International Roaming Issues
Created by: David
Crowe (Cellular Networking Perspectives Ltd.),
|TLDN conflict||Many systems send a TLDN to roaming partners in the national (usually North American) format (e.g. 10 digits, without a prefixed country code).||Preferred implementation is to use internationally formatted TLDNs, as per ANSI-41-D. If this is not possible, it is probably possible to send the full E.164 number and arrange for special translations (e.g. Mexican numbers can be distinguished based on 52 prefix and different length than national numbers).||2.4||1.4|
|ANI compatibility||When an international roamer user coming from a country
outside of the Numbering Zone 1 North American Numbering Plan Area
(NANPA) goes to a visited network and tries to make a call to the
PSTN or another interconnected network, the visited network may be
configured to send the IRM beginning with 0 or 1 to the PSTN or the
interconnected network, as the calling/billing number (ANI).
However, if the PSTN or the interconnected network is configured to reject calls from an invalid A number (and in most countries numbers beginning with 0 or 1 are not valid), the roamer calls will fail.
|When the roaming service between two parts is established for the first time some tests will be necessary to ensure that ANI compatibility will not be a problem. From the time of signing of the roaming agreement these issues should be considered, to include negotiations with the PSTN or the interconnected network to solve this incompatibility.||4.3||3.3|
|SID Uniqueness||A unique System Identification Number (SID) is required for the correct operation of roaming and billing.||A SID should be assigned by the national SID assignment authority. Carriers should verify that it conforms to the ranges defined by IFAST (www.ifast.org/SIDCountry.htm) and by TIA TSB29 for the country of operation of the carrier, and should avoid SID codes with known conflicts (www.ifast.org/SIDConflict.htm).||2.3||5|
|MIN Uniqueness||A unique Mobile Identification Number is required for international roaming.||Cellular and PCS systems within North America generally use the MDN assigned to a mobile as the MIN. Other systems (data systems within North America, and voice and data systems in other countries) should assign MIN codes from an IRM block assigned by IFAST.||2.2||3|
|IMSI||IMSI is the future identifier for cellular and PCS systems that currently use MIN.||Mobile phones or UIM cards may be programmed with an IMSI, in addition to a MIN. This is particularly valuable for systems that provide GSM roaming. Ensure that the IMSI is GSM-compatible. It may require a 2 digit MNC to be assigned. In North America, the assignment of a GSM-compatible MNC may require coordination between countries in order to support ITU-T E.214.||2.5||8|
|Emergency Number Dialing||People making an emergency call in a foreign country may dial the wrong code.||Ensure that Mobile Stations are programmed to set the
emergency call bit when the subscribers home
emergency digit string is dialed. This ensures that the call can
still be recognized as an emergency call, even when the wrong digit
string is dialed.
This system may fail if the home emergency string matches a non-emergency phone number in the roaming country.
|International Dialing||International roamers are less likely to make calls to their home country if they are confused by the national dialing plan.||Ensure that + code dialing is supported, and that customer education is provided. This means that international roamers do not need to know the local access number in order to make an international call.||3.1||10|
|SS7 Routing||ANSI-41 generally relies on point code routing to route messages between a home and serving system. Point code routing is only valid within a national network.||Obtain an ANSI SS7 point code for your network, and subscribe to a service that either provides ANSI SS7 connectivity, or that can convert to ANSI SS7, including converting your national point code to its ANSI equivalent.||4.2||18|
|Network Selection||The roamer has just arrived in a foreign country, and
turned on their cellular phone and no network is selected. This is a
very common situation, often for the following reasons:
IRDBs (Intelligent Roamer Data Bases) and PRL (Preferred Roaming Lists) should be sufficiently large, and should not deny service because a system is not in the IRDB. IRDBs should be updated frequently over the air interface using OTA (over-the-air activation).
|Validation Failures||The telephone selects a suitable network, but the
subscriber cannot make calls. Possible reasons are:
||Carriers should strive to arrange for roaming based on common travel patterns to maximize revenues from international roaming and customer satisfaction. Carriers should educate visitors on the availability of international roaming, e.g. through advertisements targeted at tourists, businessmen and other types of visitors.||4||N/A|
|Accessing Customer Care||The subscriber cannot access the customer care centre,
often for one of the following reasons:
||*611 should be implemented, and at least minimal recorded information should be provided in languages that are commonly used by international roamers.||8.2||10|
|Services||Roamers may have trouble accessing services, often for
one of the following reasons:
||Carriers should ensure that feature codes dialed by
roamers are transmitted back to the home system (HLR) for analysis
via ANSI41 signaling.
Expansion of digital coverage would improve the number and quality of services provided by ANSI41 networks.
Calling number service should be tested to ensure that the correct number is presented. Numbers received from the PSTN may require editing by the system before presentation to user's mobiles.
|Fraud||Authentication is not generally implemented. The lack of authentication, mainly in analog networks, is a source of cloning fraud, and obliges carriers to implement a very strict fraud control policy which significantly restricts the services (such as long distance calling) available to international roamers.||Authentication should be implemented. This increases the likelihood of being able to sign roamer agreements, protects carriers against fraud and may reduce the cost of international roaming services to consumers, may reducing the amount of revenue that must be set aside for compensating for fraudulent use.||5||N/A|