3SEM MC U3 BLUE.....

Bluetooth(P10U4)

Bluetooth wireless technology is a short range communications technology intended to replace the cables connecting portable unit and maintaining high levels of security. Bluetooth technology is based on Ad-hoc technology also known as Ad-hoc Pico nets, which is a local area network with a very limited coverage.

History of Bluetooth

WLAN technology enables device connectivity to infrastructure based services through a wireless carrier provider. The need for personal devices to communicate wirelessly with one another without an established infrastructure has led to the emergence of Personal Area Networks (PANs).

• Ericsson's Bluetooth project in 1994 defines the standard for PANs to enable communication between mobile phones using low power and low cost radio interfaces.
• In May 1988, Companies such as IBM, Intel, Nokia and Toshiba joined Ericsson to form the Bluetooth Special Interest Group (SIG) whose aim was to develop a defacto standard for PANs.
• IEEE has approved a Bluetooth based standard named IEEE 802.15.1 for Wireless Personal Area Networks (WPANs). IEEE standard covers MAC and Physical layer applications.

Bluetooth specification details the entire protocol stack. Bluetooth employs Radio Frequency (RF) for communication. It makes use of frequency modulation to generate radio waves in the ISM band.

The usage of Bluetooth has widely increased for its special features.

• Bluetooth offers a uniform structure for a wide range of devices to connect and communicate with each other.
• Bluetooth technology has achieved global acceptance such that any Bluetooth enabled device, almost everywhere in the world, can be connected with Bluetooth enabled devices.
• Low power consumption of Bluetooth technology and an offered range of up to ten meters has paved the way for several usage models.
• Bluetooth offers interactive conference by establishing an adhoc network of laptops.
• Bluetooth usage model includes cordless computer, intercom, cordless phone and mobile phones.

Piconets and Scatternets:

Bluetooth enabled electronic devices connect and communicate wirelessly through shortrange devices known as Piconets. Bluetooth devices exist in small ad-hoc configurations with the ability to act either as master or slave the specification allows a mechanism for master and slave to switch their roles. Point to point configuration with one master and one slave is the simplest configuration.

When more than two Bluetooth devices communicate with one another, this is called a PICONET. A Piconet can contain up to seven slaves clustered around a single master. The device that initializes establishment of the Piconet becomes the master.

The master is responsible for transmission control by dividing the network into a series of time slots amongst the network members, as a part of time division multiplexing scheme which is shown below.

The features of Piconets are as follows −

• Within a Piconet, the timing of various devices and the frequency hopping sequence of individual devices is determined by the clock and unique 48-bit address of master.
• Each device can communicate simultaneously with up to seven other devices within a single Piconet.
• Each device can communicate with several piconets simultaneously.
• Piconets are established dynamically and automatically as Bluetooth enabled devices enter and leave piconets.
• There is no direct connection between the slaves and all the connections are essentially master-to-slave or slave-to-master.
• Slaves are allowed to transmit once these have been polled by the master.
• Transmission starts in the slave-to-master time slot immediately following a polling packet from the master.
• A device can be a member of two or more piconets, jumping from one piconet to another by adjusting the transmission regime-timing and frequency hopping sequence dictated by the master device of the second piconet.
• It can be a slave in one piconet and master in another. It however cannot be a master in more than once piconet.
• Devices resident in adjacent piconets provide a bridge to support inner-piconet connections, allowing assemblies of linked piconets to form a physically extensible communication infrastructure known as Scatternet.

Spectrum:

Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHZ, using a spread spectrum hopping, full-duplex signal at a nominal rate of 1600 hops/sec. the 2.4 GHZ ISM band is available and unlicensed in most countries.

Range

Bluetooth operating range depends on the device Class 3 radios have a range of up to 1 meter or 3 feet Class 2 radios are most commonly found in mobile devices have a range of 10 meters or 30 feet Class 1 radios are used primarily in industrial use cases have a range of 100 meters or 300 feet.

Data rate

Bluetooth supports 1Mbps data rate for version 1.2 and 3Mbps data rate for Version 2.0 combined with Error Data Rate.

3RD SEM MC U3 GPRS

GPRS Network Architecture(P9U3)

The following new GPRS network adds the following elements to an existing GSM network.

• Packet Control Unit (PCU).
• Serving GPRS Support Node (SGSN): the MSC of the GPRS network.
• Gateway GPRS Support Node (GGSN): gateway to external networks.
• Border Gateway (BG): a gateway to other PLMN.
• Intra-PLMN backbone: an IP based network inter-connecting all the GPRS elements.

General Packet Radio Service (GPRS):

• GPRS introduces packet data transmission to the mobile subscriber.
• GPRS is designed to work within the existing GSM infrastructure with additional packet switching nodes.
• This packet mode technique uses multi-slot technology together with support for all coding schemes (CS-1 to CS-4) to increase the data rates up to 160 kbit/s.
• The GPRS system uses the physical radio channels as defined for GSM. A physical channel used by GPRS is called a Packet Data Channel (PDCH).
• The PDCHs can either be allocated for GPRS (dedicated PDCH) or used by GPRS only if no circuit-switched connection requires them (on-demand). The operator can define 0-8 dedicated PDCHs per cell. The operator can specify where he wants his PDCHs to be located.
• The first dedicated PDCH in the cell is always a Master PDCH (MPDCH). The on-demand PDCHs can be pre-empted by incoming circuit switched calls in congestion situations in the cell.

Coding Scheme	Speed(kbit/s)
CS-1	8.0
CS-2	12.0
CS-3	14.4
CS-4	20.0

Serving GPRS Support Node (SGSN) Functions:

The SGSN or Serving GPRS Support Node element of the GPRS network provides a number of takes focused on the IP elements of the overall system. It provides a variety of services to the mobiles:

• Packet routing and transfer
• Mobility management
• Authentication
• Attach/detach
• Logical link management
• Charging data

There is a location register within the SGSN and this stores the location information (e.g., current cell, current VLR). It also stores the user profiles (e.g., IMSI, packet addresses used) for all the GPRS users registered with the particular SGSN.

