| What voice codecs does Callcentric support? |
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For calls from one Callcentric user to another any codec can be used.
For calls to the voicemail system and for error prompting the following codec's can be used:
G.711 u-law
G.711 A-law
G.729A
For calls to the PSTN (traditional landline and mobile phones) the following codec's can be used:
G.711 u-law
G.711 A-law
G.729A
For calls from the PSTN to your Real Phone Number the following codec's will be used:
G.711 u-law
G.729A
We recommend that you configure your user agent's codec selection in the following order (with 1 being the highest priority, and 3 the lowest), assuming your user agent supports each of the following. If your user agent doesn't support all of these codec's, just skip the ones that it does not have.
1 - G.711 u-law
2 - G.711 A-law
3 - G.729
All other codecs should be disabled for compatibility reasons. If you do enable codecs which are not listed above then keep in mind that this will only work with calls on the Callcentric network or to SIP URIs. If you wish to configure other codecs then the following order may be considered:
4 - G.722 48Kbps
5 - G.722 56Kbps
6 - G.722 64Kbps
7 - Speex 8Kbps
8 - Speex 16Kbps
9 - Speex 32Kbps
10 - G.726 16Kbps
11 - G.726 24Kbps
12 - G.726 32Kbps
13 - G.728
14 - iLBC |
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| Can I use the Callcentric service with a dialup modem? |
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Yes, you can use the Callcentric service with a dialup modem of 28.8 kbps or faster. However, in general you will find the Callcentric service to be less reliable and you may experience quality problems with calls on a dialup connection. We strongly recommend that you use the Callcentric service on broadband Internet connection such as ISDN BRI, DSL, Cable, T1, E1, Wi-Fi, Wi-Max, etc.
In order to use the Callcentric service with a modem connected to your computer, you will need user agent software that supports the G.729 codec. For more information on software user agents such as X-Lite and X-Pro, please visit the support area to see compatible software. |
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| Does Callcentric support DTMF? |
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Yes Callcentric does support DTMF.
We support both In-Band DTMF and Out of Band signaling through the industry standard RFC2833 specification.
We recommend sending DTMF through the RFC2833 standard since it provides a more reliable way of transmitting DTMF signals compared to In-Band where compression, especially with highly compressed codecs such as G.729, in combination with poor connection quality can distort DTMF signals and make them unrecognizable.
If you choose to use the In-Band DTMF signaling method and experience problems with sending DTMF tones you can try to solve this by choosing G.711 as your preferred/default codec. This way your signals will be sent but won't be as compressed as when they are sent with G.729, or more highly compressed codecs.
If you are not able to choose RFC2833 standard as your DTMF type in your device, you may also be able to select AVT which is the name used for RFC2833 on some devices. You may also try setting your DTMF signaling type to Auto; this will allow your UA to choose the most suitable signaling type.
Callcentric does not support SIP-Info at this time as a method of transporting DTMF signals.
Here is a short list which explains Callcentric DTMF support for SIP communications:
1 - In-Band: Requires a stable connection and works best with a less compressed codec such as G.711. An unstable connection can still affect DTMF signaling however.
2 - RFC2833/Out of band: Works with any codec, as long as your connection does not suffer from high packet loss/ poor quality
3 - SIP-Info: Not supported at this time
If you still aren't able to send DTMF tones you may open a trouble ticket by logging into your account to contact us. |
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| Why am I experiencing poor call quality? |
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Poor call quality is usually caused by a poor quality internet connection, improper codec configuration, packet loss on your internet connection, or a combination of all of these scenarios.
If you continue to experience poor call quality, even while calling our 17771234567 test number, there are a few things you can check to make sure that the problem you are experiencing isn't related to your configuration or connection.
You can first make sure that you are using G.729 as your primary/default codec or that your codecs are setup according to our recommended order of codecs.
You can also check to make sure that you are not experiencing packet loss on your internet connection.
And finally if you have quality problems with your internet connection then you will certainly experience poor calling quality.
