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Exploring network functions virtualisation

Posted: 24 Dec 2014 ?? ?Print Version ?Bookmark and Share

Keywords:Network functions virtualisation? NFV? software defined network? SDN? COTS?

Mobile operators are looking to make the most of the operational and capital cost savings that virtualisation has brought to the enterprise world. Network functions virtualisation (NFV) promises the opportunity to take network functions that sit in dedicated appliances and relocate them as virtual instances, leading to increased flexibility, reduced CapEx and OpEx, and increased innovation. Operators have already seen early successes deploying NFV on control plane elements in the network. The data plane, however is presenting unique challenges.

The control plane is the controlling signalling infrastructure of the network that establishes and manages sessions end-to-end across the network. Control plane network functions tend to be CPU-intensive processes, but are much lighter in terms of throughput and bandwidth requirements. Given these features, control plane functions are well-suited to NFV architectures and existing virtualized platforms.

The data plane refers to the actual transport and delivery of the broadband traffic and media that are flowing within those sessions. Within an EPC, the data plane elements include the serving gateway (S-GW) and packet gateway (P-GW) that move user traffic from the user device to external networks. Other data plane virtualized network functions (VNFs) include deep packet inspection (DPI) elements, as well as policy-related elements (PCEF/PCRF). IP forwarding elements that are controlled by software defined network (SDN) controllers also reside in the data plane.

The data plane has distinct scale requirements. Virtualized data plane processing involves millions of broadband streams and dynamic load balancing across hundreds of virtual machines with near-zero latency. A data plane function may require fewer CPU cycles per gigabit of traffic, but it will also need to transport, encrypt, and encode millions of bits or potentially multiple Tbps through the network. As an example to contrast the scale of the challenge, a 3-minute VoIP call requires approximately 10-15 SIP signalling packets in the control plane and approximately 36,000 RTP packets in the data plane. Therefore, to address the data plane processing demands in the network using NFV, operators need a different class of virtualisation platform.

NFV for the data plane requires a focus on retaining carrier-grade reliability, density and capacity with minimised latency. The vision of NFV is that network functions could all be hosted on commercial servers instead of dedicated "telco" equipment; however, there are concerns that commercial off-the-shelf (COTS) hardware supporting virtualized functions is not carrier-grade. Some of the potential solutions to these challenges come from gains in silicon technology and improvements in virtualisation software, but there is also another option beyond these technical solutions. A class of open commercial server products could be optimised for hosting data plane VNFs with a blend of networking, switching and compute resources.

An ideal NFV platform architecture for the data plane would intelligently classify and load-balance tens of millions of data plane sessions across hundreds of virtualized functions. An intelligent switch within the NFV platform could be designed to apply wire-speed packet classification at packet ingress, and then rapidly decide what virtualized processing may be required against each flow. An integrated load balancer would distribute the data plane flows to relevant and required virtualized functions.

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