Cisco QoS for 3560 Switch, Cisco 1242 Wireless AP's and Siemens HiPath phone system with Siemens Optipoint WL2 handsets

I have a client who has about 7 x Siemens Optipoint WL2 wireless VoIP handsets configured to talk to a Siemens HiPath system (I dont have any experience with Siemens kit) - or much experience with QoS for that matter - but Im a fast learner ;)

I am however, competent in dealing with most other aspects of cisco kit (just to give you guys an idea on where Im at)

The wireless setup consists of 4 x Cisco 1242AG Access Points all connected to a Cisco 3560.
The wireless access points are also used by a handfull of roaming users with laptops.

A lot of calls being made using the handsets are affected badly by echo.

So, Im guessing I need to look into the QoS options in a bit more detail - firstly, the access points do have some basic QoS configuration (based on tech notes I obtained from the Siemens phone system installers) - but nothing has been done on the switch (I should mention that the phone system is also plugged into the same 3560 switch).

The QoS configuration in the wireless access points is in the code snippet.

The wireless access points are also configured with multiple ssid's - But only two, one of which links directly to an ADSL router for visiting sales reps allow net access (via VLAN configuration on the AP's and 3560) and the other handles the data and voice traffic for the corporate LAN (i.e. the handsets and the company laptops connect to this ssid) - and of course both ssid's are encrypted.

Any assistance on configuring up the QoS would be appreciated - Oh, and I am waiting for the Siemens phone installers to get me more info on what (if any) qos options there are within the phone system.


dot11 phone
class-map match-all _class_VoiceQOS1
 match ip dscp ef
class-map match-all _class_VoiceQOS0
 match ip dscp default
class-map match-all _class_VoiceQOS2
 match ip dscp af31
policy-map VoiceQOS
 class _class_VoiceQOS0
  set cos 0
 class _class_VoiceQOS1
  set cos 6
 class _class_VoiceQOS2
  set cos 1
interface dot11radio0.1
service-policy output VoiceQOS
Interface FastEthernet0.1
service-policy input VoiceQOS
service-policy output VoiceQOS

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Are you sure it is echo they are experiencing? Echo is not a symptom of any issues that can be resolved using qos. This will most likely be a result of the siemens handsets leaking audio from the speaker to the microphone. You will probably find that turning down the speaker volume on the handset will reduce the problem.

All the code above is doing is remarking the packets to the wrong cos values (dscp ef should be mapped to cos 5 :) ). This will have no useful affect if there is no qos configured on the switch.

If you want to implement qos, you will need to set up the queues on the switch and set it to trust incoming cos markings. Auto qos would be the easiest way to do this.

 However, in this case, I don't think it will have much affect given what I said at the beginning. Let me know if you are experiencing issues such as delay, choppy voice or Jitter, and I can go into what you will need to do to configure the switch.
paul-adamAuthor Commented:
Hi cstosgale
Thanks for the response and suggestion - at this point all the info I have is what the customer has told me so far....although I am not sure about any other issues that might be happening.

I never even thought about about leaking audio, I'll certainly get the contact at the customer site to check that out.

I'll send him an email just now and should hear from him tomorrow at some point - and he can fill me in.

I had also seen a posting on a forum that suggests echo could be caused by a problem with the phone lines (ISDN30 - again, a technology Im not overly familiar with).

I'll keep you posted.

Many thanks again

paul-adamAuthor Commented:

Ive now had a chat with my client and he is saying the the issue is definately only echo, where he is hearing his own voice back at him with a second delay (probably less than a second, but thats just what he has told me).

So it looks like it may not be a QoS issue after all - bizarrely though, the QoS values above were put in on recommendation of Siemens after we found a document regarding serious jitter and disconnection issues - these issues stopped immediately on putting those QoS settings in the AP's - So they must be doing something correct?

Ive attached the config guide provided by Siemens for info

The client is going to test out the echo by reducing the volume on his handsets - to see if it makes any change.

I'll post his test results once I hear back from him


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paul-adamAuthor Commented:
and to further update, the echo'ed voice is quite faint....typically it only happens on random calls

Could this be something else (going back to my mention about seeing another forum posting somewhere mention a possible issue with the phone lines).


Interesting, that would indicate that there is some basic QOS set up on your switch, and it must be set to trust the cos markings from the access point. By default, a switch will not trust any qos markings from anywhere, it needs to be specifically configured.

All the config above is doing is remarking the traffic, it is not doing any prioritisation.

With regards to the DSCP to cos mappings they recommend, I would expect they have chosen 6 instead of 5 to map to expedited forwarding as this ties in with the default settings on some cisco switches. however, oddly this is not cisco best practise.

Why they map an expedited forwarding class to cos 1 is beyond me, but if you have no other devices marking traffic on yuor network, and so long as your switch is set to trust cos markings, will work.

With regards to your echo, echo is typically a problem isolated to the analogue network. What type of phone lines connect them to the PSTN? Are they normal analogue lines or digital PRI/BRI trunks?

If they are normal analogue lines, then the echo is most likely related to the phone lines as you suggest. Usually an impedance mismatch between the siemens system and the PSTN can cause this.

If it is happening reandomly, it could be one of the phone lines is problematic but this is only being used when the other phone lines are in use. Do they have any fixed handsets, and do they experience the same problem with these?

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paul-adamAuthor Commented:

Thanks for getting back to me again.

Well...there's no QoS in the switches at the moment - I configured them using the cli only so I know that for sure - I just wonder if the settings in the AP's are maybe enough to provide some separation of the traffic from the wireless laptop users over the wireless network and therefore ease the jitter issues that they were getting??

The lines are digital ISDN30 lines (if your in the US Im not sure what the equivalent service is) - I can tell you as much as the lines are presented via fibre to the service providers CPE and then via an RJ45 connected link into the phone system.

They have fixed lines as well....and they never have the issues on those - So I guess that rules out the lines anyway (they have about 80 wired phones and 7 or 8 wireless).

I think it will take a couple of days for the customer to get back to me to say whether turning down the volume has made any difference (seeing the random nature of the echo problems).

Have you ever dealt with these Siemens handsets? - Im hunting around for any specifc support/forum sites that speak about dealing with them (and any issues they may be having) - Im just wondering if this is a known it definately is affecting all handsets (at random times).

Will wait and see - you never know it might be the volume thing after all!

thanks again

paul-adamAuthor Commented:
Well, its been a couple of weeks or so since my last update.

My client has told me that the echo has improved slightly after turning down the handset volume - but that it is still apparent on some calls.

I am starting to suspect something with the phone system itself.

But still looking for any advice thats out there to assist in brining this to a resolution.

One thing I did wonder was if there is anything in the Cisco Access Point configs that might be doing it - not QoS related though??


p.s. Ive increased the points available to 500 as I think this might be a little more complicated than I originally thought!
paul-adamAuthor Commented:
Well....I still havent 100% fixed this issue and the phone system support company are now involved in regards to looking into this.

Im going to leave this call open for another week to see if they come up with anything (and to see if any other suggestions come from everyone here at experts exchange.


Paul Adam
paul-adamAuthor Commented:
Hi - Im going to award the points to you for this as you were kind enough to assist - although I never did get it sorted in the end - and like I say the Phone installation company got involved and stuck in their own "Siemens" Wireless access points and everything was fine (grrr!!!) - Im just wondering if its a problem with incompatibilities between the siemens handsets and the Cisco AP's - but I guess I might never know...

Cheers again

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