01-09-2014, 11:17 AM
It is a telecom company tata teleservices limited in Delhi which is a cdma company. Basically it has 5 msc in Delhi. Its deals with huawei and Ericson company in my whole training i deal with wireless and wire line complaints . I was dealing with wired complaints which includes SIP and PRI.PRI are del ISDN user and sip is internet calling its mostly preferred in cooperate companies and its has child series and also know about the location of a person its calling and called numbers.
Chapter 1 Introduction TO TATA GROUP 1.1 Introduction
The Tata Group comprises 114 operating companies in seven business sectors: information systems and communications; engineering; materials; services; energy; consumer products; and chemicals. The Group was founded by Jamsetji Tata in the mid 19th century, a period when India had just set out on the road to gaining independence from British rule. Consequently, Jamsetji Tata and those who followed him aligned business opportunities with the objective of nation building. The Tata family of companies shares a set of five core values: integrity, understanding, excellence, unity and responsibility. These values, which have been part of the Group's beliefs and convictions from its earliest days, continue to guide and drive the business decisions of Tata companies.
The Group and its enterprises have been steadfast and distinctive in their adherence to business ethics and their commitment to corporate social responsibility. This is a legacy that has earned the Group the trust of many millions of stakeholders in a measure few business houses anywhere in the world can match. The 2009 annual survey by the Reputation Institute ranked Tata Group as the 11th most reputable company in the world. The survey included 600 global companies.
1.2 Tata group of companies
The Tata Group operates business in seven key industry sectors. The chart below illustrates how, in percentage terms, Tata companies in each of these sectors contribute to the overall makeup of the group. The table that follows shows the group's sector-wise financial performance.
The seven business sectors are:
· Materials
· Engineering
· Energy
· Chemicals
· Consumer products
· communications & Information systems
· Services
Fig 1.1 Group sector-wise financial performance
TTSL has been a pioneer in many avenues, some of them are
· First private operator to launch CDMA based wireless connections
· First private operator to launch Limited Mobility services in the country
· First to launch Smart Card based Pay Telephones
· First to launch Centrex - a virtual exchange for the corporate customer
1.3 Organizational structure of TTSL
There are 8 departments in TATA TELE SERVICES LIMITED.
· Marketing Department.
· Operation support Department.
· Finance Department.
· IT Department.
· Human resource and administration Department.
· Technical Department.
· Sales Department.
· Networks Department.
· Customer care department
1.4 Technical department hierarchy
Fig 1.2 Technical department hierarchy
Technical department deals with why the customers is facing problem in wireless and wire line connections. It also provide the location for security purposes
Wireless complaints is of two types
· CRM-Customer relationship management
In CRM we have post paid customer’s complaints like- customer not able to make or receive calls, SMS, voice issue, etc.
· TIPPS- Tata indicom prepaid service
In TIPPS we have prepaid customer’s complaints like- customer not able to make or receive calls, sms, voice issue, etc
The various products and services are provided in TTSL are:
· Voice
1. TATA Indicom CDMA Mobile
2. TATA Indicom Phone Connection
3. ISDN Lines
4. Centrex
5. E1 Links
6. Basic/Primary Interface
7. Managed Leased Lines
8. Direct Inward Dialing
9. Public Phone Booth
· Data
1. Shared and Dedicated Internet Bandwidth
2. Virtual Private Networks(VPN)
3. Tata Indicom International IP VPN Services
4. Tata Indicom Hosting Services
5. Industry Specific Solutions
6. ADSL & DSL
· Internet
1. Tata Indicom Post-Paid Internet connection
2. Tata Indicom Broadband Internet Services
1.5 TATA Indicom Conference Services
1. Conference Call Service
2. Videoconference Service
3. Web Conference Service
Apart from the products that TTL provides, it also has the facility for the following value added services.
1.6 Call Waiting
Allows a customer to attend two calls at the same time without disconnectingthe existing call.
1.7 Call Forward
There are three types of Call forward:
· Call Forward Immediate
· Call Forward Busy
· Call Forward No Reply
1.7.1 Call Forward Immediate
This facility allows the customer to forward any calls coming to his/her telephone immediately to any other telephone number of his/her choice.
