GSM Architecture


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  • © Alcatel University - 8AS 90125 0142 VH ZZA Ed.02 - March 2001 To Introduce BSS components and to give some details about them. A BSS comprises:  At least one Base Transceiver Station (BTS) which provides the radio links between the Mobile Stations and the BSC.  A Base Station Controller (BSC) which controls several BTSs.  A Transcoder (TC) located between the BSC and the NSS. The BSS can include additional transmission equipment to perform multiplexing and monitoring functions.
  • The very first aim of a communication system is to transport user information (speech or data). The BSS provides radio coverage for GSM subscribers in a defined area. Its principal role is to provide and support signalling and traffic channels between MSs and the NSS A BSS comprises:  At least one Base Transceiver Station (BTS) which provides the radio links between the Mobile Stations and the BSC. A Base Station Controller (BSC) which controls several BTSs. The main role of the BSS is to provide and support both bi-directional signalling and traffic channels between Mobile Stations and the Network Switching System which is in charge to manage communications within the Public Land Mobile Network (PLMN) (Mobile to Mobile calls) and with the Public Switched Telephone Network (Mobile /Fixed telephone calls)
  • GSM Architecture

    2. 2. LEARNING AIM• To introduce participants to the GSM field/industry. This is an introductory, hence basic content, simple and deliberately non technical training. It’s approach is interactive and demonstrative, to bring the training as close to hands-on as possible. This should be the first class in a 3step training towards becoming a Certified GSM Architecture Professional in Etisalat Nigeria.
    3. 3. LEARNING OUTLINEModule 1: Brief History Module 4: Connecting… • Loading and checking airtime• GSM history • Network components• Packages – HLR – AuC – EIRModule 2: A fresh start – MSCVLR • Making and receiving calls• The role of the SIM card.• The starter pack Module 5: Standard Services on GSM •• The phone’s components The role of the billing system • Post paid first invoice • Barring • Call waiting and holdingModule 3: Accessing… • Diverts – The PIN • Voicemail – The PUK • International calling • SMS – Phone and network locks • Roaming – Radio coverage • Conference calling
    5. 5. GSM EVOLUTION FROM 1946 - 1979The first cellular service was introduced in U.S.A at about 1946. Similar services followed in Europe soon after. The system was manually operated and had several disadvantages: 1. Terminals were heavy and expensive. 2. The service was restricted to coverage of a single Transceiver site. 3. Little frequency spectrum was available; as a result, the capacity of the system was small and easily saturated. 4. As congestion worsened so did the quality of service. • During the 50’s and 60’s transistor technology was introduced enabling automation of the systems. No drastic change was experienced in the industry until the development of microprocessors in the 70’s. This new development facilitated large scale integrations and development of more complex systems. • Cellular analogue technology was developed and launched in 1979. Bell laboratories in Chicago U.S.A developed AMPS (Advanced Mobile Phone System), closely followed by NMT (Nordic Mobile Telephone) and TACS (Total Access Communication System) in Europe.
    6. 6. LIMITATIONS OF THE ANALOGUE SYSTEMSFrom the early 80’s, several European countries agreed that the existing analogue systems had serious limitations, which include:1. The potential demand was more than the expected capacity of the systems being used.2. The system did not offer compatibility i.e. an NMT terminal could not access the TACS networks and vice versa.3. The development of a new cellular system would require hugely unaffordable capital outlay.
