As mobile operators evaluate alternatives to addressing backhaul bottlenecks, several considerations arise.  Primary among them are cost, capacity, availability, scalability, flexibility and maturity.  Depending upon the relative importance of each of these factors for a given site, cellular backhaul networks will continue to reflect a mix of backhaul technologies.

That mix will change as demand for capacity rises, as IP base stations become more common and as new backhaul technologies become more widely available.

The dizzying array of backhaul technologies from which operators can choose can be categorized into a few major groupings:

  • Leased infrastructure versus owned infrastructure.  The vast majority of last mile leased infrastructure is TDM-based copper, e.g. T1/E1, STM1/OC3.  In contrast, microwave and fiber make up the bulk of owned infrastructure.
  • Copper, fiber, microwave or other physical layer access media.  Microwave accounts for about 50% of global last mile backhaul connections, while copper and fiber each account for about 25%. 
  • TDM-based, IP-based or both.  Most low capacity TDM circuits are delivered via copper leased lines and Ethernet-over-copper technology has seen small-scale deployment, as well.  Fiber can carry any combination of TDM or Ethernet and is the most widely used physical access method in the “middle mile” aggregation network and in the core network, typically using PDH or SONET/SDH connections. Most deployed microwave systems are TDM-based, but newer microwave systems support Ethernet or, in the case of Exalt, both TDM and Ethernet simultaneously and natively.

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Copper
Leased TDM-based copper offers the advantage of being widely available in some geographies, most notably North America, and the disadvantage of being neither cost-effective nor scalable.  Although the use of leased T1/E1 circuits can make economic sense when only a few are required, the cost of this approach scales linearly with capacity, making it poorly suited for backhaul in a 3G/4G environment.  In fact, the average mobile operator spends an estimated 20% of its total operating budget on leased lines today.  Furthermore, leased lines are known for their poor availability, unable to deliver the up-time required for critical connections.

Ethernet-over-copper approaches in the form of xDSL or Mid-Band Ethernet offer a more attractive price per Mbps than leased T1 lines for the capacity, along with a pricing structure that is more cost-effective than fiber and scales better.  On the downside, these approaches suffer from:

  • Limited availability, as they can typically be used only within 3 km or less of a central office or DSLAM;
  • Limited capacity, as they typically accommodate only up to about 10 Mbps in each direction and often less;
  • Limited ability to support the latency requirements of TDM voice services;
  • Threat of failure due to rising rates of copper theft.

Fiber offers the advantage of essentially unlimited capacity and is used for high capacity TDM connections (e.g. OC3, OC48, OC192) in the last mile, aggregation and core segments of the network.  Fiber is also the primary means of delivering high capacity Metro Ethernet services.  When leased, the price of TDM or Ethernet services over fiber is comparable to the price of the same services over copper.

The well known downsides of fiber are:

  • In most geographies, fiber availability is extremely limited and the ability of either the mobile operator or a service provider to install it is often constrained by urban topologies;
  • Because of the high fixed cost of installation, it makes economic sense to deploy fiber as owned infrastructure only in very high capacity scenarios and/or when capacity can be resold to other entities; and
  • It is subject to less than 99.999% reliability as a result of the threat of fiber cuts caused by construction equipment (the “backhoe effect”).

Microwave
Microwave backhaul is the most widely used approach to owned infrastructure in the world due to a low cost of entry, cost-effective capacity scaling, 99.999% reliability and rapid time to deployment.  And as compared to leased lines, microwave radios offer a rapid payback period of as low as a year or less (see Economics of Backhaul) by shifting the purchase model from OpEx to CapEx.

The primary disadvantages of microwave for backhaul applications are:

  • Spectrum must be available for use;
  • Line of sight is required between two points for carrier-class operation in which guaranteed throughput availability is required.

The Exalt Microwave Difference
Exalt builds on the benefits already offered by microwave technology by offering:

  • Native TDM and native Ethernet capability in every radio, ensuring the flexibility to accommodate any mix of TDM and Ethernet traffic;
  • Fully software configurable and upgradeable systems that minimize the need for hardware swaps and ensure that capacity can be inexpensively scaled when needed;
  • Licensed band and license-exempt band radio systems, the latter of which feature CarrierTDD™ technology, making them the only TDD systems in the world capable of supporting native TDM traffic with FDD-like latency and providing operators with a new tool to meet site-specific or application-specific challenges;
  • A rich set of Ethernet features such as VLAN and QoS, enabling easy integration into existing data networking architectures;
  • The highest level of security available for data and management traffic; and
  • Indoor, outdoor and split-mount physical configurations to meet the installation requirements of any site, however challenging.

Put simply, Exalt microwave radios are designed to allow mobile operators to deploy a single system that will allow them to easily and cost-effectively scale capacity for any TDM to IP migration plan.  The Exalt microwave product portfolio provides operators with a range of frequency, configuration and protocol options to support that migration plan at just about any site.

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