Heterogeneous network policies, the Access Network Discovery and Selection Function (ANDSF) and Hotspot2.0 all play a role in delivering better quality of experience (QoE) in complex mobile multi-operator environments.
Current approaches are inadequate
Heterogeneous access networks allow mobile operators to move traffic from congested macro cellular networks to less expensive, shorter-range Wi-Fi® and small cells networks. However, the diverse mix of technologies in the air interface and in backhaul and core networks make shifting traffic among networks a complicated task. Inter-operator roaming agreements further complicate hand-off among networks.
Today, there is little consistency between the mechanisms used by Wi-Fi operators and those used by cellular operators to control key factors such as:
- Network discovery
- Network selection
- Traffic prioritization
- User authentication
- Roaming capabilities
- Quality of service (QoS)
These inconsistencies mean QoE in heterogeneous networks depends heavily on the device connection manager — and, as a result, on the device vendor. Device connection managers use connectivity preferences, various network policies and what they can discover about the available access networks to automatically make the right connectivity decision on behalf of end users (Figure 1).
However, connection manager behavior varies significantly among operating systems and can often result in incorrect decisions or missed opportunities to connect to better networks. This leads to end-user QoE problems that are difficult to diagnose and fix.
Some operators have tried using third-party applications to overcome the challenges of device connection managers. But third-party applications have limited ability to fix connectivity behavior. In many cases, the third-party application is in a constant battle with the native connection manager. Even where appropriate standards do exist, the lack of device support for such standards makes it difficult or more expensive for operators to use network-provided policies to influence the behavior of the device connection manager.
In heterogeneous environments, the current simplistic behavior of device connection managers is inadequate. Inconsistent methods of prioritizing of network traffic and varying enforcement levels for core network policies lead to inconsistent QoE. For example, not all services may be available on all networks, or content filtering may be different across networks. These inconsistencies make seamless heterogeneous roaming impossible.
Heterogeneous network policies are needed
Policy controls help operators manage traffic demands while maintaining QoE by:
- Constraining traffic within the available network resources
- Responding effectively to changes in dynamic loading levels
- Offering differing levels of user subscriptions
- Prioritizing QoS-dependent services, such as VoIP, Internet TV and online gaming, that require guaranteed connectivity
- Blocking certain traffic types based on factors such as tariff caps, content blocking and age restrictions
- Exploiting routing efficiencies in backhaul networks with techniques such as selective IP traffic offload
To date, most network policy control infrastructures are applied within a homogeneous network where a single operator owns and controls the end-to-end network. As we move to heterogeneous operator environments (Figure 2), each network may be owned by a different operator. In addition, the various technologies used may not always offer the same underlying policy enforcement mechanisms.
Delivering the policy control necessary for high QoE within heterogeneous environments comes with challenges:
- End users may have a different billing relationship for each access network so it may not be clear which provider owns the end-user QoE.
- Different access technologies are standardized by different standards bodies so there will be inevitable differences in policy control frameworks.
- As new radio and backhaul technologies roll out, heterogeneous networks are showing greater variations in performance.
- As public Wi-Fi coverage increases, there is overlap in Wi-Fi network coverage and a greater variety of Wi-Fi networks that end users can connect to.
- New IP interconnection and roaming architectures, such as trusted Wi-Fi offload, are emerging. The trusted versus untrusted relationship adds a new dimension to network selection and traffic routing policies, further complicating the decision process.
- Higher device costs and end-user investments in applications and content are driving SIM-only contracts. This means the home cellular operator has less control over the device, and consequently, less influence over the behavior of device connection managers and device support for standards-based provisioning mechanisms.
- Original equipment manufacturers (OEMs) are taking more control of the user experience and are imposing their own network selection and traffic routing policies. It can be difficult to override this device behavior. In addition, the diversity among OEM device policies can make it difficult to guarantee QoE.
Combining the ANDSF and Hotspot2.0
Combining new standards, such as the 3rd Generation Partnership (3GPP) Access Network Discovery and Selection Function (ANDSF) and the Wi-Fi Alliance Hotspot2.0 initiative helps operators create heterogeneous network policies and deliver a “pain-free” end-user experience across Wi-Fi and cellular networks. In particular, for cellular operators looking to offload data traffic onto roaming partner Wi-Fi networks, the improvements in Wi-Fi network selection and authentication offer significant improvements to QoE and to the operator’s ability to manage how different networks can be optimally used.
