A tether is a length of cable which connects the Onboard Computer to the Topside Computer. Radio frequency (RF) waves do not travel far through water and acoustic modems have limited bandwidth, so a tether is a critical component to connect the vehicle to a surface computer.
The Onboard Computer communicates with 10/100/1000 Base Ethernet. If 10/100 Base is acceptable, a standard Cat 5 cable may be used to connect to the vehicle and topside computer. The maximum transmission length of Cat5 cable is around 100m.
Alternative tether types (twisted pair, fiber optic, etc) and lengths require a Tether Interface.