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Compression

Viewing 5 posts - 1 through 5 (of 5 total)
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  • #19923 Reply
    Medi
    Guest

    If I choose G.723.1(ACELP)5.6kbps compression,will that effect the quality of voice transmission and to what degree.

    Medi

    #19924 Reply
    voip_guru
    Guest

    Medi,
    Here is the deal on voice quality. You need to measure a couple of things. First of all when you run a compression algorithm, you need to make sure that you have the processing capabilities to handle to it. For instance, if you are going through a cisco router, do a show proc cpu to see your cpu utlization. But typically the MOS will be about 3.3. Keep in mind if bandwidth is available , do not compress if you do not have to. Once again, voip rides on rtp which rides on udp which rides on ip. So figure between 20-28k of overhead. In terms of QOS, what type of ciruit are you going over? You may want to interleave and fragment packets depending upon what type of application you are running over the lines.
    voip-guru

    #19925 Reply
    voip-guru
    Guest

    Forgot to mention. If your are planning on running voip interms of iptelephony here is what you need to do. 1st of all in your network use g.711, there will be plenty of bandwidth internally and ip voice messaging systems need to talk g.711. After that uses good switches that will support qos and do .1q tags. This should get you going in the right direction.

    #19926 Reply
    Rommel
    Guest

    If quality is key, use G.711 unfortunately it takes a lot of bandwidth. G.711 is generally benchmarked with a MOS score of 4.1. But as always MOS is one of those things that just depends. I rarely see G.711 in Service provider deployements of VoIP unless they have “more bandwidth than god”. G.729 has the next highest MOS score as far as ITU codecs go with a MOS of 3.9. G.723.1 (5.3k or 6.3k) both have a MOS of 3.3-3.65 depending where you get your information.
    Are you sending both data and voice on the same pipe? If so, LFI in conjunction with various queuing techniques would help prioritize voice traffic.
    You can also use RSVP for Call admission control on your links which will help reject calls if bandwidth is gone. If its an H.323 based network use RAI in conjunction with a gatekeeper to signify resource availability which can trigger on processor, bandwidth and available dsp resources. Of course this would depend highly on the vendor’s impelementation of these features.

    #19927 Reply
    kawfee
    Guest

    G.723 & G.711 are 2 extemes at looking at appropriate CODEC’s. Although the less compression used. If G.723 does not provide a sufficient QoS, there are other alternatives than going to a full blown uncompressed format (G.711, 64kbps). G.729 Annex B uses a compression of 8kbps, used with IP-RTP & VAC, will signifigantlty reduce the size of your header information, thus reducing the size of your packets that need to be sent and the overall bandwidth requirements needed.

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