Gateway GPRS Support Node (GGSN) Functions

• The GGSN, Gateway GPRS Support Node is one of the most important entities within the GSM EDGE network architecture.
• The GGSN organizes the inter-working between the GPRS/EDGE network and external packet switched networks to which the mobiles may be connected. These may include both Internet and X.25 networks.
• The GGSN can be considered to be a combination of a gateway, router and firewall as it hides the internal network to the outside. In operation, when the GGSN receives data addressed to a specific user, it checks if the user is active, then forwards the data. In the opposite direction, packet data from the mobile is routed to the right destination network by the GGSN.

Upgradation of Equipment from GSM to GPRS:

• Mobile Station (MS): New Mobile Station is required to access GPRS services. These new terminals will be backward compatible with GSM for voice calls. Three types of handsets are available. Type-A: GPRS & Speech (simultaneously), Type-B: GPRS & Speech (Auto switch), Type-C: GPRS or Speech (manual switch).
• BTS: A software upgrade is required in the existing base transceiver site.
• BSC: Requires a software upgrade and the installation of new hardware called the packet control unit (PCU). PCU is responsible for handling the Medium Access Control (MAC) and Radio Link Control (RLC) layers of the radio interface and the BSSGP and Network Service layers of the Gb interface. There is one PCU per BSC. The Gb interface, carry GPRS/EGPRS traffic from the SGSN (Serving GPRS Support Node) to the PCU.
• GPRS Support Nodes (GSNs): The deployment of GPRS requires the installation of new core network elements called the serving GPRS support node (SGSN) and gateway GPRS support node (GGSN).
• Databases (HLR, VLR, etc.): All the databases involved in the network will require software upgrades to handle the new call models and functions introduced by GPRS.

Location Information - GSM Service Area Hierarchy

• Cell: Cell is the basic service area and one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell.
• LA: A group of cells form a Location Area. This is the area that is paged when a subscriber gets an incoming call. Each Location Area is assigned a Location Area Identity (LAI). Each Location Area is served by one or more BSCs.
• MSC/VLR Service Area: The area covered by one MSC is called the MSC/VLR service area.
• PLMN: The area covered by one network operator is called PLMN. A PLMN can contain one or more MSCs.
• GSM Service Area: The area in which a subscriber can access the network.

3RD SEM U3 GSM SERV...

Type of GSM services(P8U3)

GSM offers much more than just voice telephony. Contact your local GSM network operator to the specific services that you can avail.

GSM offers three basic types of services:

• Telephony services or teleservices
• Data services or bearer services
• Supplementary services

Teleservices:

The abilities of a Bearer Service are used by a Teleservice to transport data. These services are further transited in the following ways:

Voice Calls-

The most basic Teleservice supported by GSM is telephony. This includes full-rate speech at 13 kbps and emergency calls, where the nearest emergency-service provider is notified by dialing three digits.

Videotext and Facsmile-

Another group of teleservices includes Videotext access, Teletex transmission, Facsimile alternate speech and facsimile Group 3, Automatic facsimile Group, 3 etc.

Short Text Messages-

Short Messaging Service (SMS) service is a text messaging service that allows sending and receiving text messages on your GSM mobile phone. In addition to simple text messages, other text data including news, sports, financial, language, and location-based data can also be transmitted.

Bearer Services-

Data services or Bearer Services are used through a GSM phone. to receive and send data is the essential building block leading to widespread mobile Internet access and mobile data transfer. GSM currently has a data transfer rate of 9.6k. New developments that will push up data transfer rates for GSM users are HSCSD (high speed circuit switched data) and GPRS (general packet radio service) are now available.

Supplementary Services-

Supplementary services are additional services that are provided in addition to teleservices and bearer services. These services include caller identification, call forwarding, call waiting, multi-party conversations, and barring of outgoing (international) calls, among others. A brief description of supplementary services is given here:

• Conferencing : It allows a mobile subscriber to establish a multiparty conversation, i.e., a simultaneous conversation between three or more subscribers to setup a conference call. This service is only applicable to normal telephony.
• Call Waiting : This service notifies a mobile subscriber of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call.
• Call Hold : This service allows a subscriber to put an incoming call on hold and resume after a while. The call hold service is applicable to normal telephony.
• Call Forwarding : Call Forwarding is used to divert calls from the original recipient to another number. It is normally set up by the subscriber himself. It can be used by the subscriber to divert calls from the Mobile Station when the subscriber is not available, and so to ensure that calls are not lost.
• Call Barring : Call Barring is useful to restrict certain types of outgoing calls such as ISD or stop incoming calls from undesired numbers. Call barring is a flexible service that enables the subscriber to conditionally bar calls.
• Number Identification : There are following supplementary services related to number identification:
• Calling Line Identification Presentation : This service displays the telephone number of the calling party on your screen.
• Calling Line Identification Restriction : A person not wishing their number to be presented to others subscribes to this service.
• Connected Line Identification Presentation : This service is provided to give the calling party the telephone number of the person to whom they are connected. This service is useful in situations such as forwarding's where the number connected is not the number dialled.
• Connected Line Identification Restriction : There are times when the person called does not wish to have their number presented and so they would subscribe to this person. Normally, this overrides the presentation service.
• Malicious Call Identification : The malicious call identification service was provided to combat the spread of obscene or annoying calls. The victim should subscribe to this service, and then they could cause known malicious calls to be identified in the GSM network, using a simple command.
• Advice of Charge (AoC) : This service was designed to give the subscriber an indication of the cost of the services as they are used. Furthermore, those service providers who wish to offer rental services to subscribers without their own SIM can also utilize this service in a slightly different form. AoC for data calls is provided on the basis of time measurements.
• Closed User Groups (CUGs) : This service is meant for groups of subscribers who wish to call only each other and no one else.
• Unstructured supplementary services data (USSD) : This allows operator-defined individual services.

