A Tactical Transport Toolbox for Strategic 5G Deployment

Planning and deploying a mobile network to support myriad 5G applications is no easy feat, especially considering the complexities of the new architectures, as well as the interdependencies between the radio access network (RAN) and transport network. In addition to dark fiber availability, mobile network operators (MNOs) need to consider the radio spectrum capacity, coverage, and latency for each service type being deployed. A centralized RAN (CRAN) architecture is typically preferred for maximum service performance and efficiency; however, the availability of dark fiber that meets the latency requirements of the RAN as well as of urban or dense urban MNO deployment sites will vary from region to region. Small cells and picocells, installed to complement coverage and capacity of the macro cell sites, will also add to the deployment challenges. A final concern is legacy 4G traffic, which utilizes the same transport facilities.

All these challenges have one thing in common – they require fiber transport. New fiber facilities can take a year or more to install and can be cost-prohibitive. The quickest option is to use available dark fiber with an aggregation technique to maximize capacity and reduce the number of fibers needed per site. However, different access and connectivity requirements exist beyond the fiber transport. The challenge facing MNOs is there is no one-size-fits-all option; various RAN transport solutions are needed.

Let’s look at possible 5G transport solutions for small cell, macrocell, and network slicing applications that utilize innovative optics, passive wavelength-division multiplexers (WDMs), time-sensitive network components, Layer 3 routers, and service orchestrator operation.

400G optics and TSN for C-Band traffic

The new C-Band RAN spectrum that was recently auctioned to MNOs in the United States along with legacy 4G traffic can require up to 400 Gbps of capacity per macrocell site in a centralized RAN topology. A fiber relief method using an end-to-end combination of an IEEE 802.1CM-based time-sensitive networking (TSN) platform and O-Band optics can efficiently address this application.

The IEEE 802.1CM TSN platform utilizes packet technology to aggregate 5G eCPRI, 4G CPRI, and Ethernet channels over high-speed 100G links in the fronthaul. 5G C-Band radios use 25G eCPRI ports on the TSN platform. 4G CPRI channels are encapsulated using IEEE 1914.3 Radio over Ethernet (RoE) to transport over the packet structure. Ethernet service delivery uses frame pre-emption, as per IEEE 802.3br and 802.1Qbu, enabling CPRI and eCPRI services with bounded low latency to be transported along with Ethernet traffic. The TSN platform uses IEEE 1588v2 for precision time protocol (PTP) to distribute clock input from a grandmaster throughout the network. The accuracy of the TSN platform’s PTP minimizes latency. TSN platforms with clock accuracy at class D have almost no latency—exhibiting the characteristics of bare fiber-optic cable and offering greater deployment flexibility to the MNO. This enables the TSN multiplexer at the hub location to operate as a boundary clock, transporting in-band timing and synchronization to remote cell sites. Having this timing distribution capability eliminates GPS receivers at the cell sites.

O-Band 100G pluggable optics are used in place of broadband optics on the TSN platform’s high-speed links (Figure 1). These optics use the O-Band optical spectrum for their low-to-no dispersion characteristics and low cost as compared to traditional C-Band optics used in DWDM and coherent optical technology, respectively. As 5G eCPRI, 4G CPRI, and Ethernet channels are added to the TSN platform, the 100G O-Band high-speed links scale, offering a pay-as-you-grow first-cost benefit. The 100G O-Band links are aggregated onto a passive, bidirectional WDM for a fiber relief solution at 400G capacity over a single fiber. The second fiber in the pair can be used for maintenance and future scaling. At full capacity, this approach results in an 8:1 fiber savings.

Figure 1. TSN platform in CRAN topology with O-Band optics for 400G.

Addressing the millimeter-wave challenge

The high-band 5G or millimeter-wave (mmWave) spectrum has the largest capacity, but its coverage is limited to about 100 m because walls, trees, and obstacles absorb high-frequency signals. Therefore, separate indoor and outdoor RANs will be needed. In the outdoor environment, a cell-densification strategy is also a necessity. This means radio deployments on streetlights, utility poles, and on the sides and rooftops of buildings (much like small cells). These nontraditional sites will require fiber facilities for each radio channel, and yet have very limited access to electrical power and footprint.

Figure 2. All-passive end-to-end transport with smart self-tuning optics.

Addressing this challenge is another instance of innovative optics at the 10G and 25G rates replacing the optics in the mmWave radios. At these lower rates, C-Band optical spectrum in a smart self-tuning pluggable is connected to a passive bidirectional WDM, offering a single-fiber access solution to each cell site. Since the WDM is passive and can be deployed in a small outside plant enclosure about the size of a shoebox, no additional power or space is needed for this fiber-relief transport solution (Figure 2).

