Light Peak is a proprietary optical cable interface designed by Intel to connect devices in a peripheral bus. The technology has a high bandwidth at 10 Gbit/s,[4] with the potential to scale to 100 Gbit/s by 2020.[5]
Light Peak is being developed as a single universal replacement for current buses such as SCSI, SATA, USB, FireWire, and PCI Express in an attempt to reduce the proliferation of ports on contemporary computers. Bus systems such as USB were developed for the same purpose, and successfully replaced a number of older technologies. However, increasing bandwidth demands have led to higher performance standards like eSATA and DisplayPort that cannot connect to USB and similar peripherals. Light Peak provides a high enough bandwidth to drive these over a single type of interface, and often on a single daisy chained cable.
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[edit] History
Intel has designed a prototype PCI Express card for desktop PCs as an add-on.[6], enabling many people to use the new technology without a motherboard upgrade to support the new cable type. The card has two optical buses powering four ports. On some machines, however, such a card would not be able to achieve the full 40Gbit/s bandwidth of four Light Peak ports, as that bit rate would require a 16× PCIe slot (1× PCIe is 4Gbit/s) for optimal performance, and some motherboards only have one 16× slot, usually occupied by a video card.
On May 4, 2010, in Brussels, Intel demonstrated a laptop with a Light Peak connector (indicating that the technology had become small enough to fit inside such a device) and had the laptop send 2 distinct simultaneous HD video streams down the connection (indicating that at least some fraction of the software/firmware stacks and protocols are now functional). At the same demonstration, Intel maintained that it expected hardware manufacturing to begin around the end of 2010.[7]
In September 2010, some early commercial prototypes from manufacturers were demonstrated at Intel Developer Forum 2010.[8]
[edit] Copper vs. Optical
In January 2011 Intel's David Perlmutter in a Computerworld interview said that initial Light Peak implementations would be copper-based.[9][10] Intel has neither confirmed nor denied this. It is unclear if transmission speed will be affected by this change.[11]
[edit] Design
As a single universal replacement for current buses such as SCSI, SATA, USB, FireWire, PCI Express and HDMI, Light Peak aims to remove some of the problems in the computer industry that are now apparent such as the limited transfer speeds and multiple connectors, many of which must be supported and then are often fated to go completely unused.
A major problem in single-cable connection is the maximum length of electrical cables – DC power and electrical signals diminish rapidly over more than 5 meter distances.
In theory, a device under 5 m away could be easily served by either a 10 Gb DC PoE or 4.8 Gb USB 3.0 interface on a single cable for both power and data. However, if the device must be more than 5 m away it will be separately powered by AC and must necessarily rely on an optical cable anyway to achieve sustained 10Gb speeds, whether this is an Ethernet "short reach" (300 m) or Light Peak (100 m) cable.
[edit] Development
[edit] Electrical power supply uncertainty
The major uncertainty in Light Peak is what type of power interface it supports, if any. Originally, "Intel said it's working on bundling the optical fibre with copper wire so Light Peak can be used to power devices plugged into the PC"[12] and so seemed to compete with Power over Ethernet (PoE), USB and G.hn in this regard. However the clear announced intention as of 2010 [13] was "to have one single connector technology" that would allow "electrical USB 3.0 […] and, or, other protocols could, down the road, be run over optical" suggesting that Light Peak is a bus rather than an interface and further suggesting that Light Peak would piggyback on USB 3.0 or 4.0 DC power and possibly also (to support monitors) pass through AC (possibly IEEE P1901).
[edit] Comparison
To succeed, most commentators believe that Light Peak must replace single-use types of connectors such as HDMI, DisplayPort (which requires more than double the initial 10 Gbit/s in its higher end incarnations – see list of device bandwidths), eSATA, at least some uses of Ethernet and ultimately the smaller and slower speed USB devices as cost of a Light Peak connector comes down.
