Comtech EF Data CDM-750 - Manual (Page 96)

CDM-750 Advanced High-Speed Trunking Modem Revision 2
Front Panel Operation MN-CDM750
5–18
On the top line, use the ST arrow keys to set Flow Control as Enabled or Disabled, and then
press ENTER.
When Flow Control is Enabled, the modem will begin to send Pause Frames when the WAN buffer
is approximately 87% full. Pause Frames will be 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 Ethernet ports (J5 | DATA, J6 | DATA, or J7 | OPTICAL)
does not honor Pause Frames, Flow Control should be set to 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 Sect. 5.2.2.8.2 (CONFIG) Remote
Control: Inband), any device connected to the management port (J4 | MGMT) must also honor
Pause Frames to properly ensure system operation.
(CONFIG: INTF) GBEX Æ Learning
MAC Learning: Disabled
Applies To All Ports
On the top line, use the ST arrow keys to set Flow Control as Enabled or Disabled, and then
press ENTER. Note the following:
• With MAC Learning set as 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 set as 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 as follows:
FRAME GOING FROM LAN TO WAN (Tx)
Source MAC Destination MAC Action
Don’t care Unknown Packet is sent to WAN, Source MAC is learned to exist on LAN
Don’t care Known to exist on LAN side Packet is 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