In order to analyze the impact of 5G evolution on the transmission network, based on the progress of the 5G evolution standard and typical application scenarios, the key requirements for transmission of 5G network deployment are ultra-high bandwidth, low latency, network fragmentation, inter-station traffic, and high precision. Time synchronization. Based on these demands, key issues such as basic resource reserve, network fragmentation, high-precision time synchronization deployment, and three-layer network downshifting are discussed, and the bandwidth of each layer of transmission is measured through the establishment of a model, and the core layer of the metro transmission network is proposed. , The evolution direction and networking characteristics of the convergence layer and access layer.

After the widespread popularization of 4G networks in mobile communication networks, the user experience and network speed of Chinese users have been greatly improved. Driven by technological progress and various factors, 5G testing and commercialization in the United States, Japan, South Korea, and Europe are accelerating. Domestically, the Ministry of Industry and Information Technology is also actively promoting the 5G process. The 5G technology research and development verification of the IMT2020 Promotion Group has moved from the key technology verification stage. At the stage of technical solution verification, China Mobile Group is also actively deploying 5G and stepping up the field verification of 5G.

1.1 3GPP timetable

According to the current 3GPP standard, it is predicted that the trial commercial will be relatively mature in 2020. With the acceleration of the industrial environment, it is also possible to carry out a pilot or trial commercial based on the current Rel-14 or Rel-15 version, and the trial commercial is in progress. It will focus more on enhanced mobile broadband (eMBB) application scenarios. As shown in Figure 1.

1.2 Typical application scenarios of 5G

The typical application scenarios of 5G as shown in Figure 2 include eMBB (enhanced mobile broadband) application scenarios, mMTC (large-scale machine communication) application scenarios, and uRLLC (high reliability and low latency communication) application scenarios.

The most typical applications of these three types of scenarios in the early stage of 5G network construction are enhanced mobile broadband (eMBB) application scenarios, such as HD video live broadcast and sharing anytime, anywhere, virtual reality, and high-speed Internet access. With the development of the Internet of Things, there will be more and more applications in large-scale machine communication (mMTC) application scenarios, such as smart meter reading, automatic parking, and smart transportation. Relatively speaking, high-reliability and low-latency communication (uRLLC) application scenarios may not have many initial applications. For example, autonomous vehicles, industrial interconnection, remote mechanical operation control, etc. will appear as applications mature with the deployment of 5G networks, but such applications are not The transmission network delay requirement will be relatively high, between 1ms and 4ms, which will have a greater impact on the network architecture.

2 The key requirements of 5G network deployment for transmission

2.1 Ultra-high bandwidth requirements

Since the access rate per unit area of ​​5G is 1000 times higher than that of 4G, the 1000 times here is generally regarded as "a thousand times the rate increase = 10 times the base station density x 10 times the spectrum bandwidth x 10 times the spectrum utilization". In practical applications, leave the base station aside Due to the density factor, the bandwidth of a single base station is increased by 30-50 times. Therefore, the average bandwidth of 5G base stations will exceed 2G, and the peak value will exceed 10G. Taking the S111 station type as an example, the CIR/PIR will reach 4G/16G. If one station reaches the peak bandwidth of 6 stations in each access ring, the access ring bandwidth will reach 40G. Taking into account the density of 5G base stations, the 100G group The network is more likely, and the core/aggregation layer may reach T-level networking.

2.2 Low latency requirements

Among the scenarios and requirements defined by 5G, the high-reliability and low-latency communication (uRLLC) application scenario mentions the end-to-end 1ms delay, and the low-latency mainly meets some special scenarios. The main scenario mentioned by the relevant standards organization is autonomous driving. But the 1ms scenario is controversial. For example, in an autonomous driving scenario, at a speed of 100km/h, a moving distance of about 3cm in 1ms is not necessary for automatic driving, and there is no threat to safety. Relatively speaking, the one-way delay of the S1 interface that is more suitable for the application is 10ms, the delay of the transmission network is 2ms, the one-way delay of the X2/ex2 interface is 20ms, and the delay of the bearer network is 4ms, so the transmission network uses 2ms The low latency of ~4ms is more reasonable.

