Half-Duplex Flow Control; Full-Duplex Flow Control; Ethernet Daisy Chain; Ethernet Qos Type - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem
J.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.
J.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.
J.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.
When Port 4 is selected for Daisy Chain, any data received on Port 4 (JS4) is forwarded to of the
other LAN side ports (Ports 1 - 3) and is not transmitted over the satellite. This is extremely useful
in a point-to -multipoint configuration as illustrated in Figure J-1.
J.1.3 Ethernet QOS Type
When Normal QOS is selected, the interface determines a packets priority based on the following:

IEEE 803.3ac Tag when present

IPv4 Type of Service / Differentiated Services Field

Ipv6 Traffic Class
When Port Based QOS is selected, the interface determines the priority of a packed based upon
the port on which it arrived.

Port 1 (JS1) has the highest priority

Port 2 (JS2) has the second highest priority

Port 3 (JS3) has the second lowest priority

Port 4 (JS4) has the lowest priority
J.1.4 Ethernet QOS Queue
When Fair Weighted queueing is selected, the interface transmits packets at a rate of 8, 4, 2, and
1 from the highest priority queue to the lowest respectively. With fair weighted queueing, all
queues with data in them are guaranteed to receive some bandwidth.
MN-DMD50 - Revision 3
Ethernet Data Interface Setup
J–2