Comtech EF Data CDM-IP 300L - Manual (Page 43)

CDM-IP 300L IP-Centric Satellite Modem Rev. 1
CD/CDMIP300L.IOM
15
1.4.4 Q
UALITY OF
S
ERVICE
Quality of Service (QoS) is an optional feature of the CDM-IP modem. The user may
select one of three modes of QoS operation:
• Mode 1 – QoS Rules based on Maximum Bandwidth and Priority
• Mode 2 – QoS Rules based on Minimum and Maximum Bandwidth
• 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.
1.4.4.1 M
AXIMUM
B
ANDWIDTH
/P
RIORITY
M
ODE
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 CDM-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.
Filtering - QoS also allows specific flows to be designated as “filtered”, so the CDM-IP
will discard traffic that the user does not want to forward over a satellite link.
QoS Rule Hierarchy - It is quite possible to have traffic that meets the definitions of
several QoS Rules. All traffic will be classified into the first QoS Rule that is a match, or
fall into the Default Rule. The most specific QoS Rule will always be first. For example,
a QoS Rule that identified a Source and Destination IP Address would be assigned ahead
of a rule that just defined RTP protocol. QoS Rules that have the same amount of
variables defined are sorted as follows: