03-11-2014 08:30 AM - edited 07-05-2021 12:24 AM
How do I troubleshoot a 7925 G wireless phone connectivity issues. Dropped words and phrases, cutting in and out?
03-11-2014 11:01 AM
Take a look at this:
https://supportforums.cisco.com/document/112171/how-get-your-792x-wireless-phones-performing-reliably
12-24-2014 08:08 PM
Hi,
Voice over WLAN (VoWLAN) is one of the most challenging technologies that Cisco provides. For VoWLAN to work satisfactorily - especially in the high-stress environments in which it is deployed, such as healthcare - the network, and the phone, must be able consistently to transport a real-time, bidirectional, securely encrypted audio stream, with almost no dropouts, while the endpoint moves across four dimensions (space and frequency).
This document explains how to get 792x wireless phones (7921G, 7925G, 7926G) to work well in a Cisco Unified Wireless Network.
Though delivering a reliable VoWLAN service is difficult, it is possible, provided that the network provider adheres to the following basic design guidelines.
Your network's ability to perform is fundamentally dependent on a solid physical layer. VoWLAN uses both the 2.4GHz and 5GHz bands. Of these, the 2.4GHz band's lower frequency signals carry further - however, the constrained bandwidth (only three non-overlapping channels) and ever increasing interference, render 2.4GHz, in most cases, unsuitable for reliable voice. Network providers who want to deliver a reliable VoWLAN service will ensure that their design adheres to the following standard:
Every spot in the coverage area is serviced by at least two viable 5GHz access points, at -67dBm or stronger.
You can easily validate the necessary coverage by setting your phone into site survey mode, and walking throughout your coverage area.
Additionally, AP placement, antenna selection, building construction, etc. must be such that multipath distortion is kept to a minumum. To ensure gap-free roaming, a moving phone must be able to hear each roamed-to AP at least 5 seconds before it needs to roam to it - so place all APs in the middle of halls, at corridor junctions, etc., rather than in blind spots.
The 1.4.2 firmware introduced a greatly improved scanning and roaming algorithm in the 792x phones. 1.4.3 introduces other critical fixes. If you are experiencing audio problems with your phones - never, ever run any firmware prior to 1.4.3.
Be aware that, for newer hardware revisions of the 792x phones, it is not possible to run any firmware prior to 1.4(3)SR1 - see the release notes. Therefore, for new or RMAd phones, you can't run the old firmware, even if you want to.
If using FlexConnect (H-REAP) local switching, watch out for the following:
Other reasons to avoid FlexConnect for 792x phones are:
If your WAN link between the APs and the WLC is high latency, unreliable, or low bandwidth, then consider installing a WLC at the site where the phones are.
WPA2/AES Enterprise with CCKM is the recommended security scheme for 792x phones - it is the most secure method, and provides for the fastest roaming times. You may use Local Authentication on the WLC, if you do not want to use an external RADIUS server. (When using CCKM, use the WLC command "config wlan security wpa akm cckm timestamp-tolerance 5000" to increase the likelihood of performing a fast roam.) (Also see the CCKM Client Disconnect Bugs in 7.0/7.2 tip.)
Avoid TKIP which is susceptible to MIC error triggered service interruptions.
If security is not a concern, then static WEP will work well.
With 7925G phones, avoid WPA/WPA2 Preshared Key (PSK.) This is because the 7925G phones suffer from the following problem, which intermittently prevents WPA key exchanges from completing:
CSCtt38270 7925 sometimes takes 1+ second to respond to WPA M1 key message
This bug does not affect 7921G or 7926G phones. It will not be fixed for the 7925G; if you must use PSK with 7925G, you can mitigate the impact to some extent with: config advanced eap eapol-key-timeout 250 on the WLC, and by disabling Java on the phone (if using 1.4.6.3 firmware or above)
If 792x users roam from AP to AP frequently, then continuous scan mode should be enabled; however idle battery life can be reduced to some extent. (A fresh battery should still last an 8-hour shift.) Without continuous scan mode, the AP may be intermittently associated to an AP with a weak signal, which may have an rare impact on incoming calls and pages.
Go through the entire 7925G Deployment Guide, and configure the phones and the wireless network as per its recommendations. In particular, make sure that all QoS configurations are set as per best practice, throughout your wireless and wired network.
With strict adherence to every single one of the above guidelines, there is a high probability that your VoWLAN service will meet your clients' performance expectations.
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: