SDN & NFV in Mobile Networks

With some analyst firms reporting that SDN-driven backhaul could save carriers up to $9 billion by 2017, mobile network operators (MNOs) are evaluating software-defined networking (SDN) and network functions virtualization (NFV) because they provide the opportunity to make the transition from appliance-based, proprietary hardware implementations to software-based, open platforms.

Already, there has been tremendous focus from MNOs in the evolution of their mobile edge to incorporate virtualization into their infrastructure, from cloud RAN through virtual LTE evolved packet core and Gi-LAN virtual services. These technologies are crucial in refining their operational models to improve margins in existing businesses, and critical as MNOs attempt to capture new revenue streams, such as machine-to-machine and next-generation mobile virtual network operators, with economics that are substantially different from their current business.

Mobile networks: architectural vs operational reality

The LTE architecture, as defined by 3GPP, is functionally split between the evolved UMTS terrestrial radio access network, the evolved packet core (EPC), and policy, identity and charging infrastructure. This represents a simplified architecture in which the mobile network is realized through the deployment of eNodeBs, mobility management entities (MMEs), serving gateways (S-GWs) and PDN gateways (P-GWs), as in the diagram below.

A simplified architecture

A 3GPP standards-based architecture in which the mobile network is realized through the deployment of eNodeBs, mobility management entities (MMEs), serving gateways (S-GWs) and PDN gateways (P-GWs).

In this simplified architecture, control plane functions, such as the online and offline charging systems (OCS, OFCS), policy and charging rules function (PCRF), and home subscriber servers (HSS), interact with the mobile network infrastructure through a variety of 3GPP-d efined interfaces.

However, because the foundation of the mobile network is built on IP, it looks more like the following diagram. Responsible for the transport of consumer traffic between the mobile device and the Internet, and for the transport of 3GPP control traffic between the mobile network elements, this IP network connects up to tens of thousands of macrocells to thousands of network locations performing various network functions, such as aggregation, tunnel termination, policy enforcement and traffic optimization.

The mobile network built on IP

The mobile network, built on IP, is responsible for the transport of consumer traffic between the mobile device and the Internet, and for the transport of 3GPP control traffic between the mobile network elements.

SDN and NFV in the mobile backhaul network

Operationally, the mobile backhaul network is highly complex, with 10+ hops from the mobile device to LTE EPC, leveraging multiple transport technologies and strict requirements for latency, timing transport, and operations, administration and management.

This complex backhaul network directly affects operator margins, with as much as 30% of OPEX consumed by the backhaul network. However, according to a study conducted by Strategy Analytics, SDN-driven backhaul could save carriers up to $9 billion by 2017, with over half of that savings originating from the introduction of SDN for cloud RAN, local breakout and metro aggregation.

Indeed, SDN could be the single biggest opportunity for operational improvement in mobile backhaul networks since the transition from circuit switching to packet switching. Specifically, the three areas where SDN will change the existing mobile backhaul paradigm include:

• Virtual routers: By virtualizing the cell site router, mobile operators can standardize on software functionality that scales up or down independently of the hardware form-factor to support both macrocell backhaul and small cell backhaul, and future deployment of C-RAN fronthaul. Multiple virtual routers can be deployed on the same physical cell site infrastructure, supporting multi-tenancy for metro Ethernet backhaul providers. The virtual routing technology may also be embedded in existing mobile network elements (macrocells, small cells or microwave radios), reducing the physical footprint at the cell site.

• Controller-based intelligence: Introducing a SDN controller in the mobile backhaul network reduces opex by centralizing the intelligence required to provision, modify, monitor and troubleshoot the mobile backhaul network, including routing/forwarding decisions and QoS rules, across cell site routers, pre-aggregation nodes and aggregation nodes. Open southbound interfaces enable the SDN controller to support multiple vendors in the backhaul network, extending the capabilities to include transport functions in SDN-capable eNodeBs and microwave radios.

• Integration with other dynamic systems: As dynamic policy capabilities, such as self-optimizing networks (SON) servers for RAN self-configuration, self-optimization, and self-healing and PCRF for flow-based QoS and charging and rating rules, are added to the mobile network, the mobile backhaul network has largely remained static. By integrating an SDN controller with other network decision points through REST APIs, mobile operators can leverage mobile backhaul analytics to improve SON/PCRF decisions, and program the mobile backhaul network to match RAN and service requirements.

SDN and NFV for mobile b ackhaul

An illustration of one potential role that SDN and NFV could play in mobile backhaul networks.

Ultimately, as the eNodeB and the LTE EPC transition to virtual functions to improve elasticity, the underlying transport infrastructure between these virtual functions must be capable of adapting and scaling in the same manner. This will be achieved by incorporating SDN and NFV capabilities into the mobile backhaul network and integrating the intelligence and understanding of the RAN, backhaul and IP flows into a holistic understanding of the mobile network capabilities, conditions and constraints.

Once this level of visibility and cross-domain programmability is achieved, MNOs will be in the position to realize the economic (reduced CAPEX, OPEX) and operational (simplified management, improved time-to-market) benefits that SDN and NFV provide, and be in a better position to successfully deliver new consumer, enterprise and M2M services and applications.