Comtech EF Data CDM-570L Installation And Operation Manual page 289

CDM-570/570L Satellite Modem with Optional IP Module
IP Module Ethernet Interface Overview
Weighted Random Early Detection (WRED) – The Min/Max BW QoS mode allows
the user to select Weighted Random Early Detection (WRED).
WRED allows for more graceful dropping of packets, as QoS queues get full. Without
WRED, typically packets are dropped based upon a simple tail drop algorithm which was
applied to packets as they were being added to the QoS queues. This can result in large
numbers of contiguous packets being dropped which causes many protocols such as RTP
and TCP to ungracefully degrade performance in a over-consumed or bursty scenario.
WRED applies a randomization which means that the percentage change to drop 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.
Maximum Bandwidth - This can be assigned to a flow to restrict the Maximum
Bandwidth that any particular flow will utilize, or the default of no bandwidth restriction
can be selected.
Minimum Bandwidth - Minimum specification that allows a committed information rate
(CIR) to be applied to user defined classes of traffic, or the default of no minimum
bandwidth can be selected.
Filtering – Any specific flow can be designated as filtered (see Maximum
Bandwidth/Priority QoS).
QoS Rule Hierarchy – The QoS Rule Hierarchy is the same as Maximum
Bandwidth/Priority QoS.
QoS Statistics - QoS Statistics are displayed as Maximum Bandwidth/Priority QoS.
15.4.4.3 DiffServ QoS Mode
The IP Module QoS can also be set to DiffServ Mode to make it fully compliant to the
Differential Services QoS RFC standards.
Class Selector DiffServ Code Points (DSCP) – Some implementations of DiffServ will
prioritize traffic by Class Selector assignment. This is defined in the DiffServ Code
Points (DSCP) within the IP header. The first 3 bits of the DSCP define the Class
Selector Precedence (or Priority):
Class Selector DSCP
Precedence 1 001 000
Precedence 2 010 000
Precedence 3 011 000
Precedence 4 100 000
Precedence 5 101 000
Precedence 6 110 000
Precedence 7 111 000
Default 000 000
15–13
IP Module Priority
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Revision 4
MN/CDM570L.IOM