DSCP mapping toward 802.11e QoS

Unanswered Question
Aug 19th, 2009
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According to product bulletin no 3209 for the Cisco 4400 series, the Access Point supports 802.11e WMM.

My question goes to DSCP mapping, according to IEEE and your bulletin the DSCP field in the IP header should be set to 46 (10110 00) for mapping to a 802.11 QoS voice priority 6/7.

But my Wireshark trace revealed 4400N is mapping toward with 802.11 QoS is set to Priority 5 Video.

If I google DSCP mapping toward 802.11 QoS all IEEE documention I found says EF /Voice should have 46 or 101xxx in the DSCP IP field but running through Cisco and HP docs gives 46 or 48 as value, that is the correct value....

Regards Karl Henrik Nielsen

Added Wireshark packet from 4400N AP.

o.     Time        Source                Destination           Protocol

Info

   5817 25.523410   192.168.0.1           192.168.0.4           RTP

PT=ITU-T G.711 PCMA, SSRC=0x505BE4FD, Seq=25853, Time=0

Frame 5817 (168 bytes on wire, 168 bytes captured) Radiotap Header v0,

Length 14 IEEE 802.11 QoS Data, Flags: ......F.

    Type/Subtype: QoS Data (0x28)

    Frame Control: 0x0288 (Normal)

    Duration: 44

    Destination address: ThraneTh_01:d2:39 (00:11:cf:01:d2:39)

    BSS Id: Cisco-Li_d7:dc:f6 (00:23:69:d7:dc:f6)

    Source address: ThraneTh_00:f4:be (00:11:cf:00:f4:be)

    Fragment number: 0

    Sequence number: 0

    QoS Control

        Priority: 5 (Video) (Video)

        ...0 .... = EOSP: Service period

        Ack Policy: Normal Ack (0x00)

        Payload Type: MSDU

        QAP PS Buffer State: 0x0

Logical-Link Control

Internet Protocol, Src: 192.168.0.1 (192.168.0.1), Dst: 192.168.0.4

(192.168.0.4)

    Version: 4

    Header length: 20 bytes

    Differentiated Services Field: 0xb8 (DSCP 0x2e: Expedited Forwarding; ECN: 0x00)

        1011 10.. = Differentiated Services Codepoint: Expedited Forwarding (0x2e)

        .... ..0. = ECN-Capable Transport (ECT): 0

        .... ...0 = ECN-CE: 0

    Total Length: 120

    Identification: 0x03c8 (968)

    Flags: 0x00

    Fragment offset: 0

    Time to live: 64

    Protocol: UDP (0x11)

    Header checksum: 0xf49f [correct]

    Source: 192.168.0.1 (192.168.0.1)

    Destination: 192.168.0.4 (192.168.0.4) User Datagram Protocol, Src

Port: 1027 (1027), Dst Port: connected

(16384)

Real-Time Transport Protocol

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cindy toy Wed, 08/19/2009 - 13:11
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Hi Karl,

This is the incorrect doc:  http://www.cisco.com/en/US/prod/collateral/wireless/ps6302/ps8322/ps6366/prod_bulletin0900aecd80394844_ps6108_Products_Bulletin.html

I don't think this info is in the WAP4400N admin guide so here it is:

The WAP4400N supports 802.1p to WMM Mapping:

Wireless Queue       CoS      Access Category            

Q1                            7,6        WMM Voice Priority

Q2                            5,4        WMM Video Priority

Q3                            0,3        WMM Best Effort Priority

Q4                            2,1        WMM Background Priority


Thanks,

Cindy Toy

Cisco Small Business

Support Community Manager

KarlHenrik001 Wed, 08/19/2009 - 23:30
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Thanks, but my real question was:


Which DSCP values maps to Q1 through Q4, in the IEEE documentation DSCP value 46 should map to Q1 but I proved above the 4400N maps to Q2.

cindy toy Thu, 08/20/2009 - 20:23
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Hi Karl,




The WAP4400N supports layer-2 prioritization.  For DSCP you'll need to check your layer-3 device to see how the queues are mapped.

Here's an example:

802.1p Class of Service        From DSCP Range

0                                          0-7

1                                          8-15

2                                          16-23

3                                          24-31

4                                          32-39

5                                          40-47

6                                          48-55

7                                          56-63

Based on this mapping a DSCP value of 46 would map to 5 and corresponds to the WMM Video Priority queue.


Regards,

Cindy

KarlHenrik001 Mon, 08/24/2009 - 01:34
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Thanks for your answer, and I was aware of 802.1p and 802.1Q header, but the Ethernet frame the 4400N receives, as you can see in my previous entry, does not have a 802.1Q field only the DSCP field is set and the 4400N is mapping into QoS for the 801.11 header. So the 4400N must have some mapping included based on the DSCP field. I have experimented on changing only the DSCP field and the mapping from the 4400N changes.


Regards Karl Henrik

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