4G has only two parts: front haul and backhaul. With the reconstruction of the RAN architecture, the 5G bearer network has become cloud-based, C/U separation, and distributed deployment of the data plane, making the network more flattened. It is divided into a front haul and mid-haul networks. There are three parts of the transmission network and the return network.
The DU part of the AAU connection is the 5G front haul, the middle pass refers to the part of the DU connected to the CU, and the backhaul is the communication bearer between the CU and the core network.
There is no requirement for a unified bearing solution for the bearer of the front haul network. According to different access conditions and scenarios, solutions such as optical fiber direct drive, passive WDM, active WDM/OTN, and semi-active can be flexibly selected. As for the mid-haul and backhaul networks, the requirements for the bearer network in terms of bandwidth, networking flexibility, and network slicing are basically the same, so a unified bearer solution can be adopted. This article mainly introduces the mid-haul and backhaul bearer solutions based on OTN technology.
The metropolitan area OTN network architecture includes a backbone layer, an aggregation layer, and an access layer. The metropolitan area OTN network architecture matches the bearer requirements of 5G mid-haul/backhaul. The backbone/aggregation layer corresponds to the 5G backhaul network. The layer corresponds to the mid pass/front pass.
As OTN introduces packet switching and processing capabilities such as Ethernet and MPLS-TP, OTN has evolved into a packet-enhanced OTN, which can well match the 5G IP-based bearer requirements.
The OTN-based 5G mid-transmission/back-transmission bearer solution can give full play to the powerful and efficient frame processing capabilities of the packet-enhanced OTN, and complete fast framing, compression, decompression, and mapping functions through FPGA, dedicated chips, DSP and other dedicated hardware, effectively realizing DU transmission connections The function is extremely sensitive to delay requirements such as air interface MAC/PHY.
For the CU, on the one hand, the packet-enhanced OTN constructs an ultra-large bandwidth and ultra-low delay connection between CU and DU, effectively realizing the real-time, efficient and reliable PDCP processing, and supporting fast signalling access. The integrated WDM capability of the packet-enhanced OTN can realize long-distance transmission to suburbs and counties, and increase the bandwidth capacity of the transmission link as needed.
In order to meet the needs of flexible networking for intermediate transmission/backhaul, it is necessary to consider enhancing the routing and forwarding function on the basis that the packet-enhanced OTN already supports the MPLS-TP technology.
Packet Enhanced OTN+IPRAN Solution
In this solution, the packet-enhanced OTN equipment with enhanced routing and forwarding functions is used to form an intermediate transmission network. The intermediate OTN equipment can be configured as an ODUk pass-through mode as required to ensure 5G bearer requirements for low latency and bandwidth guarantee. In the backhaul part, continue to use the existing IPRAN bearer architecture, as shown in the following figure. The packet-enhanced OTN and IPRAN exchange routing information through the BGP protocol.
In order to meet the 5G bearer's need for high-capacity and network slicing, IPRAN needs to introduce high-speed interface technologies such as 25GE SFP28, 50GE QSFP28, and 100GE QSFP28, and consider adopting new interface technologies such as FlexE to achieve physical isolation and provide better bearer quality assurance.
End-To-End Packet Enhanced OTN Solution
The whole process of this solution is implemented by packet-enhanced OTN equipment with enhanced routing and forwarding functions, as shown in the figure below.
Compared with the packet-enhanced OTN+IPRAN solution, this solution can avoid the problems of interconnection and inter-professional coordination between the packet-enhanced OTN and IPRAN, so as to better exert the powerful networking capabilities and end-to-end maintenance of the packet-enhanced OTN Management ability.