GSM Operation

Once a Mobile Station initiates a call, a series of events takes place. Analyzing these events can give an insight into the operation of the GSM system.

Mobile Phone to Public Switched Telephone Network (PSTN):

When a mobile subscriber makes a call to a PSTN telephone subscriber, the following sequence of events takes place:

• The MSC/VLR receives the message of a call request.
• The MSC/VLR checks if the mobile station is authorized to access the network. If so, the mobile station is activated. If the mobile station is not authorized, then the service will be denied.
• MSC/VLR analyzes the number and initiates a call setup with the PSTN.
• MSC/VLR asks the corresponding BSC to allocate a traffic channel (a radio channel and a time slot).
• The BSC allocates the traffic channel and passes the information to the mobile station.
• The called party answers the call and the conversation takes place.
• The mobile station keeps on taking measurements of the radio channels in the present cell and the neighboring cells and passes the information to the BSC. The BSC decides if a handover is required. If so, a new traffic channel is allocated to the mobile station and the handover takes place. If handover is not required, the mobile station continues to transmit in the same frequency.

PSTN to Mobile Phone:

When a PSTN subscriber calls a mobile station, the following sequence of events takes place:

• The Gateway MSC receives the call and queries the HLR for the information needed to route the call to the serving MSC/VLR.
• The GMSC routes the call to the MSC/VLR.
• The MSC checks the VLR for the location area of the MS.
• The MSC contacts the MS via the BSC through a broadcast message, that is, through a paging request.
• The MS responds to the page request.
• The BSC allocates a traffic channel and sends a message to the MS to tune to the channel. The MS generates a ringing signal and, after the subscriber answers, the speech connection is established.
• Handover, if required, takes place, as discussed in the earlier case.

To transmit the speech over the radio channel in the stipulated time, the MS codes it at the rate of 13 Kbps. The BSC transcodes the speech to 64 Kbps and sends it over a land link or a radio link to the MSC. The MSC then forwards the speech data to the PSTN. In the reverse direction, the speech is received at 64 Kbps at the BSC and the BSC transcodes it to 13 Kbps for radio transmission.

GSM supports 9.6 Kbps data that can be channelled in one TDMA timeslot. To supply higher data rates, many enhancements were done to the GSM standards (GSM Phase 2 and GSM Phase 2+).

3RD SEM U3 GSM SECU...

GSM Security (P7U3)

Since the air interface is vulnerable to fraudulent access, it is necessary to employ the authentication before extending the services to a subscriber. Authentication is built around the following notions.

• Authentication Key (Ki) resides only in two places, SIM card and Authentication Center.
• Authentication Key (Ki) is never transmitted over air. It is virtually impossible for unauthorized individuals to obtain this key to impersonate a given mobile subscriber.

Authentication Parameters

The MS is authenticated by the VLR with a process that uses three parameters:

• RAND which is completely random number.
• SRES which is an authentication signed response. It is generated by applying an authentication algorithm (A3) to RAND and Ki.
• Kc which is cipher key. The Kc parameter generated by applying the cipher key generation algorithm (A8) to RAND and Ki.

These parameters (named an authentication triplet) are generated by the AUC at the request of the HLR to which the subscriber belongs. The algorithms A3 and A8, are defined by the PLMN operator and are executed by the SIM.

Steps in Authentication Phase:

• The new VLR sends a request to the HLR/AUC (Authentication Center) requesting the "authentication triplets" (RAND, SRES, and Kc) available for the specified IMSI.
• The AUC using the IMSI, extracts the subscribers authentication key (Ki).The AUC then generates a random number (RAND), applies the Ki and RAND to both the authentication algorithm (A3) and the cipher key, generation algorithm (A8) to produce an authentication Signed Response (SRES) and a Cipher Key (Kc). The AUC then returns an authentication triplet: RAND, SRES and Kc to the new VLR.
• The MSC/VLR keeps the two parameters Kc and SRES for later use and then sends a message to the MS. The MS reads its Authentication Key (Ki) from the SIM, applies the received random number (RAND) and Ki to both its authentication algorithm (A3) and Cipher key generation Algorithm (A8) to produce an Authentication Signed Response (SRES) and Cipher key (Kc). The MS saves Kc for later, and will use Kc when it receives command to cipher the channel.
• The MS returns the generated SRES to the MSC/VLR. The VLR compares the SRES returned from the MS with the expected SRES received earlier from the AUC. If equal, the mobile passes authentication. If unequal, all signaling activities will be aborted. In this scenario, we will assume that authentication is passed.

Encryption/Ciphering:

Data is encrypted at the transmitter side in blocks of 114 bits by taking 114-bit plain text data bursts and performing an EXOR (Exclusive OR) logical function operation with a 114-bit cipher block.

The decryption function at the receiver side is performed by taking the encrypted data block of 114 bits and going through the same "exclusive OR" operation using the same 114-bit cipher block that was used at the transmitter.

The cipher block used by both ends of transmission path for a given transmission direction is produced at the BSS and MS by an encryption algorithm called A5. The A5 algorithm uses a 64-bit cipher key (Kc), produced during the authentication process during call setup and the 22-bit TDMA frame number (COUNT) which takes decimal values from 0 through 2715647, and has a repetition time of 3.48 hours (hyper frame interval).The A5 algorithm actually produce two cipher blocks during each TDMA period. One path for the uplink path and the other for the downlink path.

