International roaming offers a great opportunity for wireless service providers to improve revenues and generate more profits. They are continuously exploring new ways to attract more roamers to their networks. Generally, roamers in a visited network register automatically, as most mobile phones are set to automatic network selection ON as a default. Mobile phones in the automatic network selection mode choose a network with the best signal strength at that particular point and place. Reselection may also happen automatically as a roamer moves from one area to another. In general, roamers are not loyal to any particular network while visiting outside their own network domain. They may switch to any network if they like, and if there is any reason to do so. The question is how to attract them to manually select a particular network.
The cost of usage, services, discounts, etc. may surely attract more roamers to switch to a particular network. A promotion has to be carefully planned to offset revenue losses due to discounts with the acquisition of additional roamers. The majority of roamers are business users, and they may not really worry too much about the cost. This approach, therefore, has its own limitations.
The brand awareness, strategic relationship with partners, and alliances with service providers serving different geographic areas are influencing factors too. Aggressive and sound marketing strategies are required to build an image to gain roamers’ favor.
The quality of service is a very important factor to influence a roamer to select a particular network. Most roamers are business customers; they rely on roaming services to conduct their businesses. They are very particular about QoS offered and switch easily, if not satisfied.
Another important factor that may influence roamers to be loyal to a particular network are the value-added services offered. This section focuses on the common value-added services generally offered by many wireless service providers. The services listed in this topic are not exhaustive.
Figure 12-1 shows two PLMNs, i.e., PLMN A and PLMN C in country x and PLMN C in country y. When a PLMN A subscriber (MS A) dials to call a subscriber in PLMN B (MS B), the originating switch analyzes the dialed digits and routes the call to PLMN B using the international network. The GMSC at PLMN B queries the HLR for routing information. The HLR checks for subscriber data to identify the current serving MSC/VLR, which is a VLR in PLMN C in this example. The HLR requests the VLR to send a routing number. The VLR assigns a routing number and sends it to the HLR in a response message. The HLR passes back the MSRN to the GMSC, which routes the call to PLMN C using an international network. This is surely not an efficient routing, as two international call legs are required even though both calling and called parties are currently in the same country. The calling party pays international call charges for the originating leg and the called party pays for the international terminating leg plus a roaming surcharge.
Many wireless service providers are implementing optimal routing (OR) as a value-added service to attract and retain roamers in their network. Optimal routing allows a call to be routed directly from the originating MSC to the MSC currently serving the roamer. This way both the international call legs can be avoided, saving cost. Part of the cost saving can be passed to the roamer and the caller. Optimal routing is also referred to as local direct dial (LDD) because it reduces international call legs to a single local call.
Depending upon implementation, optimal routing can be applied to the following call scenarios.
■ Inbound roamer calling another inbound roamer, currently roaming in the same network.
■ Inbound roamer calling another inbound roamer, currently roaming in a different network but in same country.
■ A local subscriber calling an inbound roamer in the same network. 12.1.1 Implementation
Wireless service providers educate their own subscribers and inbound roamers about optimal routing, its benefits, and methods to invoke this service. For the local subscribers, a normal marketing mechanism is used. The only way to inform inbound roamers is to send SMS on their arrival or registration in the PLMN or by advertising at entry and other prominent places.
Figure 12-1 Call routing to a roamer.
Usually, to invoke this service, an access code is used followed by the regular B party international number. All the OR/LDD calls are then routed to a special platform (let us call it the OR platform for explanation purposes), which enables optimal routing.
There could be several different ways to implement OR in the network. The three important requirements for any OR implementation are:
1. Acquire, maintain, and manage the data for all inbound roamers currently in the network in real time.
2. Analysis of the B party number to check if it is an inbound roamer currently in a network implementing OR or in any other PLMN within the same country, where the call could be routed locally.
3. If OR is possible, then acquire MSRN from the serving MSC to route the call locally.
One of the efficient ways to build roamers’ information in real time is to monitor MAP transactions between the HPLMN and VPLMNs. Figure 12-2 shows a typical implementation of a probe-based solution to monitor the transaction nonintrusively.
Figure 12-2 Creating roamer information.
It consists of acquisition hardware and the necessary processing capabilities to extract the signaling messages from the CCS7 links carrying MAP traffic to partner networks. The key advantages of this overlay solution approach are:
■ It is nonintrusive
■ No additional processing is required on the network side
■ It operates in real time
■ It is independent of make and version of the network elements involved
■ It is scalable
The key roaming procedures, such as update location, insert subscriber data, authentication, and cancel location messages provide all the critical information to build the database for OR purposes. For example, by decoding a UL/ISD procedure, the following parameters can be extracted.
■ Subscriber’s IMSI
■ MSISDN
■ HLR address
■ Serving MSC/VLR address
■ Timestamp for first and subsequent UL
Figure 12-3 shows a typical implementation. A fixed line subscriber, a local mobile subscriber, or a roamer dials the OR access code followed by a B party number. The B party number is the international number of a roamer currently roaming in PLMN B. The local originating switch or originating MSC analyzes the OR access code and passes the ISUP IAM to the OR platform. The OR platform checks if the B party is currently roaming in PLMN B by querying the roamer database. If no, the OR platform releases the call after feeding an appropriate announcement to the calling party or processes the call in the normal nonoptimal way. If yes, it extracts the roamer information from the database, using MSISDN as the key. The information includes roamer IMSI, last known VLR, etc.
The OR platform then invokes the MAP provide roaming number procedure with the serving VLR to get the MSRN. Once the MSRN is available, the OR platform routes the call to the serving MSC.
In the above implementation, it is not possible to route the call if the roamer moves to another PLMN in the same country. Figure 12-4 shows a minor variation to overcome this problem. In this case, the OR platform invokes the MAP send routing information (SRI) procedure with the HPLMN HLR to get routing information. The HLR, on receiving the SRI request, invokes the MAP provide number procedure with the serving VLR.
Figure 12-3 Optimal routing implementation 1.
Figure 12-4 Optimal routing implementation 1.
The serving VLR assigns a temporary identity to the roamer, i.e., MSRN, for call routing purposes and sends the assigned MSRN to the HLR in its response message. On receiving the MSRN, the OR platform analyzes to check if the roamer is currently in another PLMN within the same country. If yes, it routes the call as a local interconnect call.
The typical implementations discussed in this section are just for illustration purposes. No attempt is made to cover all the functionalities required to build a system for commercial purposes. More intelligent solutions can be deployed by using IN and CAMEL capabilities.
