1. Market environment

Wireless carriers are massively deploying 3G networks while improving their 2G/2.5G networks at the same time. Their goal is to increase the revenue-generating potential of their networks while simultaneously striving to reduce their cost.

While from a carrier's perspective, one unit of traffic density (erlang) in a UMTS network may be cheaper than in GSM, new opportunities to grow revenue come from data services. The data services offered in 2.5G may serve as appetisers for the more sophisticated and faster data services offered in 3G networks. Buzz words like “Internet in the pocket” or “Broadband goes mobile” and “Triple play” describe the trend in the industry to offer broadband data services to the mobile terminal. These services will be attractive enough to make the user move over from 2G/2.5G to 3G networks but their acceptance will rely on convenience of usage and the experience of a reasonable price to performance ratio.

New data services demand much higher bandwidth than voice services and they take advantage of network convergence trends in the transport and core network. They are also a driver for the migration to IP based transport in the Radio Access Network (RAN). The subsequent requirements for data service provisioning include flexibility and backwards compatibility. These, combined with the expected cost savings of various kinds represent the main drivers for convergence in the backhaul.

2. Definition of Converged Backhaul

Converged backhaul enables multi-standard, multi-service Base Transceiver Station (BTS) platforms that are radio interface agnostic. In general, multi-standard BTSs can support multiple radio standards like GSM/GPRS/EDGE, W-CDMA and potentially CDMA2000, 1xEV-DO, WiMAX and other emerging radio standards. Their ability to connect to multiple backhaul interface types such as Abis and Iub implies multiple physical interface types (PDH, SDH and Ethernet) with the associated data formats and protocols (TDM, ATM and IP) and the capability to process multiple traffic types including voice, real time data, high speed data and best effort data.

Using this approach, dedicated UMTS Node Bs and GSM/GPRS/EDGE BTSs can migrate to a common platform and, as a final step, become “Hybrid” BTSs, offering a large amount of flexibility. This means the mobile carrier can select the most appropriate, cost efficient backhaul and radio technology simply by choosing the right equipment configuration. In rural areas, for example, this could be GSM/GPRS/EDGE connected via E1/T1 (either wired or using µWave radio) on the backhaul side. In urban and densely populated areas, UMTS/W-CDMA could be connected either via E1/T1, STM-1 or, in the future, via Ethernet.

3. Drivers for Converged Backhaul

There are a number of drivers for converged backhaul from the mobile network operators' side as well as from the OEMs' side. They are associated with expected cost savings, enhancement of flexibility and, last but not least, easing the introduction of new data services.

Mobile operators have spent enormous amounts on 3G licences as well as network deployment and they are now under increasing pressure to generate positive return on investment (ROI) as quickly as possible. The consolidation among mobile operators that has created larger buying power and the intense rivalry among the OEMs leads to a huge pressure to reduce equipment prices. Furthermore, the ongoing Node B industrialisation causes carriers to expect decreasing prices. Consequently, OEMs pass the pressure on and request aggressive prices and more complete subsystem-like solutions from their silicon suppliers.

Another means for OEMs to manage their research and development (R&D) effort is through the “one platform approach”. Hardware, as well as software development effort, can be reduced substantially as fewer versions and variants have to be maintained. Test and integration effort is reduced significantly, as well as manufacturing cost, management of parts and bill of materials.

Carriers may appreciate the “one platform approach” as it drives volumes up and costs down. Network maintenance charges go down dramatically. Not forgetting the enhanced flexibility when adding new protocols, an extension of the radio standard or even a new one. This approach, together with a converged backhaul leads to the Hybrid BTS described above.

The biggest chunk of a mobile operator's operating expenditure (OpEx) is the backhaul line cost. This results in the necessity to select the most favourable backhaul technology possible and to make efficient use of backhaul transport bandwidth. Today, this is becoming even more significant, as wireless carriers begin to add support for emerging high speed data services such as HSDPA and HSUPA, in the near future. These new data services also fuel the migration towards an IP based transport in the backhaul which ideally would use Ethernet where possible.

4. Ethernet as Backhaul technology

In this context, an important aspect is the future use of Ethernet for backhaul connectivity. Apart from resolving the bandwidth bottleneck issue, Ethernet can be seen as a way to reduce the leased line cost significantly. Even today, where available and depending on the transport carrier, the cost for a Fast Ethernet leased line may be more attractive than 4*E1/T1. Additionally, using Ethernet with an SLA enables the potential realisation of a remote configurable bandwidth “pay-as-you-grow” model. Today's SONET/SDH equipment already has Ethernet add/drop capability and the transport carriers are in the process of upgrading their installed nodes wherever business potential exists. This is seen as an excellent means to generate new revenue opportunities maintaining the existing proven, manageable and reliable SONET/SDH infrastructure. µWave radio systems also include Ethernet interfaces on the client side today or on their near term roadmap.

