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Emerging markets have become an intense battleground for multinational mobile operators, with the strategy to enhance their global footprint. These operators are facing enormous challenges to build backhaul networks with their TCO efficient, and quick time-to-market (TTM) strategy. This article identifies the challenges to build these backhaul networks, and recommends potential solutions from both a technical and business perspective.

Backhaul Challenges and Strategies
TDM based architecture has traditionally met requirements of 2G operators. Several major operators such as Vodafone, FT Orange, Etisalat, MTN, and Zain are still investing heavily in expansion of their 2G mobile networks. Thus, increase in traffic volumes, and pressure of new service deployment demand an exponential growth of bandwidth on backhaul networks.

The gradual migration from 2G to 3G will definitely lead to long-term co-existence of the two networks, which in turn poses a challenge in backhaul to support multi-services transport requirement for a longer duration. This leads to a requirement to bear native TDM services, plus TDM + Ethernet services, and IP in future.

Operators in this case, bear a high cost for capacity expansion in SDH networks, leased lines, and microwave equipment. This leads to a need to improve transmission media to accommodate increased service demands.

Mobile operators are facing considerable operational challenges, as they seek to maintain their existing networks with multiple backhaul technologies, including PDH & SDH microwave, SDH multiplexers, and regional WDM technologies. The evolution to 3G backhaul, creates additional hurdles that lead to high TCO in short and long term.

The main challenges that increase TCO of 2G operators, on their existing backhaul networks are analyzed below.

Challenges on Stacking Many Boxes
Approximately 80% of existing backhaul networks comprise legacy PDH; SDH microwave links; and multiplexers stacking many PDH, SDH boxes in coexisting sites. This increases capex, as well as operational difficulties.

Existing TDM backhaul modes may meet immediate day-to-day requirements. However, in the event of adding more subscribers, or even migrating to 3G, there will be a need to rebuild, or introduce new backhaul technology, leading to more boxes within the network to sustain increased traffic. It would then become difficult to have an overview of the whole network. In addition, problem of maintenance, as well as efficient media transfer could also arise.

Nevertheless, a series of steps exist to address these problems:

Reduce Complexity via Unified Solution
Vendors intend to solve operators' complexity-arising out of stacking many boxes in their networks-with flexible solution equipped with diversified interfaces in an integrated solution. The existing stack of SDH boxes can be easily replaced by a single highly integrated MSTP platform.

For example, MSTP boxes and microwave IDUs support integrated microwave, and optical networking features. Microwave RF card is pluggable to either of these boxes. Hence, there is no requirement for MUX and DDF in hub sites, and no cabling is required. These features ensure higher reliability, flexible networking, faster service provisioning, and lesser equipment.

Support All Backhaul Scenarios to Avoid Stacking
Given the long-term nature of 2G, 3G, and HSPA co-existence, backhaul solution should be applicable in diversified scenarios to avoid stacking boxes. To meet growing demand of 3G services, ATM IMA can be plugged within the same box, thus avoiding stacking of ATM switches. Native E1, IMA E1, and FE interfaces at cell sites offer seamless access of cell sites and network aggregation. On RNC side, a single equipment can support STM-N, ATM STM-N, and FE/GE interfaces to cover all scenarios of RNC side aggregation.

Each of these features need to support card level expansion to enable faster deployment, and realize rapid TTM requirement of cellular networks. Directly upgrading from an existing system incurs less capex, and is easier to deploy. A single network management system (NMS) operates the whole network with less O&M demands, and thus less manpower.

Daily Network Operation Challenges
It is extremely difficult to locate failures across multiple network management platforms, that lack both end-to-end (E2E) provisioning, and unified performance monitoring mechanism; as it makes troubleshooting extremely complex, and causes high OSS integration costs.

In medium-level operators' (consider using tier-2 operators' networks) networks, thousands of alarms are generated daily by backhaul equipments. However, alarm correlation techniques to determine faults over multiple network platforms, such as microwave, SDH, etc, are absent. This delays rectification of faults. The need to maintain multiple maintenance teams of engineers, without a unified NMS will hamper quick fault detection, and have adverse effects on the opex of the operator.

