Most operators are working on migrating the technology for 5G network deployment. The process involves a complete redesign of the current’s mobile broadband service, to lower unit costs, improve end-user performance, and address new business segments using 5G capabilities.
The big challenge will be designing network architectures that can scale the device and traffic densities better than LTE networks and meet the latency and reliability required for the demand of the new services. The critical point will be enabling operators to extend reach into diverse markets.
In this particular case, the essential part for the new design is concentrated in the transport network, which provides connectivity between Radio Sites, Edge Data Center and Cloud Applications. The new services will require more bandwidth and less latency, so the investment is a critical asset for the operators. However, the network improvements will generate unique advantages for the customer experience and their interaction with the services.
Architecture and Requirements
The NG-RAN (Release 15) introduces new terminology, interface, and functional modules. The network consists of a set of radio base stations (gNBs) connected to the core (5GC). The gNB incorporates three functional modules: Centralized Unit (CU), Distributed Unit (DU), and Radio Unit (RU).
The decisions on where to place 5G RAN and core network functions depend on the service requirements, the transport and the compute capabilities deployed in the network.
Figure 1: 5G Network
Figure 2: 5G RAN – Transport Network
5G RAN introduces new physical topologies, more functional split options, and low latency services, which demand shorter distances between user and compute.
Network designs for 5G can be simplified by having one network that can provide ultra-reliability and ultra-low latency to handle the needs of fronthaul, mid-haul, backhaul and the core.
X-Haul represents a converged network that supports traffic typically of the fronthaul, midhaul, and backhaul/core. With X-Haul, the network can communicate with all aspects with minimal latency and full reliability to ensure seamless connectivity.
Figure 3: X-Haul architecture
The major requirements for X-Haul are:
• standards-based (interoperability between segments)
• packet-based system (meshed connectivity)
• synchronization
• latency
• multiple fronthaul protocols (eCPRI, TSN, XRAN, TIP etc.)
• bandwidth & 100Gbps access
• meshed L3 connectivity/routing
• programmable & automated
• integrated with cloud infrastructure
The Market for 25G in the 5G
Fronthaul is generally the link between the core controller and the radio head or small cell. It also needs optical networking to fulfill its functional mission. In the fronthaul, the fiber connects the remote radio heads (RUs) and the baseband units (BBUs) or distributed unit (DU). The growing interest in the fronthaul is also due in part to the use of the relatively new C-RAN architectures for 5G infrastructure, which has heavy and costly bandwidth requirements, creating significant new opportunities for fiber optic deployments. These opportunities are not just at 10G and 100G, but also at the relatively new 25G data rate. The fronthaul network may incur significant costs for the 5G service providers, but these transceiver/optical networking costs can be justified since C-RANs can reduce cell site civil engineering costs, power consumption and maintenance.
There is a movement from 5G service providers to try out 10G transceivers for the front haul. Typically, the 10G module is deployed in this market DWDM SFP (40 km and 80 km). When the 10G data rate isn’t enough, 100G transceivers may be a solution. However, what seems to be emerging as an optimal fronthaul solution is a 25G infrastructure.
There are several reasons why 25G optics is on the rise in 5G. The first is that for fronthaul applications, 100G is overkill while 10G doesn’t offer enough bandwidth. The advantage of 25G in mobile infrastructures is that 25G is notably low cost because it uses an SFP format (SFP28), unlike the inherently more costly QSFP28 transceivers used for 100G.
About a year ago, the 3rd Generation Partnership Project (3GPP) released the first version of the specification on the Ethernet Common Public Radio Interface (eCPRI) used for 5G fronthaul, which will be used for the 5G fronthaul interface and is based on the current literature. eCPRI may well be implemented over 25G WDM-PON, but a standard 25G transceiver can also handle eCPRI. This networking type is likely to be used in this application because it provides important benefits including low latency, fiber savings, plug-and-play Optical Network Units (ONUs), and simplified Operation and Maintenance (O&M).
AXIOM 10G to 400G
The AXIOM transceiver product family addresses a wide range of network optical interconnect applications including service provider access aggregation, wireless 5G X-haul networks, as well as data center interconnects. With support for Ethernet/OTN clients, and line-side transmission of 10G, 25G, 100Gbps QPSK modulation up to 400Gbps 16QAM, the product family offers enhanced flexibility in a pluggable solution.
The CFP2-DCO product family features an expansive list of interoperability modes as documented by OpenROADM MSA, CableLabs, and the Optical Internetworking Forum (OIF).
AXIOM’s 400Gbps QDD optical module is designed with adherence to OpenZR+, OIF 400ZR specifications to optimize 400Gbps to support access aggregation, wireless backhaul, and metro/long haul data center and service provider network interconnects.
AXIOM’s bi-directional pluggable optical module solution is designed to transmit and receive data in both directions on a single fiber for 1G and beyond, providing an operationally efficient and cost-effective way for telecommunications and cable operators to increase capacity in fiber-limited networks. The bi-directional module can provide 5G RAN a solution to migrate from 10G to 100G and beyond, meeting growing bandwidth demands in situations where only a single fiber is available.
The 25G SFP28 optical transceivers are being used in the 5G front-haul network with more frequency. The commonly 25G SFP28 transceiver includes 25G SFP28 SR, 25G SFP28 LR, 25G SFP28 ER, 25G SFP28 BiDi, 25G SFP28 CWDM, and 25G SFP28 DWDM.
The 25G SFP28 transceiver is essential for the 5G front-haul network as it offers high performance and low latency solutions. Here are some of the critical challenges that need to be considered when deploying this optical transceiver in 5G front-haul networks:
1) Scalability – The widespread deployment of 5G will require many transceivers, which presents scalability issues. In particular, if there is a high demand for a specific transceiver type, it will become challenging to find a supplier.
2) High performance – The 25G SFP28 transceiver offers significantly higher performance than the current optical networks. It means that the 5G network runs faster and has less latency.
3) Low power consumption – The low power requirements of 5G make using a low-power 25G SFP28 transceiver necessary.
4) Compatibility – The 25G SFP28 profiles are compatible with a wide range of current and future network equipment, meaning that the deployment of 5G can be seamless for network operators.
5) Cost-effective – The 25G SFP28 transceiver pricing will significantly affect the 5G network deployment cost.
6) Availability – The 25G SFP28 transceiver is available from a wide range of suppliers, so there is always a transceiver available when needed