Key ANDSF capabilities
ANDSF is a cellular technology standard that allows an operator to provide a list of preferred access networks with policies for their use. Policies can be applied to all traffic for a given packet data network, or to the granularity of a single IP flow. ANDSF supports a number of capabilities that are important for policy control in heterogeneous networks:
- Downloading policy information from any network and in-advance storage of policies and network maps (Table 1).
- Reporting a mobile device location based on one or several technologies at the same time, including:
- A 3GPP location
- A geo-location (latitude, longitude)
- A wireless LAN (WLAN) location
- Tailored information based on both mobile device location and time-of-day.Discovery information and policies can be sent in advance and cover a very wide area. However, because the mobile device reports its location when querying the ANDSF, the operator can choose to send only tailored information based on the mobile device location. Time-of-day can also be used for validating when a given policy should be applied.
- An available access networks list that provides information on the location of WLAN access networks.
- A restricted or preferred access networks list that provides policies for restricted or preferred access networks.
- Push and pull mode. The ANDSF can be queried by the mobile device (pull mode) but also supports push mode to send network-initiated updates to the device.
Key Hotspot2.0 capabilities
Hotspot2.0 is a Wi-Fi technology standard that allows mobile devices to:
- More easily discover Wi-Fi roaming relationships
- Determine access point capabilities and loading conditions
- More easily make secure connections to Wi-Fi networks
Hotspot2.0 capabilities are derived from 2 Institute of Electrical and Electronics Engineers (IEEE) specifications. Hotspot2.0:
- Builds on the recently ratified IEEE 802.11u specification. This specification is an extension to the IEEE 802.11 standard to improve the ability of devices to discover, authenticate and use nearby Wi-Fi access points.
Among other capabilities, the 802.11u specification improves the ability of the Wi-Fi network to manage traffic for multiple Subscription Service Providers (SSPs). For example, a Wi-Fi network, as part of the roaming agreement, can be provided with a QoS Mapping from the SSP. This mapping determines how downlink IP traffic classes should be mapped to the over-the-air IEEE 802.11 QoS traffic classes.
- Incorporates the long-ratified IEEE 802.11i-based WPA2-Enterprise security specification. This specification enables secure authentication and encryption for Wi-Fi data using a variety of user credentials. Importantly, it defines a standard for establishing a secure, mutually authenticated channel between a Wi-Fi device and an access point prior to the establishment of any IP-based communications.
Mutual authentication is performed using the Extensible Authentication Protocol (EAP) over IEEE 802.1x. Data confidentiality (encryption) is provided using Counter Mode with Cipher Block Chaining Message (CCMP). CCMP uses the 128-bit Advanced Encryption Standard (AES) and offers similar cryptographic strength to 3G cellular networks.
Further enhancements are needed
While the ANDSF and Hotspot2.0 offer many of the capabilities needed for QoE in heterogeneous networks, there are many cases where enhancements to current capabilities will be required. Situations where there are only Wi-Fi operators or where the end user has separate subscriptions from a Wi-Fi operator and a cellular operator are just two examples.
In our detailed analysis we identify areas for further discussion. We also outline potential contributions to the relevant standard bodies that could improve end-user and operator experience in heterogeneous networks. Our proposals include:
- Improving consistency between Hotspot2.0 and ANDSF network naming and identification through the addition of Roaming Consortium IDs in ANDSF policies.
- Enabling ANDSF policies to better exploit Hotspot2.0 information such as the access network type (residential, enterprise, public).
- Clarifications to Wi-Fi authentication mechanisms to differentiate between authentication and service authorization failures. This would enable devices to behave appropriately in failure conditions. It would also enable operators to provide differentiated subscriptions.
- A new ANDSF policy delegation mechanism to enable the ANDSF infrastructure to refer devices to local ANDSF servers. This will improve the ability of ANDSF to cope with the increased variety of networks and roaming partners that will be available in future.
For more information about ANDSF and Hotspot2.0, the research behind the above recommendations and our analysis of expected scenarios for network selection, please read our white paper Wi-Fi Roaming – Building on ANDSF and Hotspot2.0.
To contact the authors or request additional information, please send an e-mail to firstname.lastname@example.org.