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The large-scale campus network system is divided into the core layer, the convergence layer and the access layer from the design; from the function can basically be divided into campus network center, teaching subnet, office subnet, dormitory area subnet, etc.
The hierarchical thinking makes the network have a structured design, and the modular analysis of each layer is very helpful for the unified management and maintenance of the network. At present, layered design has become a trend. This section first analyzes the three levels, and then briefly introduces the campus' functional subnets.
Core layer: The function of the core layer is mainly to achieve optimized transmission between backbone networks. The focus of the design tasks of the backbone layer is usually redundancy, reliability and high-speed transmission. The control function of the network is best implemented as little as possible on the backbone layer. The core layer has always been considered as the ultimate bearer and convergent of all traffic, so the requirements for the core layer design and network equipment are very strict. The core equipment will account for the main part of the investment.
Convergence layer: The function of the convergence layer is to connect the access layer nodes and the core layer center. The aggregation layer is designed to connect to the local logic center, and still needs higher performance and richer functions.
Access layer: In the design of the core layer and the aggregation layer, we mainly consider that the network performance and functionality are higher. Then we advocate the use of high-performance equipment in the design of the access layer. The access layer is the interface between the end user (teacher, student) and the network. It should provide plug-and-play features and should be very easy to use and maintain. Of course, we should also consider the issue of port density.
Campus network structure diagram In general, the network center is considered to be the best location for core layer switches. The server for the entire school will also be connected to the core switch, making full use of the routing, control and security functions of the core switch to achieve the effective use of server resources. The egress of the public network is generally connected to the core layer switch. There must be a firewall (software or hardware) between the public network and the internal network to ensure security and prevent reactionary, pornographic content from invading the campus network.
In principle, switches at the aggregation layer can be either layer 3 switches or layer 2 switches. This depends on the investment and the switching capabilities of the core layer. At the same time, the traffic sent by the end user will also affect the choice of aggregation layer switches. If you choose a layer 3 switch, the distributed routing idea is reflected in the design of the entire network, which can greatly reduce the routing pressure of the core layer switches and effectively balance the routing traffic. If you choose a distributed routing method, you can consider reducing the investment cost of the routing capabilities of the core switch. On the other hand, if only the layer 2 equipment is selected for the aggregation layer equipment, the routing pressure of the core layer switches will increase. We need to increase investment in the core layer switches and choose stable, reliable and high-performance equipment. In terms of investment, we recommend selecting equipment with a high performance-price ratio at the aggregation layer, and at the same time, the function and performance should not be too low. As the logical core of the local network, if the local application is complex and the traffic is heavy. Consider using high-performance switches.
The access layer switches do not have too many restrictions, but the access layer switches or hubs must have strong adaptability to the environment. Almost all schools in China have a difficulty-investment. It is unrealistic to set up a well-ventilated equipment room with good ventilation and anti-electromagnetic interference conditions in each building. Most floor switches are placed in corridors, so the equipment on the access floor should first have a good environment for harsh environments resistance". Access layer devices do not need to pursue too many functions, as long as they are stable.
The overall design should be beneficial to support the transmission of multimedia information, especially voice and video, and should provide end-to-end Multicast support. This mainly depends on the application requirements of the campus.
Application of Shenzhou Digital Network Equipment in Layered Structure
Large-scale school structure and network equipment connection diagram The large-scale campus network solution core switch uses DCRS-7504, with 4 slots, supports up to 32 Gigabit ports, can provide extremely high performance and reliability, usually suitable for more than 400 points Larger campus network. Corresponding modules can be selected according to the number of access layer switches and servers. The single-mode bare optical fiber is directly connected to the information center of the education committee through gigabit. As a core node.
For a large campus network, the design of the core layer is very important. We must consider its functionality, controllability, reliability, stability, and specific performance. If the core chooses an independent device, we should achieve as much redundant performance as possible, such as the use of hot standby management modules, redundant power supplies, and redundant link designs. Dual-system hot backup will be the best solution, and the equipment at the aggregation layer and the core equipment should be redundantly connected. The public server should be connected to each one.
