Ethernet Flow Control; Half-Duplex Flow Control; Full-Duplex Flow Control; Ethernet Daisy Chain - Comtech EF Data DMD-2050E Installation And Operation Manual

DMD2050E Universal Satellite Modem
When Ethernet Data Interface is selected, the Tx Clock Source will default to SCTE and the Clock
Polarity will default to Normal. In addition, the Buffer Clock will default to RxSat and the Buffer
Clock Polarity will default to Normal.
See also:
Chapter 4, User Interfaces
H.1.1 Ethernet Flow Control
When disabled, if a packet is received for transmission and no packet buffer space is available,
the incoming packet is discarded.
When enabled, flow control is used to throttle the transmission station in order to avoid
overrunning the transmit buffers, which would in turn cause packets to be dropped. The throttling
mechanism used depends upon the interface and whether it is half-duplex or full duplex.
H.1.1.1

Half-Duplex Flow Control

In half-duplex mode, the unit uses industry standard backpressure to support flow control as
follows:
When available buffer space is almost gone, the modem will force a collision on the input port
when it senses an incoming packet. This collision will cause the transmitting station to back off
and retry the transmission.
The interface will stop forcing collisions as soon as free buffer space becomes available.
H.1.1.2

Full-Duplex Flow Control

In full-duplex mode, the interface implements IEEE 8802.3x flow control as follows:
When available buffer space is almost gone, the unit sends out a pause frame with the maximum
pause time to stop the remote nodes from transmitting.
The interface sends out another pause frame with the pause time set to zero as soon as free
buffer space becomes available.
H.1.2 Ethernet Daisy Chain
When disabled, Port 4 (JS4) on the Ethernet Data Interface operates normally. Data received on
Port 4 that is not addressed to other equipment on the LAN side, is transmitted over the satellite.
MN-DMD2050E Revision 2
Ethernet Data Interface Setup
H–2