    7. 7. GSM EVOLUTION FROM 1946 - 1979The Europeans realized this earlier on and in 1982, the conference of European Posts and Telecommunications (CEPT) formed a study group called the Groupe Speciale Mobile (G.S.M) to study and develop a Pan-European Public and Mobile System. The proposed system had to meet certain criteria:1. Good subjective speech quality.2. Low terminal and service cost.3. Support for international Roaming.4. Ability to support handheld terminals (MS).5. Support for a range of new services and facilities.6. Spectral efficiency.7. ISDN compatibility.In 1989, G.S.M responsibility was transferred to the European Telecommunication Standards Institute (ETSI) and phase 1 of G.S.M specification was published in1990. First system trial run was conducted in 1991 while Commercial services were started in 1992. The acronym now stands for Global System for Mobile Telecommunication**ETSI till date is responsible for the technical specification of GSM
    8. 8. MOBILE TELEPHONY MILESTONE Before GSM: Mobile Telephony Milestones 1876 1970 Electric transmission 10101010 (Graham Bell) Digital Technology (1st digital switch) • • • 1897 ——— • • • 1982 1st wireless transmissions 1st analog cellular (Marconi) network 1946 1992 10101010 1st public mobile 1st GSM communication telephone (digital cellular network)
    9. 9. THE MOU (Memorandum of Understanding)As GSM is a global standard, there has to be a central point of control. That point is now in Dublin,Ireland and is known as the GSMA. Members of the association are bounded by the MOU(Memorandum of Understanding). Should a country and network sign the MOU they bind themselvesto operate in the confines and specifications of the MOU. By doing this GSM operators worldwiderun networks that comply with the international GSM standard. Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signedin 1987 by network operators of 13 countries. The MoU was put together to see to several issues notcovered by the technical specifications. These are:1.Roaming agreements (when a subscriber makes use of a network(s) other than his/her homenetwork.2.Tariff principles.3.System deployment.4.Concerted service introduction.5.Routing plans6.Timescales7.Procurement
    10. 10. SOME FACTS ABOUT THE MOUThe MoU was first signed by participating countries in 1987 and wasupdated again in 1991.GSM was evolved from a purely Pan European initiative to a worldwideorganization. There are more than 210 members from over 105 countriesbelonging to the MoU.Every four months or so, the GSM MoU plenary committee meets todecide on future GSM direction, developments and improvements.All the proposals are tabled and voted on. The number of votes allocated to a member is dependent on various factors; these include the GDP of the member country and the number of subscribers.
    11. 11. Key dates in the evolution of GSM Date Event A European body known as CEPT (Conference of European Posts and Telecommunications) 1982 formed a committee to begin work on specifying a mobile digital system. The first network operators signed the MOU. They committed themselves to implementing 1987 GSM by 1991 1992 First networks were launched and the first roaming agreement was signed
    12. 12. PHASES OF GSM Phase Features Start date Digital voice telephony International roamingPhase 1 Basic data and fax services 1992 Call diverts Call barring Short Message Service (SMS) Multi Party Calling Mobile Data Services Mobile Fax ServicePhase 2 Conference calling 1994 Call waiting and holding Calling Line Identification (CLI) Cell Broadcast Enhancements to data services such as:Phase 2+ HSCSD 1998 GPRS
    13. 13. GSM BAND/OPERATIONS• GSM 900 (using the 900 MHz band)• GSM 1800 (using the 1800 MHz band)• GSM 850 - 1900 (using the 850 -1900 MHz band and is found in the USA and some parts of Asia)
    14. 14. ADVANTAGES & UNIQUENESS OF GSM1. Increased radio spectrum efficiency to provide even greater network capacity. (Which means it can support a high amount of subscribers!) 2. Provides highly sophisticated subscriber authentication which reduces the possibility of fraud.3. Prevents the eavesdropping of conversations by employing sophisticated voice encryption techniques which are totally secure.  4. Provides better voice clarity and consistency, eliminating interference due to digital transmission. (Turns speech into binary numbers!)
    15. 15. GSM ADVANTAGE cont…5. Simplifies the transmission of data which allows the connection of laptop and palmtop computers to GSM cellular phones.6. A single standard allowing International Roaming between the worlds GSM networks - (International Standards.)7. Settle ones bill in the subscribers’ local currencies at home. (No unnecessary use of your currency limit!)8. One phone - one number.
    16. 16. GSM BENEFITS GSM BenefitsAdvantages of the GSM standard Digital Advantages Technology low cost Worldwide market $ High resistance Open system to interferences Transmission data rate Roaming Transmission Security
    17. 17. Billing Principles in GSMIn GSM Billing is carried out based on some fundamental principleswhich include:1.TIME: Peak, off peak.2.DATE: Public holidays, weekends, special days etc3.UNITS: Per Second, Per Minute or Half Minute4.FREE MINUTES5.BUNDLED PACKAGE
    19. 19. ELEMENTS OF THE GSM SYSTEM • MS: Mobile Station ( Mobile Phone + SIM) • BTS: Base Transceiver Station • BSC: Base Station Controller • TC: Transcoder • NSS: Network Switching Subsystem (MSC, HLR, VLR etc) BSS NSS B T T BSC S C B TMobile SStations BSS: The major role is to provide and support both Bi-directional signaling and Traffic channels between the MS and NSS NSS: It manages the communication and interconnections within mobile to mobile and mobile/ fixed telephone calls.
