Verifying International Roaming

Roaming pertains to using mobile services

anywhere the subscriber goes. For roaming to other countries, the subscriber needs only

subscribe to the international roaming service. He uses the same Mobile Equipment (ME) to

access the services of different networks on a regional, national, and/or an international

level.

color="#FFFFFF">LMN Architecture

width="373" height="220" alt="This diagram shows a mobile network with all its network components. The red boxes show the relevant interface, which is "> src="roaming2.gif" width="373" height="220" alt="This diagram shows a simplified network configuration with only a few network components relevant for international roaming testing. The System Under Test (SUT) is the gateway MSC/VLR and the roaming partner’s PLMN. Testers simulate the interfaces connected to SUT.">

Subscriber Identification Module (SIM)

roaming occurs in cases where the handset is incompatible due to difference in radio

technology. The subscriber takes his SIM card containing his personal data and inserts it

in a rented ME, which is able to transmit and receive on the network he or she is roaming

in. An example is the usage of different frequency bandwidth like GSM 900, DCS/PCN also

known as GSM1800, PCS 1900 in the US. Of course, it is also possible to get a dual-band MS

for DECT-GSM, AMPS-GSM, and GSM-PCN. Later on, multi-mode would be feasible.

Simply equipped with a single number and a

SIM card, the subscriber unlocks the world of telecommunication at his disposal. The

object of identification is focused on the SIM card. COLOR="#016077">

GSM MoU

The GSM Memorandum of Understanding (MoU)

Association represents the interests of administrative, regulatory network operators. Its

main responsibility is to forge a commercial agreement between potential operators who

would commit themselves to implementing standards in a given time frame to upkeep global

GSM services.

One of the working groups, the

International Roaming Expert Group (IREG) is primarily responsible for international

roaming issues. These documents describe the following aspects: SIZE="1">

• Network operator
  
  databases

• SCCP signaling aspects,
  
  optimized routing

• End-to-end functional
  
  capability test

• Included are also services
  
  aspects when roaming.

The specification is for Phase I and Phase

II basic services, supplementary services, SMS, data, and fax. COLOR="#016077">

Testing Needs

In order to guarantee correct

international roaming operation, one solution would be to implement test cases as

stipulated by IREG.

The needs of testing arise from the

following situations:

• Network configuration changes
  
  due to introduction of new services and inclusion of new roaming partners

• Modifications in addressing and
  
  numbering data for routing

• Addition of new network
  
  elements such as MSC, VLR, HLR, EIR, etc.

• Major SW upgrade of SS#7
  
  signalling on the protocols like SCCP, MAP, and ISUP.

Any changes on either side, the home

Public Land Mobile Network (PLMN) and/or its roaming partner mean renewed testing.

Furthermore, periodic verification for detection of problems and potential alarm errors

are necessary preventive measures. The most obvious testing method is manual. This means

to have real mobile phones with international SIMs and fixed telephone lines and then

literally making calls in all possible test configurations. The current testing needs

calls for more automated testing solutions.

The better solution is to stimulate some

parts of the network, i.e., replacing the handphones and telephones with a system

generating such calls.

Features of the IR Testing Tool SIZE="2" COLOR="#000000">

The air interface is excluded from the

test environment. Therefore, the BSS part of the network is simulated. This prevents air

interface errors and allows re-runs of tests to reproduce errors detected. SIZE="2">

alt="Viraj Pradhan, is business manager (telecom), Tektronix India Ltd" align="right"

hspace="6" vspace="6">Since BSC and MSC is based on the SS#7

network, the underlying SS#7 layers of SCCP must also be tested. MAP is tested, as it is

the protocol used in MSC procedures. Included are also supplementary services like call

forwarding and call barring.

A list of roaming PLMNs is available. At

least three subscriber profiles of a PLMN roaming partner are stored in a configuration

file.

The execution of the test cases is

automatic with an unlimited number of roaming partners. Selective test cases and roaming

partners are possible. The starting of the tests can be pre-scheduled at low traffic time,

e.g., at night. The system stores the data of each roaming partner. During live testing,

it can be left unattended. The signalling data together with the test results are stored

on disk for later review.

The testing time for each roaming partner

is greatly reduced. Thus, the network operator can afford to run the test cases repeatedly

any time.