This article sets out the strategic value and planning logic of a unified optical cable network and offers carriers advice on how to plan network architecture according to FMC strategy.
By Zhang Jun, Huawei Carrier BG Network Chief Consultant, the Ex-CTO of Shanghai Telecom
Your procurement department may save you a little money, but the right network architecture will save you a fortune and boost your revenues by accelerating TTM.
Architecture is the key to determining both performance and efficiency, with a strong strategy leading to a robust plan that can result in well-designed architecture. Target network planning involves three elements:
The first is capacity planning, such as 10G to base station and 100G to CO (Central Office, full-service access site). The second is key technology planning, for example, OXC/ASON/C+L/400G/800G for transmission networks, IPV6+SRV6/Flex/Ifit/BIER/APN6 for IP bearer networks, and GPON/10G PON/50G PON for access networks. And the third – and most important for saving costs and achieving your target network – is network architecture planning, which is determined by infrastructure architecture.
As shown in Figure 1, planning aims to use one network to achieve fixed-mobile convergence and cloud-network synergy (one network is not the same as one plane).
Figure 1: Panorama of full-service target network
There are two access scenarios: mobile and fixed.
Mobile access networks are geared towards B2C and B2B services. In today’s network environments, 2G and 3G networks need to be phased out, frequency re-farmed, and equipment rooms progressively reconstructed. At the same time, the deep coverage of 4G networks provides a solid foundation for enhancing VoLTE quality, and 5G will gradually be deployed at scale instead of only in hotspots.
Fixed access networks are oriented towards B2H and B2B services. They primarily adopt PON access technology, which is evolving from GPON to 10G PON (Combo PON). This serves as a full-service access technology in fixed network scenarios and is rarely used for base station backhaul or high-quality private lines. Fixed access also includes IP and transmission access, which can meet the diverse service needs of VPNs and high-quality private lines.
OTN+IP collaboration exists in the middle layer, enabling transmission and bearer networks to be used in mobile and fixed access scenarios, as well as east-west and north-south interconnections between DCs and clouds, which can support the cloud migration of both users and services. From the perspective of the ICT architecture, IDC and cloud are above the network layer, including CT cloud, IT cloud, private cloud, public cloud, and hybrid cloud.
In Figure 1, the most critical elements are full-service access areas, a unified optical cable network, and infrastructure (such as DCs and sites). Much like how the foundation of a building directly impacts its height and stability, designing a foundational network infrastructure architecture that is stable, reliable, flexible, and efficient is crucial.
I. Case study: Planning a unified optical cable network for optimal investment
Twenty years ago, a carrier planned and built its metro optical cable network and transmission network strictly based on PSTN. However, as emerging services like private lines, DSL-based broadband, and base station backhaul developed at scale, and voice services became saturated, the carrier needed to transform the architecture of its optical cable and transmission networks from supporting just voice to supporting full services. Therefore, the carrier started planning the infrastructure of a unified optical cable network, as shown in Figure 2.
Figure 2: Topology of a unified optical cable network of a carrier 20 years ago
Planning involves two steps
Step 1. First, organize the sites and equipment rooms on the entire metro network; evaluate the location, space, power supply, stability, and outgoing routes of each equipment room; and determine the role of each site.
Second, based on geographical and administrative boundaries, determine the long-term ownership relationship between core and aggregation sites and between aggregation and CO sites. A metro network is divided into four areas: east, west, south, and north. Two core sites are set up in each area and each pair of core sites for the metro network connects to multiple pairs of aggregation sites, after which the aggregation sites connect to multiple COs. This forms the architecture of a trunk optical cable network.
In terms of the topology of the optical cable network, the core layer is fully meshed, but the aggregation layer is not. While a mesh network is far superior to a ring network in terms of network robustness, bandwidth, and latency, mesh networks require optical cable network topology. A target optical cable network will not be built in one go; instead, its topology will be gradually improved as optical cables are laid year by year.
Step 2. The network is divided into full-service access areas, with COs at the heart, no gaps existing between access areas, and each CO corresponding to a particular full-service access area. B2H, B2B and B2C service needs in each full-service access area are coordinated to help guide optical cable network planning, so as to prevent optical cables from providing cross or repeated coverage.
When following these two steps, the target optical cable network has a clear hierarchical architecture that guides the architectures of the transmission and IP target networks.
