New optical interface standard aims at 5G

-October 03, 2017

The name Optical Data Interface was carefully chosen. First of all, Optical refers to the multimode fiber-optic transmission medium that connects from one device to the other. Data implies that the standard is aimed at data transmission, not control. Control plane communication is performed over a product’s standard interface, such as LAN or PCI Express, to set up the optical connection, which then runs independently until a “stop” event. Interface refers to the concept of a pluggable port, which can be placed anywhere on a product. ODI is high-speed point-to-point optical data connection, not a traditional parallel bus. It is not specific to backplanes at all, though ODI ports may be placed on backplanes.

Figure 2 shows the three key technologies behind the Optical Data Interface standard. The physical medium is 12-lane multimode fiber optics, delivering more than 160 Gb/s per port. The protocol layer is the Interlaken protocol, which delivers packet data between devices. Finally, the packets and their content are defined by the VITA Radio Transport protocol.

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Figure 2. ODI incorporates physical-layer optics and Interlaken Protocol combined with VITA 49 data packets. Source: Modular Methods and the AXIe Consortium.

The ODI standard leverages three layers of technology, as shown in Fig 2. The physical layer is defined as optical technology consisting of 12 lanes of 14.1 Gb/s each, enabling 20 GBytes/s per optical port. Multimode fiber cables connect ports together, using the standard MPO (Multi-fiber Push On) connector. Ports may be aggregated, with four ports delivering 80 GBytes/s. Samtec announced immediate support of the ODI standard, with ready-made optical engines and cables based on its FireFly Micro Flyover System.

The protocol layer is defined by the Interlaken standard, a chip-to-chip interconnect standard common in data centers, conceived by Cortina Systems and Cisco Systems. Interlaken is supported by the major FPGA suppliers, and is managed by the Interlaken Alliance. It delivers packets of data over any number of serializer/deserializer (SerDes) lanes, at any speed. Interlaken doesn’t define the packets, only their boundaries as a block transfer. Intel and Xilinx have both announced their intent to offer ODI-compliant Interlaken cores for their FPGAs.

Packets play a critical role in ODI. They envelope the data payload that contains single channel or multi-channel sample data. Consecutive packets are sent to stream data. Data is stored as packets. Packets enable error recovery from an outage, such as could be caused by an electrostatic discharge. Packets allow port aggregation, the combining of ports to achieve proportionally higher data rates.

ODI has adopted the VITA 49 family of standards for packet definition. VITA is a trade and standards organization well known for its VME and VPX standards, common in many mil/aero embedded applications. VITA 49.0 is titled as the VITA Radio Transport (VRT) specification. VRT defines common packet formats and protocols for software defined radios, but is applicable for sending any sampled data or block data.

You can see how the three layers map into the three ODI specifications. ODI-1 is the physical layer, which combines the optical layer and the protocol layer. ODI-2 introduces packets and port aggregation. With ODI-2, block data of any format may be sent between devices. Finally, ODI-2.1 defines the actual data formats for the sampled data. ODI-2.1 focuses on 8-bit to 16-bit real and complex binary data, the most practical resolutions for high-speed transfers.

VRT packets on top of optics create a remarkable opportunity. According to VITA Executive Director Jerry Gipper, the VITA Radio Transport standards define packet structure and formatting for a wide set of software defined radio and mil/aero applications. With its adoption by the test-and-measurement industry, VRT has expanded its reach, which sets up numerous opportunities for synergy. Gipper also noted that there is no apparent reason that ODI couldn’t be adopted by the embedded industry as well. Thus, ODI could be as applicable to operational systems as to instrumentation systems. ODI delivers high-speed sampled data in an industry standard software defined radio packet structure, so why not?

Imagine the possibilities for synergy. Instruments and operational systems sharing the same interfaces and data formats. Don't have the RF front end yet for your embedded design? Don't wait. Grab your ODI-capable digitizer or oscilloscope and stream the data into your prototype. Have an embedded processor design, but no RF output stage? Connect your embedded processor to your ODI-capable arbitrary waveform generator (AWG) and generate the signal. Need some real-world signals to test your design? Record them from a RF digitizer to a storage array using ODI, and then play them back using an ODI-capable signal generator.

Speaking about applications, let's review a few.

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