Submarine Optical Fiber (Fiber) Cable, also known as submarine communication cable. The submarine optical cable system is mainly used to connect optical cables and the Internet. It is divided into two parts: onshore equipment and underwater equipment. Onshore equipment packages and transmits communication services such as voice, image, and data. The underwater equipment is responsible for the processing, sending and receiving of communication signals. The underwater equipment is divided into three parts: submarine optical cable, repeater and "branch unit"
Someone used Google Maps to make an interactive map of the distribution of submarine cables in the world. This is the best map of this type I have seen.
As you can see from the map, there are only a few submarine optical cable connection points in mainland China, so it is very easy to control entry and exit information
The first one is Qingdao (2 submarine cables, including EAC-C2C and TPE submarine cables)
The second is Shanghai (3 submarine cables, including EAC-C2C, FEA, Seamewe-3 submarine cables)
The third is Fuzhou (1 submarine cable, including TSE-1)
The fourth is Shantou (3 submarine cables, including APCN-2, Seamewe-3, SJC)
1. APCN2 (Asia Pacific Number Two) Submarine Optical Cable
Asia Pacific Cable Network-2 (APCN-2) was jointly initiated by 26 investment institutions to connect Asian countries and regions, with a total length of about 19,000 km and a total of 10 landing stations, including Shanghai Chongming and Guangdong Shantou, New Taipei City, Taiwan, China; Lantau Island, Hong Kong, China; Minamibo City, Chiba County, Japan; Kita City, Ibaraki County, Japan; Busan Metropolitan City, South Korea; Kuantan, Pahang, Malaysia; Katong, Singapore; and Peta, Batangas Province, Philippines Yanshi. The backbone path is composed of four pairs of optical cables. The transmission speed of each group of optical cables can reach 640Gbps, the total capacity is 2.56Tbps, and it adopts a self-healing ring network structure. NEC, Chunghwa Telecom, PCCW, China Telecom, China Unicom and many other major telecommunications organizations have participated in the construction of this submarine cable.
2. TPE (Pan Pacific) Submarine Optical Cable
Place of entry: Qingdao, Shanghai
Owner: China Telecom, China Unicom, Chunghwa Telecom, KT, Verizon, NTT, AT&T
3. EAC-C2C Submarine Optical Cable
EAC-C2C is a group of submarine optical cable networks connecting countries in East Asia. It consists of EAC (East Asia Crossing) and C2C (City-to-City Cable System). Combined composition.
EAC (East Asia Crossing), with a total length of 19,500 kilometers, uses dense wavelength division multiplexing technology. At this stage, the flow rate is 160 Gbit per second. The plan is to provide a maximum flow rate of 2.5 Tbit per second.
C2C (City-to-City Cable System), which also uses dense wavelength division multiplexing technology, is designed to provide up to 7.68Tbit per second.
Place of entry: Shanghai, Qingdao, Hong Kong
4. FLAG submarine cable
Fiber-Optic Link Around the Globe (Fiber-Optic Link Around the Globe, referred to as FLAG) is a 28,000-kilometer-long submarine optical cable network connecting the United Kingdom, Japan and other countries. Global Cloud Xchange is responsible for operation and management.  The system connects to Japan from the east coast of the United States.  The Eurasian section was the fourth longest optical cable in the world in 2008,  It was led by Maritime Cable and Radio Company in the mid-1990s.
Optical cable landing is divided into point-to-point direct connection, or establishing a landing site to connect multiple optical cable network systems. The total length of the optical cable is 27,000 kilometers, including 1,020 kilometers of transit optical cables on the road, of which 6,600 kilometers of optical cables are only buried one meter below the seabed, and the optical cables are buried in the seabed through submersible ploughs or remote control buried devices.  Through several years of development, the capability of multi-channel redundant switching has been developed. There are two transit landing sites on land, one in Egypt and the other in Thailand. There are multiple different connection lines, which can allow 50 milliseconds. Rapid switching of redundant lines in case of routing failures
5. NCP (New Crossing-Pacific Cable System) submarine optical cable
The new Trans-Pacific Submarine Cable System (NCP) network structure is a fishbone single branch structure. The total length of the submarine cable network is about 14,000km. The submarine cable will land in Shanghai Chongming, Shanghai Nanhui, South Korea, Japan, Taiwan and other regions. The NCP Nanhui section project is laid eastward from the landing point after landing in Shanghai Nanhui Lingang New City, and is connected to the NCP backbone optical cable through the submarine branch point BU1