The analysis of the advantages and disadvantages of passive light network in college applications

As the access network technology, PON (Patriotic Light Network) has become more mature with related technologies and equipment models, and has been deployed by the three major domestic business commercial deployments for more than 15 years, and has accumulated rich experience in construction implementation and operation and maintenance.

At present, the mainstream implementation technology of the university campus network is traditional Ethernet, but the medium twisted twisted transmission performance used by Ethernet is insufficient. The transmission distance of the six types of non -shielding twisted twisted lines in Ethernet generally can only reach 100 meters, and the maximum rate can only reach reaching only reaching the maximum rate. In order to break through this bottleneck, some colleges and universities in China have begun to use PON technology to build campus networks.

Compared with the traditional Ethernet, PON has certain advantages in transmission distance, medium cost, and space occupation. It is in bandwidth rate, ONU electricity extraction, network box installation, leather line optical cable laying, safe reliability, equipment compatibility openness, and openness, and openness of equipment compatibility, and openness, and openness of equipment compatibility, and openness, and openness of equipment compatibility, and openness, and openness of equipment compatibility. There is a shortage of operation and maintenance management and network applicability.

The advantage of PON's deployment on campus network

Network architecture optimization

Figure 1 compares the network architecture of the campus network using the traditional Ethernet and PON. In the traditional Ethernet, in the central computer room, convergence of machine rooms, core switches, convergence switches, and access switches, respectively. In PON, only the core switches are deployed in the central computer room. In order to save the use of the trunk optical cable core, the OLT (optical route terminal) is deployed in the convergence of the computer room, and the OLT dual -ups to the core switch. The passive lighting device is deployed in the computer room, and the lighting ratio is generally 1:16 or 1:32, usually not higher than 1:64. Enter the machine room to each room generally deploy 2 -core -shaped leather line optical cables to replace the network cable used in the traditional Ethernet. Install a network box in each room and install onu (optical network unit) in the box. Below onu, connect to the computer terminal through network cables or wireless connection to the computer terminal, connect to wireless AP, camera and other network terminal devices through the network cable, and connect to the telephone through the telephone line.

Figure 1 Traditional Ethernet and PON deployment of comparison analysis of the network network architecture of the campus network

Lost long -distance transmission loss

In the 1550nm wavelength window, the attenuation coefficient of the G.652D standard fiber is 0.24dB/km, and the attenuation coefficient of the standard fiber of G.657 is 0.3dB/km. According to this standard, 10G PON is under the condition of 1:32 atmospheric ratio. (Insert loss is 17.5DB), the power budget is generally 29-35DB, and the network-free relay transmission distance can exceed 30km. Therefore, if the campus area is large, long -span, and large teachers and students are large, 10G PON technology deploys campus networks, which has obvious advantages. On the contrary, if the campus area is small, the spacing is small, and the number of teachers and students is small, the 10G PON technology deployment is deployed with 10G PON technology deployment. The campus network is not obvious, and the price of each set of OLT is as high as hundreds of thousands of RMB. The cost of spreading to each teacher and students is higher, and the cost performance is relatively low.

Low medium cost

At present, the market price of six types of non -shielding network cables is generally 2 yuan per meter, while the market price of the two -core leather line optical cable is about 0.7 yuan per meter, which is about one -third of the price of six types of non -shielding network cables. Cost advantage.

Small space occupation

The cross -sectional area of ​​the leather line optical cable is about a quarter of the network cable, the volume is about one -third of the network cable, and the weight is about a quarter of the network cable. It can be seen that compared with network cables, the laying of leather line optical cable will significantly reduce the occupation space and load load of weak bridge frames and wire grooves.

Pon's disadvantage of deployment on campus network

Bandwidth rate is low

10G PON uses TDM technology to carry all ONU data on the specified timeline, and send it to each ONU through the downlink 1575nm band light signal broadcast. Send their own data to OLT. Taking 10G GPON as an example, the nominal downlink line rate is 9.95328Gbps, and RS (255, 223) is encoded, and the coding efficiency is 87.45%. The up and down rate is asymmetric. According to the 1:32 luminous device per Pon port, and each optical device is full of ONU calculations, ignores the additional expenses such as the GEM packaging Baotou and the opening of the window. It is 78Mbps. In the traditional Ethernet, the connection switch is equipped with 2 10Gbps upper ports, 48 ​​1Gbps lower parts, and the upper part of the upper port configuration link aggregation can reach 20Gbps per connection. The additional expenses such as the head and IP Baotou head, the upper and lower row rate of each downwriting port on average is 417Mbps, which is greater than the upper and lower row of each ONU in 10G PON. The highest transmission rate.

It can be seen that 10G PON does not dominate the rate compared to the traditional Ethernet.

