Sec. 95.21  GMRS system description.

    (a) A GMRS system is one or more transmitting units used by station 
operators to communicate messages. A GMRS system is comprised of:
    (1) One or more station operators;
    (2) One mobile station consisting of one or more mobile units (see 
Sec. 95.23);
    (3) One or more land stations (optional); and
    (4) Paging receivers (optional).
    (b) In certain areas, point-to-point GMRS systems may be comprised 
of fixed stations only (see Secs. 95.47, 95.49 and 95.61).
    (c) A GMRS system may be operated in:
    (1) Simplex mode. (Only one station operator can speak at a time.)
    (2) Duplex mode. (Two station operators can speak at the same time. 
One or more stations transmit on one channel. The other station(s) 
transmit(s) on the channel pair counterpart.)
    (3) A combined simplex-duplex mode. (E.g., a mobile relay system 
with mobile units operating in simplex mode on a channel pair.)