Web Call Server supports audio and video calls from a browser to SIP devices, PBX servers, SIP-GSM gates, VoIP conferences and other devices supporting the SIP protocol. Therefore, a web application can work in a browser as a software phone with the support for the SIP protocol, receive and initiate voice and video calls.
Supported platforms and browsers
Supported SIP functions
- Holding a call
- Transferring a call
Management of SIP functions is performed with the REST API.
1: SIP server as a proxy server to transfer calls and RTP media
2: SIP server as a server to transfer calls only
- The browsers initiates a call using the /call/startup REST query.
- WCS connects to the SIP server.
- The SIP server connects to the SIP device receiving the call.
- The browser and the SIP device exchange audio and video streams.
Below is the call flow when using the Phone example to create a call.
session.createCall(), call.call() code
2. Establishing a connection to the SIP server
3. Establishing a connection to the callee
4. Receiving a confirmation from the SIP device
5. Receiving a confirmation from the SIP server
6. Receiving from the server an event confirming successful connection.
CallStatusEvent ESTABLISHED code
7. The caller and the callee exchange audio and video streams
8. Terminating the call
9. Sending the command to the SIP server
10. Sending the command to the SIP device
11. Receiving a confirmation from the SIP device
12. Receiving a confirmation from the SIP server
Making an outgoing call from a browser to a SIP device
1. For the test we use:
- two SIP accounts;
- the Phone Video web application to make a call;
- a software phone to answer the call.
2. Open the Phone Video web application. Enter the data of the SIP account making the call from a browser:
3. Run the software phone, enter the data of the SIP account receiving the call:
4. Click the Connect button in the browser. Then enter the identifier of the SIP account that receives the call and click the Call button:
5. Answer the call in the softphone by clicking the answer a video call button:
In a separate video, the video broadcast from the browser is shown:
6. The browser also displays the video:
7. To terminate the call, click the Hangup button in the browser or in the softphone.
Receiving an incoming call from a SIP device in a browser
1. For the test we use:
- two SIP accounts;
- a software phone to make the call.
- the Phone Video web application to answer the call.
2. Open the Phone Video web application. Enter the data of the SIP account receiving the call in a browser:
3. Run the software phone, enter the data of the SIP account making the call:
4. Click the Connect button in the browser, a connection to the server is established. In the softphone enter the identifier of the SIP account that receives the call and click the Call button:
5. Answer the call in the browser by clicking the Answer button:
6. The browser displays the video:
7. The video broadcast from a browser also displays in a separate window of the softphone:
8. To terminate the call, click the Hangup button in the browser or the end call button in the softphone.
Camera, microphone and sound output devices management
Selection and switching input and output devices
Like a video stream capture, camera, microphone and (in Chrome browser only) sound output device can be selected while making a SIP call from browser. Besides, devices can be switched during a call.
1. Choosing camera, microphone and sound output device code:
2. Switching sound output device during a call code:
3. Swithching microphone during a call code:
4. Switching camera during a call code:
Video size setting
An outgoing video size can be specified while making a call
Making a call without microphone and camera
In some cases, when a call supposes no two-way communication, e.g. when calling to voice menu, it is possible to make a call without using microphone and camera.
To do this RTP activity timer should be disabled with following parameter in flashphoner.properties file
and turn off audio and video in outgoing call constraints for Chrome, Safari and MS Edge browsers
In addition to it, an empty audio stream should be created for Firefox browser:
WebRTC statistics displaying
A client application can get WebRTC statistics according to the standard during a SIP call. The statistics can be displayed in browser, for example:
Note that in Safari browser audio only statistics can be displayed.
1. Statistics displaying during a SIP call
Supported codecs setting
WCS sets the codecs supported to INVITE SDP according to the following parameters in flashphoner.properties file
1. The codecs specified with
codecs parameter are included to INVITE SDP, by default
2. The codecs specified with
codecs_exclude_sip parameter are excluded from INVITE SDP, by default
3. The codecs specified by browser are excluded from INVITE SDP if this parameter is set
4. The codecs specified with
stripCodecs parameter in client application are excluded from INVITE SDP, for example:
Additional SDP parameters passing in INVITE request and 200 OK response
and incoming calls (to 200 OK response)
Those parameters will be added to SDP after connection information ("c=IN IP4 <WCS IP>") and before time description ("t=0 0"):
SIP calls using SIP TLS signaling
SIP TLS signaling may be enabled with the following parameter
In this case, SIP PBX cetrificate will be checked using local system certificates storage. Therefore, a valid SSL certificate from well known CA should be installed on SIP PBX server to use SIP TLS.
SIP calls via SIP PBX server with self-signed SSL certificate
To make a SIP call via SIP PBX server with self-signed SSL certificate, this certificate should be added to local storage on the server where WCS is installed:
1. Get self-signed SSL certificate from SIP PBX server
- 192.168.0.153 - SIP PBX server IP address
- 5061 - SIP TLS port
2. Copy certificates from the SIP server response
then add them to pbx.crt file. The file content should be like this:
3. Detected Java home path
For example, if the command above returned
then Java is installed to the folder
4. Find Java local certificate storage file path, for example
5. Import the certificates retrieved on step 2 to Java local certificate storage
6. Restart WCS.
Connection to an existing session
Sometimes it is necessary to connect to already existing session and receive an incoming call. It is usually actual on mobile devices where websocket session is closed automatically when browser goes to background. In this case, only push notifications are available. To keep the sesssion active after disconnection, the
keepAlive option should be set while creating the session
In this case, session stays active until the following interval in milliseconds is expired (3600 seconds, or 1 hour by default)
This interval is periodically checked. The checking priod is set in milliseconds by the following parameter (300 seconds, or 5 minutes by default)
A session token should be stored while creating the session
Then application may connect to the session again using this token (for example, if incoming call push notification is received):
1. It's impossible to make a SIP call if 'SIP Login' and 'SIP Authentification name' fields are incorrect
Symptoms: SIP call stucks in PENDING state.
Solution: according to the standard, 'SIP Login' and 'SIP Authentification name' should not contain any of unescaped spaces and special symbols and should not be enclosed in angle brackets '<>'.
For example, this is not allowed by the standard
and this is allowed
2. There are some problems with sound while SIP calls from Edge browser.
a) The outgoing sound is sometimes abruptly muffled, then it goes normally.
b) The incoming sound is heard only if you speak into the microphone.
Switch SILK and G.722 codecs usage off in SIP calls for Edge browser with stripCodecs option:
or with server setting
3. Microphone swithing does not work in Safari browser.
Symptoms: microphone does not switch using switchMic() WCS WebSDK method.
Solution: use another browser, because Safari always uses sound input microphone, that is chosen in system sound menu (hold down the option (alt) button and click on the sound icon in the menu bar). When microphone is chosen in sound menu, Mac reboot is required.
If Logitech USB camers microphone does not work (when it is chosen in sound menu), format / sample rate changing in Audio MIDI Setup and rebooting can help.
4. Outgoing video SIP call cannot be established if INVITE SDP size exceeds MTU
Symptoms: SIP server return 408 Reques timeout when trying to establish video SIP call, audio calls can be established successfully through the same server.
Solution: reduce the number of codecs in the INVITE SDP so that the SDP fit into the packet size defined by MTU (usually 1500 bytes) using the following settings
Only codecs supported by both sides of the call should be left, in this case it is VP8 and PCMA (alaw).