Tech Scan

The roaming test: The key to success

The key to the success of roaming as it increases in importance, both for the business user and the business of operators, is a Test and Measurement system, which ensures quality of service across partner networks.

The ubiquitous mobile telephone is rapidly becoming a staple of modern life, and with this growing popularity it is only natural that subscriber usage outside the home network is on the increase as well.

While some mobile network operators have responded to this roaming boom by merging and creating enormous ‘no roaming charge’ networks, most operators are still dependent on their roaming agreements. Such operators face the daunting challenge of verifying the accurate and efficient service of their networks.

Roaming customers are extremely important because, unlike local customers, they can choose to change networks whenever they want.

In addition, the issues of providing security and simultaneously quick response time and quality of service pose a great challenge to network providers. Subscriber mobility requires ‘behind the scenes’ network management, while the signalling issues involved in roaming can have major effects on network performance.

NEED FOR TESTING

For the involved network operators, there are a number of technical and administrative issues that need to be resolved to achieve a satisfactory roaming scenario. The technical issues relate to operation and maintenance. For example, the databases containing subscribers’ billing information and their subscribed service list need to be consistent at all times. Similarly, the procedure for type approvals on mobile stations, especially on new units, may differ from country to country.

Administrative issues include the fact that network operators seek alliances to increase coverage. This leads to negotiations relating to roaming agreements. In addition, there have to be agreements on tariffs and billing procedures so that it is clear who pays, and for what. Finally, security is a major consideration.

Other issues relate to the public land mobile network, which has to interface with fixed networks and other public land mobile networks via gateway mobile switching centres and signalling control points to provide interoperability.

KEY ACTIVITY

Monitoring the network is a key activity. Observing the traffic load and being able to detect errors at an early stage are important factors in the prevention of network failures and eventual system breakdown. It is also important to be able to predict trends in the networks.

The need for testing and monitoring as an aid to roaming verification results from a number of factors:

• Network configuration changes resulting from the introduction of new services and the inclusion of new roaming partners
• Modifications in addressing and numbering data for routing the addition of new network elements such as mobile switching centres, home and visitor location registers, and equipment identification registers (EIRs) major software upgrade of SS7 signalling protocols.

Any changes on either side, whether on the ‘home’ public land mobile network and/or its roaming partner, generate additional testing requirements. Furthermore, periodic verification for the detection of problems and potential alarm errors are necessary preventative measures.

The International Roaming Expert Group (IREG) of the GSM Association is the body primarily responsible for international roaming issues, including network operator databases, signalling aspects, optimised routing and end-to-end functional capability testing.

Also included are service aspects related to roaming, covering specifications for Phase I and Phase II basic services, supplementary services, SMS, data and fax.

In order to guarantee international roaming operation, operators are seeking to implement the test cases as stipulated by the IREG. In particular, the IREG 24 specification is intended to confirm the capability for roaming and to sample the quality of service those GSM users will receive when roaming.

(T&M major Tektronix has the Net-7 monitoring system for SS7 and GSM networks).