2.3 The need for network fragmentation

The 5G network will penetrate into all areas of society. In addition to the mobile Internet, the Internet of Everything will be realized. Massive connected devices, and various new services and application scenarios are constantly emerging. While bringing rich applications to the 5G network, it also contributes to the 5G network. The bearer puts forward different transmission requirements. Applications such as the Internet of Vehicles, mobile medical, and industrial control have strict requirements on transmission delay, while data services and high-definition video have higher bandwidth requirements. In order to meet the needs of various services, at the same time To make the most efficient use of the equipment resources of the wireless and bearer network, it is necessary to slice the resources of the wireless and bearer network, use different resources to carry different services, and realize the reasonable arrangement of network resources on demand.

Network slicing requires network equipment hardware and software platform support, and will be closely integrated with SDN (software-defined networking).

2.4 The demand for traffic between stations

In the 5G scenario, the characteristics of 5G high-density traffic/high-density connections will make the mobile bearer traffic model mesh: base station-base station, EPC-EPC transfer traffic may account for a significant increase compared to 4G, the traffic model Preference to mesh. There are two scenarios for inter-station traffic, one is the traffic generated by the coordinated X2/eX2 interface between base stations, and the other is part of the application, because the location of the gateway/EPC/MEC may be relatively low, resulting in inter-station traffic. The demand for traffic between stations also puts forward certain requirements on the architecture of the transmission network.

2.5 High-precision time synchronization

In the ultra-dense networking scenario, joint transmission of base stations puts forward higher requirements for synchronization: joint transmission under non-adjacent carriers requires time synchronization accuracy of 260ns; joint transmission under adjacent carriers requires time synchronization accuracy of 130ns; under the same carrier The joint transmission requires a time synchronization accuracy of 65ns. With a time synchronization accuracy of 65 ns, even if the base station obtains the time directly from the GPS, it is difficult to guarantee the synchronization accuracy, and it is necessary to consider the use of a bearer network to achieve high-precision time synchronization.

3.1 Analysis of basic resource reserves

Facing the development of 5G, the reserve of basic resources is extremely critical. Considering the actual coverage shortening of high-frequency failure, the density of 5G base stations will be about 1.5 times that of 4G, the ultra-dense distribution of micro-stations, and the low latency and inter-station traffic requirements will put forward certain requirements for the networked structure of the ring.

Based on the above characteristics, the key to reserve basic resources is:

The first is to reserve resources for important nodes such as office rooms and aggregation nodes, especially the increase in the self-owned rate of aggregation nodes and the increase in the area of ​​the computer room. First of all, to promote the capacity reserve of the core computer room. 5G requires about 30-50 racks for the core node installation, and the power consumption is about 120~200kw. The improvement of the core computer room installation conditions and the advance storage of power, air conditioning and other conditions are critical; , China Mobile’s converged computer room conditions are not good, and many of them are still rented computer rooms, and there are not many remaining installed space. The 5G-oriented network has proposed new purchases of these resources and the need for existing network remediation to improve the installation conditions. .

The second is the grid-based deployment and extension of the optical communications network, which is close to the access point to achieve grid-based, orderly, flexible and secure access to resources. 5G base stations still use optical fiber access and networking as the main means of optical fiber access. Facing the site access requirements of ultra-dense networking, optical fiber resources need to focus on planning and consideration from two aspects of "density" and "health". . The dimension of "density" takes the integrated service access area as the unit, and examines its coverage radius and access capability. Considering that the base station site density is increased to 1.5 times, it is necessary to focus on enhancing the coverage of the integrated service access area and increase the secondary level Construction of fiber splitting points. The dimension of "health" is to examine the continuous accessibility of basic resources from the perspective of "micro-grid", and assess the "regulation rate", "coverage rate", "connectivity rate" and "access rate" within the micro-grid range. Indicators such as "incoming rate" promote construction and optimization.

