Telecom in Transition, Moving at Hyper-Speed
By David Pheteplace, Bishop & Associates Inc.

Telecommunications equipment has come a long way since the days of mechanically switched phone lines. The latest step in this evolution is the IP-based routers and switches. This evolution has also significantly impacted the backplane connectors used in telecommunications equipment.

Twenty years ago, a commonly used backplane connector used in rack-based telecom equipment was the DIN 41612 (pictured right from ERNI). The connectors are rated at 2 amps per pin and 500 volts. They have a 0.1-inch pitch and have first-mate/last-break contacts to accommodate hot-swappable applications. The DIN 41612 evolved into the 2mm connector used in the Futurebus standard. Although they are still used in many rack-mount systems today, most telecom equipment uses newer connectors that have higher pin densities and are able to handle higher speed signals.

Why the move? The major factors are the advances in semiconductor technology and the explosive growth of broadband Internet. The computer processors used in today's computers pack millions of gates into increasingly denser packages. As a result, the communication links are getting shorter and the processing speeds are increasing. With the growth of the Internet, faster equipment is needed to keep up with the demand for high-speed service. This is where the IP router and core router come into play. They are the most cost-effective way to increase the capacity and speed of the telecommunications system. Rack-based IP router and core router systems require backplane connectors that can handle signal bandwidth up to 10Gb/s. On today’s drawing boards, 40Gb/s is the holy grail for these systems, so designers are in need of headroom for their interconnect systems.

The Juniper TX Matrix (left) interconnects four of Juniper's core routers to achieve a sustainable throughput rate of 2.5Tb/s, equaling three billion pps (packets per second). The T Series supports a 100Gb/s Ethernet router interface.

Cisco's 7609 series Internet router (right) has a bandwidth of 256Gb/s, a switching performance of 30Mpps, and a service performance of 6Mpps per OSM (Optical Service Module). These speeds are obtained by running multiple parallel channels at lower speeds. The aggregate speed may be 25, 40, or 100 gigabits.

In order to handle this bandwidth, backplane connector manufacturers have had to control the attenuation, impedance, and crosstalk in these multi-gigabit connectors. To meet these performance criteria, most designs originally incorporated internal shielding to minimize crosstalk and maintain consistent impedance. FCI’s AirMax design meets the requirements without shielding by closely controlling the dimensions of the connector and the mating of contact pairs. This enables system designers to more closely match system requirements with a more cost-effective product. Many connector manufacturers introduced competing designs. The shielded systems with differentially paired contacts, however, are being chosen for the higher-speed applications.


The Tyco Impact™ backplane product (right) is designed for increased speed and signal density. The connector utilizes a localized ground return path and tightly coupled differential pairs to reduce crosstalk and increase the bandwidth capabilities. The connector system is rated at 100 ohms impedance and 25Gb/s bandwidth. The product is intended for use in IP switches and routers.



The Amphenol TCS XCede© high-density connector is a similar design to the Tyco connector. It utilizes differential pairs (up to 85 pairs per inch) with 85 and 100 ohm impedance ratings. XCede HD is designed for data rates from six to 10 Gb/s, but allows the system designer an easy upgrade path to more than 20 Gb/s.



The Molex GbX I-Trac connector utilizes a broadside coupled, skew-equalized design with differential pair, allowing 56 to 300 circuits depending on the connector and pairing. The pitch of the connector is 0.073-inches by 0.146-inches. The connector is designed for telecommunication applications and can handle data rates up to 12.5 Gb/s. With the capability to be rotated 90 degrees on opposite sides of a midplane, it is also capable of orthogonal architecture.

Several enabling technologies facilitate these speeds through backplane connectors. Advances in signal conditioning - equalization and compensation - are particularly important. In the advanced signal software, the send/receive circuits are capable of ferreting out high-speed, low-level signals buried in the noise caused by an imperfect physical system. On the physical side, improvements to the connector footprint, and smaller, shorter pins, with smaller, plated through-holes on the PCB, reduce crosstalk. In the printed circuit board design, enhanced FR4 materials in the boards improves high-speed performance, and counter-boring of the plated through holes reduces stub length, thus reducing potential secondary (reflected) signals. Without all of these factors working together, the system would not work at higher speeds.

As our need for bandwidth on the Internet continues to grow, connector manufacturers will have to keep pushing the envelope with these systems to appease consumers who have come to expect constant, and rapid improvements in their technology.