    20. 20. THE ROLE OF SIM CARDAcronyms:• SIM – Subscriber Identity Module• IMSI – International Mobile Subscriber Identity• MSISDN – Mobile Subscriber Integrated Services Digital Network (Number)• MS- Mobile Station
    21. 21. SOME FACTS ABOUT SIM• The SIM card’s primary role is to identify the subscriber• The SIM card fits into the GSM handset. It can be moved from one phone to the next.• It does this by having a unique number programmed into it when the SIM card is manufactured.• This unique number is known as an IMSI number. The IMSI number identifies each and every GSM subscriber on a global level. There is no way that a subscriber can view or change this number.
    22. 22. FACTS ABOUT SIM cont...• The number that is printed on the SIM card usually starting with “89” is the SIM serial number and is mostly used for logistical and administrative purposes. This number does NOT identify the subscriber on the GSM network.• Each Subscriber is issued with a cell phone number (known as MSISDN).• When a SIM card is activated on the network a record is kept of the IMSI and the MSISDN so that when an MSISDN is dialed the network can translate this number into an IMSI so that it knows which SIM card is being called.
    23. 23. FACTS ABOUT SIM• The SIM has inbuilt memory• This memory is dedicated to: – Storing names and numbers • A range of security numbers that protect the SIM (and some handset features) from unauthorised accessSIM memory has increased over time. The table below explains this: SIM type Phone book memory SMS memory 32KB 200 20 64KB 250 30 128KB 254 40• Etisalat sells 128KB uSIM to her subscribers• The SIM also contains numbers that the GSM network uses to create a secure (encrypted) radio connection.
    24. 24. PROBLEMS WITH SIM CARDS• SIM cards do develop faults• A faulty SIM card can affect the subscriber’s ability to use the network• A replacement SIM can be issued and a SIM swap can be performed on the billing system. This allows the subscriber to keep the same MSISDN even though they are issued with a new IMSI number.• SIM memory is not backed up by the network. If a SIM swap is performed the names and numbers on the old SIM are lost.
    25. 25. THE PHONE’S COMPONENTSA GSM handset can be broken into three individual parts.• Antenna• Battery 1 – Antenna (internal)• Software 3 - Software 2 – Battery
    26. 26. PHONE COMPONENTS CONT… Facts about handset Problem with handset antennas antennas• Cell phones communicate with the • Some phones have very network by transmitting and sensitive aerials and when receiving radio waves. these aerials are even slightly• The phone requires an antenna to damaged the phone can no transmit and receive these radio waves. longer detect the radio waves• With advancements in cell phone being sent out by the aerials some manufacturers have network. opted for the internal aerial which is both more visually appealing and secure from damage.
    27. 27. PHONE COMPONENTS CONT…Facts about batteries:• The battery supplies power to the phone.• The performance of a battery can be expressed in two measurements:• Standby time - this measurement states how long a fully charged battery can last, without any calls being made, before it needs to be recharged• Talk time – this measurement states how long someone could spend talking on the phone before the battery would go flat.• There are a variety of battery types available at the moment. The table below explains: TYPE NAME COMMENT Old type battery with poor performance NiCD Nickel Cadmium A better battery. However, over a period NiMH Nickel Metal Hydride of time the performance decreases. Cost effective Current generation battery. Although Li-Ion Lithium Ion more expensive than NiMH it offers superior performance. Can be molded into small areas making Li-polymer Lithium polymer it an ergonomically appealing as well as offering good performance.
    28. 28. PHONE COMPONENTS CONT…Problems with batteries:• NiCD batteries are susceptible to “memory loss” if they are not fully discharged before they are charged again. Careless charging can seriously diminish the batteries performance• Li-Ion and Li-polymer batteries are fragile. If dropped the battery’s performance can be diminished.• Initial charge times differ – subscribers should check their handset manual for initial charge times and further tips on battery care
    29. 29. PHONE COMPONENTS CONT…Facts about software Problems with software• Cell phones work very much like • Software bugs, although computers and therefore require software to govern their actions. not common, do exist. A• Every manufacturer uses its own common result is when software and designs its own man- the phone “hangs” and machine interface.• Manufacturers always evolve their will not respond to user software. In some cases a phone input. can be sent for a software upgrade
    30. 30. MODULE 3 Accessing…
    31. 31. PIN & PUK• PIN – Personal Identification Number• PUK – PIN Unblocking Key FACTS ABOUT PINS• The PIN is a number that the phone will prompt for. The subscriber, knowing the PIN, authenticates himself by typing the number in. If the numbers matches then the phone grants the user access and the phone begins to search for the network.• By using the phone’s menu the user can turn the PIN on or off• The user can change the PIN either by using the phone’s menu or by using the following code: **04*OLD PIN*NEW PIN*NEW PIN#• The PIN can be between 4 and 8 digits long• There are two PINS. PIN I is used to protect the SIM against unauthorised access while PIN II is used to protect certain menu features against unauthorised access.• The PIN II can also be changed by using the phone’s menu.• Both the PIN I and PIN II can be blocked if the wrong number is entered three times consecutively.• When the PIN is blocked a PUK number is required to unblock it. 