Time Slot Staggering:

Time slot staggering is the principle of deriving the time slot organization of uplink from the time slot organization of the downlink. A particular time slot of the uplink is derived from the downlink by shifting the downlink time slot number by three.

Reason:

By shifting three time slots, the mobile station avoids the ‘transmit and receive’ processes simultaneously. This allows an easier implementation of the mobile station; the receiver in the mobile station does not need to be protected from the transmitter of the same mobile station. Typically a mobile station will receive during one time slot, and then shifts in frequency by 45 MHz for GSM-900 or 95 MHz for GSM-1800 to transmit sometime later. This implies that there is one time base for downlink and one for uplink.

Timing Advance:

Timing Advance is the process of transmitting the burst to the BTS (the timing advance) early, to compensate for the propagation delay.

Why is it Needed ?

It is required because of the time division multiplexing scheme used on the radio path. The BTS receives signals from different mobile stations very close to each other. However when a mobile station is far from the BTS, the BTS must deal with the propagation delay. It is essential that the burst received at the BTS fits correctly into time slot. Otherwise the bursts from the mobile stations using adjacent time slots could overlap, resulting in a poor transmission or even in loss of communication.

Once a connection has been established, the BTS continuously measures the time offset between its own burst schedule and the reception schedule of the mobile station burst. Based on these measurements, the BTS is able to provide the mobile station with the required timing advance via the SACCH. Note that timing advance is derived from the distance measurement which is also used in the handover process. The BTS sends a timing advance parameter according to the perceived timing advance to each mobile station. Each of the mobile station then advances its timing, with the result that signals from the different mobile stations arriving at BTS, and are compensated for propagation delay.

Time Advance Process:

• A 6 bit number indicates how many bits the MS must advance its transmission. This time advance is TA.
• The 68.25 bit long GP (guard period) of the access burst provides the required flexibility to advance the transmission time.
• The time advance TA can have a value between 0 and 63 bits long, which corresponds to a delay of 0 to 233 micro second. For instance the MS at 10 km away from the BTS must start transmitting 66 micro second earlier to compensate for the round trip delay.
• The maximum mobile range of 35Km is rather determined by the timing advance value than by the signal strength.

3RD SEM MC U3_GSM

GSM Architecture (P6U3)

A GSM network comprises of many functional units. These functions and interfaces are explained in this chapter. The GSM network can be broadly divided into:

The GSM network is divided into four major systems:

• Switching System (SS)
• Base Station System (BSS)
• Mobile Station (MS)
• Operation and Maintenance Center(OMC)

The switching system also called as Network and Switching System (NSS), is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units:

• Mobile Switching Center
• Home Location Register
• Visitor Location Register
• Equipment Identity Register
• Authentication Center

Mobile Switching Center

Mobile Switching Center (MSC) performs all the switching functions for all mobile stations, located in the geographic area controlled by its assigned BSSs. Also, it interfaces with PSTN, with other MSCs, and other system entities.

Functions of MSC

• Call handling that copes with the mobile nature of subscribers considering Location Registration, Authentication of subscribers and equipment, Handover and Prepaid service.
• Management of required logical radio link channel during calls.
• Management of MSC-BSS signaling protocol.
• Handling location registration and ensuring interworking between mobile station and VLR.
• Controls inter-BSS and inter-MSC hand overs.
• Acting as a gateway MSC to interrogate HLR. The MSC which is connected to the PSTN/ISDN network is called as GMSC. This is the only MSC in the network connected to the HLR.
• Standard functions of a switch like charging.

Home Location Register (HLR)

Home location register contains:

• The identity of mobile subscriber called International Mobile Sub Identity (IMSI).
• ISDN directory number of mobile station.
• Subscription information on services.
• Service restrictions.
• Location Information for call routing.

One HLR per GSM network is recommended and it may be a distributed database. Permanent data in HLR is changed by the man-machine interface. Temporary data like location information changes dynamically in HLR.

Visitor Location Register (VLR):

The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC would request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR has the information needed for call setup without having to interrogate the HLR each time. VLR contains information like the following:

• Identity of mobile sub,
• Any temporary mobile sub identity,
• ISDN directory number of the mobile,
• A directory number to route the call to the roaming station,
• Part of the data of HLR for the mobiles that are currently located in MSC service area.

Equipment Identity Register:

Equipment Identity Register consists of identity of mobile station equipment called International Mobile Equipment Identity (IMEI), which may be valid, suspect, and prohibited. When a mobile station accesses the system, the equipment validation procedure is evoked before giving the services.

The information is available in the form of three lists.

• White List- The terminal is allowed to connect to the Network.
• Grey List- The terminal is under observation from the network for the possible problems.
• Black List- The terminals reported as stolen are not type approved. They are not allowed to connect to the network. EIR informs the VLR about the list, the particular IMEI is in.

Authentication Centre:

It is associated with an HLR. It stores an Identity key called Authentication key (Ki) for each Mobile subscriber. This key is used to generate the authentication triplets.

• RAND (Random Number),
• SRES (Signed Response) -To authenticate IMSI,
• Kc (Cipher Key) - To cipher communication over the radio path between the MS and the network.

Operation and Maintenance Centre (OMC):

It is the functional entity through which the network operator can monitor and control the system by performing the following functions:

• Software installation
• Traffic management
• Performance data analysis
• Tracing of subscribers and equipment
• Configuration management
• Subscriber administration
• Management of mobile equipment

Base Station System (BSS):

BSS connects the MS and the NSS. It is composed of the following:

• Base Transceiver Station (BTS) also called Base Station.
• Base Station Controller (BSC).

BTS and BSC communicate across the standardized Abis interface. BTS is controlled by BSC and one BSC can have many BTS under its control.

