5G drives faster optical transport links
Data rates reach 800 Gbps, which will carry traffic from many more users than networks see today. Open RAN creates an opportunity, says Ciena’s Brian Lavallée.
Unlike its predecessors, 5G includes upgrades to the wired infrastructure. Without those upgrades, faster radios wouldn’t help all that much. 5G, therefore, drives the need for faster optical transport in the fronthaul, mid-haul, and backhaul parts of the network. That’s pushing the state-of-the-art optical transport past 400 Gbps to 800 Gbps, also called 800G.
Recently, Ciena and Canadian network operator Telus have demonstrated an 800G optical link running 970 km from Toronto to Quebec City (Figure 1) based in Ciena’s Wavelogic 5 Extreme optical modem. Ciena develops its own ICs that go into transceiver modules, network switches, and other equipment. 5G Technology World recently spoke with Ciena’s Brian Lavallée, senior director of solutions marketing who is responsible for 5G, submarine, edge cloud, and satellite applications.
Figure 1. A network connection covering 970 km connects Toronto to Quebec City through Ottawa and Montreal.
“We cover datacenter distances of tens to thousands of kilometers,” said Lavallée. “The same optics also run submarine links between continents. Those data rates typically run at 400 Gbps to 500 Gbps per channel.” Data rates vary based on fiber length and spacing between reconfigurable optical add-drop multiplexers (ROADMs) and amplifiers. “Undersea cables can go farther than terrestrial cables using the same optics because the ROADMs are spaced closer together, sometimes by half the distance. Intelligence in the tunable optics scans the quality of the optical link and sets data rates from 200 Gbps to 800 Gbps in 50 Gbps increments.” Figure 2 shows one end of Ciena’s 800 Gbps installation.
Figure 2. Ciena engineers installed a transport network that carries packets at 800 Gbps. Image: Ciena.
When asked how Ciena engineers measure the quality of the optical signals, Lavallée said that test capabilities are built into the DSPs used in the optical modules, which allows for testing on the fly rather than having to take the link out of service to connect external test equipment. The DSPs can product measurements such as bit-error-ratio, chromatic dispersion, and polarization mode dispersion. Software can monitor network conditions and track performance over time.
5G’s impact
“5G is more than just increased capacity,” said Lavallée when asked if 5G will cause a jump in network traffic. Because 5G is also designed for massive machine-type communication (MMTC), it will seem any more connections and aggregate traffic. Furthermore, 5G will bring users who currently lack smartphones to begin using them (assuming the prices are within reach).
According to Lavallée, 5G network slicing will guarantee not only data rates but latency as well. Network slicing should bring applications such as AR/VR, industrial automation, and private 5G. “Fixed wireless access can achieve data rates of 10 Gbps and higher in some cases,” he said. “That aggregate data flow to and from data centers will certainly drive network traffic. That’s where 800G will come into play.”
Connections to cell sites need not always use fiber. Lavallée said that sites can use integrated access backhaul, where sites are daisy chained together using some of their wireless capability. Thus, not every cell site needs fiber because they can use wireless backhaul to connect to the 5G core.
Satellite connections, which are part of 5G, can use low-earth orbit (LEO) satellites that connect to 5G cell sites in remote areas and provide service. If course, the site still needs power. Geosynchronous satellites are too far away to handle latency requirements. “LEO satellites have shown to have latency from 15 ms to 50 ms. That’s short enough make them feasible.”
Open RAN
The open radio-access network (RAN) concept of disaggregating functions that have typically run in a single box presents an opportunity for companies in the optical transport business. That’s because of a standardized set of Ethernet-based interfaces between radio units, distribution units, and centralized units (Figure 3).
Figure 3. 5G open RAN architecture differs from 4G through disaggregation the baseband unit (BBU). Image: Ciena.
“The open RAN concept is currently a battleground in the industry,” said Lavallée. “Service providers have had to buy all three functions and the networks between them from the same source or lease dark fiber. “‘Closed’ and “proprietary’ are dirty word in the industry today. Everything is opening now, from hardware to software.” Lavallée went on to say that through the Open Cable Initiative, even the submarine networks have opened after being proprietary for decades. “The RAN is the last bastion of closed network functions. With an open RAN, the fronthaul from the radio to the DU is also open.” Functions that used to be in the baseband unit (BBU) are now virtualized. “The O-RAN Alliance has opened the fronthaul and mid-haul, creating opportunities that those of us in the transport business. Indeed, the O-RAN alliance has also opened the transport networks in addition to RAN functions, which the carriers want.”