The smart self-tuning DWDM optics and passive multiplexer can be used as a standalone, passive transport solution at the hub location for connection to distributed units (DUs), baseband units (BBUs), and routers. The smart optics are disaggregated from the transport system at the cell site and plug directly into the radios at the aforementioned nontraditional cell sites, solving power and space challenges. As a passive transport solution, these 10G and 25G optics offer fast, automated service turn-up that reduces provisioning time by 98% (from hours to minutes) as compared to a transponder-based optical transport system. Two of these smart self-tuning optics replace 40 fixed, DWDM optics, resulting in spares inventory savings of 95%.

Combining the TSN platform with smart self-tuning optics at the hub site offers a powerful semi-active transport solution (Figure 3). At the hub site, the TSN platform aggregates the single fiber spans from each mmWave cell site and utilizes its operations management software to access the smart optics’ embedded service channel for remote visibility at passive cell sites. The remote visibility provides fiber span and pluggable optics performance monitoring, enabling network operations staff to proactively monitor performance and correct problems before they become service-affecting, resulting in high-availability service.

Figure 3. Semi-active end-to-end transport with TSN and remote PM.

The TSN platform also minimizes or eliminates stranded bandwidth for 5G eCPRI ports through aggregation grooming, lowering the cost of interconnect to the DU/centralized unit (CU). For example, four half-loaded 10G eCPRI user network interface (UNI) connections coming from the cell site can be groomed to a single 25G DU/CU connection, resulting in a 4:1 capex interconnect savings.

Network Slicing and Open Service Orchestration

Once the RAN evolves from centralized to cloud to virtualized (vRAN) to open RAN (ORAN), the service provider will realize the greatest flexibility and cost-efficiencies via a common RAN infrastructure with multiple microservices. The RAN virtualization sets the groundwork for an infrastructure that provides multiple virtual network slicing configurations. The transport in the midhaul and backhaul will require dynamic, multi-point connectivity at 100G to 400G rates to work in concert with the vRAN. Using a programmable, Layer 3 transport router network will facilitate this functionality.

The intelligence needed to stitch together the transport router, fronthaul transport, and vRAN elements is the service orchestrator (SO; see Figure 4). The SO automates service delivery for multi-domain network resources by abstracting complex networks and then managing what those resources do and when. The SO lays the foundation for network event response that can only be accomplished with a full-scale implementation of an open architecture.

Figure 4. Service orchestrator facilitating network slicing for mMTC, uRLLC, and eMBB services.

The open digital architecture supports dynamic services and provides the ability to enhance the network to match customer needs quickly. As a critical component of autonomous networking, the SO orchestrates closed-loop automation, with standard interfaces for network intelligence, and domain controllers. Finally, the SO receives policy-based information to establish appropriate network resource and services optimization for efficient network slicing capabilities and management.

Conclusion

As MNOs plan their 5G services deployment, they will need a variety of transport solutions to optimize performance while minimizing costs within their regions. A fiber-relief transport ecosystem is needed, offering 4G LTE/5G CRAN/DRAN connectivity options from macrocell to small cell by combining smart innovative optics, passive WDM, TSN components, Layer 3 routers, SDN control, and a service orchestrator. This ecosystem simplifies the complex and challenging 5G transport architecture, while maximizing performance and lowering the total cost of ownership.

The benefits of using this transport toolbox for 5G deployment are as follows:

C-Band transport solution with fast service turn-up and fewer fibers (up to 8:1 fiber savings)
Deploying mmWave radios using passive transport at nontraditional sites with remote visibility to all cell sites, enabling proactive maintenance and ensuring high service availability
Smart self-tuning optics that reduce provisioning time by 98% (from hours to minutes) and offer spares inventory savings of 95%
SO for automating and simplifying end-to-end connectivity for both RAN and transport, thus reducing installation and commissioning costs for network slicing

As today’s networks continue to evolve, dynamic flexibility will be key to enabling tomorrow’s architecture to meet diverse needs for capacity, latency, and performance – and thereby fulfill the 5G promise.

Joe Mocerino is principal solutions architect, packet optical networking, at Fujitsu Network Communications. In this role, he oversees solutions strategy and technical marketing for the Fujitsu 1FINITY, Smart xHaul and Smart Optics portfolios. Mocerino has a 30-year track record in product line management, marketing, business development, sales, engineering and manufacturing. His technology expertise includes packet optical networking, CPRI/eCPRI optical fronthaul, and network slicing.