Operators can take a number of measures in terms of simplifying operations, and reducing O&M costs. Some of the measures that can be looked into are:

One NMS for One Backhaul
One unified NMS for each backhaul simplifies daily operations. The solution features a complete point and click function, that defines traffic routes between BTSs/ Node Bs and RNCs/ BSCs. It avoids multi-segment provisioning to reduce repeated additional link configurations.

The NMS covers up for all equipments, such SDH, MSTP, WDM, microwave, and even packet backhaul to reduce the cost in maintaining different teams with separate products.

Accelerated Troubleshooting
Rapid troubleshooting is a key focus for major operators aiming to reduce number of site visits, minimize network interruptions, and implement preventive maintenance. Multi-segment configuration is the major factor that increases on site engineering tasks, and hinders failure location.

However, simply deploying a single unified NMS is insufficient; an alarm correlation system is necessary to clarify fault definitions throughout the network. Alarm correlation DB uses aggregation rules to generate root and non-root alarms; and can suppress 90% of non-root alarms to quickly locate the root causes. Ethernet layer OAM also assists in monitoring E2E service connectivity, and links status.

Fewer On Site Visits
Cellular networking is growing very fast, requiring quick rollout of mobile base stations. This brings the need for regular capacity adjustment, upgrade, and optimization.

Hence, field engineering becomes another important aspect of operational challenges. This situation can be ameliorated by flexibly configuring E1, IMA E1, and FE through card level, software programmable radio (microwaves), and a built-in add drop mechanism.

Moreover, field visits can be further reduced by using hot patch technology to fix bugs, online software to remotely upgrade NEs, and the NMS to monitor remote optical power. The point and click, and E2E provisioning also eases the burden of site by site configuration, previously shouldered by engineers.

Cut Inventory and Spare Parts
Unified hardware and software makes all service cards compatible with products applied to core sites for access and aggregation. When configured for specified distances, flexible SFP pluggable optical module reduces expenditure on spare parts; and same principle applies to microwave IDUs, ODUs, antennas, and RF couplers. These features can be combined to minimize TCO network wide.

Cost of Reality & Future Challenges
2G mobile operators are confronted with challenges of finding effective ways to evolve to 3G/ HSPA, while lowering opex and capex. The optimum choice must involve minimum costs; and reuse of existing network resources to bear legacy services; provide 3G/ HSPA services; and ensure seamless future expansion capabilities. Predictably, various potential solutions lack clarity, and pose great challenges for operators.

For example, increasing investment in legacy service provision, with hope of a delayed migration to all packet platforms in future, is broadly a short term expedient.

On the other hand, rushing to acquire a nascent technology, that applies to a separate IP platform will not only incur a high and immediate capex, but also pose operational problems for teams who are currently accustomed to legacy microwave and SDH networks. In terms of emerging markets, the latter approach requires specialized and highly skilled networking experts, who are currently very few in the market.

The overlapping nature of legacy and nascent technologies raises questions for operators regarding when, how, and which technology to apply, to realize backhaul for the new RAN.

Evolution not Revolution
An interesting recommended strategy is based on the unified solution that simultaneously supports TDM, and packet to seamlessly transport 2G and 3G, or HSPA data services. We recommend evolution strategy, rather than revolution. This means smooth evolution from MSTP to MSTP+ solution is proposed, instead of the need to build an overlay network.

At cell site gateway, TDM microwave network can be smoothly upgraded to hybrid microwave to achieve seamless Ethernet access. This can be achieved by simply adding RF cards into an existing RTN equipment. The upgraded solutions can effectively utilize same IDU and ODU; and can access services such as IMA, TDM, and Ethernet.

MSTP+ and hybrid microwave can be smoothly evolved by replacing cards that enable rapid deployment, and rollout of 3G networks. This saves considerable capex and opex, as well as enables operator to recoup RoI on legacy investments.

E2E Backhaul Solution for Emerging Markets
In technical context of 2G/3G coexistence, and backdrop of continual network and service evolution, Huawei has designed its solution to meet current requirements, and seamlessly evolve into future pure packet platform architecture.

Madhav Bhatta
The author is senior engineer, Huawei India
vadmail@cybermedia.co.in