    32. 32. PROBLEMS WITH PINS• People forget them!• When changing, enabling or disabling the PIN the subscriber has to enter the PIN. This provides subscribers with an opportunity to block their SIM.• When a new SIM is issued the default PIN settings are restored. Subscribers sometimes assume that the old settings still apply.• PIN II is sometimes thought to be the same as PIN I and is therefore often blocked
    33. 33. FACTS ABOUT PUKS• Each SIM has its own PUK number.• PUK I is used to unblock the PIN I and PUK II is used to unblock the PINII• PUK I and PUK II are different numbers• The standard unblocking procedure for PIN I is **05*PUK*PIN*PIN#.• The standard unblocking procedure for PIN II is **052*PUK2*PIN2*PIN2#.• The subscriber can also follow the phone’s prompts to unblock the SIM.• If the PUK is entered incorrectly 10 times in consecutive order then, the SIM will be destroyed. This is intended as a safety feature.• Should this happen, a SIM swap would need to be done
    34. 34. PROBLEMS WITH PUKS• Subscriber’s are sometimes confused when the phone prompts for a PUK and often enter a variety of numbers that are not valid.• When the SIM is replaced it comes with a new set of PUK numbers
    35. 35. PHONE AND NETWORK LOCKSFacts about network locked phones:Most networks entice prospective subscribers by reducing the price of the phone. By making a loss on the sale of the phone they hope to generate revenue by the continued use of airtime. In order to achieve this the phone is locked, or programmed, so that it will only work on that particular network. The retailer of the phone may decide to unlock the phone if the financial loss can be recovered. However, this is a matter of policy and some networks refuse to unlock phones.You will know when a phone is network locked if it states the following: PHONE ERROR MESSASGE Nokia SIM not allowed Ericsson Insert correct card Alcatel Network code?
    36. 36. Facts about Security or Phone Codes• As an additional level of security, phones can request a special code that has the same purpose as a PIN• The following are typical messages indicating that a security code is active: PHONE ERROR MESSGAE Nokia Enter security code Ericsson Enter Lock Code Alcatel Enter Product Key
    37. 37. Problems with Security and Phone Codes• Some phones do not have default security codes• When selling their phones some subscribers forget to deactivate the phone code• If the security code can not be found then the phone can only be made operational again by reinstalling the software.• Subscribers forget their security codes.
    38. 38. Radio coverage• BTS – Base Transceiver Station• BSC – Base Station ControllerFacts about coverage:• GSM makes use of radio frequencies to send and receive information between the phone and network.• The radio channel replaces the traditional line that we find on landlines.• Cell phones are able to be mobile because the radio waves are detectable over a large area.• The component that broadcasts radio waves is known as a BTS.• GSM specifies that a BTS can broadcast to a maximum radius of 35 KM.• It takes a number of BTSs to create a reasonable coverage area.• The area that receives radio waves (coverage) from a BTS is known as a cell.• Cells are constructed so that, to the customer, there is seamless coverage.
    39. 39. RADIO COVERAGE…CONT• Cells can vary in size and the number of calls that it can handle• Not all areas in a country are covered, only areas that prove cost effective are covered.• A number of base stations (BTS’s) are controlled from a central point by a computer known as the BSC. There are many BTS’s to one BSC.• As the subscriber base increases the network operator needs to keep up by setting up more BTS’s and BSC’s.
    40. 40. PROBLEMS WITH COVERAGE• Within a coverage area not all areas receive radio waves. These are known as “dead spots”. Radio waves work in a similar way to light waves so they can be blocked out.• In some areas there are more cell phone call trying to be made than the BTS can handle. The cell is therefore congested.• In some areas the radio waves might be too weak for them to carry information between the phone and the network.
