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New Member

QoS capbilities of Cisco Aironet 1121g

Dear all,

In our project we would like that the Cisco 1121G AP perform the following QoS


1. Downstream direction:

a. give priority to traffic based on Type of Service values in IP headers (DSCP or IP precedence).

b. modify SIFS, CWmin, CWmax for the traffic with a given TOS value (going

out on the radio interface of the AP).

2. Upstream direction:

a. give pripority for traffic with a given DSCP

or IP precedence value. So, on the FastEthernet interface this upstream traffic would get more priority (for example put it in a higher priority queue)

b. set the DSCP/IP precedence values for the video/voice traffic in the IP

header of the traffic coming from the voice/video client. In this case the AP would serve as a node on the perimeter of

the DiffServ network, and classifies traffic.

This would be used only if the DSCP/IP precedence values were not already

set by the voice/video client.

We read carefully:

- Cisco Aironet 1100 Series Access Point Installation and Configuration Guide

In chapter 13, Configuring QoS, the documentation writes, that the egress port of the Fast Ethernet interface performs only FIFO


- Cisco Aironet 1100 Series Wireless Quality-of-Service,




"Ethernet upstream refers to traffic leaving the access point traveling to the switch. The access point classifies traffic from the access

point to the upstream network."

We think that requirement 1a and 1b are feasible.

We don't know if 2a is feasible or not. We think that 2b is not feasible with the AP.

Which requirements are feasible with the Cisco Aironet 1121G AP?

What kind of queueing methods are possible on the FastEthernet interface in upstream direction?

Could you recommend us a good documentation about the implemented queueing methods in the AP?

New Member

Re: QoS capbilities of Cisco Aironet 1121g

I read the documentation at

I think that 2a requirement: give a priority for voice traffic in upstream direction on the FastEthernet interface is not necessary, because the designers of the AP assumed that we have a 100 Mbit/sec full-duplex Ethernet link between the AP and the switch, so there is no queue to handle -> so FIFO is good.

Am I wirte?

The sender of the first question

Re: QoS capbilities of Cisco Aironet 1121g


you are right about this. Queueing will only be invoked in case there is an overload situation, which will not occur at the FE interface, so FIFO is ok.

Regards, Martin

New Member

Re: QoS capbilities of Cisco Aironet 1121g


Then I think that the web administration interface of the Cisco 1121G access point is misleading, because why to set policies for the FastEthernet outgoing traffic. OK you can set filters, but to set policies, which aim is to apply Class ofe services (putting in different queues)

So to define filters and apply class of services at the fast ethernet interface outgoing direction doesn't serve nothing, in my opinion.

Now my problem is that after defining a new VLAN, and after assigning it to an SSID, I generated traffic from a wireless client connecting to this interface, I sniffed with Ethereal the upstream traffic on the FastEthernet interface. And I expected that there I will see 802.1q VLAN tags in the Ethernet frames. But there are no 802.1q tags. I become more and more unconvinced with this product.

What do you think about this issue?



New Member

Re: QoS capbilities of Cisco Aironet 1121g

I reply to my previous question ...

I read in a Cisco VLAN howto, that if the VLAN is a native VLAN, than the AP FE interface don't have to put the 802.1q tag, because this will be the role of the switch in the upstream direction.

New Member

Re: QoS capbilities of Cisco Aironet 1121g

Martin or any expert,

Thank you for the previos answer, it made clear many things.

Can we expect from the Cisco 1121 AP that it mark traffic in the upstream direction? For example marking in the ToS field? Or regenerating VLAN Priority?

I think that the resonse is no, but maybe it is possible.


Zoltan Faigl

Re: QoS capbilities of Cisco Aironet 1121g

Hello Zoltan,

In the found "Cisco IOS Software Configuration Guide for Cisco Aironet Access Points 12.3(7)JA" at

it is stated in the section "Configuring QoS":

QoS for Wireless LANs Versus QoS on Wired LANs

The QoS implementation for wireless LANs differs from QoS implementations on other Cisco devices. With QoS enabled, access points perform the following:

•They do not classify packets; they prioritize packets based on DSCP value, client type (such as a wireless phone), or the priority value in the 802.1q or 802.1p tag.

•They do not construct internal DSCP values; they only support mapping by assigning IP DSCP, Precedence, or Protocol values to Layer 2 COS values.

•They carry out EDCF like queuing on the radio egress port only.

•They do only FIFO queueing on the Ethernet egress port.

•They support only 802.1Q/P tagged packets. Access points do not support ISL.

•They support only MQC policy-map set cos action.

•They prioritize the traffic from voice clients (such as Symbol phones) over traffic from other clients when the QoS Element for Wireless Phones feature is enabled.

•They support Spectralink phones using the class-map IP protocol clause with the protocol value set to 119.

Especially they do not construct ToS/DSCP. What you can do is to set the 802.1Q CoS Bits based on an already existing DSCP setting. So in short: ToS marking is not supported, CoS marking is supported based on existing DSCP.

QoS on WLAN APs is limited compared to a router or switch. But it is still better than not to have any capabilities at all.

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: QoS capbilities of Cisco Aironet 1121g

Hello Martin,

Now I would like to concentrate on your statement, that

"CoS marking is supported based on existibg DSCP".

As I understand, this statement has the importance of transferring priority information on the wireless link, because 802.11 frames don't support 802.1Q tags.

I think that CoS marking based on DHCP values has importance only in uplink direction. Is this correct?

During the transmission of traffic in uplink direction, the client application or client network driver or anything writes the DSCP values in the IP header. The AP writes the priority information in the 802.1Q VLAN tag based on the DSCP value and some assignment rules.

The univoque assignment of SSID and VLAN is also an important requirement for this.

If this is correct, then I would like to ask some practical informations: where to set this?

Because in the Services->QoS menu, I can create only policies on:

if a packet matches some requirements based on DSCP, IP Precedence, client type, some filters,

or if it is in a given VLAN (default policy)

(and DSCP, IP Precedence, 802.1Q CoS bits were not already set)


apply Best Effort, Background, Spare, Video, Voice, etc class of Service.

But I don't see from this if it will mark the 802.1Q CoS bits with that priority.



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