SPLIT-MOUNT / ALL-INDOOR
Split-mount radio systems consists of (a) indoor units (IDU) that produce modem baseband and IF signals and (b) outdoor units (ODU) that convert the IF signals to carrier frequency bands. ODUs and IDUs are connected with RF cables. The advantage is that the IDU can support non-IP interfaces such as TDM (T1/E1) and STM-1 and carry such signals in a seamless manner.
All-indoor systems have RF units installed indoors typically in network racks along with IDUs. The RF signals are brought up to the antenna by way of RF waveguides with minimal loss. The advantage is that Tx output power can be very high and maintenance is easy due to all active electronics being accessible without tower climbs.