    41. 41. TROUBLESHOTING COVERAGE PROBLEM• If a customer can not receive any network signal or they have difficulty using their phone to make and receive calls and SMS they assume the problem lies with the network. When dealing with coverage issues you should always eliminate the possibility that the problem may lie with the subscriber’s phone or SIM card.• An effective tool to use when dealing with coverage problems is a feature in every handset’s menu known as the “Network search”
    42. 42. USING THE NETWORK SEARCH FEATURE ON PHONEUse these steps to operate this feature:Locate Network Search in the menu and select itSelect “Manual network search”Wait for the phone to search for all the GSM networks that it can detect.The phone returns a list of all networks that it can detect.If EMTS NGA or 621 60 appears on the list, select it.
    43. 43. TROUBLESHOOTING COVERAGE PROBLEMS Customer`s side Network`s side SYMPTOMS AND SYMPTOMS AND PROBLEMS PROBLEMS INDICATORS INDICATORS  May not pick up signal strength  Signal is weak or non existent  Network search will not yield any search  Other subscribers in the same area results experience the same problem  Other subscribers in the same area will not  Network search shows other networks Faulty handset experience the same problems BTS failure but not the home network.  Other SIM cards will also not work in the  Problem will not exist in other areas problematic phone  Problem will exist where ever the subscriber is  May not pick up signal strength  Signal is weak or non existent  Network search will not yield any search  Signal strength may fluctuate rapidly results  Other subscribers in the same area  Other subscribers in the same area will not experience the same problem Faulty SIM BSC failure experience the same problems  Problem will not exist in other areas  The SIM will not work in any phone although the affected area may be large  Problem will exist where ever the subscriber is  Phone will not log onto the network  Network will appear in the search results  No signal can be detected but still wont be able to select the home  Network search may show other networks networkOut of coverage area  Phone works in coverage areas SIM not active  Error message may state that the SIM is  Use coverage map to assist you faulty  Other subscribers do not experience the same problem  Signal strength is unaffected  Network busy error displayed on phone  Problem is isolated and intermittent Congested cell  Problem exists in a small area  Other subscribers experience the same problem in the same area Dead spot  Home network missing from search results
    44. 44. GSM ARCHITECTUREBase station subsystem architecture
    45. 45. MODULE 4• Connecting
    46. 46. FRESH ACRONYMS TO LEARN!• HLR – Home Location Register• AuC – Authentication Center• EIR – Equipment Identity Register• MSC – Mobile Switching Center• GMSC – Gateway Mobile Switching Center• VLR – Visitor Location Register• IMEI – International Mobile Equipment Identity
    47. 47. LOADING AND CHECKING AIRTIMEThe facts of loading and checking airtime:• Both loading and the checking of airtime is done by typing certain codes into the phone and then pressing the dial button.• These codes are known as USSD codes and they can be used for a variety of applications.• To load airtime the subscriber should view the access number on their recharge card and use it in the following code: *222*15 digit access code#• After a few seconds a confirmation message will be displayed on the subscriber’s phone.• In order for a subscriber to check the airtime balance they should use the following code: *232#• After a few seconds their balance will be displayed on the subscriber’s screen.
    48. 48. NETWORK COMPONENTS• The GSM network is comprised of a number of special computers and databases that work together so that the following can be achieved:• Calls can be routed between subscribers• Calls can be routed between Etisalat and other networks• Subscribers are billed• Unauthorised calls are disallowed• Stolen handsets are prevented from working on the network• Secure radio connections are established between the phone and the network• Only legitimate SIM cards are allowed access to the network.• Roaming subscribers are allowed access to the network
