WiFi and VOIP - sizzle and background noise

[LoganM]

My problem is related to a Cisco 7920. I have a WiFi VOIP phone is connected to a terminal Cisco 870. Everything is in a remote site, connected to its IP PBX via a vpn on SDSL lines. This remote site configuration is repeated over 50 times (include more than 50 remote sites).

And now the problem:
Some phone has a noise, a very low, and everything behind a horrible crackling making communication almost impossible.

Solutions:
I tried to replace the phones on 7920, but the problem returned and over again. The phones do not seem to have the problem when connected elsewhere. I did some testing on routers, but nothing seems appropriate to malfunction since they are also in place for a data network which has not problem.

Where I remain speechless, is the fact that the deterioration is not an appropriate digital talk deterioration. The conversations are not interrupted, it is as if there was interference on an analog wireless phone but it's digital.

Does anyone of you have any ideas for my problem?

[Big Fish]

This is not really my field, but this looks quite a problem with audio codecs. Not knowing any of the material used, however I can not help you more. Finally it is possible to change the codecs used, try these codecs. GSM bit greedy in terms of speed and reasonable quality.

[HiSpeed]

The common method to solve this problem is

1. understand how this works (and is supposed to work),
2. identify each element coming into play,
3. carry out tests designed to eliminate the influence of an element one after another
4 once found fault element, make the necessary correction.

How it works? (What are the components?)
- Ip phone: 1 + 1 micro codec (voice encoding) + 1 earphone + 1 codec (decoding) + stack ip (wired or wireless)
- Wireless router: router + wifi (+ encryption key) + eth port
- Network ethernet of site: switch
- Network router of site: ethernet port + SDSL ort
- SDSL: see operator (data)
- Router (central site): SDSL port + ethernet port
- Network ethernet of central site: switch
- IP PBX: local + eth port through connection to operator (Telecom)

Note that a call begins between the phone and then IPBX between the phone and the caller (if internal). The IP PBX has a role in signaling but the real communication is established between the two phones.

We see the importance of
- Codec (at each phone)
- Wifi
- SDSL connection
- Feature of the local network: switch and anything 100M advised 802.1Q if possible.

For example, a test designed to minimize the role of the SDSL line is to make a connection between two phones on the same site. (First Wi-Fi to Wi-Fi, and wireless to wired)

At the same time that I would find the fault, I would look carefully SDSL speeds given the number of sheets of this network.

Note that you need a ip connection of acceptable quality between two phones before submitting.

[LoganM]

Unfortunately for reasons independent of my will. We no longer have contact with the provider, and our ISP denies us access to your way of monitoring our bandwidth.

Actually we have no expert in this field, being more resourceful than the average, I stuck with the problem.

So I have already done a lot of interesting tests. In particular with that of the two telephones on the same sites. Since the remote site there is just one phone, so it's a test we have ever done.

Otherwise a lot of track to explore again, knowing that 150 IP phones spread over different sites, there are only a few sites or even 10 or phone with this concern.

Finally thank you for the very comprehensive answer and what is more reactive. I am aware of my research and development.

[Snake08]

It is purely hardware and requires dis-assembly of the phone. By pressing hard on the area microphone, the problem should disappear momentarily. Also use isopropyl alcohol for cleaning at the contact area between the deck and then up the microphone to reconnect the antenna. It can also come from a rotten PSU and you have to look into this matter personally.