1.7.2 Call Forward Busy
This facility allows the customer to pass on incoming calls to another number when his/her number is busy.
1.7.3 Call Forward-No Reply
This facility allows the customer to pass on his/her unanswered calls to another telephone number after a pre-set number of rings.
1.8 3-Ways Conferencing
This feature enables the customer to involve three people (including him/her) in one telephonic conversation. On an existing call, the customer can call up another party and initiate a 3-party conversation.
1.9 Abbreviated Dialing
Using this facility the customer can assign short codes to some of the numbers that he/she frequently calls and access those numbers through the short codes.
1.10 Call Hunting
Using this facility the customer can have a pilot number and allot a group of Tata Teleservices lines to this telephone number. Incoming calls to the pilot will hunt for any free line and land on that number. With this facility, the customer can ensure that he/she does not miss any incoming calls unless all his/her lines are busy.
1.11 Hotline
The customer has a choice of two types of Hotline:
1. Timed
2. Immediate
· Timed: The customer is given 5 seconds in which he/she can dial any other telephone number. If the customer does not do so, he/she will be connected to the "Hotline" number.
· Immediate: The customer is connected to the pre-specified subscriber immediately on lifting the handset. The customer does not have the option of dialing any other telephone number.
1.12 Malicious Call Tracing
This facility allows tracing malicious calls / threatening calls made to the customer. This service is free of cost.
1.13 Post-Installation Change of DEL Number
A customer post installation can request for a change in DEL number.
1.14 Safe Custody
Safe custody means protecting the usage of a phone for a customer. During the period of Safe custody all outgoing calls from and incoming calls for a number shall be disabled. This can be done to prevent the misuse of a phone by a third party when the customer is away for a period of time.
1.15 Directory Unlisting
A customer can opt for Directory Unlisting if he/she does not want his/her name and number to be listed in the telephone directory.
· Polarity Reversal
When the customer for reasons of his business wants to be able to generate bills at his end to bill people who are using his phone he/she needs to apply for Polarity Reversal.
· Reset of Password
When the customer forgets the password for "Call Control and Barring" he needs to apply for resetting of the same to the default password.
· Service Level Changes
A customer can request changes in the calling level that is allowed on his number. For example, he can request activation and deactivation of STD/ISD on his phone.
· Auto Call Back Busy
Typically when a customer calls a number and finds it busy, he/she tends to redial the required number several times to check if it has become free. With this facility, the customers are automatically connected to the party they want to speak to once it becomes free, saving them the trouble of having to try repeatedly. This feature can be used only within a group.
Chapter 2 Overview of CDMA Mobile 2.1 Introduction
In CDMA there is no division of the frequency band. The same frequency band is used repeatedly, and hence it is also called Spread spectrum. CDMA was commercially introduced in 1995. In 2003, CDMA became one of the fastest evolving technologies. In 1999, the International Telecommunications Union (ITU) selected CDMA as the industry standard for new "third-generation" 3G; wireless systems. CDMA provides clear, reliable voice communication and good data services. Many leading wireless companies are using or are switching over to CDMA to make use of its high speed services.
2.2 Access Schemes
For radio systems there are two resources, frequency and time. Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access (FDMA). Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access (TDMA). In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.
Fig 2.1: access schemes (FDMA, TDMA & CDMA)
2.3 How CDMA Works
There are five steps in generating a CDMA signal:
· Analog to digital conversion
· Voice compression
· Encoding and interleaving
· Channelizing the signals
· Conversion of the digital signal to a Radio Frequency (RF) signal
2.3.1 Analog to digital conversion:
The first step of CDMA signal generation is analog to digital conversion, sometimes called Analog to digital conversion. CDMA uses a technique called Pulse Code Modulation (PCM) to accomplish analog digital conversion.
2.3.2 Voice Compression
The second step of CDMA signal generation is voice compression. CDMA uses a device called a voice coder to accomplish voice compression. The term "voice coder" is a contraction of the words "voice" and "code." Voice coders are located at the BSC and in the phone.