The third is the addition or expansion of road pipelines to meet the needs of equipment networking. Facing 5G, the basic resource level also needs to pay attention to the addition of pipelines and the construction of dredging. It is necessary to carry out the addition of pipelines in advance, enhance the ability of line connectivity, and promote applications such as textile pipes. Prepare for DRAN deployment and networking of transmission equipment.

3.2 Discussion on the realization of network fragmentation

Network slicing is a feature of 5G, which can be divided into forwarding layer slicing, management layer slicing, and control layer slicing. Several 5G-oriented scenarios can also perform continuous wide coverage slicing, low-latency and high-reliability slicing. The application of SDN is an important way to realize these network fragments.

Relatively speaking, under the advocacy of China Mobile, introducing SDN into the PTN network is a solution that may be applied in the near future. The networking and application of SPTN can be realized by introducing S-Controller and D-Controller. At present, the verification of SPTN is being piloted in many cities, but there are few applications in the existing network. As 5G approaches, its deployment will increase.

At the same time, with the continuous development of PTN technology, it is evolving to the second generation of PTN. The second-generation PTN will have features such as FlexE (lightweight enhancement based on traditional Ethernet). FlexE can realize service isolation and bundling, and can realize fragmentation at the forwarding layer, so that the 5G network fragmentation feature can be achieved through FlexE and SDN at the same time Realize hard isolation and soft isolation, and its application is more valuable.

3.3 Requirements for high-precision time synchronization deployment

The 5G air interface requires high-precision time synchronization. The centimeter wave in the frequency band below 6G can even reach 150ns, which puts forward requirements for ultra-high-precision time synchronization. In order to meet the requirements of time synchronization, especially in the transmission network transmission scenario, on the one hand, it is necessary to deploy an ultra-high-precision time synchronization server, and on the other hand, to improve the time synchronization algorithm to improve the accuracy of time synchronization.

3.4 Discussion on the downward shift of the three-layer network

At present, the transmission network is dominated by Layer 2 equipment. The Layer 3 equipment of China Mobile’s PTN network is generally deployed at the core layer. At the same time, L2/L3 bridging equipment is deployed in pairs. Both the convergence layer and the access layer are Layer 2 equipment. The network is a small three-layer network. For X2 services such as inter-station traffic, the path is access -> convergence -> bridging -> convergence -> access. X2 services have many hops, long distances, and relatively long delays. Also larger.

The requirement for low latency, the increase of traffic between stations, and the cloudification of 5G wireless and core all put forward requirements for the three-layer downshift of the transmission network.

There are two solutions for the downward movement of the three-layer network: sinking to convergence and sinking to the access edge. The solution from sinking to access will be a very complex three-layer network, the traffic between stations and the delay to service network elements will be greatly reduced, but the network maintenance is relatively complicated. The solution of sinking to convergence can reduce the delay to less than 1.5ms, and its path is access -> convergence -> access, which can meet the requirements of most 5G services. The convergence point is relatively stable, and the network maintenance The complexity is relatively reduced. Whether it is sinking to convergence or sinking to access, this will become a large three-layer network, and the static routing method needs to be changed to the dynamic routing method.

3.5 Discussion on the evolution of metropolitan area transmission network architecture

(1) Bandwidth calculation in the metropolitan area transmission network

5G base station peak bandwidth is 7G, ​​average bandwidth is 3.5G, and 8 nodes are connected to the ring. According to 7*single station average bandwidth + single station peak, the access ring bandwidth is about 31.5G; for convergence ring, ring Network estimation, assuming 6 devices per convergence ring and 3 access rings for each pair of devices, estimated by 6*3*access ring bandwidth*convergence convergence ratio/2, the convergence convergence ratio is tentatively set to 4:3, then The convergence ring bandwidth is about 213G.