Base Transceiver Station (BTS):

BTS houses the radio transceivers and handles the radio-link protocols with the Mobile Station. Each BTS comprises of radio transmission and reception devices including antenna, signal processors, etc. Each BTS can support 1 to 16 RF carriers. The parameters differentiating the BTSs are Power level, antenna height, antenna type and number of carriers.

Functions of BTS:

• It is responsible for Time and Frequency synchronization.
• The process of channel coding, Encryption, Multiplexing and modulation for trans-direction and reverse for reception are to be carried out.
• It has to arrange for transmission in advance from the mobiles depending upon their distance from BTS (Timing Advance).
• It has to detect Random access requests from mobiles, measure and monitor the radio channels for power control and handover.

Base Station Controller:

BSC manages the radio resources for one or a group of BTSs. It handles radio-channel setup, frequency hopping, handovers, and control of the RF power levels. BSC provides the time and frequency synchronization reference signals broadcast by its BTSs. It establishes connection between the mobile station and the MSC. BSC is connected via interfaces to MSC, BTS and OMC.

Mobile Station:

It refers to the terminal equipment used by the wireless subscribers. It consists of:

• SIM -Subscriber Identity Module
• Mobile Equipment

SIM is removable and with appropriate SIM, the network can be accessed using various mobile equipments.

The equipment identity is not linked to the subscriber. The equipment is validated separately with IMEI and EIR. The SIM contains an integrated circuit chip with a microprocessor, random access memory (RAM) and read only memory (ROM). SIM should be valid and should authenticate the validity of MS while accessing the network.

SIM also stores subscriber related information like IMSI, cell location identity etc.

Functions of Mobile Station

• Radio transmission and reception
• Radio channel management
• Speech encoding/decoding
• Radio link error protection
• Flow control of data
• Rate adaptation of user data to the radio link
• Mobility management

Performance measurements up to a maximum of six surrounding BTSs and reporting to the BSS, MS can store and display short received alphanumeric messages on the liquid crystal display (LCD) that is used to show call dialing and status information.

There are five different categories of mobile telephone units specified by the European GSM system: 20W, 8W, 5W, 2W, and 0.8W. These correspond to 43-dBm, 39-dBm, 37-dBm, 33-dBm, and 29-dBm power levels. The 20-W and 8-W units (peak power) are either for vehicle-mounted or portable station use. The MS power is adjustable in 2-dB steps from its nominal value down to 20mW (13 dBm). This is done automatically under remote control from the BTS.

Transcoders:

Transcoders are a network entities inserted to interface the MSC side to Mobile side. The voice coding rate on the PSTN side is 64Kbps, and in GSM over the air the voice is coded as 13Kbps. To reduce the data rate over the air interface and to reduce the loading of the terrestrial link (4 : 1), transcoders are introduced at an appropriate place, mostly with MSC.

The transcoder is the device that takes 13-Kbps speech or 3.6/6/12-Kbps data multiplexes and four of them to convert into standard 64-Kbps data. First, the 13 Kbps or the data at 3.6/6/12 Kbps are brought up to the level of 16 Kbps by inserting additional synchronizing data to make up the difference between a 13-Kbps speech or lower rate data and then four of them are combined in the transponder to provide 64 Kbps channel within the BSS. Four traffic channels can then be multiplexed in one 64-Kpbs circuit. Thus the TRAU output data rate is 64 Kbps.

Then, up to 30 such 64-Kpbs channels are multiplexed onto a 2.048 Mbps if a CEPT1 channel is provided on the A-bis interface. This channel can carry up to 120-(16x 120) traffic and control signals. Since the data rate to the PSTN is normally at 2 Mbps, which is the result of combining 30- by 64-Kbps channels, or 120- Kbps by 16-Kpbs channels.

Other Network Elements

Other network elements include components such as SMS Service Centre, Voice Mail Box, and SMS Flow.

SMS Service Centre:

It interfaces with MSC having interworking functionality to provide Short Message Service (SMS) to mobile subscribers. SMS can be destined to fax machine, PC on the internet or another MS. The location of the recipient MS is queried by MSC and delivered.

Voice Mail Box:

When the mobile subscriber is not in a position to answer the incoming calls due to busy/out of service area, then the call gets diverted to a mail box which has already been activated by the subscriber. For this, a separate connectivity has been established from MSC. The subscriber will be alerted through SMS later and can retrieve the message.

SMS Flow:

• When a user sends an SMS, the request is placed via the MSC.
• The MSC forwards the SMS to the SMSC where it gets stored.
• The SMSC queries the HLR to find out where the destination mobile is and forwards the message to the destination MSC if the destination mobile is available.
• If the mobile is not available the message gets stored in the current SMSC itself. In most installations if a mobile is not available for SMS delivery the SMSC does not retry. Instead, the destination MSC informs the SMSC when the mobile comes back in range. SMS handling is a store and forward operation unlike USSD.
• SMS has got a validity period for which it will wait for the destination mobile to be available. After that time the SMSC will delete the message. The validity period can be set by the user. Normal validity is 1 day.

3RD SEM MC UNIT_1 CELLULAR SYSTEM

Cellular System(P4U1)

Cellular network is an underlying technology for mobile phones, personal communication systems, wireless networking etc. The technology is developed for mobile radio telephone to replace high power transmitter/receiver systems. Cellular networks use lower power, shorter range and more transmitters for data transmission.

Features of Cellular Systems:

Wireless Cellular Systems solves the problem of spectral congestion and increases user capacity. The features of cellular systems are as follows −

• Offer very high capacity in a limited spectrum.
• Reuse of radio channel in different cells.
• Enable a fixed number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region.
• Communication is always between mobile and base station (not directly between mobiles).
• Each cellular base station is allocated a group of radio channels within a small geographic area called a cell.
• Neighboring cells are assigned different channel groups.
• By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells.
• Keep interference levels within tolerable limits.
• Frequency reuse or frequency planning.
• Organization of Wireless Cellular Network.

