2. Marine Common Battery Telephones (Multi-link) This equipment allows up to 12 telephone extension sets. These extension sets can be contacted by turning the rotary switch and pressing push button at this unit. Even if one extension set is busy, remaining five sets can be contacted at the same time. In addition, the following special functions are provided : With two common battery telephone (or multi-link type) sets connected in parallel, both telephone sets can be contacted from outside telephone set at the same time.