Comtech EF Data CDM-760, Installation And Operation Manual

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Front Panel Operation Revision 4
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
6–31
(CONFIG: INTF) (GBEIX)

FlowControl
The use of Flow Control or Pause Frames is useful when ALL devices connected to the modems
are set to honor Pause Frames. When used properly, Flow Control acts as a traffic valve in an
ACM environment.
Use the  arrow keys to set Flow Control as Enabled or Disabled . Press ENTER .
When Flow Control is Enabled , the modem begins to send Pause Frames once the WAN buffer is
approximately 87% full. Pause Frames are sent to ALL ports. Pause Frames will cease to be sent to
the Ethernet interfaces when the WAN Buffer Fill Status drops below 75% full.
If ANY device directly connected to the base unit Ethernet ports (GBEI1 /
J5 | DATA
, GBEI2 /
J6 |
DATA or J7 | OPTICAL ) does not honor Pause Frames, you should set Flow Control as Disabled ,
as the interconnected device will not back off in an overflow condition and may cause all traffic
on the Tx and Rx links to become congested. All overflow traffic will be discarded.
Also note that, when the Remote InBand is set to Enabled (see Section 6.2.2.9.2 CONFIG:
Remote →Inband
), any device connected to the base unit management port (
J4 | MGMT
) must
also honor Pause Frames to properly ensure system operation.
6.2.2.4.2.1 MAC Learning Operational States
(CONFIG: INTF) (GBEIX)

Learning
Use the  arrow keys to set MAC Learning as Disabled or Enabled . Press ENTER .
•
With MAC Learning Disabled , the modem passes any traffic Entering from the GBEI (LAN)
interface to the satellite (WAN) side of the link, while traffic coming in from the satellite
(WAN) side of the link is passed on to the GBEI (LAN) interface. There is no filtering of traffic,
and the modem connection looks like a “wire.”
• With MAC Learning Enabled , the Destination MAC and Source MAC are “learned” by the
modem. If the modem sees a destination MAC on its LAN side that it recognizes as belonging
to the LAN side, it will not transmit the frame. If the modem sees a destination MAC on its
WAN side that it recognizes as belonging to the WAN side, it will not transmit it to the LAN
side. If the modem sees a Source MAC on its LAN side, it learns that going forward. Any
Destination MAC it does NOT know, it will send across to the other side.
The MAC Learning process is further explained:
Frame going from LAN to WAN (Tx):
Source MAC Destination MAC Action
Don’t care Unknown Packet sent to WAN, Source MAC is learned to exist on LAN
Don’t care Known to exist on LAN side Packet NOT sent to WAN, Source MAC is learned to exist on LAN
Don’t care Known to exist on WAN side Packet is sent to WAN, Source MAC is learned to exist on LAN
Don’t care Broadcast or Multicast MAC Packet is sent to WAN, Source MAC is learned to exist on LAN