Cellular network is organized into multiple low power transmitters each 100w or less.

Shape of Cells:

The coverage area of cellular networks are divided into cells, each cell having its own antenna for transmitting the signals. Each cell has its own frequencies. Data communication in cellular networks is served by its base station transmitter, receiver and its control unit.

The shape of cells can be either square or hexagon −

Square:

A square cell has four neighbors at distance d and four at distance Root 2 d

• Better if all adjacent antennas equidistant
• Simplifies choosing and switching to new antenna

Hexagon:

A hexagon cell shape is highly recommended for its easy coverage and calculations. It offers the following advantages −

• Provides equidistant antennas
• Distance from center to vertex equals length of side

Frequency Reuse:

Frequency reusing is the concept of using the same radio frequencies within a given area, that are separated by considerable distance, with minimal interference, to establish communication.

Frequency reuse offers the following benefits −

• Allows communications within cell on a given frequency
• Limits escaping power to adjacent cells
• Allows re-use of frequencies in nearby cells
• Uses same frequency for multiple conversations
• 10 to 50 frequencies per cell

For example, when N cells are using the same number of frequencies and K be the total number of frequencies used in systems. Then each cell frequency is calculated by using the formulae K/N.

In Advanced Mobile Phone Services (AMPS) when K = 395 and N = 7, then frequencies per cell on an average will be 395/7 = 56. Here, cell frequency is 56.

Propagational effects of signals

Antenna and Wave propagation plays a vital role in wireless communication networks. An antenna is an electrical conductor or a system of conductors that radiates/collects (transmits or receives) electromagnetic energy into/from space. An idealized isotropic antenna radiates equally in all directions.

Propagation Mechanisms:

Wireless transmissions propagate in three modes. They are −

• Ground-wave propagation
• Sky-wave propagation
• Line-of-sight propagation

Ground wave propagation follows the contour of the earth, while sky wave propagation uses reflection by both earth and ionosphere.

Line of sight requires the transmitting and receiving antennas to be within the line of sight of each other.

Depending upon the frequency of the underlying signal, the particular mode of propagation is followed.

Examples of ground wave and sky wave communication are AM radio and international broadcasts such as BBC. Above 30 MHz, neither ground wave nor sky wave propagation operates and the communication is through line of sight.

Transmission Limitations:

In this section, we will discuss the various limitations that affect electromagnetic wave transmissions. Let us start with attenuation.

Attenuation-

The strength of signal falls with distance over transmission medium. The extent of attenuation is a function of distance, transmission medium, as well as the frequency of the underlying transmission.

Distortion-

Since signals at different frequencies attenuate to different extents, a signal comprising of components over a range of frequencies gets distorted, i.e., the shape of the received signal changes.

A standard method of resolving this problem (and recovering the original shape) is to amplify higher frequencies and thus equalize attenuation over a band of frequencies.

Dispersion-

Dispersion is the phenomenon of spreading of a burst of electromagnetic energy during propagation. Bursts of data sent in rapid succession tend to merge due to dispersion.

Noise-

The most pervasive form of noise is thermal noise, which is often modeled using an additive Gaussian model. Thermal noise is due to thermal agitation of electrons and is uniformly distributed across the frequency spectrum.

Other forms of noise include −

• Inter modulation noise (caused by signals produced at frequencies that are sums or differences of carrier frequencies)
• Crosstalk (interference between two signals)
• Impulse noise (irregular pulses of high energy caused by external electromagnetic disturbances).

While an impulse noise may not have a significant impact on analog data, it has a noticeable effect on digital data, causing burst errors.

The above figure clearly illustrates how the noise signal overlaps the original signal and tries to change its characteristics.

Fading-

Fading refers to the variation of the signal strength with respect to time/distance and is widely prevalent in wireless transmissions. The most common causes of fading in the wireless environment are multipath propagation and mobility (of objects as well as the communicating devices).

Multipath propagation-

In wireless media, signals propagate using three principles, which are reflection, scattering, and diffraction.

• Reflection occurs when the signal encounters a large solid surface, whose size is much larger than the wavelength of the signal, e.g., a solid wall.
• Diffraction occurs when the signal encounters an edge or a corner, whose size is larger than the wavelength of the signal, e.g., an edge of a wall.
• Scattering occurs when the signal encounters small objects of size smaller than the wavelength of the signal.

One consequence of multipath propagation is that multiple copies of a signal propagation along multiple different paths, arrive at any point at different times. So the signal received at a point is not only affected by the inherent noise, distortion, attenuation, and dispersion in the channel but also the interaction of signals propagated along multiple paths.

Delay spread-

Suppose we transmit a probing pulse from a location and measure the received signal at the recipient location as a function of time. The signal power of the received signal spreads over time due to multipath propagation.

The delay spread is determined by the density function of the resulting spread of the delay over time. Average delay spread and root mean square delay spread are the two parameters that can be calculated.

Doppler spread-

This is a measure of spectral broadening caused by the rate of change of the mobile radio channel. It is caused by either relative motion between the mobile and base station or by the movement of objects in the channel.

When the velocity of the mobile is high, the Doppler spread is high, and the resulting channel variations are faster than that of the baseband signal, this is referred to as fast fading. When channel variations are slower than the baseband signal variations, then the resulting fading is referred to as slow fading.

3RD SEM SE RISK MANAGEMENT

Project Risk Management (P 6U1)

Risk management involves all activities pertaining to identification, analyzing and making provision for predictable and non-predictable risks in the project. Risk may include the following:

• Experienced staff leaving the project and new staff coming in.
• Change in organizational management.
• Requirement change or misinterpreting requirement.
• Under-estimation of required time and resources.
• Technological changes, environmental changes, business competition.