    49. 49. NETWORK COMPONENT AND DESC COMPONENT DESCRIPTION COMPONENT NAME DESCRIPTION NAME The HLR is a centralised database that Each MSC has a VLR built into it. The VLR contains information about subscribers that stores a copy of the subscriber’s HLR the GSM network requires so that it can profile as well as a more specific GSM process calls. The details below are stored in location. each subscriber’s profile: The reason the VLR is integrated with the 1.The ability to make and receive calls 2.Their products and services MSC is so that the MSC’s don’t have to 3.If they are a post or pre-paid subscriber query the HLR for the information any HLR VLR 4.The status of barring that were set up from time a call is set up. the handset Remember that there are more MSC’s than 5.The status and forwarding number of the HLR’s and so if all of those MSC’s were diverts querying the HLR a huge stress would be 6.The GSM location of that subscriber placed on the network. 7.Their IMSI and MSISDN All of this information is required during the call setup procedures. The MSC is a telephone exchange and is The AuC has two specific functions. One is therefore responsible for routing and to verify that the subscribers SIM card is managing calls. authentic. MSC The MSC has to perform certain checks on AuC The other is to create an encrypted radio subscribers before it can completely set up link between the phone and the network the call. It gets this information from other components – the HLR being one of them. The GMSC links the GSM network to Each phone has a unique serial number other telephone networks. A legal known as the IMEI. This number is sent by agreement must be in place before two the phone to the network each time a call is networks can connect. This is known as made or received. GMSC the interconnect agreement. EIR The EIR is a database that stores a list of IMEI numbers that have been reported as stolen. The IMEI is checked in the EIR and if a match is found the call setup procedure is terminated
    50. 50. GSM ARCHITECTUREMobile station subsystem architecture
    51. 51. MAKING AND RECEIVING CALLSSome facts of call routing (cell to cell): HLR to determine if B:• When a call is made the calling party’s phone – Is an active subscriber sends the following to the network: – Has the required permission to receive calls – Its IMSI – Has services that should be used on the call – Its IMEI (eg. CLI) – The called number (B-number) – Has diverts or handset barring setup• This information is relayed to an MSC via the BTS – The GSM location (which MSC it is using) and BSC • If B is cleared then the MSC will notify B’s MSC• The MSC uses the IMSI number to check it’s that a call is coming for B. inbuilt VLR to verify that the calling subscriber • B’s MSC then pages the phones in its service area can make calls and what services to use on the call (using the IMSI). (eg. CLIR) • When B responds it’s IMEI is checked in the EIR• The MSC consults the AuC to authenticate the and the AuC is consulted to authenticate the SIM SIM card and to create an encrypted radio link card and to create an encrypted radio link between between the phone and the BTS the phone and the BTS• The MSC uses the IMEI to check if the calling • When all of these checks are complete B’s phone party’s phone is black listed. begins to ring and a connection is created between• If the calling party is cleared then the MSC uses the two MSC’s. the B number to check the
    52. 52. PROBLEMS DURING CALL SETUP PROBLEM SYMPTOM DESCRIPTION This is when the fixed dial list is active. The subscriber needs to turn thisFixed dial active “Call not allowed” is displayed off. Knowledge of the PIN II is required Own number sending feature in the settings menu of Nokia phonesOwn number sending “Error in connection” is displayed needs to be turned to ON or Set By Network Barring error message is displayed. This Some phones have a barring option that resides on the phone itself.Handset’s own barring happens quickly as the phone stops the call This feature needs to be deactivated. Some phones protect this feature before even contacting the network with a code Because the ringer is turned either too low or off completely theSilent ringer on Subscriber claims not to receive calls subscriber can’t hear their phone ring. The ringer should be turned up Phone will not log on. Faulty SIM error While no record exists of a subscriber on the HLR the subscriber will notNot active message may also appear be allowed access to the network. Either triple tone is heard or message is The network can place a barring of calls on subscriber’s HLR profiles.Network barring This is done when account is in arrears or the phone has been reported played as stolen. This applies to both incoming and outgoing calls By using the menu or a GSM code a subscriber can bar themselves onHandset barring Triple tone is heard the network from making or receiving calls An unconditional divert will always route the call away from the BUnconditional divert No calls received number. The divert should be cancelled Either triple tone is heard or message is The IMEI sent by the phone matches a number in the EIR. The call isBlack listed handset played terminated Sometimes the IMSI is not provisioned in the AuC. This is a networkNo IMSI in AuC error.
    53. 53. Practical examples1. A client calls the call centre and complains that he is unable to make calls. The message heard is ‘insufficient credit’ and the call ends. The client can receive calls. What is the issue with the Customer’s phone and what is the remedy?  
