31) What is the function of the SDCCH?
The SDCCH carries all signaling between the BTS and the MS when no TCH is allocated. It is used for service requests (eg. SMS), location updates, subscriber authentication, ciphering, initiation, equipment validation and assignment to a TCH. 32) Draw and explain the protocol layer between the Mobile Station and the BTS?
33) What are the functions of the Radio resource Management Layer in GSM?
The main function of the Radio resource management layer is to establish and release stable connections between mobile stations and the MSC for the duration of the call and to maintain the connection despite user movements.
34) What are the functions of the Mobility Management sub layer in GSM?
The mobility Management layer manages the location updating, handovers, and registration procedures. The machines concerned with mobility management are mainly the MS, the HLR and VLR. The security function is performed by the AuC.
35) What are the functions of the Communications Management sub layer in GSM?
Communications Management sub layer terminates at the MSC and contains entities that currently consist of CC including call-related supplementary services, SMS, and call independent supplementary services support (SS).
36) What is Idle Mode?
A mobile is said to be in idle mode when it is active (powered on) but is not allocated any traffic channel. In the idle mode the MS listens to broadcast channels in order to intercept paging messages, monitor the radio environment in order to evaluate its quality and choose the most suitable base station.
38) What is Base Station Identity Code?
The BSIC is a color code which the MSs use to be able to discriminate between the cells transmitting their beacon channels on the same frequency. Many cells bear the same BSIC and it is common for neighboring cells to have the same BSIC.
39) What is IMSI/TMSI?
Every Subscriber is assigned an IMSI associated with its SIM card. The IMSI is known only to the subscriber and is kept internal and transmitted as rarely as possible for security reasons keeping the identity of the subscriber confidential (in case some one is listening on the air interface). The IMSI consists of Mobile Country code (MCC) which identifies home country of the subscriber, the Mobile Network Code (MNC) which identifies the PLMN of the subscriber and the Mobile Station Identification Number (MSIN) which identifies the subscriber within a PLMN.
`The MSC/VLR allocates a TMSI temporarily to a subscriber present in the geographical area served by the MSC/VLR. Only the VLR stores the TMSI not the HLR. The TMSI serves to identify the MS when it needs to communicate with the network. It is used instead of the IMSI to avoid transmitting the IMSI. Several MSC/VLR’s can use the same TMSI
40) What is IMSI attach /Detach?
When a MS station is switched off(or when the SIM is removed by the user), call towards that MS station cannot be completed. Hence important resources are consumed for nothing. To alleviate this load, the IMSI attach and IMSI detach procedure is used. The subscribers record in the MSC/VLR contains a binary information indicating whether or not it is useful to try to complete the call toward the subscriber. The IMSI detach procedure will set the binary bit to “ Not Useful To Try” whereas the IMSI attach procedure will do the reverse.
41) What is the structure of IMSI?
3 Digits
MCC
2 Digits
MNC
MSIN
Mobile Country
Code
Mobile Network
Code
Mobile Subscriber Identification
Number
42) What is MSISDN?
Mobile Station ISDN Number This is the subscriber phone number. It is the identity of the subscriber known by the external world. It is the number dialed when someone needs to call the mobile subscriber. The MSISDN consists of the Country Code (CC), National Destination Code (NDC) and Subscriber Number.
43) What is Mobile Station Roaming Number (MSRN)?
The MSRN is used to identify a subscriber when routing the call from the GMSC to the visited MSC for mobile terminating calls.. It is allocated by the MSC/VLR currently serving the subscriber on a call basis (temporary assignment)
44) What is discontinuous Reception?
For the sake of battery consumption in MS, it is important to minimize the amount of information the MS has to receive, demodulate and analyze when it is in idle mode. Therefore the downlink common control channel is divided into several paging sub channels and all messages pertaining to a given
subscriber are sent on the same sub channel. Such a scheme allows the MS to restrict the monitoring of paging messages to their own paging sub channel, thereby increasing the life time of the battery at the expense of a small increase in the delay for the setting up of incoming calls.
45) What is Discontinuous Transmission?
Discontinuous transmission (DTX) is a method that takes advantage of the fact that a person speaks less that 40 percent of the time in normal conversation by turning the transmitter off during silence periods. Power is conserved at the mobile unit by appling Discontinuous Transmission. Whether DTX should be applied or not is decide by the MSC while its execution is controlled by the BSC.