Risk Management Process :

There are following activities involved in risk management process:

• Identification - Make note of all possible risks, which may occur in the project.
• Categorize - Categorize known risks into high, medium and low risk intensity as per their possible impact on the project.
• Manage - Analyze the probability of occurrence of risks at various phases. Make plan to avoid or face risks. Attempt to minimize their side-effects.
• Monitor - Closely monitor the potential risks and their early symptoms. Also monitor the effects of steps taken to mitigate or avoid them.

Project Execution & Monitoring :

In this phase, the tasks described in project plans are executed according to their schedules.

Execution needs monitoring in order to check whether everything is going according to the plan. Monitoring is observing to check the probability of risk and taking measures to address the risk or report the status of various tasks.

These measures include -

• Activity Monitoring - All activities scheduled within some task can be monitored on day-to-day basis. When all activities in a task are completed, it is considered as complete.
• Status Reports - The reports contain status of activities and tasks completed within a given time frame, generally a week. Status can be marked as finished, pending or work-in-progress etc.
• Milestones Checklist - Every project is divided into multiple phases where major tasks are performed (milestones) based on the phases of SDLC. This milestone checklist is prepared once every few weeks and reports the status of milestones.

 Project Management Tools (P7U1)

There are tools available, which aid for effective project management. A few are described -

GGantt charts was devised by Henry Gantt (1917). It represents project schedule with respect to time periods. It is a horizontal bar chart with bars representing activities and time scheduled for the project activities.antt Chart

 PERT Chart

PERT (Program Evaluation & Review Technique) chart is a tool that depicts project as network diagram. It is capable of graphically representing main events of project in both parallel and consecutive way. Events, which occur one after another, show dependency of the later event over the previous one.Critical Path Analysis

This tools is useful in recognizing interdependent tasks in the project. It also helps to find out the shortest path or critical path to complete the project successfully. Like PERT diagram, each event is allotted a specific time frame. This tool shows dependency of event assuming an event can proceed to next only if the previous one is completed.

The events are arranged according to their earliest possible start time. Path between start and end node is critical path which cannot be further reduced and all events require to be executed in same order.

Requirement Engineering(P8U2)

The process to gather the software requirements from client, analyze and document them is known as requirement engineering.

The goal of requirement engineering is to develop and maintain sophisticated and descriptive ‘System Requirements Specification’ document.

Requirement Engineering Process :

It is a four step process, which includes –

• Feasibility Study
• Requirement Gathering
• Software Requirement Specification
• Software Requirement Validation

Let us see the process briefly -

Feasibility study :

When the client approaches the organization for getting the desired product developed, it comes up with rough idea about what all functions the software must perform and which all features are expected from the software.

Referencing to this information, the analysts does a detailed study about whether the desired system and its functionality are feasible to develop.

This feasibility study is focused towards goal of the organization. This study analyzes whether the software product can be practically materialized in terms of implementation, contribution of project to organization, cost constraints and as per values and objectives of the organization. It explores technical aspects of the project and product such as usability, maintainability, productivity and integration ability.

The output of this phase should be a feasibility study report that should contain adequate comments and recommendations for management about whether or not the project should be undertaken.

Requirement Gathering :

If the feasibility report is positive towards undertaking the project, next phase starts with gathering requirements from the user. Analysts and engineers communicate with the client and end-users to know their ideas on what the software should provide and which features they want the software to include.

Software Requirement Specification :

SRS is a document created by system analyst after the requirements are collected from various stakeholders.

SRS defines how the intended software will interact with hardware, external interfaces, speed of operation, response time of system, portability of software across various platforms, maintainability, speed of recovery after crashing, Security, Quality, Limitations etc.

The requirements received from client are written in natural language. It is the responsibility of system analyst to document the requirements in technical language so that they can be comprehended and useful by the software development team.

SRS should come up with following features:

• User Requirements are expressed in natural language.
• Technical requirements are expressed in structured language, which is used inside the organization.
• Design description should be written in Pseudo code.
• Format of Forms and GUI screen prints.
• Conditional and mathematical notations for DFDs etc.

Software Requirement Validation :

After requirement specifications are developed, the requirements mentioned in this document are validated. User might ask for illegal, impractical solution or experts may interpret the requirements incorrectly. This results in huge increase in cost if not nipped in the bud. Requirements can be checked against following conditions -

• If they can be practically implemented
• If they are valid and as per functionality and domain of software
• If there are any ambiguities
• If they are complete
• If they can be demonstrated

 Requirement Elicitation Process (P9U2)

Requirement elicitation process can be depicted using the folloiwng diagram:

• Requirements gathering - The developers discuss with the client and end users and know their expectations from the software.
• Organizing Requirements - The developers prioritize and arrange the requirements in order of importance, urgency and convenience.

·        Negotiation & discussion - If requirements are ambiguous or there are some conflicts in requirements of various stakeholders, if they are, it is then negotiated and discussed with stakeholders. Requirements may then be prioritized and reasonably compromised.

The requirements come from various stakeholders. To remove the ambiguity and conflicts, they are discussed for clarity and correctness. Unrealistic requirements are compromised reasonably.

• Documentation - All formal & informal, functional and non-functional requirements are documented and made available for next phase processing.

Requirement Elicitation Techniques :

Requirements Elicitation is the process to find out the requirements for an intended software system by communicating with client, end users, system users and others who have a stake in the software system development.

There are various ways to discover requirements

Interviews-

Interviews are strong medium to collect requirements. Organization may conduct several types of interviews such as:

• Structured (closed) interviews, where every single information to gather is decided in advance, they follow pattern and matter of discussion firmly.
• Non-structured (open) interviews, where information to gather is not decided in advance, more flexible and less biased.
• Oral interviews
• Written interviews
• One-to-one interviews which are held between two persons across the table.
• Group interviews which are held between groups of participants. They help to uncover any missing requirement as numerous people are involved.

