NTT's PON Demo Cuts 5G & FTTH Latency

By disaggregating time-critical PON functions, one recent tech demo is showing operators the way forward for speeding up 5G service deployments and running optical networks at lower costs.

On Friday, the last day of Broadband Forum's quarterly meeting, NTT showcased mobile and Fiber-to-the-Home scenarios as part of the two organizations' PON Abstraction Interface for Time Critical Applications Project, launched in 2017. This initiative investigates the application of software-defined networking (SDN) and network functions virtualization (NFV) in optical line terminals (OLTs) to eliminate operators' need for rebuilding OLTs from the earliest stages of development (such as a PON chip).

NTT demonstrated how Dynamic Broadband Allocation (DBA) software could optimize a future OLT and significantly reduce latency for 5G use cases. As a result, dense small cells can be cost-effectively accommodated by TDM-PON, according to Broadband Forum. Also, operators can apply a second DBA software to OLTs in FTTH services that need high bandwidth efficiency.

"Time Critical Applications are essential to meet changing user behavior," said Akihiro Otaka, executive manager at NTT Access Network Service Systems Laboratories at NTT, in a statement. "The demonstration we have carried out at the Broadband Forum meeting is a significant step for the project as it shows how operators can cost-effectively upgrade OLTs via a software upgrade. Standardization in this area is essential as it will achieve a vendor-agnostic system and ensure mass deployment which is key to realizing agile and flexible next-generation broadband networks and the delivery of 5G."

Indeed, this is a significant step beyond software-upgradeable OLTs, Dan Grossman, principal analyst at NetAccess Futures and a contributing analyst to Heavy Reading, told Broadband World News.

"First, BBF is disaggregating downstream scheduling and upstream dynamic bandwidth allocation (DBA) through a new API. Previously, vendor-proprietary algorithms were baked into OLT software by the vendor's development teams. This means that operators, system integrators and vendors' application engineering teams can create or modify algorithms that behave according to application- and customer- specific requirements," Grossman said.

"Second, this is a proof-of-concept for an important use case. 5G fronthaul is extremely latency sensitive because of the retransmission mechanism in the air interface. There had been doubts that XGS-PON or NG-PON2 (TWDM) could meet these requirements in the upstream direction," he added. "NTT developed algorithms that apply existing mechanisms in the *G-PON standards to ensure that ONT/RRH units are able to transmit promptly on the PON after receiving packets from the air interface and that packets received from the BBU are forwarded promptly to the ONT/RRH."

Vendors will need to make the new API available in their platforms for operators to make similar advances -- a step in line with what Grossman sees from vendors such as ADTRAN, Calix and Nokia.

"Taking it a step further into white box implementations, I assume that VOLTHA has this API or a similar one," he said. "This validates that PONs can be used instead of point-to-point fiber or DWDM for 5G fronthaul. PON architectures will often be the lowest cost alternative, especially when the operator has moved to a converged access network model."

The Forum and NTT plan to explore now whether they can establish a cooperative interface between the Central Unit in mobile networks and an OLT. This requires coordination with standards defining organizations such as 3GPP and CPRI and IEEE, the release said.

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• NG-PON2 Success Depends on Dropping Price of Tunable Optics: Ovum

— Alison Diana, Editor, Broadband World News. Follow us on Twitter or @alisoncdiana.