Optical transport for cell backhaul: SONET, Carrier Ethernet & cell-site fiber challenges
With the advent of LTE/4G technology, our communication industry frequently hears and sees that copper T1 service to cell tower sites is quickly becoming inadequate. Wireless carriers continue to increase the number of new cell sites and to upgrade existing 3G sites to 4G/LTE. These carriers are more frequently requesting a minimum of 50-Mbps Ethernet initial service to these new tower sites and Ethernet upgrades to existing T1 services -- often with follow-on commitments to add 150-Mbps Ethernet service with just a three- or four-month notice.
This surge in cell backhaul bandwidth demand threatens to overwhelm facilities sooner rather than later. For example, historically the typical cell site might have been served with eight T1s. More recently, SONET ring networks were extended to include cell sites to facilitate dropping off a mixture of T1, DS3, and Ethernet type circuits. Now, not only is the number of new cell tower sites growing, but these sites are being designed to accommodate as many as six wireless carriers each. The result of this explosion in bandwidth is the need for fiber-fed connectivity based on Carrier Ethernet.
The emergence of Carrier Ethernet transport
The SONET unidirectional path-switched ring (UPSR) architecture continues to be very popular for mobile backhaul given its huge embedded base, variety of interfaces, and scalable bandwidths across OC-3/12/48/192 backbone rates. In addition, SONET offers proven reliability with less than 50-ms ring switching time.
Yet there is a new technology trend in network architectures to support cell-site tower locations – Carrier Ethernet transport. Typically these active platforms support Gigabit Ethernet to 10-Gigabit Ethernet backbone optics and are very scalable.
The drivers behind this new service provider model are quite logical: the ubiquity of the Ethernet interface (whether copper RJ-45 or optical 10/100/1000 Mbps), the advancement of ITU-T G.8031/2 standards for ring protection switching (also sub-50 ms), and five-9s of reliability. These technological advancements will enable Carrier Ethernet to become the predominant technology for serving the ever-growing demand for cell backhaul. In addition, the sheer volume of Ethernet chip sets across the application landscape has facilitated lower silicon component costs, greater availability, and reliability improvements.
At the heart of the acceptance of this network topology is Ethernet Protection Ring Switching (EPRS). EPRS was defined by the ITU and Metropolitan Ethernet Forum (MEF), is widely accepted, and continues to evolve into more complex network architectures with the recent announcement of Carrier Ethernet 2.0 by the MEF. ERPS began at ITU-T as part of the G.8032 Recommendation to provide sub-50-ms protection and recovery switching for Ethernet traffic in a ring topology while ensuring there are no loops formed at the Ethernet layer. G.8032v1 supported a single-ring topology and G.8032v2 supports multiple ring/ladder topologies.
Additional Carrier Ethernet service definitions are expected as new standards-based features are created, implemented in silicon, and deployed in active systems.
All of this bodes well for the continued use of Carrier Ethernet to meet 4G/LTE requirements for bandwidth increases and to expedite the push for fiber ring deployments to cell sites. In some sense cell backhaul is fast becoming the FTTx of the “Mobile Device Generation.”