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OM20 Universal Outdoor Modem
6.3
Configuring the OM20 to use the Ethernet Data Interface (Optional)
The OM20 Ethernet related menus are available and can be used to control the data interface as
follows:
Under the Interface Menu:
Under the Tx Setup Menu:
Set the Terrestrial Interface to Ethernet.
Set the Ethernet Flow Control as desired (refer to Section 6.3.1 for details).
Set the Tx Clock to SCTE.
Set the Tx Clock Polarity to Normal.
Under Drop & Insert:
Under the Interface Menu:
Under the Rx Setup Menu:
Set the Terrestrial Interface to Ethernet.
Set the Buffer Size to Zero.
Set the Buffer Clock to Rx Sat.
Set the Buffer Clock Polarity to Normal.
Under Drop & Insert:
6.3.1 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 and is
described in the following sub-paragraphs:
6.3.1.1 Half-Duplex Flow Control
In half-duplex mode, the OM20 uses industry standard backpressure to support flow control as
follows:
When available buffer space is almost gone, the OM20 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 OM20 will stop forcing collisions as soon as free buffer space becomes available.
6.3.1.2 Full-Duplex Flow Control
In full-duplex mode, the OM20 implements IEEE 8802.3x flow control as follows:
When available buffer space is almost gone, the OM20 sends out a pause frame with the
maximum pause time to stop the remote nodes from transmitting.
The OM20 sends out another pause frame with the pause time set to zero as soon as free buffer
space becomes available.
TM116 – Rev. 1.2
Set the Drop Mode to None.
Set the Insert Mode to None.
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