Cell Tower Backhaul

Aurora's GT3410A T1/E1 Access Module provides the solution for the cable industry's next generation TDM-over-packet technology that will enable MSOs to aggressively pursue a huge cell backhaul opportunity. With the distinction of being among the top few products to have thus far achieved Metro Ethernet Forum MEF-18 certification, this equipment is engineered for the stringent requirements of cellular backhaul, making it vastly superior to myriad pseudo-wire solutions in the marketplace.

The Opportunity

Recent years have witnessed phenomenal growth in the number of data oriented applications on cell phones and hand-held wireless units. Consumers are increasingly using mobile phones for advanced applications such as Internet access, remote enterprise connectivity, gaming, mobile video and mobile TV. This has led to the advent of sophisticated data oriented cellular technologies such as EVDO, UMTS, HSDPA and WCDMA that greatly increase high bandwidth use of cellular links. Consequently this has increased, in particular, the bandwidth demand on backhaul links that carry the traffic between cellular base stations and base station controllers and beyond. Traditionally, wireless operators have used T1/E1 carriers leased from telephone companies to transport data from the cell towers to base station controllers. The average number of T1s at cell towers is projected to increase from 3 to around 8 per cell tower, and one study estimates a 600% growth in the number of cell tower T1 ports over the next three years, thus making it a multi-billion dollar opportunity. MSOs that are already fiber rich, thanks to HFC and Fiber Deep deployments, if provided with the right tools are well equipped to tap into this multi-billion dollar opportunity.

The Solution

Aurora's T1/E1 solution utilizes carrier Ethernet technology to transport T1 data. Carrier Ethernet is more reliable and scalable than traditional TDM technologies. Riding on optical fiber, Carrier Ethernet interfaces are very scalable and can offer Gigabit rates as compared to a typical 1.5 Mbps T1 interface. Moreover, the synchronous T1 carriers, with their limited reach, need deployment of repeaters that make the end-to-end solution less reliable and much more expensive. Gigabit Ethernet components are mature, standardized and enjoy great economies of scale, making them extremely cost effective. The Aurora T1/E1 solution aggregates the T1 links from base stations and transports them using Gigabit Ethernet uplinks over long backhaul distances.

The Product

Aurora's GT3410A is perfectly compatible with Aurora's Fast Ethernet and Gigabit Ethernet transport access solutions such as Fiber On Demand^™ and SMART Media Converters^™.

The GT3410A module provides four T1/E1 ports, a Gigabit Ethernet fiber port, and a 10/100/1000 copper interface, and functions as an inter-working agent between the T1/E1 and Metro Ethernet clouds. The GT3410A module can be conveniently installed in either the 3RU CH3000 Chassis or the 1RU CH1301 Chassis for both headend/hub and customer premise deployments. Designed for high density environments, up to 80 T1 ports can be serviced from a single 3RU platform. In addition, daisy chaining of multiple T1 CPEs at customer premises enables better utilization of fiber. Aurora's industry leading 1310, 1550, CWDM and DWDM optics enable longer reach deployment while minimizing fiber counts.

Figure 1. The GT3410A module can be installed in 1RU or 3RU chassis.

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Cellular networks pose stringent requirements on total cell packet delay and variation due to the inherent nature of voice transport as well as handoff timing requirements when subscribers cross cell boundaries. The GT3410A employs industry-standard MEF-8 protocol for CESoEth (Circuit Emulation Standard Over Ethernet). The product is engineered for very low Frame Delay and Frame Delay variation and is designed for sub-1 ms packetization delay when used in point-to-point configurations.

Figure 2. Reference architecture for MSO cell backhaul

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Timing and Clock Synchronization

Clock synchronization across multiple nodes is critical in TDM environments, particularly when the end-to-end network involves packet-based backhaul. The GT3410A T1/E1 module employs adaptive clocking methodology for achieving timing synchronization across the Metro Gigabit Ethernet network. The Master GT3410A sources clocking signals from the TDM network (PSTN interface) at the headend location. Slave GT3410A modules typically reside at customer premises. An in-band clock recovery algorithm running on the slave GT3410A device infers the clocking frequency of the original clock source on the basis of the incoming CESoETH packet stream.

The customer TDM equipment derives the clock on its line interface connected to the slave GT3410A device. Thus all elements across the TDM and packet network are tightly synchronized to the PRS clock reference at the headend location. In peer-to-peer environments such as PBX interconnect, regardless of its physical location, a GT module can be configured to behave as a Master or Slave. Figure 3 depicts the end-to-end clock recovery mechanism employed by GT3410A solution.

Figure 3. Clock recovery mechanism with GT3410A modules

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The in-band adaptive clock synchronization scheme has timing and data closely coupled in the CESoETH (MEF-8 compliant) packet stream and eliminates any extra packet overhead related to timing and clocking. Moreover, an adaptive clocking design has advantages over alternative differential recovery algorithms because it eliminates the need for expensive GPS and PRS references at client nodes.

Conclusion

The GT3410A module has successfully passed MEF-18 certification, meeting the stringent G.823 and G.824 jitter and wander requirements. This performance milestone is significant for the Aurora T1/E1 solution and makes it perfectly suitable for cell backhaul environments where considerations of strict end-to-end-to-end jitter and wander characteristics are paramount.

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