations Ability to various data rate transmissionAbility to various data rate transmission This is done to ensure that the equipments are never allowed to shut This is done to ensure that the equipments are never allowed to shut

down, as this may cause serious disruption of service. There are two down, as this may cause serious disruption of service. There are two things that are necessary for the proper working of any telecom things that are necessary for the proper working of any telecom network OSP and ISP (Inside Plant).network OSP and ISP (Inside Plant).

FIXED ACCESSFIXED ACCESS Fixed Access constitutes of the wireless (LMDS)/wireline Fixed Access constitutes of the wireless (LMDS)/wireline

(DLC) services provide for voice and data transfer. Reliance (DLC) services provide for voice and data transfer. Reliance has deployed a nationwide Fibre Optic backbone, as its main has deployed a nationwide Fibre Optic backbone, as its main mode of transport of the network traffic.mode of transport of the network traffic.

LMDS is a broadband wireless point-to-multipoint LMDS is a broadband wireless point-to-multipoint communication system operating above 20 GHz (depending communication system operating above 20 GHz (depending on country of licensing) that can be used to provide digital on country of licensing) that can be used to provide digital two-way voice, data, Internet, and video services two-way voice, data, Internet, and video services

TRANSMISSION MEDIASTRANSMISSION MEDIAS MICROWAVESMICROWAVES:-:- It is used when there is a lack of digging It is used when there is a lack of digging

area, for that we need to have the microwave’s for area, for that we need to have the microwave’s for transmitting and receiving for maturing the call or is used transmitting and receiving for maturing the call or is used when quick transmission is required.when quick transmission is required.

COAXIAL CABLESCOAXIAL CABLES:-:- It is generally used as transmission It is generally used as transmission media. It is underground & most of the places there is a use media. It is underground & most of the places there is a use of coaxial cable. This is less expensive.of coaxial cable. This is less expensive.

OPTICAL FIBERSOPTICAL FIBERS:- :- It is also known as OFT. There are It is also known as OFT. There are very less losses using optical fibers. Data is converted into very less losses using optical fibers. Data is converted into light rays. Transmission is done through glasses. This is light rays. Transmission is done through glasses. This is much expensive with concern to other transmission medias.much expensive with concern to other transmission medias.

ADVANTAGESADVANTAGES1. 1. It has high capacity.It has high capacity.2. It has the capability of using signals that arrive in the receivers with different 2. It has the capability of using signals that arrive in the receivers with different

time delays.time delays.3. It is interference limited multiple access system.3. It is interference limited multiple access system.4. It uses unique spreading codes due to which it has low noise level.4. It uses unique spreading codes due to which it has low noise level.5. High capacity increases as well as extended battery life for handsets.5. High capacity increases as well as extended battery life for handsets.6. Increased cellular communications security.6. Increased cellular communications security.7. Simultaneous conversations.7. Simultaneous conversations.8. Increased efficiency, meaning that the carrier can serve more subscriber.8. Increased efficiency, meaning that the carrier can serve more subscriber.9. Smaller phones.9. Smaller phones.10. Low power requirements and little cell-to-cell coordination10. Low power requirements and little cell-to-cell coordination needed by needed by

operators.operators.

DISADVANTAGES DISADVANTAGES 1. It causes ‘near-far’ problem i.e. a transmitter ”near” the receiver 1. It causes ‘near-far’ problem i.e. a transmitter ”near” the receiver

sending a different code than the receiver’s desired code produces sending a different code than the receiver’s desired code produces in the receiver a signal comparable wit that of a ”far” transmitter in the receiver a signal comparable wit that of a ”far” transmitter sending the desired code.sending the desired code.

2. Synchronization of the receiver and the transmitter is complex.2. Synchronization of the receiver and the transmitter is complex.3. Due to its proprietary nature,all of CDMA’s flaws are not known 3. Due to its proprietary nature,all of CDMA’s flaws are not known

to the engg. Community.to the engg. Community.4. CDMA is relatively new,and the network is not as mature as GSM.4. CDMA is relatively new,and the network is not as mature as GSM.5. CDMA cannot offer international roaming,a large GSM 5. CDMA cannot offer international roaming,a large GSM

advantage. advantage.

REFFRENCESREFFRENCES CDMA Overview Supplied by RIL.CDMA Overview Supplied by RIL. Fast Track Magazine 2006.Fast Track Magazine 2006. Study Materials Supplied by MCN Patna.Study Materials Supplied by MCN Patna.

THE ENDTHE END