However, not all the technical issues are solved. Currently, radio basestation node synchronisation relies on the accuracy of PDH or SDH clocks/ timing together with an OCXO oscillator on the basestation side. This method is due to the nature of the signal not possible in the Ethernet case. Several methods such as extending the IEEE 1588 standard are currently under discussion in the standardisation groups as well as at OEMs and silicon suppliers.

5. The migration path from today's backhaul to a true converged backhaul

Today, 2/2.5G and 3G radio basestations are separate equipment, If offered at all, multi-standard exists only as mechanical integration of dedicated shelves in the same rack. The NIC card (Network Interface Card) as the interface to the backhaul is different, using varying types of silicon devices and software. The backhaul lines are also separated from each other or AAL1 is used to pass TDM traffic to a subtended GSM BTS through the UMTS Node B.

The first step towards a common platform would be to use the same silicon devices and the same software framework, with the same printed circuit board assembly as the next step. The final step, which realises the Hybrid BTS, would be a completely converged solution which shares even the backhaul lines and is therefore making use of a converged backhaul.

This migration path has the potential for significant savings on the R&D side as well as offering all other advantages of a “one platform approach”. Looking at the pure equipment costs, only one hardware network interface card (NIC) is required as opposed to two in today's configurations.

6. Agere's TrueAdvantage™ Wireless Access Solutions

Agere's TrueAdvantage solutions feature new technology that enables the migration towards a true converged backhaul with the final step of Hybrid BTSs that offer multi-standard and multi-service capability. Offering the flexibility to connect to each backhaul interface type and to support each protocol and traffic class, the OEMs are able to provide the equipment that the mobile network operator specifically requires with the option to upgrade and/or to configure remotely. The mobile carrier can select the backhaul technology which is the most efficient and save significant amounts of backhaul cost.

The TrueAdvantage solutions consist of a broad family of feature-rich networking chips such as Advanced PayloadPlus® (APP) network processor chips, LLP (Link Layer Processor), TADM, Ultramapper™, and Hypermapper™ framing and mapping devices. Additionally, the solutions offer turn-key software packages, reference designs, and hardware development systems that allow telecom equipment manufacturers to quickly and efficiently build lower-cost, higher-performance wireless access network equipment.

Agere enables the convergence of 2/2.5G and 3G backhaul into a single platform solution using the programmable LLP and APP300 device families. The LLP offers ATM-TC/IMA, AAL1, HDLC, ML/MC-PPP and Abis/ Transcoder Rate Adapter Unit (TRAU) framing capability whereas the APP300 network processor processes ATM, AAL2/5 as well as ATM/IP interworking and the IP related stacks for UMTS R4/5/6 such as IP/UDP/PPP-MUX. In particular, the APP300 handles a mix of traffic types and provides support for header compression and multiplexing protocols such as PPP-MUX (Point-to-Point multiplexing) and cUDP (compress User Datagram Protocol) for improved backhaul efficiency.

Agere's solutions also scale very well for RNC applications. There are a variety of devices available that address the higher bandwidth and channel count required in an RNC and still maintain software compatibility.

All these capabilities are delivered to OEMs in conjunction with the new production-ready Functional Programming Interface (FPI) software package. The TrueAdvantage Wireless Access FPI runs on Agere's APP300 and APP500 network processor product families and is targeted at wireless infrastructure. OEMs can either use the FPI as a black box or easily modify the source code to incorporate proprietary features and create differentiated systems. Using the FPI software, OEMs can significantly reduce their software development effort.

One important aspect for OEM's R&D efforts is the high code efficiency of Agere's network processors and the simple programming model based on the high level languages: Functional Programming Language (FPL) and C-based language C-NP. The user plane software requires significantly fewer lines of code for a given function and is much easier to maintain.

These solutions translate to reduced product development cost, less defects and improved reliability and scalability.

7. Conclusion

Converged backhaul enables mobile network operators to use their network more efficiently and eases the generation of new revenue streams through new data services. It is also an excellent means to reduce Capital Expenditure (CapEx) as well as OpEx. OEMs can reduce their R&D effort significantly and are able to develop a common platform that offers multi-standard and multi-service capability with the final step of a Hybrid-BTS.

Agere's TrueAdvantage solutions enable a smooth migration path throughout this process. The LLP and APP300 device families together with the FPI software offer the flexibility to support connectivity to all existing backhaul interface types and protocols as well as their interworking. Efficient processing of the IP related protocols also make these solutions first choice in “IP only” BTS solutions.