ONU is inconvenient

In the self -operated network of college parks, ONU generally collects electricity nearby and is managed by users themselves. The problem with this setting is that it is difficult for network managers to actively discover the fault of the device and facilities of the lighting device-lighting port-leather optical cable-ONU. However, if the power supply is distributed from the connected machine room independently, the power supply is powered by the power supply of each ONU, although it can improve the stability and reliability of the ONU power supply, and the network manager can actively discover the fault of the equipment and facilities. When setting a centralized power supply equipment in the access computer room, it deviates from the advantages of PON at the middle node for no passive equipment and no need to deploy active equipment. Increase the space and load load of the bridge frame. Therefore, comprehensive weighing, ONU can only get electricity nearby. Difficulty installation of network boxes

In order to install ONU and the end of the network cable and the telephone line, each room needs to be installed with a network box. In order to facilitate the nearby electricity, the network box is usually installed near the municipal power source panel, but the installation location of the municipal power source panel is generally low. If the network box is installed, the moisture, water vapor and dust on the ground will affect the network performance and service life of ONU; if the network box is installed, in order to facilitate the postponement of the later inspection and repair, the installation location is generally not too high, nor should it be over Low. Therefore, the installation position of the network box becomes a problem, and to a certain extent will affect the overall aesthetics and cleanliness of the room.

Cumbersome labeling of leather light cables

The leather line optical cable is crispy than the network cable and does not resist bending, so generally does not embed the leather wire as large -scale as the network cable. Therefore, the leather line optical cable generally requires a tube, a wall nail, or a bright wire laying. This will affect and destroy the original decoration, and to a certain extent, it will also affect the overall aesthetic and neatness of the room.

Insufficient security and reliability

The PON network is seriously dependent on OLT, and there is a large risk of single -point failure. The optical device is connected to OLT, OLT, OLT, a Pon port, OLT, and the trunk fiber, littering port, and dusk between the optical device and the optical device. These devices, ports, and cables will cause a large number of users (all users under one or more PON ports) to disconnect the network, such as unprecedented devices, board cards, ports, and lines. Protection, low reliability. In the traditional Ethernet, through virtualization technologies such as stacking and link aggregation, the main seamless switching can be achieved, providing protection functions such as equipment, board cards, ports, and lines.

Equipment and capacity are low open

The GPON of Huawei, ZTE, Beacon and other manufacturers use private protocols. Non -general public protocols, do not comply with different manufacturers' products, OLT cannot be compatible with ONU of different manufacturers. In addition, PON technology on the campus network is non -mainstream technology, which can easily lead to low cost performance of equipment procurement, low -sales service in time, and the equipment for after -sales and sales services cannot be guaranteed or upgraded. In short, users who use PON technology are easy to be bound by manufacturers, and the equipment is risky.

Great operation and maintenance management cost

Compared with the traditional Ethernet, PON has high technical requirements for operation and maintenance engineers. Generally, professional engineers who need manufacturers or operators to certify, and must be equipped with red pens, optical atomer, optical power meter, OTDR, optical fiber cutting knife, fiber fiber melt For professional operation and maintenance equipment such as machines, OLT configuration deployment is relatively complicated. Manufacturers' network management software cannot manage dumb devices such as controlling the dusk. The equipment failure positioning and exclusion are difficult, the operation and maintenance management pressure is high, and the operating maintenance cost is high.

From the perspective of network configuration, PON is a second -layer network, but from the perspective of network operation and maintenance, PON is at least a four -layer network composed of core switches, OLT, dusters, and onu. There is one more layer of access to the third floor of the switch; the number of OLTs is generally comparable to the number of aggregates, but the number of ONU is equal to the number of connected ports in the switch of the traditional Ethernet. Point, and onu scattered in each room. It can be seen that the application of PON technology will greatly increase operation and maintenance management costs in asset spare parts, inspection and maintenance, fault repair, etc.

The network applicability is weak

Generally, the operator introduces PON networking that can converge and reuse through the optical cables and signals by connecting the optical cables and signals. In the reservation of optical cable expansion and subsequent business development, but because of the particularity of the university campus network, there is generally no problem of optical cable expansion and business development difficulties, so the advantages of PON networking cannot be manifested.

In addition, Pon network is difficult to share horizontal resources. The two -layer isolation of the configuration port between the onu, the terminal of the crossing cannot be connected directly, such as the access of the printer across the office. If you want to achieve cross -ONU resource sharing, you need to configure the ARP agent at the gateway (generally located at OLT or core switches). This will greatly weaken PON's security performance.

PON technology is generally applicable to network scenarios with large vertical flow, small horizontal flow of east and west, and small internal exchange. This is the main feature of operators' home broadband and corporate dedicated line traffic.However, there are a large number of stiplines and internal exchange flows in the campus network of colleges and universities. The business demand is diverse and the network control strategy is complicated. Therefore, it is difficult for PON to play its advantages in the college campus network.In summary, 10G PON technology characteristics determine that it has better applicability in operators' home broadband and government -enterprise special line scenes, while the applicability of campus network networks in colleges and universities is not high.

Author: Huang Qinghai (Zhejiang Conservatory of Music)

Editor -in -chief: Chen Rong

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