How to Meet New Demands for 4G Backhaul

By Taylor Salman

Based on Clearwire's WiMAX deployments in 27 cities and on public announcements from Verizon Wireless, AT&T and others about evolving to LTE (News - Alert), mobile networks quickly are moving toward 4G, which will place new demands on backhaul networks.

Mobile operators historically have used time division multiplexing transport to interconnect cell sites. Typically that means T1 circuits, anywhere from one to four links delivering about 1.5mbps to 6mbps, respectively. With target peak data rates of 100mpbs for 4G radio downlink speeds, that presents a serious traffic bottleneck. Moreover, TDM, while a sure method for providing stable QoS, is an inherently inefficient transport mechanism – wasting frames in favor of delivering a steady stream of data.

comScore (News - Alert) data on the U.S. market shows that touchscreen mobile phone growth has no signs of slowing down. The 2008 to 2009 period featured a 159 percent growth rate, with 23.8 million consumers buying touchscreen mobile phones – the devices proven to use mobile data the most. Backhaul transport between cell towers and mobile operators' core networks is already strained, and that's not going to change unless operators examine some planning and design options now so their networks will be ready to scale down the road.

As more video and Web 2.0 traffic moves onto mobile networks, 4G backhaul networks must be designed with the following attributes:

Capacity Networks must easily scale up bandwidth to meet rising demand, as well as increased MAC address space as more end-user devices are able to connect as IP endpoints.

Performance Service providers should offer low-latency connections with multiple QoS levels with granular management to optimize service delivery and customer experience.

Survivability Connections from towers require diverse protection paths so control traffic and user data can be preserved and maximize reliability.

Hybrid architectures Operators also should consider deploying hybrid networks by connecting towers using both microwave and fiber to extend the network reach to more towers.

LTE has some specific technical requirements to consider for backhaul networks. That includes synchronization, which entails both phase and frequency clock synchronization to support network MIMO and MBMS-single frequency node requirements; and X2 interface support, which provides efficient delivery of tower-to-tower traffic.

These design considerations do not exist in a vacuum, of course. Many smartphone users enjoy unlimited data plans that, while excellent for retaining subscribers, come at an eventual expense to mobile operators. Operators do not monetize heavy usage of mobile data services, and that impacts how much they can reinvest in their networks to prepare for issues like 4G backhaul. Backhaul generally accounts for 15 percent of a mobile operator's total operating expenses and 30 percent of an operator's network operating expenses. Faster 4G connections will exacerbate this problem, so carriers have to keep costs down while improving existing infrastructure.

While it isn't always possible due to capital expense, population densities and market footprint, fiber is an ideal choice for 4G backhaul that will truly scale with subscriber demand. And there are ways to use it even more efficiently than the industry's standard SONET deployments. With some key operational efficiencies in mind, operators can minimize the costs of integrating fiber into their backhaul networks. Here are a few considerations for design and deployment:

• 1,000+ node Ethernet network design per metro region

• Turn up and provisioning of hybrid fiber/microwave Ethernet networks

• Effective performance management of multi-layer QoS service environments

• Optimization of turn up and provisioning processes with automation

For integrating fiber into backhaul networks while reducing operational costs, Ethernet is the key to making it happen. But there are different ways to deliver Ethernet services to tower sites: Ethernet VLANs, Ethernet over SONET, Layer 3 routers with multiprotocol label switching or connection-oriented Ethernet. Ethernet VLANs provide the advantage of low cost but suffer from scalability and manageability issues as the network grows. Ethernet over SONET provides the predictability and manageability of SONET but only increases long-term costs in the backhaul network. Routers with MPLS provide comparable capabilities to connection-oriented Ethernet but with significantly higher complexity when deployed on the scale required for backhaul.

There are lots of options, but here's why connection-oriented Ethernet is gaining traction: it takes MPLS routing capabilities and moves them closer to the switching layer. Ethernet is standard. Ethernet is cheap. Ethernet switches featuring protocols like MPLS transport profile and provider backbone bridge traffic engineering can take advantage of the same intelligence as expensive Layer 3 routers, but do it faster and cheaper at the Layer 2 data link level. Connection-oriented Ethernet provides the traffic engineering and protection capabilities of MPLS; the predictable and controllable circuit provisioning of SONET; and, since it's a Layer 2 technology, the price points of Ethernet VLANs.

Consumers need more mobile data, and the big carriers are rushing to provide it. Today's 4G towers are a great investment, but without faster fiber and microwave backhaul networks that can rise to meet the demand, 4G performance will suffer.

Taylor Salman is product marketing director at Ciena Corp (News - Alert).

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