    55. 55. ACRONYMS TO LEARN• CDR – Call Data Record• SMSC – Short Message Service Center• DCF – Default Call Forwarding• CLI – Calling Line Identity• CLIR - Calling Line Identity Restriction• IVR – Interactive Voice Response
    56. 56. THE ROLE OF THE BILLING SYSTEM• The billing system interacts with some • The billing system also receives GSM components. This interaction information from the network for works in both directions. billing purposes.• The billing system interacts with the HLR – When a call is made the network to update a subscriber’s HLR profile when: records the details of the call. This record is known as a CDR. – An activation or deactivation takes place on the billing system – CDR’s are stored at the switch and – A product is added or removed on forwarded to the billing system so the billing system that the costs can be calculated – A barring is added or removed and posted to the subscriber’s account – Sometimes these products and • This process is too slow for a pre-paid services are added on the billing system but the transaction fails on system. A pre-paid billing system exists the network, therefore the service is within the GSM network and calculates not truly active for that subscriber. costs as the call progresses
    57. 57. CALLING LINE IDENTITY (CLI)Facts of CLI:• CLI allows the called party to see the calling party’s number• CLIR prevents the called party from seeing the calling party’s number.• Should the calling party have CLIR and the called party have CLI the called party will NOT see the calling party’s numberProblems with CLI• Subscribers assume that because they have CLI they will see all numbers. CLIR prevents this from happening• Some networks restrict their numbers by default• When receiving an international call the CLI will not usually showNB:• You can conceal your number by dialing #31# with the recipient number.• You can present your number by dialing *31# with the recipient number.
    58. 58. BARRINGFacts about barring:• Barring is a term that refers to a service that prevents certain calls from being made or received• When a barring is activated or deactivated a barring password is required. The default barring password is 0000• Barring can be set up and cancelled using these codes: CALL ACTIVATE CANCEL CHECK STATUS BARRING Outgoing Calls - Nationally * 33 * barring code # Send # 33 * barring code # Send * # 33 # Send Outgoing Calls - Internationally * 331 * barring code # Send # 331 * barring code # Send * # 331 # Send Incoming Calls - Nationally * 35 * barring code # Send # 35 * barring code # Send * # 35 # Send Incoming Calls - When Roaming * 351 * barring code # Send # 351 * barring code # Send * # 351 # Send All Call Barring # 330 * barring code # SendProblems with barring:• Sometimes barring is set up unintentionally.• Barring can not be setup when diverts are active• In certain circumstances subscribers can bar their incoming SMS without knowing about it
    59. 59. DIVERTS – CALL FORWARDING Diverts are set up and cancelled by using the following codes:Facts about diverts (call forwarding): Call Diverts ACTIVATE CANCEL CHECK STATUS•Diverts allow subscribers to have their callsforwarded to another number under four * * 21 * number # # # 21 # Send * # 21 # Sendconditions. These conditions are: Send Unconditional – When the subscriber is busy on a call * * 61 * number # – When the subscriber’s phone has been No Reply Send # # 61 # Send * # 61 # Send ringing for a length of time Set Time Delay on No Reply * * 61 * number * 11 * 5/10/15/20/25/30 # Send – When the subscriber’s phone is not contactable (eg, turned off or out of * * 67 * number # Busy Send # # 67 # Send * # 67 # Send coverage) – Unconditional – also called an “all call” * * 62 * number # Not Reachable Send # # 62 # Send * # 62 # Send divert Cancel all the Call # # 002 #•Diverts are available for all subscribers Diverts   Send No Reply, Busy & Not * * 004 * number # Reachable Send  
    60. 60. DIVERTS CONT…• There is a divert known as DCF. This divert is one that is set by the network and is only called upon if no other diverts exist (hence the name default call forwarding).• DCF is usually configured to route calls to voicemail because diverts are instructions to the network to make a call on behalf of the called party, a divert can be considered as an outgoing call. As a result if you divert calls then that call is charged to you. This can be seen below:    B A C B diverts to C B is liable to pay the Party A calls B. call charge from B to C A is liable to pay the normal call charge During the call set up process the network will look at the diverts in a specific order. The divert types are listed below in order of priority: – Unconditional – No connection – No reply 3 conditional diverts – Busy – DCF 
    61. 61. VOICEMAILFacts about voicemail• Voicemail is a system that takes messages from callers while the subscriber is unavailable to take the call (phone is not contactable by the network, the phone rings for a specified period of time, when the subscriber is busy on a call and finally all calls are sent to voicemail.• The divert routes the calls to the voicemail system. Therefore diverts must be set up so that the call is routed correctly• Accessing the voicemail is available from landline or while roaming on the number (+234)8090000252, 08090000252• Once a message is left in the subscriber’s voicemail box an SMS is sent to his phone to inform him that a message has been left• The subscriber then dials 252 to retrieve the message if the service has been activated.Problem with voicemail:• Subscribers set the diverts up incorrectly• Voicemail boxes don’t get created properly on the network• Subscribers forget their voicemail passwords
    62. 62. INTERNATIONAL CALLINGFacts about international Problems with internationalcalling: calling:•When dialing an international number from •Subscribers can be charged for a calla GSM phone the format of the number even if the called person did notchanges. The dial out code is substituted for a answer the call. This differs+ sign and the 0 of the area or network code is depending on the company thatdropped. Therefore the South African number083 451 0429 would be dialed as routes the call internationally.+27834510429 from Nigeria (or anywhere else •International calling may bein the world) expensive•International calls cost more from a cell •International links can be downphone than they do from the landline causing frustrationoperator. The reason for this is that the morenetworks that is involved with the routing of •A large time delay can sometimesthe call the higher the cost of the call. occur.
