The basic structure of communication network includes Backbone Network, Core Network, Metropolitan Area Network, and Access Network. The Access Network types of wireless access, and wired access. Here we will introduce what is Core Network, Metropolitan Area Network, and Access Network, and the difference between them. HYC Co., Ltd provides full series of WDM (Wavelength Division Multiplexer) for communication networks, eg. DWDM(TFF/AWG) for bearer network, DWDM MUX/DEMUX/OADM for Core Network, CWDM/CCWDM for Metro Area Network, PON WDM/CWDM/LWDN/MWDM for Access Network.