46) What is Location Updating?
When a MS moves to a new location area or is switched on in a new location area, it must register with the network to indicate its current location. A location update message is sent to the new MSC/VLR, which records the location area information, and then sends the location information to the subscriber’s HLR
47) What are the various types of bursts in GSM?
Normal Burst
Synchronization Burst
Dummy Burst
Frequency Synchronization Burst.
49) Draw and Explain the Protocol architecture of the GSM Network? RR Management sub layer
Manages the Radio Interface
Terminates at BSS from MS MM sub Layer
Terminated at MSC
Messages from or to the MSC are relayed transparently from BSS Communications Management sub Layer
Terminates at MSC
Contains entities that consist of CC including call related supplementary services, SMS and call independent Supplementary Services (SS) support. TCAP and MAP
These are the interfaces between the MSC and HLR/VLR BSSAP
Used to implement all procedures between the MSC and the BSS that require interpretation and processing of information related to single calls and resource management. SCCP and MTP
SCCP and MTP protocols are used to implement the data link layer and layer 3 transport functions for carrying the call control and mobility management signaling message son the BSS_MSC link.
GSM Network Planning & Optimization
1) What is the basic procedure for RF planning using RF planning tool in GSM?
Planning Tool
Loading of digital map data of the city on the planning tool, Model tuning for proper prediction on the tool ,Nominal cell planning for the coverage ,frequency planning and interference study.
Final system planning.
2)
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,
3) 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 of the planned area. Increase in antenna height improves the coverage.
4)
What is EIRP? How is it calculated?
Effective isotropic radiated power is the total o/p power of Base station
EIRP=BTS (O/P) power+Antenna gain-cablelosses-other (combiner)losses
5)
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.
6) 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.
7)
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 adjacent channels of is called adjacent channel interference.
8)
How do you minimize co-channel interference?
proper frequency planning and proper reuse pattern.
9)
How do you minimize adjacent channel interference?
Proper frequency planning.
10) What is model tuning? Why is it used? Okarama Hatta model?
Model tuning is done for any planning tool to obtain proper prediction expected from planning tool as there will be difference in actual and predicted data for planning tool. One of the model is Okarama Hatta Hatta Model is used which considers the signal propagation losses.
11) What is link Budget Analysis used for in GSM?
Link budget analysis is used for the path balance between both uplink (Transmitter) Downlink (Receiver) part of the network.
12) How is path loss taken into calculation?
This is the total path loss occurred due to multipath propagation of the signal between transmitted signal and the received signal level.
13) What is capacity planning?
This is process of increasing traffic by adding Trxs traffic channels and proper use of frequency reuse pattern. Addition of BTSs
14) How is site selection done for planning and site acquisition?
After nominal cell planning with the geographical coordinates identifying best site candidate in a geographical area is the process of site selection.
15) What is optimization? What are the tools used for optimization?
Once GSM network is integrated in order to achieve proper planning predictionRF parameters Optimization is done. Drive test tool,Planning tool and Post processing tools are Used for optimization.
16) How do we use the above antenna patterns for optimization?
Proper antenna orientation and tilts and antenna types can be used for optimizing network.
17) How do we handle poor C/I, C/A, handover problems and blocking?
Checking proper neighbor list, changing frequency planning and proper no of radio channels availability.
18) What is system information?
System information is from BTS sent to Mobile for the idle mode and dedicated mode of the call for call management.
19) What is bench marking in GSM?
Bench Marking used for comparing performance of different network for quality and call performance parameters.
20) What is Erlang table?
This is the table for calculating Traffic in erlang for no of channels.
21) What is grade of service?
Grade of service is the blocking for the given traffic channels.
22) How do you optimize a network using OMCR performance data?
Proper increase in call success, and increase in handover success performance and drop call reduction performance.
23) What is daily report and traffic?
This is the report obtained in OMC for the performce of all BTS about traffic .
24) What is cell_reselect_hysterisis?
This is process of handover done by mobile in idle mode from selected cell to another cell.
25) What is path loss criterion (C1)? How is it calculated?
This is the signal strength measured in idle mode for selecting best serving channel.