If it fails to replace lower end USB devices, then upgrades to those would tend to be to USB 3.0 or a successor 4.0 or 10Gb powered Ethernet, or a higher speed G.hn, any of which could have power and data rates very similar to Light Peak using a much cheaper copper-only interface. It is also not clear if Intel intends to require either AC or DC power or both, meaning as many as eight variations of the specification might co-exist (with AC only, with DC only, with both, with neither, in each of 10Gb and 100Gb incarnations) – similar problems crippled eSATA and slowed adoption.
[edit] Existing 10Gbps fiber interconnection standards
Light Peak, unlike most fiber ICs, was designed to be lithographically created directly on a CMOS IC, which can reduce size and manufacturing costs. For example, its physical size, by volume, is ~120 times smaller, ~10 times cheaper to manufacture[14]. It is compatible with current lithographic techniques to allow for easy scaling and mass production.
[edit] Monitor and drive ports
The HDMI and DisplayPort connectors require more than twice the 10 Gbit/s that Light Peak was proposed to include in its higher-end implementations – very much higher than what commentators expect Copper Peak to be capable of. Given announcements that Intel would support DisplayPort 1.2 and HDMI 1.4a exclusively, it seems unlikely that Light Peak will compete with them in the near future:
In December 2010 it was announced that Intel and AMD, with backing from various computer vendors, would stop supporting DVI-I, DVI-A, VGA and LVDS-LCD technologies from 2013/15[15]. “IDC's figures show DisplayPort was on 5.1 percent of commercial desktops in 2009, but that figure will grow to 89.5 percent of them in 2014. In commercial notebooks, DisplayPort's penetration will increase from 2.1 percent in 2009 to 95 percent in 2014. Only 24.5 million of the 427 million laptops in users' hands in 2014 will be VGA-enabled, Daoud stated. Another 279 million will use HDMI, while 167 million will use DisplayPort.” The vendors' joint announcement (to which Intel also consented) did not mention Light Peak at all:
Legacy interfaces such as VGA, DVI and LVDS have not kept pace, and newer standards such as DisplayPort and HDMI clearly provide the best connectivity options moving forward. In our opinion, DisplayPort 1.2 is the future interface for PC monitors, along with HDMI 1.4a for TV connectivity.— AMD, Dell, Intel Corporation, Lenovo, Samsung Electronics and LG[16]
[edit] Ethernet (10 Gbit/s unpowered)
Assuming that Light Peak would have no power interface of its own, the most direct and relevant comparison is to 10 gigabit per second Ethernet. A typical offering such as that of Neterion[17] supports one or two ports on a PCIe 8× card. A short reach (300m) or long reach (10 km) optical Ethernet cable is supported but using copper cables the maximum reach is only 5 to 7 meters, still about three times that of USB but far less than Light Peak's promised 100m. Power is a major factor limiting cable reach because regardless of how data is carried: a long, low-voltage, power cable suffers significant loss and is impractical much beyond 5 m.
Accordingly, unpowered Light Peak is only reasonably compared to unpowered 10Gb short reach optical cable: It seems to have only one-third of 10GbE's reach.
However, 10Gb Ethernet switching is extremely expensive and while it could come down in price (as 1Gb Ethernet did) in response to competitive pressures (from Light Peak and USB 3.0) the price-insensitive backbone market tends to dominate 10Gb.
Also there is no solution to tunnel USB, SATA, HDMI/DVI or other protocols over Ethernet. There is AoE, iSCSI and NBD but little or no support in Firmware, so it cannot be used as a boot device. Tunnelling HDMI/DVI most likely also need hardware support, like a 10 Gbit Ethernet port on graphic cards and displays. There are KVM solutions that can tunnel VGA/HDMI/DVI over Ethernet but they are not a full replacement for such a port, as they are intended for server management and at most handle gigabit Ethernet.
