On Friday 10 March 2006 05:30 am, Matthew Crocker wrote: > On Mar 10, 2006, at 8:24 AM, Hugh L. Johnson wrote: > > It's all about latency. The roundtrip ping times across my DSL > > circuit > > (Verizon ATM cloud) to my ISP's router (One hop away) are approx 25ms. > > My ISP has a PRI which I use for all incoming and local outgoing > > calls. > > For these calls the quality is better than when I had an analog > > phone at > > home. > > No, it is all about jitter. Latency is irrelevant unless it is above > 150-200ms. Rapidly changing latency (aka Jitter) is what kills VoIP > quality because the echo cancelers can't train up properly.
The only option for coping with significant jitter is to have echo cancelling at both ends. If echo crosses the audio stream with jitter in it, it becomes a nightmare to fix. The ideal way around it is to stop the echo in the first place. Unfortunately this means you need control of all the endpoints before they cross the public internet. eg: if you have Office 1 with a PRI and an asterisk box, and a remote Office 2, with public internet in between, you need to echo cancel at both Offices. You've got to stop the echo coming in from the PSTN via the PRI before it travels over the internet to office 2. If echo reaches that far with jitter, it can't be reliably cancelled. Of course, there is a lot more to it than that, but in some circumstances you can mitigate the echo+jitter problem. But that generally does not help you with Internet VoIP LD providers. They seem to give you the works, including the echo. By the time you get it, the jitter makes cancelling it a real challenge. The real niche for enterprise VoIP is inside the enterprise network. Smart desktop handsets (portable! no need to reconfigure for moves!), integration into your office functions (voicemail messages sent over email or accessed via http, for example), and so on. When you control your enterprise network and have the proper infrastructure (end-to-end QoS and sufficient capacity), that should be unbeatable if it is done right. -Peter _______________________________________________ --Bandwidth and Colocation provided by Easynews.com -- asterisk-biz mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-biz