Surveys-

Organization may conduct surveys among various stakeholders by querying about their expectation and requirements from the upcoming system.

Questionnaires-

A document with pre-defined set of objective questions and respective options is handed over to all stakeholders to answer, which are collected and compiled.

A shortcoming of this technique is, if an option for some issue is not mentioned in the questionnaire, the issue might be left unattended.

Task analysis-\

Team of engineers and developers may analyze the operation for which the new system is required. If the client already has some software to perform certain operation, it is studied and requirements of proposed system are collected.

Domain Analysis-

Every software falls into some domain category. The expert people in the domain can be a great help to analyze general and specific requirements.

Brainstorming-

An informal debate is held among various stakeholders and all their inputs are recorded for further requirements analysis.

Prototyping-

Prototyping is building user interface without adding detail functionality for user to interpret the features of intended software product. It helps giving better idea of requirements. If there is no software installed at client’s end for developer’s reference and the client is not aware of its own requirements, the developer creates a prototype based on initially mentioned requirements. The prototype is shown to the client and the feedback is noted. The client feedback serves as an input for requirement gathering.

Observation-

Team of experts visit the client’s organization or workplace. They observe the actual working of the existing installed systems. They observe the workflow at client’s end and how execution problems are dealt. The team itself draws some conclusions which aid to form requirements expected from the software.

Software Requirements Characteristics :

Gathering software requirements is the foundation of the entire software development project. Hence they must be clear, correct and well-defined.

A complete Software Requirement Specifications must be:

• Clear
• Correct
• Consistent
• Coherent
• Comprehensible
• Modifiable
• Verifiable
• Prioritized
• Unambiguous
• Traceable
• Credible source

Software Requirements : (P10u2)

We should try to understand what sort of requirements may arise in the requirement elicitation phase and what kinds of requirements are expected from the software system.

Broadly software requirements should be categorized in two categories:

Functional Requirements:

Requirements, which are related to functional aspect of software fall into this category.

They define functions and functionality within and from the software system.

EXAMPLES -

• Search option given to user to search from various invoices.
• User should be able to mail any report to management.
• Users can be divided into groups and groups can be given separate rights.
• Should comply business rules and administrative functions.
• Software is developed keeping downward compatibility intact.

Non-Functional Requirements:

Requirements, which are not related to functional aspect of software, fall into this category. They are implicit or expected characteristics of software, which users make assumption of.

Non-functional requirements include -

• Security
• Logging
• Storage
• Configuration
• Performance
• Cost
• Interoperability
• Flexibility
• Disaster recovery
• Accessibility

Requirements are categorized logically as

• Must have : Software cannot be said operational without them.
• Should have : Enhancing the functionality of software.
• Could have : Software can still properly function with these requirements.
• Wish list : These requirements do not map to any objectives of software.

While developing software, ‘Must have’ must be implemented, ‘Should have’ is a matter of debate with stakeholders and negation, whereas ‘could have’ and ‘wish list’ can be kept for software updates.

User Interface requirements:

UI is an important part of any software or hardware or hybrid system. A software is widely accepted if it is -

• easy to operate
• quick in response
• effectively handling operational errors
• providing simple yet consistent user interface

User acceptance majorly depends upon how user can use the software. UI is the only way for users to perceive the system. A well performing software system must also be equipped with attractive, clear, consistent and responsive user interface. Otherwise the functionalities of software system can not be used in convenient way. A system is said be good if it provides means to use it efficiently. User interface requirements are briefly mentioned below -

·         Content presentation

·         Easy Navigation

·         Simple interface

·         Responsive

·         Consistent UI elements

·         Feedback mechanism

·         Default settings

·         various aspects of software process and software product. Purposeful layout

·         Strategical use of color and texture.

·         Provide help information

·         User centric approach

·         Group based view settings.

Software System Analyst:

System analyst in an IT organization is a person, who analyzes the requirement of proposed system and ensures that requirements are conceived and documented properly & correctly. Role of an analyst starts during Software Analysis Phase of SDLC. It is the responsibility of analyst to make sure that the developed software meets the requirements of the client.

System Analysts have the following responsibilities:

• Analyzing and understanding requirements of intended software
• Understanding how the project will contribute in the organization objectives
• Identify sources of requirement
• Validation of requirement
• Develop and implement requirement management plan
• Documentation of business, technical, process and product requirements
• Coordination with clients to prioritize requirements and remove and ambiguity
• Finalizing acceptance criteria with client and other stakeholders

Software Metrics and Measures:

Software Measures can be understood as a process of quantifying and symbolizing various attributes and aspects of software.

Software Metrics provide measures for

Software measures are fundamental requirement of software engineering. They not only help to control the software development process but also aid to keep quality of ultimate product excellent.

According to Tom DeMarco, a (Software Engineer), “You cannot control what you cannot measure.” By his saying, it is very clear how important software measures are.

Let us see some software metrics:

·        Size Metrics - LOC (Lines of Code), mostly calculated in thousands of delivered source code lines, denoted as KLOC.

Function Point Count is measure of the functionality provided by the software. Function Point count defines the size of functional aspect of software.

• Complexity Metrics - McCabe’s Cyclomatic complexity quantifies the upper bound of the number of independent paths in a program, which is perceived as complexity of the program or its modules. It is represented in terms of graph theory concepts by using control flow graph.

·        Quality Metrics - Defects, their types and causes, consequence, intensity of severity and their implications define the quality of product.

The number of defects found in development process and number of defects reported by the client after the product is installed or delivered at client-end, define quality  of product

 ·         Process Metrics - In various phases of SDLC, the methods and tools used, the company standards and the performance of development are software process metrics.

·         Resource Metrics - Effort, time and various resources used, represents metrics for resource measurement.