The R6 Interface and the Open Standards Debate
Openness will help drive lower costs and more end-user services
The value of WiMAX is becoming widely recognized as service providers solidify their plans and start delivering high-bandwidth mobile Internet services over a lower-cost WiMAX infrastructure built on open interfaces.
These deployments are a win-win for both service providers and consumers — end users can access more services, while service providers have a cost-effective way to gain revenue.
The demand for WiMAX has also set into motion the convergence of consumer electronic and mobile technologies. Companies like Intel, with plans to embed WiMAX-compatible chips in every laptop by the end of 2008, are betting on widespread adoption. Semiconductor companies are also building specialized WiMAX chips for consumer goods such as cameras, navigation tools, gaming and entertainment devices. Efforts are also underway to bring this technology into offices and homes cost effectively through picocell or femtocell base stations. Such devices are focused on high-volume, mass-market, plug-and-play deployment models to drive very low cost points.
With all the right pieces coming into place, consumer expectations for WiMAX will be extremely high. Consumers will demand more services and lower prices than current 3G technologies such as EVDO or High Speed Packet Access (HSPA) provide. And service providers are betting on a much lower infrastructure cost to build a long-term profitable business. They want to be able to negotiate for the best price/performance products in the market, and they want infrastructure equipment from multiple vendors to work seamlessly with their networks.
Achieving these objectives is only possible through open standards and bullet-proof Interoperability Tested (IOT) reference points at the air interface and at the strategic interfaces to all other network elements. Open standards are critical to delivering cost-effective infrastructure and end devices that will drive overall demand for WiMAX.
Need for open standards
The debate over standards is confusing, but the outcome can have far- reaching implications for mobile service providers making decisions about WiMAX technologies. Depending on the outcome, many face the prospect of dealing with a closed, proprietary architecture that could significantly inflate costs and limit their options.
In WiMAX, the critical R6 interface between base stations and Access Service Network (ASN) Gateways enables the WiMAX radio network and the core IP network to interoperate, thus ensuring service providers can choose best-of-breed solutions. Without an open interface, mobile service providers must work with a single, proprietary solution when building out their WiMAX network.
The WiMAX Forum® is taking steps to define standard interfaces and IOT certification, and to recommend additional steps needed for a mandatory R6 reference point. This is crucial for developing a true open WiMAX standard.
Since 802.16 focuses mainly on the wireless air interface level, the WiMAX Forum set up a Network Working Group (NWG) to create higher- level networking specifications for fixed, nomadic, portable and mobile WiMAX systems, which will enable economy of scale and standardization for large-scale WiMAX deployments. The NWG has developed five open- interface reference points: R1, R2, R3, R4 and R5. (See Figure 1. WiMAX Network Key Interfaces)
For the R6 interface, however, the NWG developed three separate profiles — A, B and C — and this has become a subject of confusion and debate. Profiles A and C expose the R6 interface, whereas Profile B neither defines the R6 interface nor exposes it for interoperability. Logically, Profile B does not seem to be a standard profile.
While some in the industry have focused on Profiles A or C, some large vendors back Profile B because it lets them hide their proprietary network architectures under the umbrella of a standard. In short, Profile B forces operators to buy ASN Gateways and base stations from the same vendor, which prevents them from leveraging the value of mixing and matching best-in-class products and limits their network functionality. Profile B also prevents operators from leveraging their core equipment for supporting off-the-shelf picocell or femtocell base stations that would become available with an open R6 interface.
CWG steps up
The Certification Working Group (CWG) of WiMAX Forum is developing a certification program for WiMAX technology to recognize equipment that has successfully passed a defined set of tests and hence has a certain level of performance and interoperability. The Wave 2 WiMAX certification program is concerned with two major areas:
Radio Conformance Test at the 802.16 Physical level (RCT)
Protocol Conformance Test at the 802.16 MAC layer (PCT)
In addition, the WiMAX Forum’s Network Interoperability Testing (NWIOT) special task group focuses on ensuring interoperability across all reference points (R1 through R6) defined in NWG specifications:
MS/CPE Interoperability with WiMAX Networks (R1, R2)
Inter-ASN Interoperability (across R4 and R3)
Interoperability between base stations and ASN gateways, when R6 is exposed
From a practical perspective, test observation points are required for controllability and for the ability to observe, and this is only possible with Profiles A and C, which have simple and open interfaces. End-to-end testing and plug-and-play scenarios are inconceivable with the proprietary R6 interface of Profile B. Multiple profiles would also reduce the number of qualified vendors needed for profile validation, given that the extensive process consisting of test development, validation and maintenance is too cumbersome.
R6’s strategic importance
The R6 is the most important interface in the commercial rollout of WiMAX networks. In a typical WIMAX network, just one ASN Gateway can support hundreds of base stations and impacts overall functionality and services over the wireless networks. As the network grows, operators will add more picocells and femtocells, especially in dense urban areas with high concentrations of traffic, which could amount to thousands of R6 interfaces per network. Exposing and standardizing this interface should thus become the highest priority for network standardization efforts.
R6 is closely related to performance-dependent events such as handover, paging and idle mode, and more. An open R6 interface is critical for operators that want to leverage the benefits of an open marketplace and ensure scalability, innovations and competitive cost structures. Within this scenario quite a few issues need to be ironed out, such as network management, Operations and Maintenance (OAM) and timers. Time is of the essence here; the WiMAX Forum needs to focus on maturing one R6 interface suitable for both IOT and open WiMAX Network certification.
Open WiMAX networks
Currently R1, R2, R3, R4 and R5 are exposed and uniquely identified regardless of the ASN Gateway profile type. A unique and mandatory R6 interface could greatly help end-to-end interoperability of WiMAX, and with its economy of scale, help service providers around the globe to penetrate larger markets and larger parts of the population. WiMAX operators have recognized the potential of an open R6 interface and are now explicitly asking for an open R6 interface. They are ruling out the proprietary Profile B to avoid risking the future scalability of their networks by getting locked into a proprietary vendor solution. Profile C seems to be the most popular profile among operators. Moving to this single interface would simplify network IOT and accelerate a real open standard, resulting in the following benefits:
Interoperability and multi-vendor support
Architecture enhancement simplification
Fewer architectural options
Economies of scale
Operators would have more choice in vendor selection
Vendors would have more market opportunity to sell
Reduced preparation and cost of tests, as more vendors will utilize the same profile
As the standard evolves, some of the network intelligence from Profile A, such as macro load-balancing and interference management, can be added to Profile C, with full backward compatibility with the current Profile C R6 interface to protect operator and vendor investment in Profile C.
What will be required to enable wireless operators to build open WiMAX networks, is one common profile that enables operators to mix and match network elements from multiple sources. The proprietary and vendor-specific Profile B advances the principle of closed and proprietary networks, enabling an equipment vendor to lock up an operator’s network and preventing the operator from enjoying the lower costs and innovative technology that come from fostering a more competitive environment.
The WiMAX Forum should focus on breaking the classic 2G/3G closed architecture model and standardize on Profile C only. This will enable operators to deploy radio and network equipment from different vendors based on a single R6 interface. Profile C will foster innovation and ensure that WiMAX equipment will be competitively priced to allow operators to build their networks cost effectively.