ANDSF (The Access network discovery and selection function) has been around for a while now—ever since 3GPP Release 8. ANDSF allows a mobile network operator to define policies on how “non-3GPP” networks are accessed. (In reality, non-3GPP means Wi-Fi.) It defines three groups of information that can be sent to a handset:
- Inter-system mobility policy (ISMP) – This specifies which network type to connect to when only one network connection will be used, for example a choice between LTE and Wi-Fi.
- Inter-system routing policy (ISRP) – If multiple networks can be used simultaneously, this specifies which type of traffic should use which network.
- Discovery information (a list of non-3GPP) – This is information about networks that might be available in the handset’s vicinity.
ANDSF allows a whole variety of policy conditions to be applied to ISMP, ISRP. and Discovery information such as location, time of day, cell id, current network provider, etc. ANDSF implementations that have integration points into the packet core can also set policy based on subscriber profiles. (More on this later.)
To complete this brief description of ANDSF, it’s probably worth mentioning that a handset actually talks to the ANDSF server over the S14 interface using an XML-over-HTTPS protocol based on OMA-DM.
Since this all sounds great, why aren’t all the carriers rolling out ANDSF? It really comes down to the complexity of heterogeneous networks and the capabilities of handsets to date.
Let’s wind the clock back five years or so, when the choices where pretty limited for deciding which Wi-Fi network to connect to. It was usually nothing or a carrier- provided network. This made the Discovery mechanism in ANDSF overkill, since the choice of which network to connected to was a simple one. All a handset needed to do was to select the one SSID it cared about. Additionally, handsets always connected to Wi-Fi when it was available, which is still the default behavior for most smartphones.
Still back in the past, the types and volumes of traffic were very different—as was the technology on handsets—and all of these considerations made the ISRP portion of ANSDSF (routing different traffic over different networks) unnecessary, and in most cases, impractical.
Wind the clock forward to the present. Data volumes are ever increasing, and the types of services people are using on their handsets are numerous and growing. It’s the data tsunami! (I know, I used that cliché….) Another big change is the explosive growth in Wi-Fi, much of it free.
So where does ANDSF fit in now?
The idea of routing different types of data across different radios is still not truly practical as it requires a change in the way the handset works, such that it’s not beneficial to the operator. The use cases where an operator wants a particular application to go only through the core are likely better handled by secure, tunnel-based solutions that route traffic to the S2a interface in the packet-core (likely the subject of a future blog posting).
The Discovery piece now faces the opposite problem. Because Wi-Fi is everywhere, and new networks are springing up in ever increasing numbers, it’s not clear that ANDSF discovery is going to scale. Nor is it clear that the information will be timely enough to be relevant. Remember, ANDSF Discovery requires a Network Elements Database that must constantly update and map to the real physical networks that are available.
Where Discovery will be useful is in setting the priority for which Wi-Fi networks to connect to when there are several choices such as choosing carrier provided Wi-Fi over an amenity network. The carrier Wi-Fi networks will likely be discovered by the handset looking at nearby networks and using Hotspot 2.0 to determine their usefulness (assuming Hotspot 2.0 ever happens).
The part I’m really excited about is ISMP. Remember, that’s the part of ANDSF where policy is specified for which network to use, cellular of Wi-Fi. This allows the connection behavior of a smartphone to be set via policy. Here are some examples of what an operator could do in this case:
- For subscribers on a tiered data plan, operators can keep them on LTE when it’s available and of high quality. If they cross their monthly plan limit, the operator can offer a data add-on for that month and maximize their LTE revenues.
- A differently structured plan might be for a subscriber who has reached their monthly limit and is now throttled at 200Kbs. Prior to reaching this limit, their ISMP policy was set to use LTE in preference to Wi-Fi. Once throttling is active, their policy reverses to now use available Wi-Fi whenever possible. As a result, the operator maximizes LTE usage, but also enables a great user experience by moving the user onto Wi-Fi when the LTE plan has been exhausted.
- For an LTE network that starts to experience congestion in a specific cell, the ISMP policy can be set up to serve 50% of the handsets with cellular, to serve the rest with available Wi-FI, and to improve the user experience for everyone.
The possibilities are endless here, but fundamentally, this changes the way handsets connect. The connection experience across all networks types is now under the control of the operator.
Enabling policy this way reflects the current and broad shift operators are making from Wi-Fi offload to an Always Best Connected experience. With the rollout of LTE and the growth in tiered and shared data plans, mobile network operators want to monetize LTE to the fullest extent possible. It’s no longer a simple choice of offloading whenever possible. Rather it’s about setting policies that help maximize ARPU and insure a great use experience for the customer.
To complete the policy story, handsets also need to make some local decisions based on the real-time network performance. ANDSF can suggest some policies around network performance, but it’s up to the handset to do the measuring, which is sometimes referred to as “local ANDSF.”
Devicescape is talking a lot about user experience and maximizing ARPU. And we’re beyond talk. We’re incorporating adaptive network selection as a powerful component of the Access services that operators can use to locally and in real-time assess network conditions and to integrate ANDSF policies. All of this provides an ideal approach for mobile network operators to deliver an “Always Best Conected” experience as they roll out LTE.