GSM General Questions and Answers & Some Practical knowledge

7/28/2019 GSM General Questions and Answers & Some Practical knowledge

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GSM General Questions and Answers

Some ExtraS.NO NAME DESCRIPTION

1 SYSTEM INFORMATION

SYSTEM INFORMATION ARE FROM 1 TO 12,1,2,3,4,7 &8

ARE IN IDLE MODE & 5,6 &9 &10

DEDICATED MODE,12 &13 GPRS.1 TO 4 ARE

FOR BA LIST. 5 & 6 DEDICATED MODE MA LIST.

2 BIT ERROR RATE

QUALITY IS IN TERMS OF BIT ERROR RATE IF

BIT ERROR RATE IS 0 T0 0.2 QUALITY WILL

BE .2 & 0.4 T0 .4 QUALITY 0.8 AND SO ON.

3 FRAME ERROR RATE

Error in per frame due to interference or

due to hardware faulty.

4 COMMON CONTROL CHANNEL Common Control channels are PCH,AGCH,RACH.

5

DEDICATED CONTROL

CHANNEL Dedicated Control Channels are SDCCH,SACCH,FACCH.

6 TASR TCH Assignment Success rate .

7 RASR Rach Assignment Succes Rate.9 SAACH slow Associated Control Channel

10 AMR HALF RATE Adaptive Multirate, Improve the call Quality.

11 AMR FULL RATE Adaptive Multirate, Improve the call Quality.

12 OVERSHOOTING

Overshootinng is the case in which cell takes call

from long distance & from the region other cell.

13 RADI LINK TIMEOUT

Radio link time out is the multiple of 4 it maintain

the Call Quality when quality is poor reduces by one

& so on if it becomes Zero Call drop occurs.

14 DTX

Discontinuous transmission,DTX is ON on Dedicated

Mode & DTX is Of on Ideal Mode ,if it is 0=off,if it is

1=on,if it is 2=of or ON.

15 SDCCH Signaling & Dedicated Control Channel.

16 MAIO Mobile Allocation Index Offset.

17 HSN Hopping Sequence Number.

18 MA LIST Mobile Allocation List.

19 CA LIST

20 BA LIST BCCH Allocation List.

21 LOCATION UPDATING

LAC Updating Occurs only when cell change from

one Lac to Another Lac, Lac Update Occurs Only when

it is in Ideal Mode.

22 CALL TO AN MS

Msc sends paging information to the Bsc & BSC to theBtS & Mobile Through Paging Channel,then if mobile

wants it request for call setup through Random Access

Channel.If bsc having the SDCCH Available then Then

it sends the information to ms by AGCH CHannel than

SDCCH is Available,then SDCCH will be alllocated to

MS then From SDCCH If TCH Will be available then it

will get the TCH channel Mobile Rings in otherway

then the if another party pickup the phone Call

will Establish .now Messages will be transferred

by SACCHduring Call.

23 CALL FROM AN MS.

24 TCH DROP

TCH Drops Generally Occurs Due to Interference

Hardware Faulty ,Cable Swaping,hanover porperly

not Defined,weak Coverage,Overshooting,Unbalance


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b/w Ul & DL Quality ,or Both Ul & DL Quality.

25 UL QUALITY

Uplink Quality this is the Quality of MS to BTS ,this is

generally Occurs Due to interference, Hardware Faulty

,or due to cable Swapping.

26 DL QUALITY

Downlink Quality this is the Quality Of Bts to Ms,This is

Generally Occurs Due to Interference ,Hardware Faulty,

Overshooting,Cable Swapping,& due to Weak Coverage.

History Of GSM

1) In short describe the evolution of GSM?

2) What are the standard bodies for the development and nurturing of the GSM standard?

General Characteristics of GSM Technology

1) What is the GSM operating frequency?900 MHz. Uplink Frequency 890-915 MHZ. Downlink Frequency 935-960 MHz.

2) How many carriers are present and how many channels are there in each carrier?124 carriers. There are 8 channels in each carrier.

3) What type of modulation is used in GSM?Guassian Minimum Shift Keying (GMSK)

4) What is TDMA?TDMA is Time Division Multiple Access. Common Resource sharing is based on the division oftime. In GSM, TDMA is employed by allocating the same frequency carrier to 8 different userson 8 time-slots. A channel gets the whole spectrum for a certain amount of time.

5) What is FDMA?FDMA is Frequency Division Multiple Access. It is based on the division of the whole frequencyspectrum into smaller bands. GSM employs FDMA by dividing the available spectrumbandwidth of 25 MHz into 124 frequencies of 200 KHz bandwidth.

6) What is a Burst Period?


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18)What is SIM? What are the functions of SIM?SIM stands for Subscriber Identity Module. It holds all of a subscriber's personal informationand phone settings. In essence, it is the subscriber's authorization to use the network. It also'holds the phone number, personal security key and other data necessary for the handset tofunction. The card can be switched from phone to phone, letting the new phone receive all

calls to the subscriber's number.

