Quality Of Service - Comtech EF Data CDM-570L Installation And Operation Manual

CDM-570L Satellite Modem with IP Module
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14.4.4 Quality of Service

Quality of Service (QoS) is an optional feature of the IP Module. The user may select one of three modes
of QoS operation:
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Mode 1 – QoS Rules based on Maximum Bandwidth and Priority
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Mode 2 – QoS Rules based on Minimum and Maximum Bandwidth
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Mode 3 – DiffServ
QoS Segmentation and Reassembly (SAR) - Packet Segmentation and Reassembly (SAR) is enabled
automatically while QoS is enabled. However, SAR is an adaptive process; it will trigger only if the
packet latency exceeds the threshold value (default to 20 msec). Latency value is calculated based on the
satellite transmission bandwidth. The minimum segment size was limited to 480 bytes excluding satellite
HDLC header in order to avoid satellite overhead and consumption of CPU cycles.
14.4.4.1 Maximum Bandwidth/Priority QoS Mode Maximum
Bandwidth/Priority Mode
QoS Rules can be assigned to up to 32 different types of flows to be defined by the user. Flows can be
defined by any combination of Protocol (FTP, UDP, RTP, etc.), Source/Destination IP (specific or range),
and/or Layer 3 Source/Destination Port.
Priority - A Priority level from 1 to 8 is assigned for each flow. The IP Module classifies each
packet that is to be forwarded over the satellite. The packet will then have a Priority assigned
according to the defined QoS Rules. Any packet that does not meet a QoS Rule is assigned to the
Default Rule and will be assigned a Priority of 8. Priority 1 packets will be forwarded
immediately, Priority 2 packets will be forwarded as soon as there are no Priority 1 packets in the
Queue, and so on. Any latency critical traffic, such as VoIP/RTP should always be assigned
Priority 1.
Maximum Bandwidth - This can also 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.
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