January 12, 2016

Flavours of Roaming Steering; a comparisons of taste and texture between OTA, Signalling and Hybrid Steering Solutions


During the many discussions I have had with different operators about Steering of Roaming, one issue which always comes up, and is a source some controversy, debate and confusion, is the different approaches used in Roam Steering solutions. The controversy revolves around which is 1) better, 2) more accurate and 3) most cost effective. In this I will share some information about:

  • Over the Air Roam Steering
  • Signalling Message Based Roam Steering
  • Hybrid Roam Steering

Over The Air Roaming Steering

Over The Air Steering of Roaming solutions (sometimes referred to as SIM based steering) operate on a preferred network list contained in the subscriber SIM card. This list needs to be regularly updated to reflect roaming agreements from the perspective of the home network operator. Updating of the SIM cards is accomplished by sending messages to the handset with the updated list.

The preferred network list is typically read during the handset power up cycle, which can be a detriment to this type of solution. Operators and OTA providers have overcome this limitation somewhat through the use of a “Refresh” OTA Command, which reloads the data from the SIM into handset memory. However, there can be issues across different handset vendors, which render this approach ineffective.

Another issue with the OTA roam steering is that the roaming subscriber must be first registered on a network to receive the SIM card update messages. If the subscriber is registered to a non-preferred network prior to receiving the update messages there can be an associated loss of revenues to the home network provider.

Some OTA steering systems can lack the flexibility to anything other than very basic steering. That is, for each subscriber in a country, it just sends the same list to everyone. This does not allow for the possibility of handling multiple discount agreements in a single country. To be effective, a system must keep track of how many subscribers are in each country and network at a given time. Systems that do not do this are quite limited in what value they can deliver.

Finally, an OTA system depends on another network to ensure that the OTA update message reaches its destination. If there is a failure in this network, or if the network blocks the message, then OTA steering will be rendered ineffective.


Good customer experience, no message blocking results in no loss of service.
Effective against an anti-steering system doing message resubmission or roam retention.
Can reduce volume of messaging on the home network as there are no Update Location messages being retransmitted, as would be the case with Signalling Based steering.
Relies on the handset to make a decision. This is a benefit because only the handset knows the true picture of which networks are available.


Some handsets may not support OTA/Refresh commands
Possible period of time roaming in a non-preferred network before an OTA update can be sent
Sometimes lacks flexibility for achieving more complex roaming targets (for example, multiple discount agreements in a country)
Any issues with delivery of the OTA message will render OTA steering ineffective

Signalling Based Steering of Roaming

Message based steering of roaming systems use the messages and protocol delivery system within both the visited and home networks. A roam steering solution is placed in the home network or an intermediate network such as a Hub Provider that delivers services to the home network. In this scenario the home network receives Location Update messages from the Visited network.

If these messages are deemed to be from a preferred network according to the configured rules, the Update Location message is allowed through the system to the Home Location Register (HLR), and the message flow will follow normal message routing criteria, thereby granting the subscriber service with the preferred network.

If the message is deemed to not be from a preferred network then the message will be rejected. This means that the Update Location message is dropped from the network. A negative acknowledgement with a configurable error code can normally be sent back to the requesting network. The handset will typically retry the same network a number of times, and the system will reject each of these. Eventually, the subscriber should try and connect to a preferred network, and this will be allowed by the steering system. Typically, there will be exceptional cases which will allow the subscriber service on a non-preferred network. These cases can include manual selection, maximum number of rejects per day etc. to ensure the subscriber is not left without service.

Subscriber spends no time roaming in a non-preferred network
Usually flexible when configuring more complex roaming targets, e.g. multiple roaming agreements in a single country
Does not require any extra message flows, i.e. does not need an OTA server to send OTA updates to the handset.


Poor subscriber experience when there is little or no coverage on the preferred network(s). At times, it can take many minutes for a subscriber to get service in a country
Exceptional cases (e.g. manual selection) can be spoofed by an Anti-Steering of Roaming system resubmitting Update Location messages.
Increased signalling load due to Update Location retransmissions.
These systems essentially guess what is going on in the roaming country. Unlike in OTA Steering, where the handset knows the full roaming picture around it, a Message Based steering solution is essentially guessing this picture, and may reject attach attempts where in reality the preferred network has no coverage, thereby creating a poor roaming experience for absolutely no reward.

Hybrid Steering of Roaming

The combination of both Over the Air Roam Steering and Message Based Roam Steering provides network operators with the best possible solution. The goal of a hybrid steering solution is to take the best of both worlds. This solution provides the advantages of each and overcomes their inherent disadvantages.

One of the disadvantages mentioned for OTA Steering is that it is ineffective for certain handsets or subscribers. Once this set of subscribers can be identified, then the hybrid system can choose to do Signalling Based steering for these subscribers only, and continue to provide OTA based steering for subscribers in which it can be effective.

Another OTA disadvantage is that it allows a subscriber to roam for a certain period of time in a non-preferred network. With a hybrid solution, it can be configured to use Signalling Based steering first to ensure the subscriber does not get to a non-preferred network. Then when the subscriber attaches to the preferred network, an OTA update can be pushed to keep them there.

In OTA systems, it is possible for a network to block messaging including OTA messages. If this is detected, a hybrid steering system can switch from OTA steering to Message Based steering for that network to overcome this issue.

In a hybrid system, the ideal situation is to use OTA steering where possible, and to cover any weaknesses in OTA with Signalling Based steering, as mentioned above. It is essential that a hybrid system is flexible enough so that different approaches can be taken for different subscriber groups, in different countries and in different networks. With this flexibility, the right balance can be struck between the following factors:

  • Subscriber’s roaming experience
  • Signalling load
  • Anti-steering resistance
  • Accuracy
  • Flexibility in setting targets (e.g. multiple preferred networks in a country)


In the hyper competitive mobile telecoms business the decreasing Average Revenue per User (ARPU) is a major concern for mobile network operators. The topic of roaming revenues and their protection can be quite complex, however there are four main categories that need to be covered including: 1) Roaming Inter-Operator Tariffs (IOTs), 2) Roaming Plans, 3) Subscribers’ Quality of Roaming Experience, 4) Steering of Roaming.

Steering of Roaming solutions, regardless of the type, are there to address these issues. It is essential that a Steering of Roaming solution provides the flexibility to use different steering strategies in different circumstances so that ultimately the operator can balance these four main categories with the pinpoint accuracy that they require to fulfil their business needs.

Categorised in:

January 12, 2016