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This chapter describes the advanced features offered by your bridge.
QoS
Quality of Service is enforced by assigning each incoming packet with a predefined priority value. Packet with
higher priority should be processed as soon as possible (fast in, fast out). In shortage of buffers, some low priority
packets should be discarded to smooth the high priority traffic flow. Higher priority traffic will have higher data rate
and lower possibility of being discarded.
The numbering priority value ranges from 0 to 7, and 7 represents the highest priority level. HP-51M supports
priority scheme as 802.1p, IP TOS and TCP/UDP protocol.
Priority in Upstream and Downstream
There are 4 priority queues for packet. Packet with priority value 0 or 1 goes to the same queue, denoted as Queue0.
Queue1 has priority value 2 and 3, Queue2 has priority value 4 and 5, and Queue3 has priority value 6 and 7.
Totally 4 levels of service are provided. Queue3 need to have higher "Service Weight', i.e. packets reside in
Queue3 will be send out faster. Packets in Queue0 should have larger 'Drop Ratio' in congestion situation since it
is classified as less important.
Refer the following table for the detail mechanism to discard packets early according to their priority to prevent
resource blocked by the low priority. For example, if 'Drop Ratio' of Queue0 is set to 75%, then HP-51M will
discard 50% of incoming packets toward Queue0 if Queue0 is one fourth full(Queue Utilization 25%). And will
discard 75% of incoming packets toward Queue0 if Queue0 is half full(Queue Utilization 50%).
Drop Ratio
Queue
Utilization
25%
50%
802.1p
Tagged packet has the 3-bit (value 0~7) 802.1p field is used for priority mapping. The default priority mapping
scheme is usually suitable and should work for most applications--for example, to map 802.1p value 7 to priority 7,
to map value 0 to priority 0, and so on. It will take effect in both downstream and upstream.
IP TOS
The bit7 to bit5 of TOS byte in IP packet is treated as TOS precedence value (0~7). By default, HP-51M uses the
precedence value to map the priority queue. Please refer RFC-1349.
TCP/UDP Port Number
Different TCP or UDP port number usually states for different protocol. You may raise the priority for important
application with specified TCP or UDP port number. In HP-51M, you can assign higher priority for total 8 different
TCP/UDP protocols.
DYNAMIX HP-51M Coax MDU Master Bridge User's Guide
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