LLD (Lom Level Design, detailed design) is to clearly design the network scope and function deployment plan on the basis of the determined target network architecture: the specific design content includes specifying the interaction process of important services concerned by customers within the scope of the contract, all business In the function allocation of each network element, the design of the peripheral docking relationship of the network element, the docking requirements and compliance with the norms, and the quantitative calculation of the docking resources.