There are a few things you need to keep in mind to get the most out of Twilio Client. Following these best practices will ensure your users have a seamless calling experience. They will also make it easier to troubleshoot connection and call quality issues.
- Give users feedback when device state changes
- Gracefully handle no-answer situations
- Monitor call quality with Voice Insights
- Manage the calling environment
- Use the closest Twilio data center
The SDK relies on events following the EventEmitter interface to control the calling experience. Alerting the user to an incoming call requires listening for the Device.on('incoming') event for example. Similarly, the SDK also provides events for monitoring the Twilio Client Device state.
Surfacing changes in the device state to the UI using these events can often be the difference between a smooth calling experience and an extremely frustrating one-
Device is ready for calls: .on('ready', handler)
The Device.on('ready') event is fired once the Device has been successfully setup using a valid capability token. Use this event to change a UI element, like a status indicator for example. This ensures the user is aware that your application is online and ready to start making and receiving calls.
Device is not available for calls: .on('offline', handler)
Similarly, it’s important to notify the user if your application goes offline at any point of time. Use the Device.on('offline') event to change the status indicator to offline to alert the user. This event is triggered if the connection to Twilio drops for some reason or if the capability token expires. You should also use this event to attempt to reconnect using Device.setup().
Something’s wrong: .on('error', handler)
Handling this event allows you to catch and handle device errors gracefully. You can see the full list of errors surfaced by this handler here. Some commonly encountered errors are-
- Errors with the capability token, either due to expiration or invalidation
- The user denying your application access to the microphone. You can use this to disable the call button and instruct the user to provide microphone access
It’s also important to gracefully handle situations where a call to the Client goes unanswered in spite of the it being online. This depends on how the Client is being brought into the call-
Incoming calls can be connected to the Client using the <Dial> verb’s <Client> noun. In this case, you should set the timeout attribute to a value that works best for your use case. You should also configure an action URL using the action attribute. Twilio will make a request to this url with these parameters once the call gets concluded, which include the outcome of the call.
Using the REST API
The REST API can also be used to bring the Client into the call. This is involves first placing an outbound call to the client. When the Client picks up, the Url parameter retrieves TwiML that is used to set up the call. You can learn more about using the REST API here. It’s important to set a Timeout on the API request that works best for your use case. Note that the max is 60 seconds for calls made to Client. Be sure to configure a status callback URL using the StatusCallback parameter and specify the call progress event webhooks using the StatusCallbackUrl parameter. This ensures your application knows the outcome of the call.
If the call outcome in both situations is no-answer, it’s important this is conveyed to the caller. One way to do this is by directing them to voicemail. You can use the <Record> verb to set up voicemail. If the call is unanswered, the caller is directed to TwiML that uses the <Record> verb to leave a voicemail.
Voice Insights fires two types of events on the front end - network warnings and audio level warnings.
- Network warnings are fired when there is a reduction in call quality as indicated by three measures - round trip time or RTT, mean opinion score or MOS, jitter, and packet loss.
- Audio level events are fired when Insights detects unchanged audio levels. While these could indicate an issue, they usually indicate that the audio has been muted on the microphone or input device.
By implementing handlers for these events and surfacing them in the UI, you can notify the user about degradation in call quality or issues with audio input. This can be used to prompt the user to take remedial action like checking their internet connection or input device audio.
Implementing Voice Insights for Client can also make troubleshooting issues a lot easier. The Client Insights dashboard in the console provides aggregate call quality metrics across all client calls. This is useful in seeing trends in your call quality stats. For example, you could see that Client’s with a particular browser version are seeing more issues with quality. It also records call setup events, allowing you to diagnose issues with call connection. The same data is also made available for individual calls.
You can learn more about Voice Insights by checking out the docs.
VoIP call quality is heavily influenced by environmental factors like firewall configuration, network conditions and available bandwidth, browser version (for webRTC) and OS and microphone and speaker hardware. It’s important you review our deployment best practices and connectivity requirements documentation before taking your app to production.
If possible, you should also take advantage of the DSCP support enabled in Twilio Client 1.3 onwards. DSCP, or Differentiated Services Code Point allows packets to be tagged to prioritize them on the network. Browsers that support DSCP are capable of tagging call media packets sent by the Client in this manner. Your router or network element can then use these tags to prioritize call media packets over other traffic on the network. Also, note that your router or network element needs to also be DSCP-compliant. DSCP is currently supported only by Google Chrome currently, and setting DSCP on Windows machines does not currently work.
Twilio has a global presence with data centers in the US, Ireland, Brazil, Singapore, Tokyo and Sydney. This minimizes latency by allowing your Twilio Client Device to connect to the closest point of presence. There are two ways you can set up your Client to connect to Twilio-
- Use Twilio’s Global Low Latency routing to let Twilio use latency-based DNS lookups to pick the closest data center. You can do this by omitting the ‘region’ parameter while calling Twilio.Device.setup().
- Force region selection by using the ‘region’ parameter while calling Twilio.Device.setup(). You can find the list of regions and their IP addresses here. This approach makes sense if all Twilio Clients are going to be based in the same region.