By Wang Bing
As access aggregation devices, smart next-generation optical line terminals (smart NG-OLTs) must support ultra-broadband, fixed-mobile converged services, and smart capabilities to build broader, faster, and smarter access networks that satisfy the access requirements of any bandwidth, service, or location, and deliver better service experience.
Broader, faster, smarter access networks
As broadband prices drop, 4KTV is proliferating, with the content getting richer. Certain FIFA World Cup matches were broadcast in 4K this year. Vodafone has launched a 4K IPTV service with network speeds of up to 200Mbps in Germany. Meanwhile, major broadband access terminals have shifted from PCs to tablets and smartphones (fixed and mobile multi-terminal access). Broadband services have also shifted from home services to those that integrate enterprise service, Wi-Fi hotspot backhaul, and video surveillance. More and more carriers are shifting from providing basic broadband access to user experience-centered operation. They are trying to improve network operation capabilities by optimizing service experience and will offer integrated ICT services such as smart home/community/enterprise services in the future.
As access aggregation devices, OLTs must enable ultra-broadband, fixed-mobile convergence, and smart capabilities so that broader, faster, and smarter access networks come into being that satisfy access requirements for any bandwidth, service, or location, and deliver better service experience. Smart NG-OLTis developed to meet these demands.
Smart NG-OLT features
Ultra-broadband
Smart NG-OLT features distributed architecture that is scalable and flexible, with 400G switching capacity per slot. In order to guarantee 100M access in the 4K era, smart NG-OLT must support ultra-broadband, high-capacity 4K video access and aggregation. The switching capacity per slot must reach 400Gbps, so each slot supports 16x10G passive optical network (PON), 4x40G PON, and 2x100G PON non-blocking access. Overall, an entire OLT system can deliver 100M 4KTV service free of congestion to 32,000 families.
The switching architecture decides the actual performance of network devices. High-performance switching architecture is critical to core network devices. As broadband services have grown, centralized switching architecture and distributed switching architecture have emerged. The former relies on the central forwarding engine on the main processing unit (MPU) to provide high-performance access with all ports, with said engine checking every packet before forwarding it on a certain route. The centralized switching architecture will experience forwarding delay, struggle with issues related to bottleneck from limited switching capacity. Costs and power consumption for the system will also surge as its capacity expands. Most legacy networks and last-generation OLTs adopted centralized forwarding architecture, leading to those aforementioned bottlenecks. The switching capacity is only dozens or hundreds of Gbps, which can hardly satisfy future development needs for broadband service.
Smart NG-OLT adopts distributed switching architecture, supporting ultra-broadband services such as 4K video, online education, and e-health. Distributed architecture is applied to both the forwarding and control planes. In the forwarding plane, the smart NG-OLT does not rely on the central forwarding engine on the MPU, as each service card has its own independent forwarding engine for distributed routing and data packet forwarding, thus reducing the MPU workload and boosting the switching capacity and performance of the entire system. In the control plane, the CPU is also distributed, with the CPU on the MPU responsible for the control and scheduling of the entire system, the learning and delivery of the forwarding table in Layer 2/3. The CPU of the service card is responsible for checking the local forwarding table and status maintenance of service cards. This enables distributed computing, routing and forwarding, increasing the forwarding efficiency of OLTs.
Distributed switching architecture can help to build a large-capacity non-blocking system. A single smart NG-OLT slot can support bidirectional 400G switching, with the OLT itself highly scalable. Carriers can expand the switching capacity of their OLT systems gradually, which means they can meet their growing demands for data traffic and new services. This is one of the main reasons why mainstream core switches and routers have all adopted distributed switching architecture.
Fixed-mobile convergence
Smart NG-OLT also features full-service (family/enterprise/mobile) access, unified access/aggregation, and high reliability. Global carriers are using FTTx for high-value business customer access and mobile bearing. By reusing existing access resources, a single optical network can support full-scenario application, including home and enterprise access and base station bearing.
