We installed an 8x8 VoIP phone system about 6 months ago ontop of our CC Business Internet, and things have generally worked well. However, we have weeks periodically where there is more upstream quality degradatation (people can't hear us, but we can hear them). We've had CC replace the modem, and do all of the normal troubleshooting, but today, for example, there were 7 15-second patches in about 20 minutes where PingPlotter showed very high latency and jitter, and in one patch there was 100% packet loss for about 15 seconds. PingPlotter looks to me to be showing this in the hops after the ping has left our premises (see image below). Some days and weeks there is very little of this; some days and weeks there is more.
My question is: is it a reasonable to expect consistently hiqh quality VoIP traffic on CC Business or should I be lookint at fiber or other dedicated line solution?
There's a known issue with VoIP and the Netgear modem you should not use that model of modem with a public SIP provider.
However with that said here is my $0.02 on this.
SIP is subject to jitter damaging call quality and it is IMPOSSIBLE to control jitter on a link on the Internet when that link is not completely contained within a provider.
For example if your SIP provider peers with Comcast, you can complain to Comcast and they can complain to Comcast and since the path that the packets take to reach you from them is entirely within Comcast's network, it is possible for Comcast to troubleshoot and fix the problem.
But it is NOT possible to do it if your SIP provider peers with someone else (frontier or whatever) and their packets to you cross a peering connection between ISPs.
So no it's not reasonable to expect this if that is not the case. A good SIP provider knows this and they have connectivity to all the major ISPs out there. But there's a lot of guys out there who read up a little bit on VoIP and figure I can setup a Linux box running asterisk in my basement and get a couple PRIs then go into business as a phone company.
You can traceroute from your desktop to your SIP providers PBX and see if it's within Comcast - if it is, contact your SIP provider and work with them and Comcast on this. If not - well then you have some decisions to make.