5G Transport

Introduction

According to a recent Cisco Annual Internet Report (AIR), more than 70 percent of the global population – approximately 5.7 billion people – will have mobile connectivity by the year 2023.This connectivity includes 2G, 3G, 4G, and 5G. More than 66 percent of the global population will be Internet users. More users equate to more devices, all with an insatiable appetite for bandwidth to service their new business and consumer applications.

Some of the many bandwidth needs include video, online gaming, and virtual or augmented reality, challenging service providers with the need for high-density, high-bandwidth connections with low-latency performance requirements. Service providers therefore need to provide the bandwidth to support these requirements, but also meet stringent Service Level Agreements (SLAs) they demand.

Mr. Joachim Horn, Chief Technology and Information Advisor of PLDT and Smart Communications, the Philippines’ leading digital service provider, notes the realities of these challenges.

For operators to capitalize on this growth and generate new revenue, they must re-architect their network with an eye on efficiency and scalability, while reducing their Total Cost of Ownership (TCO). Efforts to make 5G scalability requirements cost effective is a primary focus of network operators. The effort requires keeping close track of production costs per Gigabyte on the network, and it needs to be considerably lower very soon.

Evolution of the same architecture isn’t enough. Technology continues to evolve with Application Specific Integrated Circuits (ASIC) development following Moore’s Law and Dennard Scaling Law, while optical continues to push Shannon’s limits. From an operational perspective, we see a strong push towards software with automation enabled by Software Defined Networking (SDN), telemetry, machine learning, and artificial intelligence. Network architectures continue to see evolution around multiple layers of the network, from packet to Optical Transport Networking (OTN) to Dense Wavelength Division Multiplexing (DWDM) layers. Each layer evolves around capacity and flexibility, along with added complexities.

Service providers must support the following objectives:

• Enhance the user experience while maintaining or exceeding existing SLAs
• Simplify operational models
• Provide a utilization and cost-optimized network
• Build a highly scalable network, meeting tomorrow’s needs today
• Reduce time to market for new services
• Decrease total cost of network ownership

Meeting these objectives require focus on four key areas:

1. Build faster networks – higher interface speeds, greater horizontal scaling to increase flexibility and, in essence, follow Moore’s Law to lower the cost per bit.
2. Improve network utilization and efficiency – enhance traffic engineering capabilities through a centralized controlling entity.
3. Increase network operational efficiencies - enable service agility and improve time to market for new services and bandwidth scale-out requirements with a consistent, predictive, and simplified operational model.
4. Optimize network architecture – maximize capacity within the constraints of physics while collapsing layers and reducing functional overlap. Reduce total cost of ownership with a reduction in power, footprint, and components, therefore enhancing mean time between failures (MTBF) and providing improved network simplification.

With these objectives in mind, providers must ask themselves if they can meet the demands of tomorrow with an evolution of their current network. Do they need to re-examine technology trends and rethink how to build their network to meet the objectives?

“For PLDT to meet the requirements of 5G, a new transport network was built (and) this transport network has huge capacity, commensurate with the invested resources on the radio network which is needed to commit to a consistent and superior customer experience,” adds Mr. Horn of PLDT. “The network needs to be more efficient and simplified, redundant layers removed, and the number of hops need to be reduced to allow for the most direct traffic path. At the same time, the network needs to allow for flexible placement of edge compute nodes for 5G low latency use cases. End-to-end network slicing capability is also key to support 5G services.”

Networks today are hierarchical and Multilayered (ML) with each layer acting individually and operating on its own life cycle. These ML networks focus on the layer rather than the services due to technology limitations and the multiple services that require termination on different layers of the network. These network layers consist of OTN/TDM Switching, Packet Routing / Switching and DWDM / ROADM Switching to deliver these services as depicted in Figure 2b below.

These ML networks introduce complexity and redundant functions. The functions must be operationalized and have direct impacts on capital costs. Providers need simplified operations and cost-effective ways of delivering new and existing services with strong service-level agreements as well as enabling 5G and the associated new revenue generating opportunities.

Figure 2(b). Services terminate at different layers of the network. Each layer provides redundant functions, management, control, and life cycle management.

Technology enabling new architectures

Technology is advancing, enabling innovation to address the challenges of today and meet future network requirements. These advancements include::

• Router capacity increasing multi-fold – recent industry announcements outline performance capacity greater than four times the largest platforms with a fraction of the footprint and power consumption. These units based on new Network Processing Units (NPUs) that enable multi terabits per second capacity are opening new doors of opportunity for new services and architectures.
• Commoditization of coherent optics – with OTT, web scale and service providers moving to coherent optics at 400G for distances above 10Km, along with the standard efforts, increases the adoption rate and enables higher volumes not seen before.

Figure 3(b). As coherent moves deeper into the network, adoption rates increase and within three years might be on par with 100Gig interface quantities.

To deliver a network optimized around services that scale well beyond today’s capacity and performance requirements means taking advantage of innovations in technology. The 5G network architecture uses the following approaches to meet these needs:

• Supporting legacy TDM services and high-speed private line services over the packet switched network leveraging CEM and PLE to enable network simplification with a single network layer while meeting existing SLAs
• Integrating 400G Coherent optics into high capacity routing platforms with zero density trade-offs
• Segment routing to provide the network with the most cost-effective end-to-end network slicing capability required for 5G networks
• Central SDN-based solution to enable a programmable network with automation platforms that utilize real-time network telemetry for advanced traffic engineering and control
• Moving from a mesh-based ROADM architecture to a Hop-to-Hop (H2H) Digital ROADM architecture
• Eliminates layers with operational simplification, reduced power and footprint
• Provides optimal capacity by shortening endpoint distances
• Gracefully transitions from bypass to H2H networks

The 5G Transport network provides simplification and enablement of true optimization as well as advanced service delivery. It supports not only the low-latency demands of new services and stringent 5G requirements, but also provides a future-proof, single-layered network.
 

Figure 5. Moving from a layer-centric approach to a service-focused network

Benefits of 5G transport architecture

As we continue to increase the data rates of the interface, we must contend with Shannon’s limits, which we’re already pushing up against. To overcome this, one of two things must take place:

1. Pick up and move cities closer together (not likely!)
2. Shorten the distance between endpoints

Shortening the distance between endpoints occurs with a Hop-to-Hop (H2H) architecture. H2H allows true network capacity optimization with network simplification by collapsing network layers and eliminating the complexity and redundant nature of Multi-Layer networks.

Figure 7 below provides a general comparison of three models for a network, with relative costs defined for the three different architectures:

1. Hollow Core (HC) – Hub and Spoke type architecture; dedicated wavelength per terminating site
2. Optical Bypass (OB) – Based on traffic demands optimally bypass a site to optimize capacity
3. Hop to Hop (H2H) – Point-to-point architecture where all wavelengths terminate at all sites

Even though H2H requires more interfaces than either HC or OB, we see relative cost savings based on converging the layers, moving to simplified filtering structures, and using industry standard 400Gig ZR/+ interfaces. Based on modeling of real service provider networks for the different scenarios we see a relative savings in the order of 40% over a Hollow Core network and an approximate savings of 34% over an optimal bypass network. From the traffic-routing diagrams in Figure 8, you can see the simplification an H2H network brings to traffic routing, which provides overall simplification for the network and life cycle management.

Figure 8. Model showing traffic routing and relative cost models for, from left to right, Hollow Core network, Optimal Bypass, and H2H.