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Disaggregating the Broadband Access Network

Sterling Perrin
3/26/2018
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The telecom industry continues to advance its efforts to re-invent the telecom central office with data center-inspired technologies and architectures, including general-purpose hardware, open interfaces/APIs, disaggregation, SDN and virtualization. The ONF-led Central office Re-Architected as a Data Center (CORD) project has been the most visible example of this trend to date, and announcements continue at the annual Open Networking Summit, including ONAP and CORD integration.

But CORD is not the only project aiming to re-build the telecom central office in the data center model. The Broadband Forum launched the Cloud Central Office (CloudCO) project with similar goals of re-building the central office in the cloud (or data center) model. There are many similarities between the two projects with one key difference: while CORD is an open source project, CloudCO is part of a traditional standards process and will produce interoperability and implementation standards. Another difference is that CloudCO is newer. While the group was formally launched in 2016, its Cloud Central Office Reference Architectural Framework was published in January 2018.

A major focus area for CloudCo (and CORD) is disaggregating and virtualizing the broadband network gateway. In an access network, the BNG router serves an intermediary function aggregating broadband subscriber traffic and connecting the subscribers in a service provider’s network to the Internet. Because of its connectivity to all broadband subscribers, authentication, policy management, and security are also basic BNG functions.

Separating the BNG control plane from the data plane allows operators to centralize management and control of the routed network under SDN, with benefits of greater management scalability and better utilization of network resources due to the global network view (basic benefits of SDN). Additionally, this control and data plane separation is a pre-requisite for running individual functions as software VNFs on commodity hardware (i.e., migration to NFV).

An important theme across the telecom industry in 2018 is ensuring the integration and co-existence of physical and virtualized elements. For the vast majority of operators, a hybrid access network environment -- including a mix both physical network elements and VNFs -- will be the norm for many years to come, and operators can’t afford multiple VNF silos. Significantly, hybrid virtualized and physical network co-existence is a critical tenet of the CloudCO reference architecture.

Work to disaggregate the BNG is on the right track and aligns well with network operator goals, according to recent Heavy Reading research. In a global operator survey published in February 2018, Heavy Reading asked network operators to identify the most important network segments for SDN implementation over the next three years. Metro/aggregation networks topped operators’ priority list. Additionally, layer 3 edge routing was near the top of the list among network functions targeted for disaggregation – coming after data center switching/routing and essentially tied with CPE equipment.

There is still much work to be done to reinvent the central office, but efforts that focus on edge routing disaggregation, such as BNG functions, and provide a blueprint for physical and virtual element co-existence should prove worth the effort.

— Sterling Perrin, Principal Analyst, Heavy Reading

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