If none of the above tests can reveal or solve the cause of your poor call quality experience then you may contact us for further assistance. |
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| Can I send and receive faxes with my Callcentric account? |
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Yes you can. If you only wish to only receive faxes we actually have a very convenient fax reception feature. This feature allows you to receive faxes and then send them to a configured email address, or you can download them right from your My Callcentric account.
If you wish to use your own device or software to both send and receive faxes then the simplest way is to use a hardware UA with a fax machine connected to one of the analog ports. You can then setup your hardware UA to register to our servers and simply connect your fax machine to the line currently registered to our servers.
If you do not have a hardware UA or wish to receive your faxes on a computer/software you should make sure that your default/preferred codec is set to G.711 or if supported T.38.
If you are having problems with sending/receiving faxes you can always contact us for further assistance.
*Please read the detailed information regarding Callcentric's support of IP faxing (FoIP) below:
Technically we support fax using either the T.38 protocol or transparently with G.711. However, both largely depend on the reliability/stability of your internet connection. An internet connection with regular packet loss, high latency (ping) to our servers, and/or jitter (large variations in the latency) will cause problems for faxing. While we do support it, and it does work - we can't tell you how reliable it will be on your internet connection without you actually trying it. We have a number of Frequently Asked Questions (FAQs) that address your internet connection quality, speed, and such:
Click here to test your bandwidth and see the bandwidth requirements for two example codecs
Click here to test your ping, latency and see if there is any packet loss between your IP and our servers
Click here to test your connection for general quality for VoIP and or faxing
And finally the major factor which may determine your experience with faxing will depend on where you are sending the fax. Sometimes some carriers we purchase our termination through will not have networks that are compatible or sufficient for faxing. We suggest that you try testing to send a fax to a USA/Canada number first (to make sure your settings are correct) prior to attempting faxes outside the USA/Canada. |
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| Why can't I always send or receive faxes? |
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Faxing, as mentioned previously, may not always be successful for various reasons:
- We use different carriers for termination within the US and Canada. Most carriers will support T.38; however there may be carriers who either do not fully or simply do not support T.38. The carriers available for locations may change hourly, daily or monthly and as such a fixed method for faxing may not work all of the time
- Connection quality could vary depending on the clients bandwidth usage
- Configurations on the user end may be incomplete or could be affected by changes
- Pass through negotiation for faxes may not always work and may require multiple tries for proper completion
In short there are various things which could affect faxing over an internet connection. Most of our carriers support T.38 and most devices which use T.38 should work reliably on those carriers. However if changes in our routing take place it should be understood that you will want to make sure that you have configured support for pass through faxing.
As there are many devices and software options available you will want to make sure you have configured the correct options on the UA of your choice. There are some common configuration options which would need to be set:
Fax machine
- Try using the slowest possible speed on your fax machine. Normally 9.6k or 14.4k would be the best options, as speeds faster than 14.4k may not work properly with faxing
- Disable error correction
T.38
- Enable T.38
- Disable echo cancellation and echo suppression
- If available enable re-INVITE for faxes
Pass through
- Try using the G711 codecs as these would offer more bandwidth
- Disable echo cancellation and echo suppression
- Disable NSE, usually on Cisco/Linksys devices
Finally you may want to begin testing on the slowest available speed first. |
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| What video codecs does Callcentric support? |
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Video codec support on the Callcentric network is supported entirely as a pass through option, as in we do not interfere or transcode video codecs. Support for video entirely dependent on the UA involved in the calls.
Before reading further please be ware that we do not provide support for video calling to or from PSTN numbers. We will not investigate such scenarios if presented and will inform users of this ability not being supported.
Support for video over SIP is very dependent on two factors:- Codec support between UA
- Bandwidth available for calls
If you are using software with video codec support then the codec used must be available on the called end. If you are still unable to establish video data then we can attempt to assist you, however limited our assistance may be.
For reference below are some of the more popular video codecs used:
H.261
H.263
H.263+
H.264
Some devices may also support other less known video codes such as:
Theora
x264
You will want to disable any unused codecs for compatibility reasons as some codecs may affect call establishment. Ideally choosing a single video codec should be the best option.
Please keep in mind that the support for video calls mentioned above is highly dependent on your internet connection and UA. If you have problems you may contact us for further assistance. |
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