2.3.2.1 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 voice coder.
2.3.2.2 Variable Rate Voice coder
A CDMA voice coder 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 voice coder 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.
2.3.3 Encoding and interleaving
Encoders and interleaves 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.
2.3.3.1 How encoding works
The type of encoding done at this stage is called "convolution encoding."
A digital message consists of four bits (A, B, C, D) of voice coded 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.
2.3.3.2 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. (When more than one bit got damaged). Encoding and interleaving reduce the effects of burst errors.
2.3.3.3 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.
2.3.4 Channelizing
The encoded voice data is further encoded to separate it from other encoded voice data. The encoded symbols are then spread over the entire bandwidth of the CDMA channel. This process is called channelization.
The receiver knows the code and uses it to recover the voice data.
Fig 2.3 Coding and spreading
2.3.5 Digital to analog conversion
After the CDMA signal is transmitted, the receiver must reverse the signal generation process to recover the voice, as follows:
· Conversion of RF signal to digital signal
· Dispreading the signal
· De interleaving and decoding
· Voice decompression
· Digital to analog conversion
2.4 Problems in a CDMA Channel
2.4.1 Near-Far Problem:
If all mobiles transmitted at the same power level, signals received by the base station from mobiles further away would be weaker than those signals received from mobiles which were closer to the cell. This issue reduces, if not resolved, the capacity of a CDMA system.
2.4.2 Solution
In CDMA systems and similar cellular phone-like networks, the problem is commonly solved by dynamic output power adjustment of the transmitters. That is, the closer transmitters use less power so that the SNR for all transmitters at the receiver is roughly the same. This sometimes can have a noticeable impact on battery life, which can be dramatically different depending on distance from the base station. In high-noise situations, however, closer transmitters may boost their output power, which forces distant transmitters to boost their output to maintain a good SNR. Other transmitters react to the rising noise floor by increasing their output. This process continues, and eventually distant transmitters lose their ability to maintain a usable SNR and drop from the network. This process is called power control runaway. This principle may be used to explain why an area with low signal is perfectly usable when the cell isn't heavily loaded, but when load is higher, service quality degrades significantly, sometimes to the point of unusability.
2.4.3 Other possible solutions to the near-far problem are:
· Increased receiver dynamic range - Use a higher resolution ADC. Increase the dynamic range of receiver stages that are saturating.
· Dynamic output power control – Nearby transmitters decrease their output power so that all signals arrive at the receiver with similar signal strengths.
· TDMA – Transmitters use some scheme to avoid transmitting at the same time
· FDMA – Decrease the number of users per signal bandwidth to fewer stations are required to share the same bandwidth at the same time
2.4.4 Path Loss
The more distance between the cell and a phone the weaker the signal becomes
2.4.5 Fading
Fading occurs when more than two signals from the same transmitter are received due to multipath.
2.5 Advantages and disadvantages of CDMA
This chapter lists many advantages and some disadvantages of CDMA. Many of these advantages and disadvantages can be also found from other multiple access schemes, like in frequency hopping TDMA.
2.5.1 Advantages
· Wide bandwidth: fading is less deep than in the narrowband systems.
· Multipath diversity: RAKE improves the performance, because individual Multipath can be combined. However the RAKE has to be able to estimate delays of these paths, which may be difficult. Also the implementation may limit the number of paths.
· Narrow band interference rejection
· Interference averaging: The interference caused by other users is averaged by processing gain
· Interference limited capacity: Discontinuous transmission is an advantage.
· Re-use one: Frequency management easy. No frequency planning needed when a new cell is added.
· Soft handover: Improves the capacity and gives more range in cellular network.
· Soft capacity: Because other users are seen as noise like interference, an one extra user causes only slight degradation in the performance of other users.
· Low peak power: Less electromagnetic interference. Also if the peak power is limited, then more range.