    63. 63. SHORT MESSAGE SERVICE (SMS)FACTS ABOUT SMS: Problems with SMS:• SMS is text messages that are sent • Messages can be duplicated from a GSM phone.• These messages may be up to 160 • SMS can be sent late or characters (including spaces) sometimes not at all• The message is stored in a computer • Subscribers do not delete called an SMSC while the phone that messages from their SIM the message was sent to is located on the network. cards. When the SIM memory• The SMSC has an address called a is full no new messages can be message center number. Etisalat’s received. Ensure that message center number is subscribers delete their SMS +2348090001518 • International SMS• The cost per SMS ranges between N10 per msg (availability)• SMS is available for ALL subscribers• Activation cost is FREE
    64. 64. INTERNATIONAL ROAMINGThe facts of international roaming:• The cellular term “roaming” refers to the process whereby a subscriber uses a network other than that subscriber’s home network. Typically this network is located in a foreign country.• A legal agreement is signed between networks that allow the networks to interact so that their subscriber’s may roam on that network.• The roaming agreement also serves to specify how the two networks will bill each other for the costs generated by roaming subscribers• This agreement is known as a “roaming agreement”
    65. 65. INTERNATIONAL ROAMING CONT.Still on facts about roaming:• In order for a subscriber to roam certain things need to be checked. This is specified below in the roaming checklist: – The visited country must have a GSM network with which Etisalat has a roaming agreement. – The subscriber must be a post-paid/ pre-paid subscriber – The subscriber’s handset must be compatible with the visited network. When visiting the USA the subscriber would need to have a tri band phone. Failing this they can rent a GSM 1900 phone in the USA. – The subscriber must have requested roaming from Etisalat – The subscriber should have set and remembered a voicemail box password• When the subscriber’s phone is switched on in the foreign country it will automatically search for available GSM networks and will log onto the network with the strongest signal with which Etisalat has a roaming agreement• If the subscriber wishes to roam with a specific network (assuming that Etisalat has an agreement with more than one network in the same country) they would need to perform a manual network selection on their phone
    66. 66. INTERNATIONAL ROAMING CONT.The rules of calling and billing while roaming:• When roaming the calls (and therefore the call charges too) are recorded by the visited network.• The roaming phone is subject to the same restrictions and rules as local subscribers.• If the roaming subscriber wants to contact a number in the visited country they would dial the number as if they were a local subscriber. As the call is a local call the visited network will bill that call at a specified local rate• Should that subscriber wish to contact a number outside the visited country they would need to make an international call (using the international format). This call will be billed as an international call as per the visited networks international calling rates.
    67. 67. INTERNATIONAL ROAMING CONT.• The subscriber’s HLR profile (stored in the home country) records which MSC (any MSC in the world) the subscriber is using. Therefore, if the MSISDN is dialled in the home country the network is able to route the call to the international destination.• Therefore, when calling a roaming subscriber the caller need only dial the MSISDN and the network will do the rest.• The caller of such a call will pay as if the subscriber is not roaming. The roaming party will be liable for the international part of the call.• As the subscriber’s HLR is the only computer which stores the subscriber’s international location all calls must be routed via the home country. Therefore all calls that the subscriber receives come from his home country.• Therefore, all call that the roaming subscriber receives has an international call cost attached.
    68. 68. INTERNATIONAL ROAMING CONT.• International calls require a separate company to carry them and usually this company will invoice the originating company for the call even if the call is not answered.• If the subscriber has diverts that are activated to his voicemail and he receives a call that he doesn’t answer he is charged for two international calls as the call is routed back to his home country.• The visited network records all calls that the roaming subscriber made. These CDR’s are collated and forwarded to the home network.• The home network records all calls that it routed to the visited country and rates these calls.• All these CDR’s are collated and rated and invoiced to the subscriber in his national currency.• To retrieve voicemail while roaming or on landline the subscriber should dial(+234)8090000252, 08090000252