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 |
| Maximum Data Fragment size | |||
|
| based on upstream bandwidth (bytes) | ||||
VIF | (ms) | (ms) | 100kbps | 150kbps | 200kbps | 250kbps |
10ms | 200 | 100 | 207 | 363 | 519 | 675 |
20ms | 200 | 100 | 82 | 175 | 269 | 363 |
30ms | 200 | 100 | x | x | 19 | 50 |
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: DSCP Mark: xx1000
Medium Priority Marking: | DSCP Mark: xx0100 |
Low Priority Marking for Best Effort: | DSCP Mark: xx0000 |
The four TOS bits (the ‘TOS field’) are defined as:
Binary |
| Meaning |
|
|
|
1000 |
| Minimize delay (md) |
|
|
|
0100 |
| Maximize throughput (mt) |
|
| |
0010 |
| Maximize reliability (mr) |
|
| |
0001 |
| Minimize monetary cost (mmc) |
|
| |
0000 |
| Normal Service |
|
|
|
|
|
|
|
|
|
TOS | Bits | Means | Linux Priority | Queue Priority | Band |
0x0 | 0 | Normal Service | 0 | Best Effort | 2 |
0x2 | 1 | Minimize Monetary Cost | 1 | Filler | 2 |
YML754 Rev1 | NB5Plus4/W User Guide |
www.netcomm.com.au | 47 |