The redundancy design of the network can be divided into 3 levels
1. The redundant design of the network equipment adopts the single machine or multiple equipment of redundant configuration to be hot standby for each other. Of course, the best way is to have multiple devices hot standby for each other. But this solution is generally more expensive.
2. Redundancy design of network links The redundancy design of links is often the most easily implemented and accepted redundancy method by users. The main reason is that this redundant design is simple and cheap. Link redundancy can be achieved through a variety of technologies, currently the most popular link aggregation technology (802.3ad) and spanning tree technology (802.1D). These two technologies can be used in different environments and needs, and each has its own advantages and disadvantages. Of course, link aggregation technology can be used in conjunction with spanning tree technology. Link aggregation technology is aimed at point-to-point applications and is commonly used in core multi-machine hot backup and secondary switches to connect the core single machine. Spanning tree technology is often used on the link between the secondary switch and the core switch. Link aggregation technology provides the characteristics of expanding bandwidth, link hot backup, balanced load and fast switching (generally less than 4 seconds). Spanning tree technology is a pure backup technology. During application, one or more links are in the blocking state. Only after the main link is broken, the backup link will start. This process takes about 45 seconds (convergence time). Link aggregation technology is relatively expensive (ports, lines), but has excellent reliability; spanning tree protocol has long been an industry standard, compatibility is very good, and it is cheaper, but it wastes link bandwidth. Many vendors have also developed vendor standards that replace spanning tree protocols, mainly to reduce convergence time. The current IEEE standard 802.1W is called the second generation of spanning tree technology and can replace the traditional 802.1D. 802.1W shortens the convergence time to within 4 seconds.
For the situation in this article, it is recommended to use link aggregation technology in the core, and use spanning tree technology for the connection between the aggregation layer and the core layer.
3. Server redundancy design The server redundancy design includes many aspects: links, hardware and software. The redundancy of the link can adopt the method of dual network cards or the link aggregation technology on the single-chip multi-port network card; the redundancy of the hardware can adopt the method of dual-server hot backup; the redundancy of the software can adopt the method of dual-server software mirroring. Redundancy design is an important part of network design and an important means to ensure the overall reliability of the network. But investment will also increase. Of course, the three-level design can run through the entire network, and each redundant design is targeted. We can also choose to apply some or several of them to the network to target important applications.
The convergence layer considers 2 situations here:
1. For applications with large burst traffic, high control requirements, and good support for QoS (multimedia streaming-voice, video, and data fusion applications, such as multimedia classrooms and teaching), choose high-performance but cost-effective DCRS-6512 Multilayer switch;
2. For subnets with no special requirements (multimedia transmission, security, control, etc.), such as logistics subnets. In general, the most common application for this type of subnet is data. Therefore, the requirements for the aggregation layer equipment responsible for such subnets are not high. You can consider using medium-level Layer 2 switch equipment.
The access layer can adopt DCS-3726S 24-port stackable switch or DCS-3750 48-port switch for different access densities. Usually, the number of multimedia classrooms is more than 50, and China Digital is used to "customize" DCS-1064 for the education metropolitan area network. DCS-1064 can provide 64 10 / 100M Ethernet interfaces, fully adapting to the needs of campus network multimedia teachers . If the number of access points is less than 24, such as student dormitory, etc., you can also choose a 24-port independent switch DCS-3526, these three switches can support 100M fiber or Gigabit uplink, DCS-3726S can also achieve stack Gigabit port aggregation across switches in the group can effectively improve the bandwidth and reliability of the uplink, eliminate network bottlenecks, and achieve true non-blocking Gigabit backbone and 100M switching to the desktop.
The classroom is equipped with multimedia teaching terminals to complete multimedia teaching such as VOD / AOD, courseware on-demand, intelligent teaching broadcasting, digital monitoring, and network central control. 
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