For the CRAN method, each access ring can carry 20 RRUs. The 5G base station has a peak bandwidth of 7G, an average bandwidth of 3.5G, and an access ring with 4 nodes. According to 23*single station average bandwidth + single station peak, then The incoming ring bandwidth is about 87.5G; for the convergence ring, it is estimated by ring networking, assuming that there are 6 devices per convergence ring, and each pair of devices has 3 access rings, according to 6*3*access ring bandwidth*convergence convergence ratio/ 2 It is estimated that the convergence ratio is tentatively set to 4:3, and the convergence ring bandwidth is about 590G.

The above calculation shows that the access layer equipment needs to consider the 40GE ring or the direct group 50G/100G ring; the aggregation layer equipment needs to gradually consider the group 400GE ring or overlay.

For the core layer, each pair of nodes can carry more than 3000 stations. Assuming the 4:2 convergence algorithm, the estimated bandwidth is about 6T, and the core layer needs to use large-capacity equipment.

(2) Discussion on the evolution of metropolitan area transmission network architecture

Combining the lowering of the three-layer network, the realization of network fragmentation, and the measurement of bandwidth, the architecture of the metropolitan area network will develop in the direction of intelligence, flatness, high-speed bandwidth and flexible networking.

1) In terms of moving down the three-layer network, whether to move down to the convergence layer or the access layer is still controversial. From the utilization of the existing network to meet the 5G pilot and initial development, moving down to the convergence layer will be a compromise choice, which can smooth the service path through the convergence layer to the sinking service endpoint, and the delay is compared with the current It has been greatly reduced; from the perspective of satisfying all the scenarios and long-term development of 5G, moving down to the access layer will also be an option. The entire metro transmission network will become a three-layer network, which can satisfy all types of business termination and Low-latency transmission and shortest path transmission of traffic between stations, but the entire network will have a new plane, and the investment cost is high.

2) In terms of network fragmentation, FlexE and SDN are currently discussed more frequently. FlexE is a lightweight and enhanced technology of traditional Ethernet. The bearer technology of Ethernet-based multi-rate sub-interfaces on multi-PHY links realizes service isolation and bundling. It supports multi-rate interfaces, network fragmentation, and integrated multi-service bearing. At present, there are many controversies about the application of this technology, but the application at a certain level is relatively large. The introduction of SDN, especially the application of SPTN, currently has a lot of consensus, and the realization of network fragmentation through SDN is more likely in the future.

3) In terms of bandwidth rate increase and network networking, it will present the characteristics of high-speed bandwidth and flexible networking.

The core layer network of the big city will be mainly mesh network, through the partition network to realize the access of the partition, using the L3 equipment for the architecture construction, the large-capacity equipment with a single port of 400G or more is required.

The aggregation layer gradually adopts L3 equipment to build the structure, and the ring network can be considered to be gradually changed to lip-type uplink. According to the sinking network element setting of the network, a semi-mesh structure flexible networking is required, and a large capacity above 400G for a single port is also required. Equipment to meet the rapidly increasing demand for 5G bandwidth.

The access layer can still be accessed in the form of a ring network, or a flexible networking with a semi-mesh structure. The bandwidth is upgraded from the current GE ring/10GE ring to a single ring 40G or 50G/100G.

As 4G networks provide people with high-quality communication services such as videos, pictures, voice, and text messages, people’s mobile communication experience has been very different and improved compared to 10 or even 5 years ago, which also makes people Full of expectations for the 5G network. Starting from the progress of the 5G standard and typical applications of scenarios, this article discusses the key transmission requirements of 5G network deployment are ultra-high bandwidth, low latency requirements, network fragmentation, inter-station traffic, and high-precision time synchronization. Through the calculation of bandwidth flow, the bandwidth model of each layer was established, and the bandwidth rate improvement and network networking characteristics of the core layer, convergence layer, and access layer of the transmission network were proposed, and the 5G-oriented transmission network will gradually move down the three layers. , Carrying out the efforts of network fragmentation, the reserve of basic resources and the deployment of high-precision time synchronization, the network architecture is developing in the direction of intelligent, flat, high-speed bandwidth and flexible networking.

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