[edit] USB 3.0
Light Peak is often billed as a "USB3 replacement" though its 2010 rhetoric suggests it is a fibre optic enhancement of it. Its initial data rate is double that of USB 3.0, but is insufficient to replace all current monitor cables. The pre-draft USB 3.0 specification proposed 24 volts DC at 6 amperes (up to 144 W), which would be a great improvement on the actual USB 3.0 delivered specification of 5 VDC and 0.9 A, and the PoE specification (600 mA in IEEE 802.3at). Light Peak would require quite high power levels to run large bright monitors as seems to be its primary purpose, and even 144 W would seem to be low for this purpose. Gigabyte shipped USB 3.0 mainboards sourcing 2.7 A of current in 2010 so there is some evidence that USB 3.0 vendors would welcome a drastically greater DC power supply and would support Intel in pushing for a fully integrated AC, DC and fibre optic cable.[18]
[edit] PoE/Powered Ethernet
Because it is a general purpose bus, PoE (specifically IEEE 802.3at and IEEE 802.3af) at 10Gb would be Light Peak's most direct competitor with some advantages over any new fiber-based non-power-carrying model:
- 10Gb PoE will rely on widely available, cheap cabling (Cat6a).
- PoE provides up to 30 watts DC at variable voltage (1.5V to as much as 80 VDC) which is sufficient for many devices including smaller monitors hooked up to PCs.
- PoE has an obvious upgrade path to 10 Gigabit Ethernet compatibility which is the same data rate as Light Peak – it is compatible with Gigabit Ethernet and will be compatible with 10GbE and 100GbE.
- PoE devices are already widely deployed.
[edit] Configuration
The Light Peak cable contains a pair of optical fibers that are used for upstream and downstream traffic. This means that Light Peak offers a maximum of 10 Gbit/s in each direction at the same time. The prototype system featured two motherboard controllers that both supported two bidirectional buses at the same time, wired to four external connectors. Each pair of optical cables from the controllers is led to a connector, where power is added through separate wiring. The physical connector used on the prototype system looks similar to the existing USB or FireWire connectors.[19]
One key piece of the device chain that has not been shown is a controller for the device-end of the bus. In the USB case, a single controller can contain the power circuitry, USB device logic, along with off-the-shelf, custom or programmable logic for running devices. A simple USB device can be built by adding a connector, one driver chip, and the hardware the system is meant to drive; a mouse is a good example of a system that is typically implemented using a single off-the-shelf chip.[20] A similar single-chip solution will be in demand for Light Peak as well, but to date Intel has simply suggested it is working with industry partners to provide one.[21] According to Intel, the companies that will produce Light Peak technology include Foxconn, Foxlink, IPtronics,[22][23] SAE Magnetics,[24] FOCI Fiber Optics Communications Inc, Avago,[25] Corning, Elaser, Oclaro, Ensphere Solutions,[26] and Enablence.[27] Several necessary components from the mentioned suppliers need to play together in order to bring the first Light Peak-enabled PCs and other consumer products to the market. A few of the suppliers and their respective areas are listed:[28]
- SAE Magnetics: optical module
- IPtronics: driver and receiver silicon
- Oclaro: VCSELs
- Enablence Technologies Inc.: large-area, dual-wavelength 10-Gbps photodiodes
- FOCI Fiber Optic Communications Inc.: connectors and cables.
- Avago Technologies: optical module with embedded optical engine
- Ensphere Solutions Inc.: transceiver IC
[edit] Cables
Light Peak uses optical fiber cable containing two 62.5 micron wide fibers that can transport the infrared signal up to 100 meters.[29] The optical fiber is typically coated with plastic layers that protect the cable from moisture and other damage.
[edit] Characteristics
- 10 Gbit/s over optical cable (up to 100 metres in length)
- Connect to multiple devices at the same time
- Multiple protocols
- Bi-directional transfer
- Quality of service implementation
- Hot pluggable
- Intel is working on bundling the optical fiber with copper wire so Light Peak can be used to power devices.[30
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