· Capacity: The capacity of CDMA has been very controversial issue. The problem has maybe to which systems CDMA is compared. For example comparing CDMA with AMPS, tenfold capacity increment can be found [4]. However this is not fair, because AMPS is first generation system and CDMA is not. When comparing GSM1900 and IS-95, the results has been totally opposite, depending on who is presenting them. Third generation wideband CDMA and enhanced GSM is compared in [8] and the result is that there is no great differences in capacities. So, as a result it can be said that the capacity of CDMA is good.
· Flexibility: Wide range of bitrates (8 kbit/s to 2 Mbit/s) with one 5 MHz carrier.
· Politically popular: CDMA is a candidate for global 3rd generation cellular system.
2.5.2 Disadvantages
· Wide bandwidth: High bitrates are difficult to achieve, because CDMA requires a lot of bandwidth. Due to intra-cell interference a single cell capacity is lower than in other cellular systems.
· Near-far-problem: CDMA requires good power control, otherwise near-far problem will decrease capacity.
· Soft handover: More interference and more complex network structure.
· Fast power control: May cause problems like power competition.
· TDD mode is difficult to support with CDMA.
Chapter 3 SWITCHING SECTION
The telecommunication network can transmit variety of information, in two basic forms, analog and digital. This information may be transmitted over a circuit/channel or over a carrier system.
If you could only use your telephone to talk to just one other person! You would not be very productive. So there are requirements for switching systems to route your calls around the world.
3.1 Operation and maintenance center and machine communication
In the E1 OB exchange the management functions are integrated with the system functioning itself and are carried out under the control of a computer.
The interaction between maintenance personnel and the electronics switching system is through computer terminals such as teletypewriter and VDU etc. using man machine command. It is also possible to get data through billing traffic measurement etc.
The key responsibilities of an OMC are administration, maintenance, data integrity, software download, network updating, and database download operations of the base station systems, switching centers. The OMC connects to all the equipment present in the switching center and to the BSC.
3.2 functions of OMC
· Subscriber management
· Routing and analysis management
· Call charging management
· Semi permanent connection management
· Unit positioning
· Call tracing
· Fault clearing
· Fault and alarm message processing
3.3 Common Channel Signaling 7 (CCS7)
The digital signaling system used by the telephone companies to route telephone calls and to provide other services
Common Channel Signaling 7 (CCS7 or C7), also known as Signaling System #7 (SS7), is a telecommunications protocol suite defined by the ITU-T which is used by the telephone companies for interoffice signaling SS7 uses out of band or common-channel signaling (CCS) techniques. SS7/C7 uses a separated packet-switched network for the signaling purpose. SS7 is known as C7 outside North America.
Modern form of signaling (SS7 is based on this method) Signaling occurs out-of-band on dedicated channels Uses a separate packet-switched signaling network which is not related to circuit switched connection send-to-end signaling between originating and terminating local exchanges (or to/from databases) is possible anytime Exchange signaling possible anywhere anytime
3.4 Signaling
Signaling provides the ability to transfer information inside networks, between different networks, and more importantly between the customers that use the network services for which they are charge. A signaling protocol defines a standard set of information elements and a method of transport in order to enable components of a network to interoperate. There are two types of signaling, Channel Associated Signaling (CAS), where the signaling information is carried down the same physical channel as the voice or data.
Common Channel Signaling (CCS) concentrates the signaling information in a single dedicated channel, such that all of the signaling information for many voice channels in a telephone system can be conveyed over a single channel dedicated to signaling.
Signaling System Number 7 is an example of a common channel signaling system, defined for use in public switched networks where large numbers of circuits are switched between subscribers. SS7 is a global standard used throughout the world within networks and on international interconnects; it is the signaling technology inside the network that delivers (Integrated Services Digital Network) ISDN, mobile/wireless and Intelligent Networking.
The subscribers or service users access the network using an Access protocol, such as multi-frequency dialling or ISDN. These types of protocol are targeted at providing services to the subscribers, allowing interaction of the subscriber with the network. Inside the network however, a reliable and robust method of signalling is required, this is provided by SS7.
3.5 The SS7 protocol
SS7 is defined as a number of independent blocks of functionality, each implementing a specific function and having a defined interface.