Nera SatLink 1000, User Manual

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Nera SatLink Terminal User Guide – Revision P
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8. Quality of Service
QoS is used to provide differentiated handling of different types of IP traffic. The aim is to be able to
satisfy traffic flows for applications with different requirements. For example, to assure a given return
link bandwidth with minimal delay jitter for VoIP or other UDP based continuous rate real time traffic by
avoiding influence from traffic that are not so sensitive to delay jitter, e.g. Web browsing and FTP.
The Nera SatLink Terminal can be configured to support two different QoS groups on the return link.
QoS on the forward link is handled by the DVB-RCS Gateway and not discussed further in this manual.
The QoS implementation in the terminal is based on a multi-field classifier, i.e. the DSCP/TOS field and
other fields in the IP header are used to classify which QoS group each IP packet belongs to. IP packets
belonging to different QoS groups are then treated differently by the terminal. The terminal can be
configured to support traffic differentiation based on DSCP values as used in DiffServ based networks.
The two QoS groups that are supported on the return link are
1) VoIP/other real-time continuous rate traffic
2) Best effort (typically used for Web browsing, FTP, and similar).
Associated with each QoS group is a QoS policy. Parameters that impact the QoS policy are:
•
Capacity request algorithm and parameters
-
The capacity request algorithm for real-time traffic is tailored to request a continuous rate
capacity,
-
the capacity request algorithm for best effort is designed for more bursty and delay insensitive
traffic such as Web browsing and FTP.
•
Transmission PID
-
Used to give precedence to real-time traffic when interleaving traffic from different QoS groups
at the MPEG level
•
Drop policy
-
Real-time traffic is placed in shorter transmission queues at IP level than best effort traffic
-
Real-time traffic packets are dropped at the head of the transmission queue if the queue
overflows, while best effort traffic packets are dropped at the tail of the queue.
•
Precedence
-
Real-time traffic is given precedence over best effort traffic.
Typing CLI command
# ip qos show
will output among other the QoS Policy Table:
QOS Policy Table
Group CRClass Strategy FwdPri QLength DropPolicy Timeout
0 0 0 0 400000 0 120
1 1 1 1 15000 1 120
QoS Classification table
Idx Grp Classification Parms
The parameters in the QoS policy Table are not user configurable.