Nortel-networks NB5PLUS4/W Instrukcja Użytkownika Pobierz pdf (Strona 47)

YML754 Rev1 NB5Plus4/W User Guide

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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 trafc shared over same PVC with Data trafc, the simple packet classi-

cation and prioritization will not sufce to achieve the low latency required by voice.

In this case, a voice call triggers dynamic ushing 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

end-to-end budget 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 trafc priority an extra EF queue was added to PRIOWRR. This extra

queue should not be exposed via WebUI cong 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 cong. This means that voice signalling can be mixed with data if user

congures 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 eld’) are dened 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

1 2 ... 42 43 44 45 46 47 48 49 50 51 52 ... 111 112

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Nortel-networks NB5PLUS4/W Instrukcja Użytkownika Strona 47