What If Light Peak Was Electrical Rather Than Optical?

As I considered the possibilities of the new Apple/Intel interconnect technology known as Light Peak, an odd parallel with 10 Gb Ethernet popped into my head. Much of the confusion around Light Peak revolves around connectors, power conduction, and backward-compatibility. Then, like the Grinch, I thought of something I hadn’t before: Why use optical at all? 10 GBASE-T does just fine over twisted pair, and short interconnect distances would reduce power draw to reasonable levels. What if Light Peak was electrical rather than optical?

Optical: Perennial Underdog of Local Connectivity

In 1996, I worked at an R&D lab for famed connectivity company, US Robotics. At that time, the transition from 10 Mb Ethernet to 100 Mb “Fast Ethernet” was under way, and I recall one of the switching engineers (yes, USR produced Ethernet switches before 3COM) patiently explaining that a transition to optical interconnects was inevitable. Twisted pair wiring, he explained, just couldn’t handle the high frequencies needed at mind-bending speeds like that. And the voltage required to send such a signal 100 meters over 22 gauge wire would make port density unacceptable for data center use.

We all know how this turned out: Many facilities (including those where I worked) invested in optical cabling to “future proof” the in-wall infrastructure, only to see 100 BASE-TX Fast Ethernet over twisted pair stomp all competitors. The same story came with Gigabit Ethernet in the late 1990’s, and yet copper 1000 BASE-T is widely used. Cabling has improved (today’s Cat 6a can handle the 500 MHz of 10 GBASE-T) and electrical engineering has worked wonders to make 10 Gb copper practical.

In short, optical cable has always been exposed as an unnecessary luxury in local interconnects. Optical TOSLINK or S/PDIF cables are common in home theater applications (though purists actually prefer coaxial copper), and optical interconnects are used in storage area networking (SAN) and other high-performance networking applications. These are mainly historical anomalies, however: In both cases, the needed bandwidth pushed the capabilities of copper cable at the time, but improvements have rendered the use of optical interconnects moot.

Light Peak Over Copper

I wrote about Light Peak/USB 3.0 convergence yesterday

The same is true for Light Peak. While an optical interconnect seems like a sure-fire way to bring massive bandwidth and consolidate ports on a computer, it’s neither necessary nor really all that valuable. Light Peak could easily use twisted pair or coaxial cable, especially over the short runs that personal computers require. While it’s interesting to see 10 Gb carried over a 30 meter cable, no home or office user would need this. And they’re supposed to be Light Peak’s target audience!

A “Light Peak over Copper” spec for a maximum 10 meter run between repeaters would be sufficient and would reduce the cost and complexity of the whole system. Rather than cobble together an optical-plus-copper interconnect, Light Peak over copper would carry both high-speed multiplexed data and reasonable electrical current to power attached peripherals. It could even be made natively backward-compatible with some existing spec like USB 3.0 or HDMI!

Ever heard of HDBaseT?

Light Peak over Copper could still carry multiple protocols at a data rate of 10 Gb/s. It could still enable single-port laptop-to-dock (or monitor) connectivity. But it would also be useful as an internal connection (replacing SATA) and as a power transmission system. What if Apple’s next MagSafe connector included power as well as USB, FireWire, HDMI, and DisplayPort signals? This is absolutely feasible and could be delivered at low cost. Optical Light Peak requires components from a number of manufacturers and demands precise plug/receptacle tolerances, while copper could be delivered as cheaply as USB.

Stephen’s Stance

I love the concept of one-wire connections, especially for laptop computers. It would be awesome (and very Jobsian) if my next MacBook Pro had a single port for every type of connectivity, from power to networking to display to storage. But this doesn’t require a nifty new optical connector; it just requires high bandwidth. Light Peak over Copper would do all that, and is far more practical than the “science project” systems demonstrated by Intel so far. Let’s have it!