Quality Of Service (Qos) (802.1P And Diffserv) - Trango Systems TrangoLINK GigaPlus User Manual

Quality of Service (QoS) (802.1p and Diffserv)

GigaPlus internal switch fabric performs QoS on all incoming packets to provide priority
to allow the operator to give priority to certain traffic types. The following fields are
used to direct the incoming traffic:
- Layer 2 using the COS bits in the VLAN tag on incoming Ethernet traffic (Tagged
traffic only)
Layer 3 Diffserv (DSCP) using the Differentiated services field in IP packets. The
-
DSCP mapping can be controlled on a port by port basis from CLI or Web.
Port Priority for untagged traffic
-
The incoming traffic is mapped into 8 queues (FIFOs) which are emptied into a single
data pipe going into the modem and subsequently over the air. The scheduling of the
queue traffic into the modem data pipe can be either strict or Weighted Round Robin
(WRR)
Strict QoS Mode, which applies to the VLAN COS field only, follows the logic rule below:
COSQ7> COSQ6> COSQ5 > COSQ4>COSQ3> COSQ2> COSQ1 > COSQ0
This rule essentially means that the system will empty COSQ7 before sending any
COSQ6 packets across the link, and if both COSQ7 and COSQ6 are empty then COSQ5
packets will be sent, etc. Note that while strict priority ensures that ALL high priority
traffic will go through (up to max burst size and link capacity limits), it may block lower
priority traffic or increase the latency significantly for lower priority packets during
traffic congestion.
The default priority mapping of the packet will be set as follows:
COS priority 0 
COSQ0
COS priority 1 
COSQ1
COS priority 2 
COSQ2
COS priority 3 
COSQ3
COS priority 4 
COSQ4
COS priority 5 
COSQ5
COS priority 6 
COSQ6
COS priority 7 
COSQ7
These default mappings can be changed with the qos command, allowing the packets to
be mapped into any one of the 8 queues based on the COS bit in the VLAN tag. Different
priority tags may be mapped into the same queue if desired.
Trango Systems, Inc.
, Lowest Priority Queue
, Highest Priority Queue
GigaPlus User Manual Rev 3.1
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