Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs

Roaming: Basics

Dheeraj Kumar

12/03/2009

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs2

What is Roaming?

> Roaming is a general term in wireless telecommunications that refers to the extending of connectivity service in a location that is different from the home location where the service was registered.

> 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 when traveling outside the geographical coverage area of the home network, by means of using visited network.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs3

Types of Roaming

> National Roaming: If the visited network is in the same country as the home network, this is known as National Roaming.

> International Roaming: If the visited network is outside the home country, this is International Roaming (the term Global Roaming has also been used).

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs4

Roaming Agreements

> Roaming is technically supported by mobility management, authentication and billing procedures.

> The legal roaming business aspects negotiated between the roaming partners for billing of the services obtained are usually stipulated in so called Roaming Agreements.

> An agreement between two or more wireless telephone companies outlines the terms and conditions under which the participating companies will provide wireless service to each others subscribers.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs5

Roaming process

> When the mobile device is turned on or is transferred via a handover to the network, this new "visited" network sees the device, notices 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, maintenance of service is impossible, and service is denied by the visited network.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs6

Roaming process contd.

> The visited network contacts the home network and requests service information (including whether or not the mobile should be allowed to roam) about the roaming device using the IMSI number.

> If successful, the visited network begins to maintain a temporary subscriber record for the device. Likewise, the home network updates its information to indicate that the mobile is on the host network so that any information sent to that device can be correctly routed.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs7

HLR

> A Home Location Register (HLR) is a database of user (subscriber) information, i.e., customer profiles, used in mobile (cellular) networks.

> It is a key component of mobile networks such as GSM, TDMA, and CDMA networks. A HLR contains user information such as account information, account status, user preferences, features subscribed to by the user, user’s current location, etc.

> HLRs are used by the Mobile Switching Centers (MSCs) to originate and deliver arriving mobile calls.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs8

VLR

> A Visiting Location Register (VLR) is a database, similar to a HLR, which is used by the mobile network to temporarily hold profiles of roaming users (users outside their home area).

> This VLR data is based on the user information retrieved from a HLR.

> MSCs use a VLR to handle roaming users.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs9

How are the HLR and VLR used?

> Each mobile network has its own HLRs and VLRs. When a MSC detects a mobile user’s presence in the area covered by its network, it first checks a database to determine if the user is in his/her home area or is roaming, i.e., the user is a visitor. > User in Home Area: HLR has the necessary information for

initiating, terminating, or receiving a call.

> User is Roaming: VLR contacts the user’s HLR to get the necessary information to set up a temporary user profile.

> The user’s location is recorded in the HLR, and in case the user roaming, it is also recorded in the VLR.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs10

Making and Receiving a call

> The user wants to make a call: > User in Home Area: MSC contacts the HLR prior to setting up

the call.

> User is Roaming: MSC contacts the VLR prior to setting up the call.

> There is a call for the user (call goes to the home MSC): > User in Home Area: Home MSC delivers the call immediately.

> User is Roaming: Home MSC contacts the VLR to determine the appropriate switch in the roaming area to handle the arriving call and then transfers the call to the roaming area MSC.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs11

Billing

> The usage by a subscriber in a visited network is captured in a file called the TAP (Transferred Account Procedure) for GSM / CIBER (Cellular Intercarrier Billing Exchange Roamer) for CDMA, AMPS etc... file and is transferred to the home network.

> A TAP/CIBER file contains details of the calls made by the subscriber viz. location, calling party, called party, time of call and duration, etc.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs12

Billing contd.

> The TAP/CIBER files are rated as per the tariffs charged by the visited operator.

> The home operator then bills these calls to its subscribers and may charge a mark-up/tax applicable locally.

Information Security Level 2 – Sensitive © 2008 – Proprietary and Confidential Information of Amdocs

Thank you