First 50G-PON merchant silicon spurs operator trials

Broadcom has unveiled the industry’s first merchant silicon for the 50-gigabit passive optical network (50G-PON) access standard. Until now, only access equipment players such as Huawei and ZTE had their own 50G-PON silicon.  

A 50G-PON network. Source: Adtran.

Broadcom has announced two 50G-PON devices: an optical line terminal (OLT) chip and the optical networking unit (ONU) 50-PON port to the users.  Both chips include custom hardware from Broadcom to run artificial intelligence (AI) machine-learning algorithms. 

Jim Muth, senior manager of product marketing at Broadcom, says supporting AI benefits the operator and the quality of the end user’s broadband service. 

High-speed PON

The 50G-PON is the ITU-T’s latest high-speed access standard.

50G-PON follows the organisation’s XGS-PON, a 10-gigabit PON standard, and before that, the original Gigabit PON (GPON) fibre-to-the-home scheme. GPON supports 2.5 gigabit-per-second (Gbps) downstream (to the user) and 1.25Gbps upstream. 50G-PON is backwards compatible with XGS-PON and GPON. 

The leading three Chinese operators—China Mobile, China Telecom, and China Unicom—will deploy 50G-PON and have been trialling the technology. Working with Huawei, Orange has undertaken a 50G-PON field trial in Brittany. Meanwhile, European operators such as Altice, BT, Deutsche Telekom, Swisscom, and Telefonica plan to deploy the technology. “It’s too far into the future for them to make a public statement about their activity,” says Muth.

In a separate announcement, Adtran announced that it is working with alternative network (altnet) operator Netomnia to offer 50G-PON services to the UK market. Adtran is using Broadcom’s 50G-PON chips.

Netomnia, after merging with bsk, has the UK’s fourth-largest full-fibre network. Netomnia says adopting 50G-PON will enable it to scale. Its target is to serve one million customers by 2028. 

“Many altnets in the US and the UK are interested in 50G-PON technology,” says Stephan Rettenberger, head of marketing and corporate communications at Adtran. “As they’re much smaller than Tier-1 providers, they’re more agile and generally able to deploy new technologies much faster.”

25GS-PON

A competing PON scheme is 25 Gigabit Symmetrical PON (25GS-PON). The 25GS-PON is not a standard but an industry multi-source agreement (MSA) whose members include operators AT&T, Cox Communications, Chunghwa Telecom and equipment makers Nokia, and Ciena. The MSA uses work developed for 25 gigabit Ethernet PON and XGS-PON standards.

Google Fiber offers customers a 20-gigabit connectivity service that includes Wi-Fi 7 that costs $250 a month in select US markets. The high-bandwidth access service uses 25GS-PON. 

Adtran favours 50G-PON because it is a standard. “The ITU-standardised generations of PON (GPON, XGS-PON and 50G PON) all co-exist and are the recommended evolutionary steps in the access network,” says Rettenberger.

Applications

Having 50 gigabits of access bandwidth enables other applications besides traditional connectivity services for businesses and residential users. Broadcom cites autonomous driving, where comprehensive cellular coverage is required. For that, many small-cell phone towers are needed along a highway. Instead of each having a backhaul fibre link, several cell towers could share the 50G-PON.  

Autonomous driving is some years out, but Muth says infrastructure first needs to be in place. "It's going to happen over the decade or more, so you have got to start deploying that sooner rather than later," he says.

Having 50 gigabits of capacity also allows a service provider to offer businesses dedicated bandwidth links, In contrast, XGS-PON is more restricted with its total 10 gigabits of capacity.          

Machine learning and PON 

The training of AI/ machine-learning algorithms for access is performed by the operator, or by the operator working with a third party.  Broadcom says it too works with interested operators. 

The training results are weights that are downloaded to its 50G-PON chips to perform inferencing and run the machine-learning algorithms on the operator’s network data. “Most operators are already using AI machine-learning algorithms, but they are running them in the cloud,” says Muth. By adding inferencing hardware on-chip, data remains local to the user and the PON OLT without using precious bandwidth to upload the data for processing in the cloud. 

The on-chip AI performs such tasks as intrusion detection and flow classification. Using AI on-chip, intrusion detection can be shut down quicker.  Flow classification identifies such traffic as video conferencing, voice calls, and bulk data. 

PON hardware has packet processing and traffic management functions, but the issue is that packet headers are increasingly encrypted. Using a machine learning algorithm allows traffic to be identified based on a flow’s nature. "The number of packets over time identifies it," says Muth. A voice call’s flow has regular if small amounts of data. A video conferencing flow is also regular but has more data. Video traffic can be prioritised ensuring a better experience for the user. 

50G-PON chips

Broadcom uses a 7nm CMOS process for the 50G-PON OLT and ONU chips. 

The BCM68660 OLT chip integrates what was previously three chips.  The chip combines the switch function with packet and traffic processing and two media access controllers (MACs). This allows the chip to support 16 XGS-PON and 16 GPON ports. Each channel supports up to 256 users, but a small split ratio of 1:128 or 1:64 is used in practice. "Now, if you're going to do 50-gig, it's a little bit smaller," says Muth. "It's eight ports of 50 gig, eight ports of XGS-PON, and eight ports of GPON so that you can do all three simultaneously."  

The chips also support 50-gigabit symmetrical (download and upload), 50Gbps downstream and 25Gbps upstream and 50Gbps downstream and 12.5Gbps upstream. The capacity of the BCM68660 OLT chip totals 500 gigabits.

Having an OLT-on-a-chip reduces power consumption. Muth says the switch chip consumes about 60W, and each PON MAC 15W, for an OLT total of 90W. In contrast, the 7nm CMOS single-chip PON OLT consumes 45-50W.

The ONU BCM 55050 chip is an Ethernet bridge chip. "It terminates the 50-gigabit PON and provides Ethernet to something else, either a switch chip for distribution within a home or a company, or to a gateway chip."     

Meanwhile, Adtran says it is seeing growing interest in the latest PON standard.  Now having silicon for a 50G-OLT line card, Adtran can start trialling work. Five customers will trial 50G-PON in the coming months, it says.