NetComm NB1 - Manual (Page 42)

NB1 User Guide YML780 Rev1
42 www.netcomm.com.au
Traffic Queuing Configuration
Based on the TOS (DSCP) marking, the NB1 shall prioritize the traffic servicing on
the outgoing interface (facing the Access Network) using a 3-band priority mecha-
nism as described below.
Queue Priorities:
One Expedited Forwarding (EF) Queue: High Priority queue with non-preemptible
service. The EF queue is always scheduled first prior to the medium and low priority
queues and runs to completion
Two Queues (Medium and Low Priority) with Weighted Round Robin service. Based
on the associated weights, packets on these queues share the remaining link
bandwidth (after the EF service). The low priority queue corresponds to Best Effort
service. Looking forward, the medium priority queue will play the role of Assured
Forwarding Queue.
Configuration:
a.) The Medium, and Low Priority Queue weights will be selectable via the Web UI.
User weights for these two queues are entered as a percentage in increments of
10%. The sum of the 2 weights must be equal to 100 percent.
En-queuing Policy
Inter-queue isolation to make greed work on the Residential Gateway: the transmit
interface buffer (a common pool for all queues) can be monopolized by a greedy
flow on the low priority queue thus preventing en-queuing high priority traffic. To
prevent such conditions the en-queuing process is using a simple configurable al-
location of per-queue lengths, adding up to the total queue length.
Configuration:
The Expedited Forwarding queue (fast service queue) length will be configurable via
the config.xml file. This parameter will not be configurable via the Web UI. Please
call NetComm Support and request to speak with an engineer should you require
this XML file to edit.
The Medium and Low priority queue lengths will be proportionally calculated via the
queue weights selected in 1.) Queue Priorities above.
Total queue length for all three queues will sum to the transmit queue length set in
the system.
Packets overflowing their queues will be tail-dropped, penalizing stochastically the
greediest flow within each queue.
Future implementations may introduce a “buffer stealing” policy. This policy will re-
move the fixed buffer limits and allow a particular queue buffer to decrease to some
predefined minimum limit.
De-queuing Policy
Expedited Forwarding Queue (High Priority) is always serviced first at each packet
scheduling cycle and serviced to extinction. Therefore, the EF queue is non-preemti-
ble by the Medium and Low priority queues.