Testing the Limits of DOCSIS as a Backhaul for 5G
By Tom Conklin
Cable operators are making plans to get into the wireless business for a number of reasons. 5G specifically satisfies a need for lower cost last mile service for high demand fixed broadband customers as an alternative to fiber to the home. But mobile network operators are working hard on business to business use cases for 5G with an expectation for dedicated fiber as a back haul. For cable companies deploying 5G for fixed wireless, the option to use DOCSIS as a backhaul technology looks attractive as do the resulting revenues. The specific needs of B2B services using the access and transport network present some challenges to the technology.
Advances made with 5G technology have communication service providers preparing to support business models not possible with LTE or Wi-Fi or fixed broadband access technologies before. Picture augmented reality implemented in a pair of glasses that helps an airplane technician access instructions and wire frame video overlays depicting the wiring diagram of a part in real time, eliminating individual interpretation as a contributor to critical mistakes. Or warehouse robots picking a single order for shipment accross multiple facilities and suppliers based on real time inventory, weather and traffic data to ensure the fastest and most efficient path to the customer. These use cases require data transfer speeds that LTE does not provide and predictable latency that Wi-Fi can’t. And the speed and latency of the access technology is dependent on the backhaul technology, core and associated platforms to provide the end-to-end performance required of the use case. When DOCSIS is used as a backhaul, considerations need to be made for which use cases can be supported and what adaptations need to be made to support their demands.
5G can easily provide the 500 Mbps of bidirectional throughput and sub 20 ms of latency the augmented reality and robotics use cases require. It is a good choice for a wireless technology because unlike with Wi-Fi, latency does not go up significantly as new users and devices connect. These two use cases do not require mobility like you might need in a moving car or on a train, with sessions supported between cell sites. They will likely be supported by 5G small cells deployed in an industrial enterprise consuming the service. DOCSIS 3.1 can provide the requisite data rates downstream and also upstream if the price is right. Latency is improved by active queue management (AQM) in the latest release, but still suffers from upstream contention taking a potential of just 5 ms of additional latency for backhaul up to a more realistic 30 ms to 50 ms. Implementation of bandwidth report (BWR) to provide coordination of scheduling between the 5G small cell and the DOCSIS CPE can theoretically fix this down to the lower limits of the DOCSIS link.
So it is possible to achieve the performance requirements of the augmented reality and industrial robotics use cases, but it is going to require tight collaboration between the 5G small cell vendors and the DOCSIS CPE vendors to ensure the equipment works together and enables the right throughput and latency performance for the features. Also, contention on the upstream path needs to be eliminated as predictability is important to the service level agreement required by these use cases. The practicality of making these adjustments probably makes it a better idea for the cable operator to just use fiber for the backhaul. DOCSIS can be used as a backhaul for 5G for residential and other fixed wireless applications but is not a natural fit for some of the more demanding services.
Tom Conklin
Vice President of End to End Architecture
Ericsson
Tom Conklin has 25 years of global leadership experience in IT and telecom and specializes in cloud software and infrastructure. He is on Ericsson’s North American Digital Services CTO Team helping communication service providers transform to embrace 5G, cloud, and automation.
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