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Electronic Design

Octal T1/E1/J1 Transceiver/Framer Keeps Legacy Backhaul Available

The bottleneck in most cellular systems implementing 3G and soon 4G data-centric networks is the backhaul. Legacy T1/E1/J1 wired telephone networks have sufficed for years. They’re expensive and slow, yet they’re still widely used. Some networks are adding more microwave or fiber where feasible. But wouldn’t it be nice if carriers could continue with the proven links?

Exar is making that possible with its XRT83VL38 octal long-haul and short-haul line interface unit (LIU) for T1, E1, and J1 applications as well as its XRT86VX38 framer/LIU combo. According to John Williams, VP of Exar’s Datacom and Storage business unit, “These highly integrated solutions enable high-density, cost-effective solutions for backhaul over existing copper networks to meet the needs of the evolving infrastructure.”

The XRT86VX38 is an octal 1.544-Mbit/s or 2.048-Mbit/s DS1/E1/J1 universal integrated framer and LIU solution that complies with ANSI/ITU-T specifications. This framer/LIU combo provides many features for enhanced messaging and testability. The physical interface has Exar’s optimized R3 functionality, providing reconfigurability with a choice of internal impedance, in addition to relayless hot-swap protection with redundancy circuits.

The framer function provides finer granularity to monitor DS-0 timeslots. The device’s performance-enhancing features include increased buffering and hardware-based messaging support for bit-oriented or packet-oriented network messaging protocols. It supports B8ZS, HDB3, and AMI encoding and decoding functions as well.

The transmitter provides a selectable or a programmable transmit pulse shaper for flexibility with any type of T1 or E1 circuit. Optimal performance is achieved via two on-chip crystal-less jitter attenuators and adaptive receive equalizers. A variety of loop-back and diagnostic features support in-circuit fault isolation and help reduce development time.

Exar’s R3 Technology—reconfigurable, relayless redundancy—targets T1/E1/J1 interface cards. The devices are reconfigurable with integrated termination supporting all common T1/E1/J1 line impedances, enabling customers to build one board with a single bill of materials (BOM). The relayless redundancy eliminates the need for external relays in some configurations by establishing a backup channel that can be brought online in the event of failure.

Samples of the XRT83VL38 are available now. It comes in a 255-pin ball-grid array (BGA) package and operates from –40°C to 85°C. The device costs $18.08 in 1000-unit quantities. Samples of the XRT86VX38 also are available. It costs $30.08 in 1000-piece lots.


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