From VoIP to Unified Communications and WebRTC
Desired video codecs mainly fall between VP8 (and its evolution VP9) and H.264 and H.265. Other formats, such as H261 – H263 – H263p, can be mainly found in legacy conferencing systems and should be avoided.
Let’s examine the main differences between these codecs.
H.264, also known as MPEG-4 Part 10, Advanced Video Coding (MPEG-4 AVC), is a block-oriented, motion-compensation-based video compression standard.
Continue reading “Understanding Video Codecs in Unified Communications”
Wideband audio provides high-definition voice quality for telephony calls, and offers better quality than standard digital telephony. It does so by extending the frequency range of audio signals transmitted over telephone lines, resulting in higher quality speech.
The great advantages of wideband audio, also marketed as high-definition (HD) audio, are:
The final result for users is better phone calls, where both the effort required to understand each other and the need for callers to frequently repeat themselves is greatly reduced.
Continue reading “Wideband Codecs and High-Definition (HD) Audio”
This time we will analyze what are the main characteristics to take into consideration when choosing codecs for communication systems.
Codec stands for coder-decoder. A codec codes a signal into a digital data stream and decodes a digital stream into a signal.
In the case of VoIP, when choosing a codec, we are mainly interested in two characteristics:
Adequate bandwidth is necessary for a high-quality conversation. Even when implementing jitter buffers and packet loss concealment in the endpoint, if the current connectivity cannot withstand the traffic transmitted over it, there is going to be huge packet loss, making it impossible for users to have a conversation.
The SIP specification has been extended over time to support a general mechanism allowing for subscription to asynchronous events. Such events can include SIP proxy statistics changes, presence information, session changes and so on.
A user agent interested in event notification sends a SUBSCRIBE message to an SIP server. The SUBSCRIBE message establishes a dialog and is immediately followed by the server replying with 200 OK response. At this point the dialog is established. The server sends a NOTIFY request to the user every time the event to which the user subscribed changes. NOTIFY messages are sent within the dialog established by the SUBSCRIBE.
ACK method confirms that an entity has received a final response to an INVITE request. In its turn, BYE method signals termination of a dialog and ends a call.
Here is the example: