Advanced Settings
From Ekiga
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Managing Codecs
Audio Codecs
The Ekiga audio codecs table in the preferences permits you to change the codecs order as well as disabling the codecs you don’t want to use. Each codec has strong and weak points. For example, G.711 (aka PCMU/A) will give the best voice quality but will use the most bandwidth while SPEEX will give an average voice quality but requiring a very low bandwidth usage. Notice that there are two versions of SPEEX, one of them is SPEEX WideBand. You can see that to the 16 kHz clock rate.
Reordering the codecs
When you reorder the codecs, you are reordering the local capabilities table, ie the codecs you will use for sending. You will always transmit audio using the first codec in the table that is in common with the remote user. The remote user will transmit audio using the first codec in his table that is common with you.
Forcing the use of a specific codec
You can force the use of a specific codec by disabling all other codecs, but it will result in failed calls if the remote user doesn’t allow that specific codec. The best is to put your prefered codecs at the top of the list so that you always transmit with them if the remote user allows it and to disable the codecs that you don’t want to use for transmission and reception.
Adjusting the jitter buffer
You can adjust the delay to wait before playing the sound buffers that you have received using the jitter buffer adjustment. If there is too much packets loss, the delay required to have received all packets could be so important that it will exceed the jitter buffer. In such a case, the sound you are receiving will be of bad quality. A solution to that problem would be to increase the maximum limit of the jitter buffer to a few seconds, resulting in a big delay but in an improved voice quality.
The jitter buffer will readapt itself to the lowest delay allowing for optimum transmission, and that a bad voice quality in reception is not due to a too low jitter buffer value, but to bad internet connection quality.
Using echo cancellation
Echo cancellation will only work if you use the same sound device for in and out audio. e.g. echo cancellation won't work if you use the microphone on your webcam and the output sound from your soundcard (PCI). The reason behind this is the echo cancellation mechanism needs to sync the in and out sounds and this can't be done properly using two different drivers.
Controlling the SIP Settings
Misc Settings
Outbound Proxy
The outbound proxy is the SIP proxy that will relay your calls. The behavior of a SIP proxy is similar to the behavior of an HTTP proxy, ie some entity that issues the requests on your behalve and proxies the streams.
At the moment, the proxy will be used by all accounts. See feature request #340251: outbound SIP proxy setting should be attached to accounts
Forward URL
The URL to which SIP incoming calls should be forwarded if configured in the preferences.
Controlling the H.323 Settings
Misc Settings
Default gateway
The default gateway is the H.323 gateway to use when doing calls. For example, if you are calling h323:123443 with a default gateway set to foo, gateway foo will dial 123443 on your behalve. Usually, you will be registered to a gatekeeper, and gateway is not used.
Forward URL
The URL to which H.323 incoming calls should be forwarded if configured in the preferences.
Advanced Settings
Ekiga permits a fine control of the H.323 settings in the Advanced H.323 Settings section of the preferences. You can enable H.245 Tunneling, Early H.245 and Fast Start.
H.245 Tunneling
H.245 Tunneling is the encapsulation of H.245 messages within H.225/Q.931 messages (H.245 Tunneling). If you have a firewall and enable H.245 Tunneling, there is one less TCP port that you need to allow for incoming connections.
Early H.245
This enables H.245 early in the setup and permits to achieve faster call initiation.
Fast Start
Fast Connect is a new method of call setup that bypasses some usual steps in order to make it faster. In addition to the speed improvement, Fast Connect allows the media channels to be operational before the CONNECT message is sent, which is a requirement for certain billing procedures. It was introduced in H.323 version 2.