The infrastructure architecture of the carrier has not changed significantly over the past 20 years. This gives it a solid foundation on which to maintain leadership in the fiercely competitive areas of FMC and cloud-network synergy. Such planning greatly improves investment efficiency, exemplifies cross-discipline collaborative planning, and achieves cost-saving goals.
II. Ideas and methods for the overall planning of target networks
A robust network depends on architecture and robust architecture depends on planning.
1. Collaborative planning
Business plans drive technology plans, which in turn drive network plans. Building infrastructure takes time, so if carriers build networks based on demand, they will miss the strategic window of opportunity. They should at least produce a business strategy to guide network rollout even if they lack a business plan.
Strategies ideally involve collaborative planning – i.e., top-level design – across disciplines, departments, front-end and back-end, industry chains, and even industries.
2. Fixed mobile convergence planning
The purpose of FMC is to reduce CAPEX and OPEX, the key to which lies in site convergence. As long as sites are converged, optical cable networks, transport networks (i.e., OTNs), and IP networks will also naturally converge. Therefore, site planning is the primary task, including core, aggregation, full-service access sites, base stations, and data centers.
3. Value-oriented planning
Planning is not the same as investment. Investment comes in when a plan is implemented, whereas planning is the process of creating a vision for your target based on strategic positioning. Implementation is carried out step by step based on plans that prioritize high-value areas. For example, the planning departments of tourist cities will develop a vision focusing on the tourism industry, which will in turn guide step-by-step city reconstruction based on priorities. Without strategic positioning, there can be no vision. In the case of a city, something reconstructed today may be demolished tomorrow.
4. Coordinated investment planning
Pipes represent carriers’ core competitiveness where the CAPEX to revenue ratio is basically fixed every year and where focusing investment on pipes can increase that core competitiveness. For instance, optical fibers are high-quality assets that will pay off over 30 years. If carriers determine their FMC strategies early and formulate overall plans, they will not need to invest separately in the optical cables required for B2C, B2H, or B2B scenarios, and can thus avoid repeated trenching and optical cable installation on the same road.
III. Architecture and deployment of the unified optical cable network
1. Relationship between the ODN and optical cable network
The ODN (optical distribution network) is not the same as the optical cable network. It is instead placed on top of the optical cable network and consists of optical fibers connected to splitters. The ODN resolves bandwidth issues, while the optical cable network enables full B2H, B2B and B2C services, meaning network rollout costs are shared between the three and investment efficiency is increased. The optical cable network/ODN is not a line but a network, so its planning and design should adopt a top-down, end-to-end approach.
2. Infrastructure architecture transformation of mobile operators
Under the FMC strategy, mobile operators must transform their infrastructure architecture first if they hope to develop fixed network services at scale.
Figure 3 Infrastructure differences between mobile and fixed network operators and the direction of architecture transformation
As shown on the left of Figure 3, a mobile operator typically has only core sites, aggregation sites, and base stations within a metro network. Installing the FTTH OLT at the aggregation site causes two problems: First, the aggregation equipment room will be too small to house many devices. Second, the coverage of aggregation sites will be too large and the optical power budget insufficient. Moreover, if the OLT is installed on a base station, three problems will arise. First, various types of base stations will exist, including tower, rooftop, and pole sites. So, which base stations should the OLT be installed on? Second, most base stations are leased, if the lease renewals can not be continued by various reasons, such OLTs cannot be migrated to aggregation sites, because the insufficient optical power budgets. As a result, smooth network evolution is impossible. Third, as 4G coverage deepens and 5G networks are built, base station density will increase. Without proper planning, this will result in cross or repeated FTTH coverage between base stations.
For mobile network operators (MNOs) that build fixed networks, determining COs is both a key planning task and main challenge. As MNOs lack the CO layer of infrastructure, they should instead transform well-resourced macro sites into COs. As shown on the right of Figure 3, the base stations, which are in a good physical location, own large space, and convenient for routing can be transformed into COs. They can then divide the network into seamless grids (or full-service access areas) with COs at the center, and plan the access optical cable network in each grid. This also paves the way for establishing a grid-based operations system for fixed network services and coordination between the front and back end.
3. A reference architecture of the target unified optical cable network
Figure 4 shows a reference architecture of the target unified optical cable network in the metro network.
Figure 4: A reference architecture of the target unified optical cable network in the metro network
Key points of planning logic
- 1. Determining site functions and establishing the ownership relationship. Carriers need to determine whether the network functions of each physical site should be considered core, aggregation, or access sites. They can then define service boundaries based on administrative divisions and establish an ownership relationship between sites in each area.
