One of the more popular options of the time was to use high pressure, fluid filled cables.
当时更流行的选择之一是使用高压流体填充电缆。
英语百科
Filled cable
In telecommunication, a filled cable is a cable that has a non-hygroscopic material, usually a gel called icky-pick, inside the jacket or sheath.
The nonhygroscopic material fills the spaces between the interior parts of the cable, preventing moisture from entering minor leaks in the sheath and migrating inside the cable.