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7921 Slow Response

Hi,

I have some 7921 phones and 15 1240 AP's in two adjacent warehouses. All had been working fine (no complaints from users) for over a year. Recently, every phone drops connectivity occassionally. Ping from the AP to the phones shows very high latency: over 1000ms. But pings to wireless data scanners associated with the same AP are good: around 50ms. No vlans separate the data and voice. The ping latency happens even when only one 7921 is associated with the AP. So I suspect the firmware issue.

I upgraded the phone firmware from factory default to CP7921G-1.2.1.LOADS. But this did not solve the problem.

Any ideas?

Thanks in advance.

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Cisco Employee

Re: 7921 Slow Response

To clear up the ping latency question, the 7921/7925 phone utliizes power save and if proxy ARP is enabled, it doesn't have to wake up for each DTIM, so could see around 800ms of delay if the phone is not on a phone call.

If you want to use ping for latency tests, then ensure that the phone is on a call, then ping the phone.

8 REPLIES
New Member

Re: 7921 Slow Response

The ping latency is normal and it does not show the real latency between the phone and the AP. I don't know the reason why but I have seen in several installations very high latency between AP and phone but this didn't create any problem at all. So I figured that it is not a good indication. Check the RSSI instead.

Since this is a warehouse with several APs, I would suggest you do a site survey and connect to each AP separately to make sure that all Access Points are working normally. I have seen different kinds of problems developing on 1240's after long time of operation. Usually a reload brings them back to normal though.

Also check the uplink of the APs to the switch and make sure it is 100Mbps full duplex.

New Member

Re: 7921 Slow Response

Thanks Georgios,

AP's to switches and then to cme's is fine: only 1ms. On one AP, I setup 2 vlans to separate the data and voice. But ping to phones still experiences high latency, even after a reload. The connectivity is maintained though.

When one phone is taken to my office where a 1310 bridge is installed, the ping latency is only 2ms.

Site survey shows strong signals.

I will reload all the AP's after hours and see if that solves the problem.

thanks again.

New Member

Re: 7921 Slow Response

I would like to clarify that I also see high latency between my AP and ip phones. I have seen it in several installations. It doesn't matter, don't take it into account. It will only give you a wrong impression.

Cisco Employee

Re: 7921 Slow Response

To clear up the ping latency question, the 7921/7925 phone utliizes power save and if proxy ARP is enabled, it doesn't have to wake up for each DTIM, so could see around 800ms of delay if the phone is not on a phone call.

If you want to use ping for latency tests, then ensure that the phone is on a call, then ping the phone.

New Member

Re: 7921 Slow Response

I have seen this happening with 7920s too

Cisco Employee

Re: 7921 Slow Response

Yes the 7920 doesn't wake up at DTIM, but every other 2 seconds if in idle mode (not on a call). So if there are any ARP requests, they could be missed, therefore must have proxy ARP enabled on the AP to answer on behalf of the client.

If on call with the 7920 it only supports active mode (no power save when on call), so ping times should be quick.

Re: 7921 Slow Response

thanks for sharing.... 5 stars!

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
New Member

Re: 7921 Slow Response

I see you got the explanation for the slow ping times, but that may not have solved your problem. If you have autonomous APs then make sure you have "admit traffic" configured in the ssid config.

dot11 ssid voice

vlan 10

authentication open eap eap_methods

authentication network-eap eap_methods

authentication key-management wpa cckm

admit-traffic

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