Roaming

Roaming is one of the fundamental mobility management procedures of all cellular networks. Roaming is defined as the ability for a cellular customer to automatically make and receive voice calls, send and receive data, or access other services, including home data services, when travelling outside coverage area of the home network, by means of using a visited network. This can be done by using a communication terminal or else just by using the subscriber identity in the visited network.

WHAT IS ICRIf a Service Provider does not have adequate coverage in a circle (Eg. Mumbai) then it may tie-up with some other operator within the same circle which would allow his subscribers to use other operator’s network in the areas of low coverage. Thus a subscriber of operator 'A' would be latched onto the network of operator 'B' within the same circle. This is INTRA CIRCLE ROAMING.

WHY ICR

All operators are not having 3G license in all circles but still they want to provide 3G services to its customers. So Roaming agreements - both inter and intra circle - are the norm in the Indian telecom industry since they help a service provider offer seamless service to its customers. Also, In an effort to reduce cost and offer Pan India 3G service, all operators have started sharing the 3G infrastructure on the ICR concept to allow 3G services to its customers. (For the operators which do not have 3G spectrum in that particular circle).

NOTE:-ICR concept is applicable for both 2G and 3G.

For example:- Idea has entered into an intra-circle roaming arrangement with Vodafone for introducing 3G services in Delhi and Kolkata circles while Bharti Airtel will partner Idea in providing 3G services in Karnataka - primarily in Bangalore and Mysore. Similarly, in Himachal Pradesh Aircel is going to launch 3G service with an INTRA CIRCLE ROAMING agreement with Reliance.

In Himachal, Reliance has both 2G and 3G license where as Aircel has only 2G license. But still Aircel wants to provide 3G service. So under ICR concept, Aircel 3G subscribers will latch onto Reliance 3G Network.

Configuration to be done in MSC for Aircel ICR

In Himachal, Aircel only wants to use Reliance 3G network. It means we need to change some configuration in Reliance as well as in Aircel end so that their customers can latch onto Reliance 3G Networks only.

HOW LOCATION UPDATE WILL HAPPEN

When the Aircel mobile device is turned on or is transferred via a handover to the Reliance network, than, the Reliance network sees that it is not registered with its own system, and attempts to identify its home network. If there is no roaming agreement between the two networks, than service is denied by the visited (i.e. Reliance) network.

But, as there is a roaming agreement among the two Networks, when Aircel’s subscriber sends a location update request to Reliance MSC, the Reliance MSC is further required to send the location

update request message to the Aircel HLR to request the subscriber data. On receiving request HLR will check whether subscriber is allowed to roam in reliance VLR or not. If allowed, HLR will send a location update accept message and also sends a copy of subscriber data to local VLR.

Definition to be done for Location update

1. First of all, definition to be done in Reliance MSC, so that Aircel 3G subscriber can update Location in our n/w. For that we have to define IMSI of Aircel in IMSI GT table.

ADD IMSIGT: MCCMNC=K'404351270002061, CCNDC=K'9198570, MNNAME="AIRCEL_ICR_TEST";(Note-It is recommended that for testing purpose, only particular IMSI of test number should be defined instead of defining generic IMSI)

The above definition can be checked by running:-LST IMSIGT: MCCMNC=K'404351270002061;

In this table IMSI 404351270002061 is converted to MSISDN prefix-9198570. The type of GT used here is MSIDN. (MSISDN=CC+NDC+SN). So on the basis of this GT, the IMSI 404351270002061 is converted to 919857070002061.The local VLR queries the IMSI GT Translation Information table to obtain the GT address of the HLR.

For that we need to define GT address of the HLR in SCCP Global Title table.

ADD SCCPGT: GTNM="AIRCEL_HP_HLR", NI=NATB, GTI=GT4, ADDR=K'919857099001, RESULTT=STP1, SPC="4a2", GTGNM="GTG-0";

The above definition can be viewed by running command: - LST SCCPGT: GTNM="AIRCEL_HP_HLR", LTP=LOCAL;

After this, AIRCEL subscriber can successfully update location (2G and 3G both) in our VLR. But we have to restrict AIRCEL subscriber to latch on to our 2G network. For that we need to make following changes in our MSC.

1. To enable Enhanced roaming Restriction we need to set:

SET MAPACCFG: IFUSROAMR=YES;

By using this command system will perform enhanced roaming restriction analysis upon a location update request.

