Comtech EF Data VMS v3.12.x Vipersat - Manual (Page 252)

Network MN/22156, rev 12
4-34 VMS User Guide
packets in the queue, and so on. Any latency-critical traffic, such as VoIP/RTP
should always be assigned Priority 1.
WRED
Selecting the WRED (Weighted Random Early Detection) check box enables
this function in the modem/router. WRED allows for more graceful dropping of
packets, as QoS queues get full.
Without WRED, output buffers fill during periods of congestion. When the
buffers are full, all additional packets are dropped. Typically, packets are
dropped based upon a simple tail drop algorithm applied to packets as they were
being added to the QoS queues. This can result in large numbers of contiguous
packets being dropped all at once, which causes many protocols such as RTP
and TCP to ungracefully degrade performance in an over-consumed or bursty
scenario.
WRED applies a randomization, which means that the percentage change to
dropped packets increases as the queue becomes full, and minimizes the
chances of global synchronization. Thus, WRED allows the transmission line to
be used fully at all times.
Enable Filtering
QoS allows specific flows to be designated as “filtered,” so the modem/router
will discard traffic that the user does not want to forward over a satellite link.
Selecting the Filter check box enables filtering.
IP Addressing
Specific Source and Destination IP Addresses can be specified for a rule, if
desired.
Source and Destination Ports
Selecting Source and Destination Ports should only be done if the user is aware
of the port used by the desired protocol or application. There are well known
ports for various protocols, but often only command messages use these specific
ports and data is transferred through a negotiated port.
Either specific port numbers or a range of ports can be entered using the Source
Port and Destination Port Minimum and Maximum fields. The valid port
range is 0 to 65535.
Minimum & Maximum Bandwidth
Minimum and Maximum Bandwidth values can be assigned to a flow to restrict
the bandwidths that any particular flow will utilize.