Maintenance M7/M7L/M7LT Modular Satellite Modem
3-90 M7/M7L/M7LT - Rev. 0.05
“Auto” but each port can be configured to “1000BASE-T”, “100BASE-T Full Duplex”, “100BASE-T Half
Duplex”, “10BASE-T Full Duplex”, or “10BASE-T Half Duplex”.
3.8.2.2. SFP Interface - Port 5
This port allows the E7 to offer a wide variety of optical interfaces (1000Base-T, 1000Base-SX
multimode, and 1000Base-LX and BX single mode) from qualified vendors. In addition, the SFP
interface can offer an additional GbE interface port to the internal Ethernet switch. The M7 will
recognize if there is a SFP module installed and will provide the appropriate menus for control.
NOTE: <Intf: I/O Port 5 Mode = Data I/O> Port 5 will only show in the menu when there is an SFP
module installed in the SFP slot.
3.8.2.3. Flow Control
The M7 transmission is classified as FDMA and as such has a constant bit rate for transmission over
the satellite, which is the WAN side of the E7 interface. Conversely, an Ethernet interface can have
significant variability in the instantaneous bit rate and through flow control will settle in to a long term
average of the constant bit rate of the FDMA link. QoS buffering is provided at the output of the
internal Ethernet switch to store data until it is needed for transmit to the WAN. The QoS mode can
be configured in the menu <Intf: QOS Mode> to either “WRED” (Waited Random Early Detection) or
“Strict Priority”. These settings will determine the procedure for dropping packets at the point where
the QoS buffer has reached the point of congestion. The default setting is WRED.
Additionally, the E7 allows the user to set flow control for the QoS buffer for a non-congested state
and full congestion of the WAN traffic. This is set in the menu item <Intf: QOS WAN Drop None> for
the non-congested state and <Intf: QOS WAN Drop All> for the congestion point where all incoming
packets will be dropped until the QoS buffer drops below this setting. Between the QoS buffer
settings of “Drop None” and “Drop All”, there is an expectation that some packets will be dropped in
line with the “QoS Mode”.
The proper setting of “Drop None” and “Drop All” is dependent on the type of traffic, i.e. VoIP, Web,
Streaming Video, FTP, etc., that is transiting the network and the constant data rate of the WAN
satellite link. These settings correspond to the fill status of the QoS buffer. The “Drop None” setting
is the point below which there is no flow control activated.
The “Drop None” minimum setting should represent the time, in mSec, that is equivalent to at least 2
Ethernet packets. For example if the M7 modulator is set to transmit at 1Mbps toward the WAN, set
the menu item <Intf: QOS WAN Drop None = 24 ms>. This would be the minimum setting for this
configuration. The recommended maximum setting would be set to half of the “Drop All” setting.
The “Drop All” setting will determine the maximum delay that the QoS buffer will add to the network.
Certain traffic types that are sensitive to delay will require that the “Drop All” value be set to a
minimum value but if this is set too low, the E7 will drop packets when large packet Web content is
transmitted toward the WAN. The recommended minimum setting for the “Drop All” would represent
the time, in mSec, that is equivalent to at least 20 Ethernet packets. For example if the M7 modulator
is set to transmit at 1Mbps toward the WAN, set the menu item <Intf: QOS WAN Drop All = 240
ms>. The setting of the “Drop All” can be arbitrary and may need to be adjusted to optimize the
network performance once the traffic types are known.
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