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Similaire à Sip technology overview
Similaire à Sip technology overview (20)
Sip technology overview
- 1. Media VoIP
Notes de l'éditeur
- When both protocols are used in conjunction, RTP is usually originated and received on even port numbers, whereas RTCP uses the next higher odd port number.
- A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. Lossy codecs: Many of the more popular codecs in the software world are lossy, meaning that they reduce quality by some amount in order to achieve compression, but use some algorithm to create the impression of the data being there, and by that save substantial amounts of space
- The G.7xx protocol suite compose the following protocols: G.711 - Pulse code modulation (PCM) of voice frequencies on an 64 kbps channel.G.721 - 32 kbit/s adaptive differential pulse code modulation (ADPCM) G.722 - 7 kHz audio-coding within 64 kbit/sG.722.1 - Coding at 24 and 32 kbit/s for hands-free operation in systems with low frame loss G.722.2 - Wideband coding of speech at around 16 kbit/s using adaptive multi-rate wideband (AMR-WB) G.726 - 40, 32, 24, 16 kbit/s adaptive differential pulse code modulation (ADPCM) G.727 - 5-, 4-, 3- and 2-bit/sample embedded adaptive differential pulse code modulation (ADPCM) G.728 - Coding of speech at 16 kbit/s using low-delay code excited linear prediction G.729 - Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP)
- H261 supports two image resolutions, QCIF (Quarter Common Interchange format) which is (144x176 pixels) and CIF (Common Interchange format) which is(288x352). H.263 supports five resolutions. In addition to QCIF and CIF that were supported by H.261 there is SQCIF, 4CIF, and 16CIF. SQCIF is approximately half the resolution of QCIF. 4CIF and 16CIF are 4 and 16 times the resolution of CIF respectively.