2. To block Aircel’s subscribers to latch on Reliance 2G network.

MOD LAIGCI: GCI="40418EA9D", IFROAMANA=YES, LOCNONAME="2G-ICR-BLOCK";

Here, we need to set Perform roaming analysis (i.e. IFROAMANA) parameter “YES”. Also we need to add Location number name (LOCNONAME="2G-ICR-BLOCK"). On the basis of this definition, system will perform enhanced roaming restriction, when a location update request from a location area (i.e. 40418EA9D) is received.

The above definition can be viewed by running command:-

LST LAIGCI: GCI="40418EA9D", QR=ALL;

3. When enhanced roaming restriction parameter is set to “YES”, the relevant table query flow is as follows:

a) System will look for Location number name (LOCNONAME="2G-ICR-BLOCK"). b) On the basis of LOCNONAME system will look for Location number group name. So we need

to define Location group name also. This is to be done by running following command:-

ADD LOCGRP: LOCNONAME="2G-ICR-BLOCK", LOCGRPNAME="2G-ICR-BLOCK";

Here Location number name (LOCNONAME) is 2G-ICR-BLOCK which we have already defined in LAIGCI and Location Group name (LOCGRPNAME) is 2G-ICR-BLOCK.

c) Now we have to add Roaming restriction group. It defines the way used to classify the roaming-restricted subscriber groups. The roaming-restricted subscriber groups can be classified by subscriber numbers (MSISDN or IMSI) or the type of the roaming subscriber. For Aircel 3G ICR we restrict the subscribers on the bases of IMSI. Also a user group name is added here, and this user group is mapped to Location group Name (i.e. 2G-ICR-BLOCK). This is to be done by running following command:-

ADD ROAMRESTGRP: SERVICETYPE=ENROAMRST, RSTRIBY=IMSI, BEGINNUM=K'404351270002061, ENDNUM=K'404351270002061, UGNAME="3G-ICR-AIRCEL";

Here UGNAME="3G-ICR-AIRCEL" is user group name. This can be viewed by running following command.

d) Now a subscriber group roaming authority data is to be added to the configuration database. This will decide whether the specified subscriber group (UGNAME="3G-ICR-AIRCEL") is restricted to roam in the specified location area group (i.e. LOCGRPNAME="2G-ICR-BLOCK"). The ROAMREST parameter will decide whether roaming is allowed or restricted.

ADD USROAMRT: UGNAME="3G-ICR-AIRCEL", LOCGRPNAME="2G-ICR-BLOCK", ROAMREST=YES;

After completion of these definitions in MSOFTX3000, AIRCEL subscriber will only be allowed to latch on Reliance 3G network and restricted to Reliance 2G network.

3. After successful Location update, network name (i.e. Aircel) of the operator to which subscriber belongs to has to be displayed on the subscriber handset This can be done by running following command:-

ADD USRNTWK: IMSIPFX=K'40435, CELLGROUPNAME="ALL", TYPE=BIT7, NETWORKFULLNAME7BIT="Aircel 3G ", NETWORKSHORTNAME7BIT="Aircel 3G ";

After this definition, system will send a MM_INFORMATION message to BSS after successful location update. This message will contain the network name (i.e. Aircel 3G) and time zone.

NOTE : - We also need to check whether we have the license to send network full name in MM_INFORMATION message or not. This can be checked by running command:-

DSP LICENSE: DT=BAM;

The following output is displayed, and NITZ function should be equal to 1.

Now, as AIRCEL subscriber has successfully latched on to our 3G network, so for call routing, we have to make certain definitions in our MSC.

FOR MO/MT calls:-

1) We have to create a new TG for only AIRCEL ICR subscribers.2) In IMSIBIT analysis table we will change the DNSET=0 to NEW DNSET=15 for MO calls

originated by Aircel IMSI.

ADD IMSIBITANA: CSCNAME="ALL", IMSI=K'40435, CALLCAT=CC_ALL, PFX=K'EEEEEEEE, CLDNCN="DEFAULT", CLINCN="DEFAULT", FPFLG=FALSE, NP=15, NRSSNAME="0";

3) Now, some generic numbers will be defined in CNACLD table with DN set 10 and will be routed to new Aircel-Route (for ICR only- ARCLSMLRGM1T1B)