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WMM support on the DD-WRT firmware.

Discussion in 'Articles' started by Toxic, Apr 2, 2006.

  1. Toxic

    Toxic Administrator Staff Member

    I noticed that DD-WRT for some time now has supported WMM (Wi-Fi Multimedia) on the QoS section, however there was no explanation on all the settings of what they all done. I have now compiled some info from numerous sites as to what each setting is. At the time of writing DDWRT v23 SP1 (02/Apr/2006) is the latest. no doubt the WMM Support panel on the QoS page will be updated somewhat to show some meaning of the abbreviations.

    Below is the QoS Field for WMM Support from the DDWRT v23 SP1 Firmware

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    EDCA AP Parameters - This affects traffic flowing from the access point to the client station

    <table id="table3" border="1" height="196"> <tbody><tr> <td align="center" bgcolor="#c0c0c0"> Queue </td> <td align="center" bgcolor="#c0c0c0"> Data Transmitted
    AP to Clients
    </td> <td align="center" bgcolor="#c0c0c0"> Priority</td> <td align="center" bgcolor="#c0c0c0"> Description</td> </tr> <tr> <td align="center">AC_BK </td> <td align="center"> Background.</td> <td align="center">Low</td> <td>High throughput. Bulk data that requires maximum throughput and is not time-sensitive is sent to this queue (FTP data, for example).</td> </tr> <tr> <td align="center">AC_BE</td> <td align="center">Best Effort</td> <td align="center">Medium</td> <td>Medium throughput and delay. Most traditional IP data is sent to this queue</td> </tr> <tr> <td align="center">AC_VI</td> <td align="center">Video</td> <td align="center">High</td> <td>Minimum delay. Time-sensitive video data is automatically sent to this queue</td> </tr> <tr> <td align="center">AC_VO</td> <td align="center">Voice</td> <td align="center">High</td> <td>Time-sensitive data like VoIP and streaming media are automatically sent to this queue</td> </tr> </tbody></table>
    Configuring QoS options consists of setting parameters on existing queues for different types of wireless traffic. You can configure different minimum and maximum wait times for the transmission of packets in each queue based on the requirements of the media being sent. Queues automatically provide minimum transmission delay for Voice, Video, multimedia, and mission critical applications, and rely on best-effort parameters for traditional IP data.

    As an Example, time-sensitive Voice & Video, and multimedia are given effectively higher priority for transmission (lower wait times for channel access), while other applications and traditional IP data which are less time-sensitive but often more data-intensive are expected to tolerate longer wait times.

    EDCA AP Parameter Fields:

    CWmin
    - Minimum Contention Window. This parameter is input to the algorithm that determines the initial random backoff wait time ("window") for retry of a transmission. The value specified here in the Minimum Contention Window is the upper limit (in milliseconds) of a range from which the initial random backoff wait time is determined.

    The first random number generated will be a number between 0 and the number specified here. If the first random backoff wait time expires before the data frame is sent, a retry counter is incremented and the random backoff value (window) is doubled. Doubling will continue until the size of the random backoff value reaches the number defined in the Maximum Contention Window.
    Valid values for the "cwmin" are 1, 3, 7, 15, 31, 63, 127, 255, 511, or 1024. The value for "cwmin" must be lower than the value for "cwmax".

    CWmax
    -Maximum Contention Window. The value specified here in the Maximum Contention Window is the upper limit (in milliseconds) for the doubling of the random backoff value. This doubling continues until either the data frame is sent or the Maximum Contention Window size is reached. Once the Maximum Contention Window size is reached, retries will continue until a maximum number of retries allowed is reached. Valid values for the "cwmax" are 1, 3, 7, 15, 31, 63, 127, 255, 511, or 1024. The value for "cwmax" must be higher than the value for "cwmin".

    AIFSN
    - The Arbitration Inter-Frame Spacing Number specifies a wait time (in milliseconds) for data frames

    TXOP(b) and TXOP a/g)
    - Transmission Opportunity for "a" "b" and "g" modes is an interval of time when a WME AP has the right to initiate transmissions onto the wireless medium (WM). This value specifies (in milliseconds) the Transmission Opportunity (TXOP) for AP; that is, the interval of time when the WMM AP has the right to initiate transmissions on the wireless network.

    <hr>
    EDCA STA Parameters
    -
    This affects traffic flowing from the client station to the access point.


    <table id="table2" border="1" height="196"> <tbody><tr> <td align="center" bgcolor="#c0c0c0"> Queue </td> <td align="center" bgcolor="#c0c0c0"> Data Transmitted
    AP to Clients
    </td> <td align="center" bgcolor="#c0c0c0"> Priority</td> <td align="center" bgcolor="#c0c0c0"> Description</td> </tr> <tr> <td align="center">AC_BK </td> <td align="center"> Background.</td> <td align="center">Low</td> <td>High throughput. Bulk data that requires maximum throughput and is not time-sensitive is sent to this queue (FTP data, for example).</td> </tr> <tr> <td align="center">AC_BE</td> <td align="center">Best Effort</td> <td align="center">Medium</td> <td>Medium throughput and delay. Most traditional IP data is sent to this queue</td> </tr> <tr> <td align="center">AC_VI</td> <td align="center">Video</td> <td align="center">High</td> <td>Minimum delay. Time-sensitive video data is automatically sent to this queue</td> </tr> <tr> <td align="center">AC_VO</td> <td align="center">Voice</td> <td align="center">High</td> <td>Time-sensitive data like VoIP and streaming media are automatically sent to this queue</td> </tr> </tbody></table>
    EDCA STA Parameters Fields


    CWmin
    - Minimum Contention Window. This parameter is input to the algorithm that determines the initial random backoff wait time ("window") for retry of a transmission. The value specified here in the Minimum Contention Window is the upper limit (in milliseconds) of a range from which the initial random backoff wait time is determined.

    The first random number generated will be a number between 0 and the number specified here. If the first random backoff wait time expires before the data frame is sent, a retry counter is incremented and the random backoff value (window) is doubled. Doubling will continue until the size of the random backoff value reaches the number defined in the Maximum Contention Window.
    Valid values for the "cwmin" are 1, 3, 7, 15, 31, 63, 127, 255, 511, or 1024. The value for "cwmin" must be lower than the value for "cwmax".

    CWmax
    -Maximum Contention Window. The value specified here in the Maximum Contention Window is the upper limit (in milliseconds) for the doubling of the random backoff value. This doubling continues until either the data frame is sent or the Maximum Contention Window size is reached. Once the Maximum Contention Window size is reached, retries will continue until a maximum number of retries allowed is reached. Valid values for the "cwmax" are 1, 3, 7, 15, 31, 63, 127, 255, 511, or 1024. The value for "cwmax" must be higher than the value for "cwmin".

    AIFSN
    - The Arbitration Inter-Frame Spacing Number specifies a wait time (in milliseconds) for data frames

    TXOP(b) and TXOP a/g)
    - Transmission Opportunity for "a" "b" and "g" modes is an interval of time when a WME Client Station has the right to initiate transmissions onto the wireless medium (WM). This value specifies (in milliseconds) the Transmission Opportunity (TXOP) for Client Station; that is, the interval of time when the WMM AP has the right to initiate transmissions on the wireless network.
     

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