The CTI Client Professional includes an integrated SIP SoftPhone.

So you only need a headset to use your PC as a simple SIP Softphone in conjunction with a VoIP provider or a local VoIP system.


The integrated SIP softphone supports the following functions:

  • Dial, hang up, accept call, hold, consultation, transfer, pickup
  • Starting with version 3.1.025, an integrated conference call is also supported.
  • DTMF dialing
  • Audio-Codecs: G.711 (A-Law and U-Law)
  • DND
  • Busy Lamp by SIP-SUBSCRIBE

Unsupported features:

  • voice encryption


Under [Options > Phone Dialog (TAPI Device) > Select > VoIP] select the "SIP SoftPhone".

  • The entry is only visible / available in the Professional version!
  • A new SIP registration is to configure via the button [Device Configuration].
  • Later you reach the configuration via: [Options > PhoneDialog (TAPI Device) > Driver Configuration > Edit].
  • Warning: The "SIP-Monitor" lines also offered can NOT be used for making calls with a headset! They are only intended to be linked to speed dial buttons.

Notes on configuration...

Audio Settings

You can configure the audio-settings via: [Options > Audio...]

  • Here you determine the sound devices for microphone and Headset loudspeaker as well as their volume.
  • Under "Extended Settings..." you can:
    • set the ring tone volume and let signal phone calls if necessary over a second sound device (e.g., speaker),
    • declare own WAVE files for the ring tones.
  • Notes on Echo: [Options > Audio...]
  • See also: Troubleshooting - Audio connection does not work

Wireless headsets

The CTI Client supports special wireless headsets, so that a call can be answered and hung up via a button on the headset (in principle).

SIP SoftPhone in a terminal session

Kann man den CTI Client als SIP-SoftPhone in einer Terminal-Session einsetzen?

In principle, yes. Under the RDP settings / Local resources, the audio recording and playback is to be activated. You would have to test whether the audio quality meets your requirements.
Further restrictions:

  • Call answer on the headset is not supported.
  • Call signaling via a second loudspeaker is not supported.

Should there be unacceptable speech delays or audio dropouts, the following alternative solutions would be:

  • As of CTI Client Version 3.1.009 there is a solution where the CTI Client SoftPhone is installed locally. More Details...

  • Use of physical SIP phones.

Notes for some functions


[Options > PhoneDialog (TAPI Device) > Driver Configuration > Edit > SIP Service Provider > Settings > Tab "Features"].

No international calls are possible via FRITZ!Box

Please check the following setting in the FRITZ!Box: [Telephony > Own Numbers > Connection Settings > Security > Only allow calls to national and emergency numbers > Change selection].


If you are in a call and click on a speed dial key, the active call is automatically held and a consultation call is established. Further possibilities for initiating a consultation ...


For the "Pickup" function, the corresponding pickup code of your telephone system must be entered under the tab "Functions":
More infos...

Call transfer

From version 3.1.008 two transfer modes are supported.
More infos...

Conference Call

As of version 3.1.025, the SIP SoftPhone component supports an integrated conference call. Under [Options > PhoneDialog (TAPI device) > Driver configuration > Edit] you can select a conference mode:
More infos...

Call Forward / Do Not Disturb

Call forwarding and call protection can be switched via the icons at the bottom right of the orange PhoneDialog display.
More infos...

CLIR (phone number suppression)

If necessary, the transmission of your own telephone number for a call can be suppressed by means of a code prefix.
More infos...

DTMF (Postdialing)

You need the DTMF postdialing, for example, for voice announcements with menu selection.
More infos...

Outside Line Access Code

If you have configured accounts from different SIP providers and only one SIP provider requires an outside line, you can optionally set an outside line code.
More infos...

Voice recording

The integrated SIP-SoftPhone from version 3.0.060 has a toolbar for controlling the voice recording. Recordings can be started, paused or ended during a call.

Please note that the consent of the conversation partner is required before voice recording.

You can find further information on the functionality and configuration of the voice recording under [Options > Audio].

Voicemail Indicator

If you want to see if there are new voice messages, you would need to configure a special speed dial key:

  • [Right-click on a speed dial key > Edit ...]
  • Set the "Action Type" to "Dial Programming Code".
  • Enter as "Button name" e.g. "VoiceMail".
  • Under "Dialing sequence" enter the key combination to query voice messages.
  • On the right under "Monitor-LED" click on the button "..." for the TAPI device selection.
  • In the TAPI Device selection on the left, select [VoIP > SIP SoftPhone] and on the right a free "SIP Monitor" line and click on the button "Device Configuration" below.
  • Enter your data in the following dialog and select the "Voice message waiting indicator" mode.
    Close the dialog with "OK".
  • Close the TAPI Device selection dialog with "OK".
  • Close the speed-dial config dialog with "OK".
  • Now the speed dial button should show a red LED as soon as there are voice messages.
    • The button tooltip text displays the number of voice messages. The info text is transferred 1: 1 from the telephone system.
    • Tip: If you switch the speed buttons to "Large buttons", you will immediately see the number of voice messages.

BLF / Busy Lamp Field / Monitoring

a) Monitoring via CTI Server

The CTI Client can report its call status to the CTI Server and this then distributes the status to all other CTI Client instances.