GSM Air Interface

19)What is the interface between the MS and the BSS?Interface between the MS and the BSS is called Air Interface or Um Interface.

20)What are the two types of logical channels?Traffic channels and control channels.

21)What are the various types of control channels?Broadcast control channels, common control channels and dedicated control channels.

22)What are the various types of Broadcast Control Channels?Broadcast control channels (BCCH), Synchronization channels (SCH) and Frequency correctionchannels (FCCH).

23)What are the various types of Common Control Channels?Paging channel (PCH), Random Access channel (RACH) and Access Grant channel (AGCH).

24)What are the various types of Dedicated Control Channels?Stand-alone dedicated control channel (SDCCH), Slow associated control channel (SACCH) andFast associated control channel (FACCH).

25)What is the function of the FCCH?Frequency correction channel FCCH continuously transmits in downlink direction unmodulatedcarrier frequency for frequency correction of MS

26)What is the function of the SCH?SCH is used for frame synchronization of MS and contains information about TDMA frame no.and BSIC.

27)What is the function of the BCCH?BCCH broadcasts general information about the cell like neighbouring cells information, MStransmit power maximum on CCHs and local area identification.

28)What is the Function of the PCH?PCH is used to page the MS during mobile terminated call setup.Paging messages are sent to the area where the recipient MS is located.

29)What is the function of the RACH?RACH is used to transfer uplink messages in response to the call initiation request placed bythe MS or in response to a paging request or automatically as part of location update.


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30)What is the function of the SDCCH?SDCCH is a duplex pt-to-pt channel which is used for signaling. It carries all signaling betweenthe BTS and the MS when no TCH is allocated.It is used for service requests (e.g SMS), location updates, subscriber authentication, cipheringinitiation, equipment validation and assignment to a TCH.

31)What is the function of a FACCH?It is used as a main signaling link for the transmission of data e.g. handover commands.Required for every call setup and release.

FACCH is transmitted in the burst stealing mode by pre-empting a portion of thespeech/user data information bits during active call.

32)What are the different layers in GSM?Layer 1 Physical Layer

TDMA/FDMA radio interface on MS to BSS

E1 link on BTS to BSCMTP Layer1 on BSC to MSCLayer 2 Data Link Layer

LAPDm used on Air interfaceLAPD on BTS to BSCMTP Layer2 on BSC to MSCLayer 3RR Management SublayerMM SublayerCM SublayerBTSMSCCP & MTPBSSAPTCAP & MAP

33)What are the functions of the Radio Resource Management sub layer in GSM?Radio Resource Management sub layer in GSMmanages the Radio interface.It terminates at BSS from MS.

34)What is the function of the Mobility Management sub layer in GSM?Mobility Management sub layer in GSM terminates at MSC.Messages from or to MSC are relayed transparently from BSS.

35)What are the functions of the Communication Management sub layer in GSM?Communication Management sub layer in GSM contains entities that consist of CC includingcall-related supplementary services, SMS, and call independent supplementary services support(SS). It terminates at MSC.


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36)What are Service Primitives?37)What are the various types of handovers in GSM?

Intracell Handover is within same cell and between different carriers and it is controlled by theserving BSC.

Intercell Handover takes place between different cells belonging to the same BSS and iscontrolled by the serving BSC.Inter-BSS Handover takes place between cells belonging to the different BSSs and is controlledby serving MSC.Inter-MSC Handover takes place between cells belonging to the different MSCs and iscontrolled by the original MSC in charge of the call before handover.

38)What is idle mode?When the mobile station is active, in the coverage area of a cellular mobile network and nottransmitting/receiving speech or data, it is said to be in idle mode.

39)What are layer 2 and 3 messages?Layer 2 and layer 3 messages are protocols used to provide data link functions and networkaddressing and routing functions to GSM network components.

40)What are the functions of Layer 2 in GSM?Layer 2 in GSM that is data link layer provides a reliable dedicated signaling link between MSand Base station. Layer 2 protocol is based on the adaptation of ISDN link access procedure(LAPD-m) where D stands for ISDN data channel and m for modified. Standard LAPD is usedbetween BTS and BSC. Message Transfer Part (MTP) of SS7 is used to provide reliable datalink between BSC and MSC. Same protocol is used between MSCs and MSC-HLR/AUC.

41)What is BSIC?BSIC stands for Base Station Identity Code.

42)What is cell reselection/selection?Whenever a mobile station enters the coverage area of a new cell in idle mode, it is identifiedby the system as cell reselection.

43)What is IMSI/TMSI?IMSI stands for International Mobile Subscriber Identity. It is the unique network identity ofthe GSM subscriber. TMSI stands for Temporary Mobile Subscriber Identity. TMSI is thetemporary network identity of the subscriber in the visited Location Area.

44)What is IMSI attach /detach?IMSI attach/detach procedures mark the MS as attached/detached in the VLR and optionally inthe HLR on MS power up or down or on subscriber Identity Module (SIM) inserted or removed.

