Table of Contents
Advertisement
DMD50 Universal Satellite Modem
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.
When Strict Priority is selected, the interface transmits packets from the highest priority queue
until it is empty. It then begins transmitting data from the next highest priority queue. If higher
priority data arrives, the interface finishes the current packet and then goes back to transmitting
packets from the higher priority queue until it is again empty. Care must be taken when selecting
Strict Priority, as it is entirely possible for the lower priority queues to be stalled indefinitely.
MN-DMD50 Revision 4
Ethernet Data Interface Setup
J–2
Advertisement
Table of Contents