Recommended configuration via CTI Server + Speed Dial Panel:

  • In CTI Server, all clients are to configure user-related with name, first name and phone number.
    Hint: The Client must not be assigned a TAPI device in the server!
  • Then, in the Server is to create a group with all needed Clients.
    By group rights may be determined for example whether the caller phone numbers should be visible to all.
  • The group is then to integrate in the CTI Client as a speed dial panel via [Options > Speed Dial > Link CTI Server Group Panel].
  • More information to configuring...
b) Monitoring via SIP-SUBSCRIBE

The CTI Client Professional also provides SIP monitor lines based on the SIP-SUBSCRIBE protocol that signals "ringing", "talking" and "idle" states. The caller numbers are usually not transmitted/displayed.


  • In the CTI Client, right-click a blank speed dial key and select "Link Monitor LED".
  • In the next dialog, select "SIP-SoftPhone" on the left and a "SIP-Monitor for xxx" line on the right.
  • Then click on "Device configuration ..." below and configure the SIP monitor line with the number to be monitored. For the authentication you have to use your own SIP account.
  • Hint: In the basic configuration, only 3 SIP monitor lines are displayed. But once you have configured a line, an additional free line is automatically provided.


Outgoing calls do not work
  • Check the dial settings at: [Options > Telephony > PhoneDialog > Dialing Settings].

    • Verify that the settings on the tab "Location" are correct.

    • Verify that the settings on the tab "PBX" are correct. External line access code may need to be activated or deactivated.

  • As a test, activate or deactivate under [Options > PhoneDialog (TAPI device) > Driver configuration > Edit > SIP service provider - Settings] the checkmarks for "Evaluate parameter 'received'" and "STUN server". Then restart the application once.

Incoming calls cannot be accepted
  • As a test, activate or deactivate under [Options > PhoneDialog (TAPI device) > Driver configuration > Edit > SIP service provider - Settings] the checkmarks for "Evaluate parameter 'received'" and "STUN server". Then restart the application once.

The call is automatically ended after 5 seconds

This can occur due to a routing problem with the SIP control packets.

  • Switching from UDP to TCP could help here: [Options > PhoneDialog (TAPI device) > Driver configuration > SIP Registrations - Edit > SIP service provider - Settings > "TCP"].

Audio connection is not working
  • Check whether the correct audio profile is selected under [Options > Audio].

    • Run under [Options > Audio > Audio Profile > Edit] the audio test.

  • Windows 10: [Start > Settings > Privacy > App Permissions > Microphone > "Allow apps to access your microphone"] must be set to "On".

  • If you use an extra antivirus software, please switch it off as a test or add an exception for "cti_client.exe". On Windows 10, for example, Kaspersky could block the microphone. Call acceptance, hanging up or the status display may not work either.

  • If you are using an external VoIP provider (cloud) and the internal parties (CTI Client to CTI Client) do not hear the each other:

    • For each CTI Client, configure a different local port under [Options > PhoneDialog (TAPI Device) > Driver Configuration > Advanced > First Port used locally]. Each CTI Client should have its own port area (10 ports).
      Example: CTI Client 1: local port = 6000; CTI Client 2: 6010; CTI Client 3: 6020

    • Hint: The CTI Client uses the specified port for SIP control. For audio then the next available ports are used.

  • VPN: If the telephone system is connected via a VPN connection, the IP address of the VPN connection may have to be configured as "external IP" in the system. Example Yeastar PBX: [General > SIP > NAT > NAT Type = External IP Address].

You do not hear the other party
  • As a test, activate or deactivate under [Options > PhoneDialog (TAPI device) > Driver configuration > Edit > SIP service provider - Settings] the checkmarks for "Evaluate parameter 'received'" and "STUN server". Then restart the application once.

Your conversation partner only hears you very quietly
  • This has happened, for example, under Windows 11 with a jack microphone.

    • Audio tools are usually already installed on preconfigured computers/laptops. Test whether you can optimize the audio quality with these tools.

      • For example, an LG laptop had the LG Smart Assistant installed and the Realtek Audio Console.

    • Alternative solution: Installation of the "Equalizer APO":

    • Alternative solution: Using a different USB headset.

The other party only hears you after 5 seconds

This has occurred in connection with "Poly EncorePro 310/320" headsets.

  • An update of the headset firmware may help to solve the problem.

You hear an echo or your conversation partner:

You can find information at: [Options > Audio...]

Audio connection is rushing heavily

Very strong noise can result from incompatible speech coding. To troubleshoot, you could test the following setting:

  • Set [Options > PhoneDialog (TAPI Device) > Driver Configuration > Advanced > Preferred Audio Codec] to "A-Law" and check "Support only this codec".
USB LAN adapter - problems

A customer experienced the following problem with a USB LAN adapter on his laptop:

  • The call playback in the SoftPhone became worse after a few minutes.

Ghost calls / fake calls

If calls appear in the CTI Client that do not come from your VoIP provider / telephone system, then the following option could solve the problem with the fake calls: [Options > PhoneDialog (TAPI device) > Driver configuration > SIP registrations - Edit > SIP service provider - Settings > Use connected UDP socket].

No international calls are possible via FRITZ!Box

Please check the following setting in the FRITZ!Box: [Telephony > Own Numbers > Connection Settings > Security > Only allow calls to national and emergency numbers > Change selection].


More information

  • During a conversation the volume can be adjusted for microphone and speaker in the "PhoneDialog".
  • You can accept an incoming call by hotkey "Break Key". To activate the hotkey see [Options > Telephony].