42) What is the structure of IMSI?

IMSI is a 15- digit or less number in which first 3 digits are mobile country code (MCC), next 2digits are Mobile network code (MNC) and rest are mobile subscriber identification number(MSIN).

45)What is MSISDN?


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Normal burst consists of 156.25 bits in 577 micro-second time duration in which there are 2segments of 3 Tail bits, 2 segments of 57 Encrypted data bits, 2 segments of 1 stealing bit,1segment of 26 Training sequence bits and 1 segment of 8.25 Guard Period bits.

GSM Protocol Architecture Between Network Elements

56)What is the Protocol architecture between the MS and the BTS?57)What is the function of BSSAP?

BSSAP is used to implement all procedures between the MSC and the BSS that requireinterpretation and processing of information related to single calls and resourcemanagement.

58)What is the function of SCCP?The signaling connection control part (SCCP) is an ITU standardized signaling system No.7(SS7) signaling protocol and covers the layer3 functions of the OSI model. It is used between amobile station and the servicing mobile-services switching center/visitor location register(MSC/VLR) to carry call control information (circuit related) and short messages (non-circuitrelated). It is also used between the MSC/VLR and the home location register (HLR) forinterrogation procedure or for the exchange of the subscriber data

59)What is the function of TCAP?The Transaction capabilities application part (TCAP) is an application signaling protocol (OSIlayer 7, application layer). TCAP supports the exchange of messages between users indifferent SS7 network nodes via common signaling channels. It provides a set of tools andservices in a connectionless environment that can be used by a distributed application at onenode to invoke or perform remote operations at another node.

60)What is the function of MAP?Within the public land mobile network, the mobile application part (MAP) uses the TCAP

services to update the mobile subscribers location information in the home location register(HLR)(a remote operation). After the mobile station has passed on its new location informationto the mobile services switching center (MSC), the latter updates its visitor location register(VLR) and sends a TCAP/MAP message containing this information to HLR.

61)What is LAPDm?The data link layer over the radio link ( connecting the MS to BTS) is based on a LAPD-likeprotocol called LAPDm (Link Access Protocol-modified) that has been modified for operationwithin the constraints set by the radio path. LAPDm uses no flags (no bit stuffing) for framedelimitation. Instead frame delimitation is done by the physical layer that defines the

transmission frame boundries.

62)What is SS7 signaling?SS7 is an ITU-T specified signaling standard for digital, processor controlled communicationnetworks which stands for Signaling system no.7. In SS7, signaling takes place on separate


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signaling links;so the bit rate of the circuits is exclusively for communication. The signalingfunctions in SS7 are distributed among the following parts:

i. Message Transfer Part (MTP)ii. User Part (UP)

In GSM, SS7 MTP and SCCP protocols are used to implement both data link and layer3transport functions for carrying call control and mobility management signaling messages on theBSS-MSC link.

63)What is the function of MTP?The Message Transfer Part (MTP) represents a user-neutral means of transport for messagesbetween the users in SS7 signaling. It is used by all user parts as a transport system formessage exchange. Messages to be transferred from one user part to another are given to themessage transfer part. The message transfer part ensures that the messages reach theaddressed user part in correct order without information loss, duplication or sequencealteration and without any bit errors. In GSM, on the terrestrial links connecting BSS to theMSC (A-interface), MTP of SS7 is used to provide OSI layer2 functions of reliable transport forsignaling messages, such as recovery from transmission errors through error detection andretransmissions.

GSM Network Planning & Optimization

64)What is the basic procedure for RF planning using RF planning tool in GSM?Planning ToolLoading of digital map data of the city on the planning tool, Model tuning for proper predictionon the tool, Nominal cell planning for the coverage, frequency planning and interference study.Final system planning.

65)What are the different types of antennas used in a GSM network?Antennas of different types based on antenna beamwidth and gain,In GSM we have space diversity antenna and cross polorised antenna.Omni antennas,

66)How do the power, orientation, beamwidth, tilt and height of the antenna affect the coverage?Power increases the coverage, Proper Orientation,Beamwidth and tilt improves the coverage ofthe planned area.Increase in antenna height improves the coverage.

67)What is EIRP? How is it calculated?Effective isotropic radiated power is the total o/p power of Base stationEIRP=BTS (O/P)power+Antenna gain-cablelosses-other (combiner)losses

68)What is frequency planning? Why is frequency reuse pattern used?Frequency planning is to be done for the gsm network for a given operator with

A set of GSM frequency band.Frequency reuse pattern is used for capacity planning.To minimize frequency interference problems.

69)What are all the patterns available? How is frequency planning done on planning tool?4/12 pattern.3/9 pattern .Automatic frequency planning can be done in planning tool.

70)What is co-channel interference and adjacent channel interference?The interference caused by using same channels in a network is called cochannel interference

and interference caused by


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GSM General Questions and Answers & Some Practical knowledge