SDN in the Cable Access Network

Jeff Finkelstein, Executive Director of Network Strategy, Cox Communications



With a Compound Annual Growth Rate approximately (CAGR) of 50% over the past few years we may extrapolate what our network consumption will become in the next ten years. At this pace we will outgrow capacity within cable TV head-end facilities. This will cause an increase in complexity, cost and operational impacts as we work to meet customer bandwidth demand. As service providers cable operators are concerned with managing the operational impact and cost associated with this dramatic increase in network requirements.

As part of looking at a Network 2025 view, we will focus on three key technology transformations that will help us make decisions along the way and provide a north star for optimizing our network. These three choices are:

  1. Software Based Networking commonly called Software Defined Networking (SDN);
  2. New access technologies increasing the capacity on existing and new network deployments;
  3. Virtualization techniques to reduce the amount of equipment needed to provide services and manage network components.

In this article I will focus on the first item, Software Based Networking.


Software Based Networking

When discussing software based networking I break it down into three key segments: Management, Control and Data planes. 

The Management plane is how we manage the devices and services in the network. Common technologies include XCONF, SNMP, TR-069 and NETCONF as mechanisms for managing, along with languages for defining the management data constructs like Command Line Interface (CLI), YANG or JSON.

The Control plane defines how network elements are controlled, using technologies like SDN. SDN creates a software programmable network reaching from customer premise to data center, allowing dynamic provisioning of devices. It improves automation by using common APIs abstracting the underlying network from the OSS/BSS system, and provides a mechanism for rapid deployment of new services.

The Data plane is the physical and logical path taken by information and data packets as they move through the network. The Control plane allows the SDN controller to define a path for packets using protocols linked into the forwarding plane on the network devices, whether physical or virtual.

Software Based Networking is the sum of the parts allowing creation of dynamic virtual networks and services using well-defined protocols.


Application to the Cable Provider Network

From the beginnings of DOCSIS deployments in the late 1990s to today, whenever new capacity was needed in either the access, metro or backbone networks we were required to add specialized hardware to provide it. If we needed more capacity in the access network, we may have added more DOCSIS channels and/or performed a node split, dividing the customers into multiple service groups. At a 50% growth rate this works for a time, but we will eventually need to follow the same logic path again in 18-24 months.

The Hybrid Fiber Coax (HFC) plant has a long useful life and is capable of significant amounts of bandwidth, but we are limited by: silicon availability; linearity of amplifiers; frequency response of the cable itself; and many more constraints not specific to cable but common among outside plant deployments of broadband technologies. We need a better way to optimize the entire network to meet the capacity demand of our users.

Software Defined Networking is a key component for future growth within the broadband system. By leveraging the abstraction of the access network and embedding higher cognitive functions into SDN controllers we are able to have applications make decisions on network optimizations with no a priori knowledge of the physical network infrastructure.

The SDN controller may control not only the traditional network equipment such as backbone and metro routers, switches, and photonic layer devices, but customer premise equipment itself to direct traffic flows via optimal paths. In future home networks when there are hundreds to thousands of Internet of Things (IoT) equipment ranging from home automation, home security, sensors, and appliances, the SDN controller may control the in-home network itself by providing a multi-homed network to maximize connectivity for those services our customers will rely on. The methods defined are not limited to the DOCSIS network, they may be applied to any access networking technologies from DOCSIS, to PON, Wi-Fi, millimeter wave, LTE and 5G.


Legacy Device Support

Equipment that is deployed in the access network has a long life in the consumer’s home and outside plant. By taking advantage of abstraction we may take the SDN controller commands and convert that into commands understood by legacy devices. Many support SNMP and TR-069, while others rely on CLI to be configured.

Using a network services orchestrator to act on behalf of the legacy devices allows their inclusion in the future network and provides a way to optimize capital expenditures over the next 10 years as we move toward the future network state.


SDN for Virtualized Services

Virtualizing services traditionally provided by physical hardware in the home network is a popular topic for conferences, papers and magazines. There are conferences dedicated to Network Function Virtualization (NFV) as a way to solve the hardware based cycle of deploying new services. While NFV provides a method for creating network services in the cloud, we still need to get the traffic to them.

Using SDN as the way to route traffic to virtual network functions provides an opportunity to optimize the underlying network configuration in real-time. The following is an example of one way to accomplish this:

  1. Consumer device comes on-line and sends a “wake-up” message to the management controller (MC);
  2. The MC looks up the device in the customer catalog and determines what services are available to the customer;
  3. The MC communicates with the SDN controller (SC) to determine where the services are located;
  4. The SC communicates with the NFV controller (NC) notifying it that the consumer device is online and ready to transmit;
  5. The NC looks up the services in the available product catalog and notifies the NFV orchestrator (NO) of a need for those services;
  6. The NO finds available compute, network and storage resources to meet the needs of the consumer and passes the information back up to the NC;
  7. The NC creates the Service Function Chain (SFC) for the requested services and passes the entry point to the SC;
  8. The SC computes the optimal path for the consumer devices of the SFC;
  9. The consumer device sends data to the SFC entry point for transit through the virtual network.



Software Based Networking and Software Defined Networking are both in a state of evolution. With each new pass through the technologies we learn more about the applicability of each to our network growth and services planning. By leveraging these technologies, we will be capable of optimizing and automating our networks for current and future services, freeing our engineers to focus on the customer.



Jeff FinkelsteinJeff Finkelstein is the Executive Director of Network Strategy at Cox Communications in Atlanta, Georgia. He has been part of the engineering organization at Cox since 2002, and led the team responsible for the deployment of DOCSIS technologies, from DOCSIS 1.0 to DOCSIS 3.0. Jeff and team have made significant contributions to the access network design and deployments at Cox, and he now has the new role of being responsible for future technology planning of backbone, metro, access, and home networks. His current focus is on defining the 10 year network strategy for Cox and leading the effort of moving to organization towards that vision.

Included in his achievements is being part of the CableLabs team contributing to the DOCSIS 3.0 PHY spec, initiating the distributed access architecture effort, creating the CableLabs Pro-active Network Management group, starting the DOCSIS 3.1 effort, defining the requirements for the Active Queue Management analysis, initiating the DPOG specification and being part of the team creating the CCAP hardware, software and management specifications. Jeff has been published and spoken worldwide on topics including distributed access architectures, future network trends, CCAP, IPDR, PHY technologies, network virtualization and IP video deployment over DOCSIS.

Jeff holds degrees in Education and began his career working on UNIX kernel development focusing on scheduling and virtual memory. In 1996 he started working in the cable industry deploying pre-DOCSIS data services and began working with DOCSIS in 1999.

Jeff has over 32 patents issued and/or pending.



Neil DaviesNeil Davies is an expert in resolving the practical and theoretical challenges of large scale distributed and high-performance computing. He is a computer scientist, mathematician and hands-on software developer who builds both rigorously engineered working systems and scalable demonstrators of new computing and networking concepts. His interests center around scalability effects in large distributed systems, their operational quality, and how to manage their degradation gracefully under saturation and in adverse operational conditions. This has lead to recent work with Ofcom on scalability and traffic management in national infrastructures.

Throughout his 20-year career at the University of Bristol he was involved with early developments in networking, its protocols and their implementations. During this time he collaborated with organizations such as NATS, Nuclear Electric, HSE, ST Microelectronics and CERN on issues relating to scalable performance and operational safety. He was also technical lead on several large EU Framework collaborations relating to high performance switching. Mentoring PhD candidates is a particular interest; Neil has worked with CERN students on the performance aspects of data acquisition for the ATLAS experiment, and has ongoing collaborative relationships with other institutions.



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