Internet telephony refers to communications services —voice, fax, SMS, and/or voice-messaging applications— that are transported via the Internet, rather than the public switched telephone network (PSTN). The steps involved in originating a VoIP telephone call are signaling and media channel setup, digitization of the analog voice signal, encoding, packetization, and transmission as Internet Protocol (IP) packets over a packet-switched network. On the receiving side, similar steps (usually in the reverse order) such as reception of the IP packets, decoding of the packets and digital-to-analog conversion reproduce the original voice stream. Even though IP Telephony and VoIP are terms that are used interchangeably, they are actually different; IP telephony has to do with digital telephony systems that use IP protocols for voice communication, while VoIP is actually a subset of IP Telephony. VoIP is a technology used by IP telephony as a means of transporting phone calls.
I am a developer and currently on the look out of available SDKs on the market. I thought I share some of my thoughts. In my opinion an SDK is good if it supports various possibilities for development. The developers can freely and rather easily use an SDK for developing applications. For instance if I want to add a better sound management to the application which I develop but there is no chance to do so with the given developer device it is easier to download and use an SDK. Other things which make a SIP SDK valuable is that the call functions work with the most PBXs. From a modern VoIP SDK people would expect that the given VoIP SDK should match today’s minimal Internet communication forms (e.g. audio-video support).
I would probably choose an SDK according to various aspects. Firstly, I would check the website of the product regarding the documentation and the feature list. Is it capable to handle the function which I require, supported programming languages, are there any other functions which can be for use later on, try it out if it has a free trial version.
Browsing on the Internet I came across many SDKs and I can say the market is really crowded offering various SDKs. Regarding the above mentiond criteria the most suitable one I have found is the SDK offered by Ozeki Informatics Ltd. It provided everything I needed and there is a free trial which can be used to test all the features.
Hopefully I could help for those who are interested in today’s VoIP technology and curious about VoIP SDKs.