Archived from groups: comp.dcom.voice-over-ip (
More info?)
In article <1107001858.288181.133410@z14g2000cwz.googlegroups.com> "Alan"
<alan@telchemy.com> writes:
>Actually there are a variety of issues to look at, and successful use
>of VoIP is going to depend not just on bandwidth. Another issue is -
>what quality are you expecting .. is intelligibility the only concern
>or do you want toll quality?
Our wide acceptance of cellular phones and their often times marginal
connection quality (with surprisingly few complaints) I think has shown,
at least for personal use, that the desire for cheap & convenience far
outweighs any desire for quality. Of course business/professional use is a
whole other matter. I might be willing to talk to a salesperson over a
marginal cell phone connection to give them driving directions to my place
of business, but when I call them to do business with them, that
connection had better be "toll quality".
>VoIP can operate over relatively low speed connections (say 128k)
>however quality will fall apart if there is ANY data traffic sharing
>the link. If any data is sharing the link then it would be desirable
>to use higher speeds - say 300k upwards.
This is largely true although with G.729 compression the bandwidth
requirements of VOIP are far less. Of course with compression, quality
suffers and we're back to our proverbial "celluar-grade" connection again.
>Delay can be significant however in many cases the user can tolerate
>quite long delays. For highly interactive discussions then one way
>delays of 100mS or so can become noticeable however for more general
>chatting delays of 300-400mS are tolerable. Obviously some satellite
>connections can introduce longer delays and this would be intrusive.
With VOIP a little packet latency can usually be tolerated, while packet
loss and packet sequencing problems cannot. I.E., there's no way to
"resend a lost word or syllable" and have it still make sense when it
finally gets to the other end. This is why successful "toll quality" VOIP
implementations must include some type of QOS (Quality Of Service) either
802.1p/q and/or V-lan'ing or else utilize its own exclusive network.
VOIP over the public Internet can sometimes yield "acceptable" results so
long as the voice call never encounters any congested paths. Once it
encounters a bottleneck, anywhere along the way, call quality will suffer.
Over severely congested paths a VOIP call will become unintelligible
gibberish.
>More info on the www.voiptroubleshooter.com web site
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