I would like to know that is there any difference in voice quality over ADSL
256kbps connection while using H.323 or SIP , would like to know which is better for VOIP communication on low bandwidth,which give better compression , less echo and good quality .Also would like to know that is there a difference in voice quality and echo while using hardphone than a softphone . Which from both gives better sound quality and less echo on low bandwidth .
Neither protocol has something to do with echo or voice quality. Both SIP and H.323 are signalling protocols which are used only to establish media channels. Those in turn are transmitted via RTP in both cases, so there shouldn't be a difference in quality between SIP or H.323 devices.
In theory there's no difference between a "hard"phone and a softphone. In practice most "tangible" VoIP phones include a real DSP doing some echo cancellation. With next to all Softphones echo cancellation is pretty uncommon, so you get better quality with a hardphone here.
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