Principle subdivision of broadband optical fiber Access Network

Broadband optical fiber access network is a common access method, but its implementation is complicated. We need to make full preparations in the early stage, A reasonable plan can be designed to avoid problems in subsequent work.

1. Principles of broadband optical fiber Access Network
1) Guiding Ideology of networking
Meet the rapidly growing business needs and support various application systems. It provides network capabilities, optimizes network structures, strengthens network management functions, and improves support systems and business platforms to meet users' business needs at the network layer. It also provides basic guarantees for business expansion at the application layer. Ensures network reliability and manageability.

2) Basic networking principles
Broadband optical fiber access network planning should be based on the existing optical fiber network structure, and should be based on the combination of the recent and mid-term. At present, the construction of broadband MAN is in the initial stage. Due to the unbalanced development in different regions and cities, the demand for services is different, and users are scattered and present uncertainty. Considering the economy of Market Occupation and investment, the principle that broadband city construction should be implemented based on the distribution plan should be adopted.

2. How to set the site selection principle for the settlement Node
As the broadband optical fiber access network project has not yet formed a set of technical standards and specifications, the selection of sink nodes mainly follows the following principles:
1) a junction node covers a residential area with a m radius or 5-15 multi-storey residential buildings.
2) the number of users hosted on a junction node is generally between 1000 and, with a maximum of users.
3) the receiving node should be used together with other telecommunications facilities to solve the node equipment room problem.
4) The position of the junction node should facilitate the entry and exit of optical cables and cables.
5) The position of the junction node should avoid corrosive gases, lightning strikes, high-voltage transmission lines, strong interference areas, wet areas, low-lying areas, flood control dams, and other areas that may be easily damaged, the device must be placed indoors.

3. node bandwidth allocation principles
Considering the actual traffic of current broadband users, a 1000 Mbit/s bandwidth is allocated between core nodes during the planning process, and corresponding interface boards or switches are added to the connection nodes as needed, to provide sufficient user access ports, when the user traffic reaches a certain scale, the load sharing of the relay traffic is adopted. The total number of ports for 10 Mbit/s should be the same as the number of hosted users. The uplink interface rate of corridor switches should be set to at least 1/5 of the total access rate, that is, each Broadband User must allocate at least 2 Mbit/s bandwidth. For residential quarters, the bandwidth is allocated at a 20% broadband access rate. For Party and government organs, financial securities, smart buildings, hotels, school hospitals, and enterprise Scientific Research Users, consider the fact that the local area network (LAN) is in place and the uplink bandwidth of Mbit/s can be allocated.

4. device Port Configuration Requirements
1) Campus switch;
Upstream port: 1-2 1000Base-Sx
Downstream ports: 20-50 10-100Base-Tx and 2-10 100/1000 Base-Sx.
2) Corridor Switch
Upstream port: 1-2 100/1000 Base-Sx
Downstream port: 20-50 100/100 Base-Tx.

5. Optical Cable Network Structure
Based on the RBB model, a broadband man can be divided into three layers: core layer, sink layer, and access layer. The core layer mainly implements data transmission functions, and is responsible for network-wide service transfer and service Dredging to achieve data exchange within the city and interconnection with IP networks. The Convergence layer is mainly responsible for business convergence and guidance in the region. It requires business scheduling and routing capabilities, multi-protocol processing capabilities, and multi-service access capabilities. The access layer is responsible for connecting businesses to the nearest node. It requires devices to have multi-service access capabilities, multiple access methods, and good networking capabilities, allowing users to access quickly and flexibly.

In a traditional telecom network, a city has multiple parent bureaus, each of which carries multiple postal parcels and narrowband Access Points of the module bureaus. Generally, two nodes are selected as the core node in the parent Bureau. In principle, the core node does not directly access the business. However, considering that the initial business volume is not large, in order to save investment, you can also consider taking on the functions of the sink node, and then separate the functions when the business volume is large. Other Parent bureaus, existing Mail bureaus, module bureaus, narrowband access points, and other devices are junction nodes and junction nodes adopt medium-capacity broadband switches with Multi-Service Convergence and distribution capabilities, connect to the core node in a dual-attribution manner to reduce the impact of core node failure on exploitation. The main device of the user access point is corridor switch, which has practical data service solutions and various broadband service access capabilities. For broadband users with high reliability requirements or conditions, you can consider using two routes to access two different physical connection nodes.

In the existing telecom network, there are generally relay optical cables between the parent bureaus of China Telecom. At the same time, the parent bureaus of China Telecom already have trunk cable rings, and many narrowband access points have been set for communications. If each junction node is connected to a core node with optical fiber cables, a large number of optical cables will be laid and a large amount of pipeline resources will be occupied, and the optical cable network will inevitably be very complex. In the planning process, the optical fiber cables are laid in one step. The selection of broadband network structure should be based on the characteristics of Broadband Access Point Distribution, routing and business requirements, comprehensive consideration, appropriate selection. It is necessary to fully consider the economic and technical nature of the network, but also the development needs, as well as the narrowband requirements for broadband optical fiber access networks and the flexibility of network operation and allocation, factors such as resizing, scheduling, and emergency response, as well as the network structure of the broadband network cable access network, mainly consider the following two solutions.

1) Star Mode
The master node is connected to the master node by a star node to form an active star or double star network structure. This structure has the following advantages: its structure is simple, easy to plan, and the investment of optical cables is relatively small. Its disadvantage is that it occupies many pipe holes, and each user uses a single route, resulting in poor security and reliability. It is an effective method for some areas with large user density generation, recent changes, and a long distance from the local area.

2) combination of ring and bus
The parent Bureau's receiving node adopts the two-way fiber loading method from the current node. The receiving ring consists of a large number of core trunk optical cables, and the ring optical cables adopt the non-decreasing method, generally, 4-6 connection nodes are connected to each connection ring. The gateway node uses a star-to-point connection to the corridor switch. The main advantage of this structure is that the convergence Ring Optical Cable occupies less pipe holes, the core usage is high, easy to schedule, and high security.

To solve the security of a single physical route, each Optical Node can bind fiber to two parent bureaus to form a bidirectional broadband optical fiber access network for the junction node. When one parent node fails, it can be opened through another parent board connection node to increase the reliability of the broadband optical fiber access network service. At the same time, when the user's optical cable is surplus, it can be used as an inter-office relay. However, this method increases the load on the sink node device and makes the network structure complex, so it is not suitable to be used in large quantities.

For some areas in the parent board that are far away from each other, users are scattered. Areas and collection nodes that need further planning and development can be networked in star mode. If the number of existing pipe holes is insufficient, the number of users is concentrated in the scope of this Council. In urban planning areas, the combination of ring and bus networks should be prioritized.

6. Core configuration principles
1) sink node
For a star network, the number of 6-core optical fiber cables under each sink node decreases step by step from the trunk to the branch. For the combination of ring and bus networking modes, the junction node provides two-way 24-core connection from the junction ring, and at least 12-24 cores are reserved on the junction ring. The Convergence ring uses a single-mode optical fiber cable, usually ranging from dozens to hundreds of cores. It is recommended to use a band-shaped optical fiber cable.

2) connecting nodes to Corridor Switches
Configure the number of fiber cores according to business requirements: each 100 M/1000 Mbit/s Ethernet port occupies 2 cores and is reserved with appropriate fiber cores. Multi-mode optical fiber cables are recommended.

7. Summary
This article provides the principle guidance for broadband optical fiber access network planning at the initial stage of Broadband Metropolitan Area Network Construction Based on the current economic development of telecom networks and various urban areas.

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