Low Latency Queue (Fragmentation And Interleaving) For Voice Traffic; Tos-To-Priority Mapping - NetComm NB5PLUS4/W User Manual

The weighted values used for the WRR scheduler will be calculated based on the
percentage weights the user inputs in the Web UI as stated above in 1.) Queue
Priorities.
Example: User selects a Medium Queue Weight = 60 %, and Low Queue Weight =
40%. Then the O(1) scheduling array will look like {L, M, M, L, M, M, L, M, M, L}
where L and M represents a scheduling cycle for the respective Low and Medium
queues.

Low Latency Queue (Fragmentation and Interleaving) for Voice Traffic

With Voice traffic shared over same PVC with Data traffic, the simple packet classifi-
cation and prioritization will not suffice to achieve the low latency required by voice.
In this case, a voice call triggers dynamic flushing of existing data packets from
device queues (including DSL device driver) for Head of Line Blocking removal, and
IP MTU resizing based on uplink bandwidth for fragmentation and packet interleav-
ing of voice and data. Below is an example of MTU calculations:
Total delay PSTN delay
end-to-end budget
VIF (ms)
10ms 200
20ms 200
30ms 200
For Voice traffic priority an extra EF queue was added to PRIOWRR. This extra
queue should not be exposed via WebUI config for data usage. Its use is triggered
internally by the voice app using the socket options system calls. Voice packets are
using this EF queue. Signalling for Voice uses the next EF queue that's also exposed
on the web config. This means that voice signalling can be mixed with data if user
configures data for High Priority.

TOS-to-Priority Mapping

High Priority Marking for Expedited Forwarding Queue:
Medium Priority Marking:
Low Priority Marking for Best Effort:
The four TOS bits (the 'TOS field') are defined as:
Binary
1000
0100
0010
0001
0000
TOS Bits
0x0 0
0x2 1
YML754 Rev1
www.netcomm.com.au
(ms) 100kbps
100 207
100 82
100 x
Meaning
Minimize delay (md)
Maximize throughput (mt)
Maximize reliability (mr)
Minimize monetary cost (mmc)
Normal Service
Means
Normal Service
Minimize Monetary Cost
Maximum Data Fragment size
based on upstream bandwidth (bytes)
150kbps 200kbps
363 519
175 269
x 19
DSCP Mark: xx1000
DSCP Mark: xx0100
DSCP Mark: xx0000
Linux Priority Queue Priority Band
0 Best Effort
1 Filler
250kbps
675
363
50
2
2
NB5Plus4/W User Guide
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