Vessels navigating in an area where vessel traffic services are provided should make use of these services.
Depending upon governing rules and regulations, participation in a VTS may be either voluntary or mandatory.
Vessels should be allowed to use a VTS where mandatory participation is not required.
Source: IALA Guideline 1068 (2009)
Vessel Traffic Services
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM