GE MDS SD Series Technical Manual page 25

Packet w/MAC is the recommended method of operation when both
serial ports are used to pass payload data if there are two hosts (e.g., Port
Sharing with multiple host case). If there is a single host polling all units,
packet or transparent mode is the preferred option even if there are two
RTUs connected to a Remote radio.
Device Settings Screen
Radio Mode: Packet w/MAC
MASTER RADIO
To Ethernet Port
HOST COMPUTER
TCP Ethernet
(Host A)
REMOTE RADIO
REMOTE RADIO
(One of several possible sites)
(One of several possible sites)
SERIAL RTU SERIAL RTU
SERIAL RTU SERIAL RTU
Figure 10. IP Polling of Two Serial Ports on One Remote
MDS 05-4846A01, Rev. H SD Series Technical Manual 17