in the 2 1 tdma communications system and the first call is currently occupying one of the two slots the fixed end 102 denies the second call fig9 illustrates one of the ways in which the situation depicted in this second example arises for example if the second requested call type is a subscriber unit to subscriber unit call with reverse channel signaling in a third example if the slotting structure required for the second requested call type is the same as the existing slotting structure supporting the first requested call type and both the first and second requested call types require only one channel each the fixed end 102 grants the second call fig1 illustrates one of the ways in which the situation depicted in this third example arises for example if the first requested call type is a subscriber unit to talk group half duplex call from subscriber 1 100 to talk group 1 1000 and the second requested call type is a subscriber unit to subscriber unit half duplex call from subscriber 3 900 to subscriber 2 500 in a fourth example if the slotting structure required for the second requested call type is different than the existing.