Smart NG-OLT is capable of full-service PON/P2P access, including gigabit PON (GPON), 10G PON, 40G PON, WDM-PON, and P2P GE/10GE access, supporting SOHO and high-speed leased-line access for government and business customers. SOHO customers have similar QoS requirements as home users, GPON/10G PON can be deployed in a way similar to FTTH to support them. Smart NG-OLT also supports WDM-PON and P2P access, enabling leased-line service for government and business customers. WDM-PON provides 32 wavelengths on a single optical fiber, saving as much as 87.5% of fiber resources. Each wavelength provides exclusive symmetrical uplink and downlink rates of 1.25G, 2.5G, and even 10G, meeting stringent demands for bandwidth, security, and QoS. Meanwhile, WDM-PON allows for maximal reuse of existing ODN network resources, adding value to the PON network.
To realize network de-layering and increase capacity while decreasing site number for CO equipment rooms, smart NG-OLT has integrated access and aggregation capabilities in order to realize one fiber for all services and a unified access layer. Smart NG-OLT integrates the functions of aggregation switches and edge routers, reducing the type and quantity of devices while reducing CO room space and power consumption. Since no independent Layer-2 aggregation network is needed, the network architecture is simpler, which reduces network fault points and improves the network quality and management efficiency.
As the unified aggregation platform for full-service optical fiber access networks, smart NG-OLT must have very reliable networking capabilities to support high-reliability design at the device/line/network side. At the device layer, all OLT components should adopt a dual-backup mechanism to prevent single-point faults. The forwarding layer is also decoupled, so faults in the control layer do not affect it, enabling online software upgrade and resetting without service interruption. Meanwhile, OLTs should support multiple cores and processes. Faults in one CPU or process cannot interfere with service. At the PON/P2P line layer, OLTs should support type-B/type-C single-homing and dual-homing protection, as well as inter-board link aggregation grouping (LAG). At the network layer, OLTs should support dual-homing protection (LAG, VRRP, and BFD) and G.8032 ring protection.
Smart capability
And finally, smart NG-OLT supports software-defined networking (SDN)-based smart service capability and N:1/1:N virtualization, while being generally open and programmable. More and more carriers are transforming from simple bandwidth operation to experience and digitized operation. The boundaries between IT and CT are blurring and ICT integration is underway. Against this backdrop, how can network construction be transformed to help carriers seize business opportunities?
As the aggregation headend of FTTx networking, smart NG-OLT conforms to the trend of ICT integration. At the data forwarding layer, the smart NG-OLT hardware platform uses programmable network processor (NP) chips, enabling programmable packet forwarding. New service requirements can be supported through microcode upgrade, without the need to replace hardware. At the control layer, the control and management planes of remote access nodes are moved to the OLT, enabling centralized control and management of the access network, simplified network planning & deployment, and reduced OPEX. With a unified control and management plane, smart NG-OLT offers open application programming interfaces (APIs), opening the network access capabilities to the application layer. Upper-layer applications, including carriers' own applications and OTT applications, can easily use network capabilities through the APIs, including dynamic bandwidth adjustment, low-latency routing, and customized QoS, realizing quick service innovation/deployment and improved service experience.
Smart NG-OLT can also be virtualized so that device and network resources can be partitioned logically. Multiple instances (virtual OLTs) can be virtualized for allocation to different services (home/business/mobile services) or retail service providers (RSPs). All virtual OLTs have independent forwarding and control planes and can be managed by different teams or customers. Differentiated service policies can also be made. Virtual OLTs also support multiple different services without additional devices or separate sub-racks, saving equipment room space, reducing power consumption, and improving operational efficiency.
Huawei SmartAX MA5800: Smart NG-OLT platform
At the Broadband World Forum 2014, Huawei launched the industry's first smart NG-OLT platform with distributed-architecture – the SmartAX MA5800. As a smart NG-OLT, MA5800 supports ultra-broadband, converged fixed-mobile services, and smart capabilities, it is the industry’s most advanced OLT for NG-PON. MA5800 is designed to help carriers to build broader, faster, and smarter access networks, delivering a better service experience.