- 2. Dividing the network into layers to form an architecture. Metro optical cable networks are divided into trunk and access networks. Trunk networks are then further divided into core and aggregation networks, forming a three-layer architecture. Fiber trunk cables can be leased because few such cables are needed. Meanwhile, needs can be planned in advance. However, massive fiber cables are needed for access networks, requiring carriers themselves to build the network to ensure TTM and leverage their core competitiveness.
- 3. Full-service access areas ensure fast response to service needs. To coordinate B2H, B2B and B2C service needs, the network is divided into full-service access areas. Carriers must shift from demand-based to plan-based network buildout and plan feeder cables to quickly respond to service needs.
- 4. Trunk optical cable networks should gradually migrate to mesh topology Carriers need to gradually improve the mesh topology of trunk optical cable networks as they build them out.
4. Architecture and network construction model of the full-service access optical cable network.
Figure 5 shows the architecture and network construction model of the full-service access optical cable network
Figure 5: Architecture and network construction model of the full-service access optical cable network
Key points of planning logic
1. Topology
The access optical cable network consists of three layers: feeder, distribution, and drop cables. Feeder cables can adopt ring, tree, or bus topology. Tree topology is usually used in residential areas, while ring or bus topology tends to be adopted for CBDs and clusters of commercial buildings.
2. Cross-connection
The access optical cable network uses cross-connection, with a maximum of two levels of cross-connection that correspond to level-1 and level-2 cross-connection points. Cross-connection devices can be outdoor floor-mounted, indoor stand-mounted, or wall- or pole-mounted. Cross-connection is key to the design of the access optical cable network, improving the utilization efficiency of optical fibers and facilitating O&M and capacity expansion.
3. ODN deployment
The ODN is deployed below level-1 or level-2 cross-connection in the distribution section. Even or uneven optical splitting may be used depending on the scenario. Uneven splitting and pre-connection technology have advantages in both aerial deployment, such as pole- and wall-mounted, and buildings.
4. Network construction model
Feeder cables should be laid based on planning, but high-value areas should first be identified by considering B2B, B2C, and B2H, and distribution cables should be laid based on either planning or demand. If service needs are clear, they should be laid based on plans. If not, actual needs should be clarified before proceeding.
5. Pre-deployment of vertical optical fibers in office buildings
B2B is where the real money is. Multitenant office buildings are the focus of carrier investment, with TTM forming the core competitiveness for developing B2B services.
However, four uncertainties exist when developing services for multitenant office buildings:
1. Uncertain number of users: Unlike the demand of residential buildings that require one fiber for each household, each floor of an office building will have a different number of users, which will change each year.
2. Uncertain service types: Office building users have diverse service needs, including fixed voice, Internet, site-to-site private lines, and indoor distribution.
3. Uncertain service quantity: It is difficult to predict required service quantity, even for one user in an office building. How many site-to-Internet private lines do they need? And site-to-site private lines?
4. No one knows who will come out on top: The carrier that will emerge as the winner remains uncertain.
Therefore, the pre-deployment of vertical optical fibers in office buildings is the key to developing B2B services. Figure 6 shows two scenario-specific solutions.
Figure 6: Two scenario-specific solutions regarding the pre-deployment of vertical fibers in office buildings
6. CO+X Planning
Figure 7 shows the CO+X planning method, where X refers to a MASN site or base station.
Figure 7: CO+X planning method
OTN/IPRAN/OLT devices are installed in the CO. In the following scenarios, the OLT can be deployed to X (Air PON) to take full advantage of existing infrastructure:
1. Laying feeder cables takes too long. Therefore, carriers must seize the window of opportunity to quickly develop service scenarios and gain users.
2. If the CO equipment room cannot meet future growth needs, priority must be given to ensuring that enough space exists to support the future growth of OTN and IP devices.
3. The service area has a high density of households, which occupy a large number of feeder cables.
4. Remote areas where service access distance is long and exceeds the optical power budget.
To evaluate the strength of a carrier's network, we must first look into its fixed network. Whether or not the fixed network is robust depends on the amount of fiber it contains and the depth and breadth of its fiber coverage. In the past decade, China's nationwide cyber power began to grow with fiber adoption for broadband services. Without fiber, a network cannot be strong, regardless of whether it is fixed or mobile. However, this does not mean the more fiber optics, the better. Carriers must plan fiber networks in advance to avoid repeated investment and improve investment efficiency.
