10-Gigabit Networking and Audio

Stephen Lampen, MultiMedia Technology Manager at Belden CDT, made a return visit to the San Francisco section to give a review of cable history and an update on current technology, especially 10-Gigabit Ethernet. The presentation took place at the Dolby theater with thirty-two people in attendance.

Lampen reminded us that packetized computer data communication was invented in 1973 and evolved into the Ethernet. The original 1 Mbps data transfer was over coax cable, however, as the industry improved the performance of unshielded twisted pair (UTP) cable, UTP was adapted for networking applications.

As bandwidth requirements have increased, cable technology has become more complex.

Lampen revealed that in a CAT 5 cable running at 100 Mbit/s, one pair of wires transmits and the other pair receives data. At 1000 Mbit/s, four twisted pairs must run in duplex mode to provide the higher bandwidth. To achieve high performance and prevent electromagnetic radiation, cables must have extremely good pairs, stable impedance, good return loss, and good skew.

CAT 6 cable is physically different from CAT 5e and represents a big jump in performance. For example, a plastic divider in the middle of the cable separates the twisted pairs to prevent pair-to-pair crosstalk. Lampen remarked that the number and precision of twists in the pairs is also critical and is determined empirically using a machine that Belden developed called the twistometer.

CAT 6a, augmented CAT 6, was developed to support 10 GHz. To prevent alien crosstalk, i.e., crosstalk resulting from identical pairs in separate cables interfering with one another, Belden runs a spiral piece of plastic under the outside jacket which prevents cables from nesting closely together. Lampen also showed us how the pins of the RJ45 connectors are part of a circuit that aids in achieving the high performance. To prevent crosstalk at the connector, the twisted pairs are connected at right angles to one another.

Although Belden markets a 10-Gigabit cable, the data rate is not 10 GHz. Since each of the 4 twisted pairs that make up the CAT 6a cable can only run at 500 MHz, the only way to achieve 10-Gigabit communication is via compression and decompression on either side of the cable.

Of course, the main question was, who in the audio business needs 10-Gigabit? Lampen noted that the SMPTE DC-28 report explored future bandwidth requirements and concluded that a 10-Gigabit pipe is needed to handle animation and HD file transfers. Several companies currently market network solutions for broadcast and studio applications. In general, the only problems that affect audio applications are latency and network overloading.

Lampen emphasized that the 10-Gigabit solution is currently very expensive – about 40% more than an optical installation (including the labor for cable set-up). However, the hope is that prices will fall eventually and that 10-Gigabit solutions will be as inexpensive as CAT 5 is currently.

Thomas Merklein