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November 19, 2015
Telecoms.com periodically invites expert third parties to share their views on the industry’s most pressing issues. In this post, Bill Kaufmann, Group Product Manager, SDN Planning at Coriant, explores the benefits of SDN to mobile backhaul networks and looks at best practice for implementation.
Mobile services and mobile backhaul (MBH) networks are under pressure from a variety of technology, market, and financial forces. Bandwidth demand from mobile devices (smartphones, tablets) is exploding, driven by streaming media and real-time communications applications. With LTE-A and 5G mobile user throughputs rising to 1G and beyond, it is becoming increasingly costly to backhaul all traffic to the network core.
A new generation of services – and rising end-user Quality of Experience (QoE) expectations – will be far less tolerant of latency and congestion. As new Over the Top (OTT) applications appear with increasing speed, carriers will struggle to respond on short notice to user and service demand. The predicted proliferation of low speed sensor traffic and network attached devices for Machine Type Communications (MTC) will require ultra-high reliability connectivity to private monitoring facilities rather than traditional mobility gateways.
These trends point to the need for a less hierarchical, more dynamic, and performance-aware mobile backhaul network at a time when financial pressures demand more efficient network utilization, more efficient network operations, and innovative new services. Fortunately, implementation of Software Defined Networking (SDN) in mobile backhaul networks can help meet these challenges.
There are 3 key SDN concepts that promise substantial benefits in mobile backhaul networks:
Centralized Control Plane Functions. A centralized controller opens the network to new classes of carrier service and faster upgrades since only the controller must be updated for new functionality. The ideal SDN architecture for mobile backhaul will selectively centralize functions best served by a unified controller while leaving packet forwarding decisions for traffic management and resiliency, OAM and performance management, network synchronization, and other functions within distributed network elements.
Open Standard Programming APIs. In order to support a broad variety of applications in a multi-vendor network, an open library of Application Programming Interfaces (APIs) is needed. Rather than expose all of the complexity of the network, APIs present a simplified, abstracted view so that carrier applications can make high-level service requests without the need to know path details or hardware configuration protocols. The SDN controller translates API service requests into hardware configuration commands. As long as the northbound interface to applications is consistent, the southbound interface to network elements can be a mature, full-featured legacy protocol, such as SNMP or NetConf, or a newer protocol such as OpenFlow. In this way both legacy equipment and new network elements can become part of a common programmable network. Increasingly, carriers are realizing that such a pragmatic approach to SDN control will be essential to the evolution of existing, multi-vendor mobile backhaul networks.
High Performance Network Elements. With thousands of network elements widely distributed across a geographic area, the MBH network demands high-performance infrastructure combined with low-touch management. Even with new SDN control and orchestration capabilities, a robust mobile backhaul network ultimately depends on high-performance network elements. Often these devices are located in remote, difficult to access, or harsh operating environments so must be built with appropriate form factors and environmental specifications. In addition to forwarding traffic, these routers must provide performance monitoring, fault detection alarm generation, outage detection and failover. They must track network layer performance that is then reported to the central control platforms. Most critical for mobile networks is the delivery of network synchronization to ever tightening standards.
Together, the introduction of an external control plane and programming APIs, on top of a robust network infrastructure, will enhance backhaul configurability and optimization to improve flexibility and responsiveness of the mobile network.
These concepts point to a distinct set of lead SDN applications for mobile backhaul networks.
Improved Network Utilization and Operation. Excess capacity is commonly provisioned in MBH networks in the form of protection links in case of network outages. In addition, steady state network traffic usage is often capped at 60-70% of total link capacity to accommodate bursty traffic patterns. This combination of design criteria leads to networks operating at only 30-40% of potential capacity. With SDN, new network optimization policies such as re-routing bursty traffic to alternate paths based on congestion, or making use of protection paths to accommodate unpredicted bursts, can be enforced.
Today’s mobile networks were designed to direct all traffic to a central core, but as traffic patterns change and pass between cell sites, and as virtualized services replace static gateways, more efficient traffic distribution to local handoff points can reduce network load to the mobile packet core. Coriant analysis has estimated that more flexible bandwidth allocation in response to application-driven traffic requirements can generate total mobile backhaul capital expenditure savings of up to 35%. Moreover, by presenting a simplified network view to higher-level management tools, the operating cost and complexity of defining new services and building connectivity to new carrier services is significantly reduced.
Operating expense benefits from SDN will be achieved through a streamlined network management and control environment.
Automated S1 Interface Provisioning, Re-homing, and Optimization. The S1 interface from cell site to Evolved Packet Core (EPC) is the most fundamental LTE interface. Today, this link is typically configured once and left in place. Manual input by network administrators is generally required for new service configuration or updates. Granular service configurations and circuit mappings must be input via cumbersome command line interface (CLI) or other legacy management protocols (e.g. SNMP). Processes involving multiple configuration and management systems are difficult to adapt to new services, and impose long service activation cycles. Optimizing in-production services poses an even greater challenge.
With SDN, this static deployment model can change to streamline operations and accommodate future virtual network designs and IoT services. A dynamic path control plane can automate S1 activation to virtual gateways, turn on small cells as needed based on network usage, and optimize the S1 path in real time based on network performance, alarms, or congestion from other sites and applications.
More broadly, SDN automation can ensure optimal routing to maintain QoE across mobile backhaul and fixed-mobile converged networks and can be linked to on-demand service delivery.
Network Support for Distributed Virtual Gateways (Smart Mobile Cloud). In the dynamic network of the future, instead of directing traffic to one central gateway, a mix of virtual resources (EPCs, ADCs, security gateways, etc.) will be available on demand, just as virtual servers are activated in data centers today. Virtual appliances will be distributed to more effectively cover urban metro areas, rural communities, enterprise customers, or dedicated IoT applications.
To support this dynamic environment, access and aggregation networks must adapt in real time to provide connectivity on the fly as virtual resources are activated. SDN-based network automation is required where destination routing using static MPLS tunnels does not provide sufficient flexibility. Using SDN, end user traffic can be re-homed toward newly activated resources, or diverted to available capacity for load balancing.
As L4-7 functions (e.g. firewalls, NAT, DPI, load-balancing, etc.) move to virtual platforms, SDN can activate connectivity on-demand to new service instances. Ultimately, the growing distribution of services throughout metro networks will lead to intelligent IP/MPLS and virtual appliances at the edge, and a multi-layer, multi-domain SDN control structure to support a dynamic new service environment.
Mobile backhaul networks are on the cusp of major re-design to support next generation wireless services. SDN promises to make this transition possible along with improving utilization and user quality of experience. While these benefits are alluring, in practical terms SDN will be implemented in networks with large amounts of legacy equipment. The migration of legacy networks to SDN control is perhaps the most critical technical challenge for service providers.
With the significant capital investment and operational complexity ingrained in existing MBH networks, network planners must carefully evaluate different approaches to SDN as they undertake initial rollouts over the next 2-3 years. Having a clear understanding of the highest potential applications for SDN in MBH, as well as developing consistent criteria for solution evaluation, will be essential to gain maximum benefit from these initial deployments.
Bill Kaufmann, Group Product Manager, SDN Planning, Coriant
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