Acrobits
Acrobits is a privately owned software development company creating VoIP Clients for mobile platforms, based in Prague, Czech Republic. Company history. Acrobits was founded in November 2008, and builds mobile VoIP software with a polished user interface, supporting encrypted calls using SRTP/SDES and ZRTP, Google Voice integration, and the G.729 Annex A audio codec. In 2009 Acrobits Softphone was released on the iTunes App Store. The following year Acrobits released their SIP Client with business features, Groundwire. In early 2011 Acrobits Softphone was released on the Android Market. In 2010 Acrobits also launched a service allowing SIP providers  to appear on the list of pre-configured providers in Acrobits Softphone. In 2012 Acrobits added video calls over WiFi support for the iOS version of its softphone. Acrobits Softphone. Acrobits Softphone is a VoIP client which uses Session Initiation Protocol. Acrobits Softphone is the leading SIP Client on the App Store, featuring push notifications and the G.729 Annex A audio codec, backgrounding, Google Voice integration and encrypted calls through ZRTP. History of Softphone. The first version of Acrobits Softphone was released on the App Store in April 2009. Version 1.0 supported only a single SIP account and the G711  and GSM codecs. During the following months new updates were released rapidly, adding new features, and the app quickly became the most downloaded paid SIP app for iOS worldwide. Support for push notifications for incoming calls was added to Softphone in September 2009, shortly after push notifications were introduced in iOS3. The G729 codec was added in Apr 2010. In August 2010, a business-caliber version of Softphone called Groundwire was released on the App Store, adding support for conferencing, voicemail, call transfers, call forwarding and other advanced features of business-grade phones. With the release of Groundwire, the app  reached the level of maturity and completeness and attracted much interest from VoIP providers, who asked for white-label versions of the app, optimized and fine-tuned for their network only. Until now, around 50 different white-label versions were created. Later, the following features were added to Softphone: ZRTP support (December 2010), NAT Bridge to help NAT traversal in difficult networking conditions (July 2011), support for video calls (Dec 2011), support for ICE (March 2012) Acrobits Softphone for Android was released in Feb 2011, followed by Android Groundwire in April 2012. Android apps are now on par with their  iOS counterparts, with the exception of video calls which are not yet supported on Android. Features. Acrobits Softphone and especially Groundwire support all features and technologies expected of the modern SIP client, plus some unique features described below. Push notifications for incoming calls. The challenge with VoIP on mobile devices is to make sure that the device is ready to receive incoming calls while keeping the power consumption as low as possible. Due to the inherent mobility of mobile devices, the network conditions change often and frequent SIP re-registrations and keep-alive traffic are needed to make sure the  mobile client is properly registered and will receive incoming call at all times. This has a significant impact on battery life. Acrobits Softphone uses a proprietary SIP Instance Server (SIPIS) to register on behalf of user when the mobile app is not running in foreground on the mobile device. As soon as the app is suspended to background or exited completely, SIPIS server takes over, registers the account and starts listening for incoming calls. When a call arrives, the mobile app is woken up using the Apple Push Notification Service (APNS) and the call is handed over to the mobile  app. The advantage of this solution is that the mobile app does not need to run at all on the device, consuming no additional battery power, and is still able to receive incoming calls. The media of the call (audio and video) are still transferred directly to the mobile app, for lowest latency and security - no extra relaying is done. Using push notifications doesn't require any support on the SIP server side and uses only SIP protocol standard. An important point and a potential drawback of this solution is the need to transfer full SIP account credentials to SIPIS  server, as it needs them to be able to register, which is an obvious security risk. One way to avoid it is to install the SIPIS server on the premises of the VoIP service provider, in which case the security risk is eliminated - the provider already knows the passwords anyway. Secure Calls. Acrobits Softphone supports encrypted voice and video calls using the standard SRTP protocol. It is able to encrypt media packets with the AES-128, AES-192 or AES-256 ciphers and authenticate them using either 32-bit or 80-bit HMAC-SHA1 algorithm. For key exchange, Acrobits Softphone offers support for  SDES and ZRTP protocols. Acrobits Softphone supports the following algorithms employed by ZRTP: Customers. In addition to their flagship products Acrobits creates white label SIP Solutions for VoIP providers around the world. See also. Comparison of VoIP software