What sort of connection is necessary for VoIP to work?

Posted on 2006-05-16
Medium Priority
Last Modified: 2010-04-12
What sort of connection is necessary for VoIP to work?  Currently we've got an SDSL 768/768 supporting 3 incoming and 1 outgoing lines coming into a SwitchVOX (Asterisk) PBX.  There are also four copper lines moving through the same box/network.  The copper lines are perfect incoming and outgoing.  I'm told the VoIP messages deposited on the PBX have no problems.

There does exist a problem somewhere between the VoIP phones and wherever the phone call is connected.  I've run Ping Plotter from here to the address given to me by JunctionNetworks and it doesn't look good.  I'm wondering if the problem might be that we're Nat'ed at least three times.  I know this because some of the IP's off the tracert are (our internal IP address) then 74.0.xxx.xxx (the inside interface of the Covad-supplied router), (further down the chain), (even further down the chain.)  Many of the hops are identified by nycmny2wcx2-pos14-1.wcg.net or something very close to this.  Right now, these hops are giving an average round trip of 31ms.  However we often have dropped packets etc.

So I'm wondering what's the least expensive internet connection that's going to consistently give us acceptable phone service.  I'd just go get a T-1 if cost was no object, but it is.  We're currently spending $170/month for what we've got and it's making me very sad :(  Any other solution suggestions are welcome.
Question by:Rossamino
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LVL 36

Expert Comment

ID: 16694238
Bandwidth wise you need 80kbps per voice call if you are using the high bandwith g711 ulaw/alaw codec so speed wise your connection is fine.

The fact that your ISP is using internal addressing for its internal network wont affect anything. It will just cause some routers to be unpingable remotely from other places on the internet but they do this to conserve IP addresses.

Get a copy of winmtr (http://winmtr.sourceforge.net/) which is windows based or you can use the 'mtr' which comes with most versions of linux. Run that against your destination with a large number of pings (I suggest 1000) and post the results.
Maybe there is a faulty router somewhere causing the dropped packets.

With SDSL you do get a contention ratio so a number of people share the available bandwidth meaning that you are not guaranteed to get full bandwidth. This is one reason why SDSL is cheaper than T1 for example. You can often buy a SDSL with a lower contention ratio.
However in your case you are only using 240kbps with your 3 lines so you should always be able to get that bandwidth. The winmtr/mtr results should help diagnose the problem.

Author Comment

ID: 16700480
WinMTR statistics
      Host                        %      Sent      Recv      Best      Avrg      Wrst      Last                        0      1101      1101      0      41      125      16
h-74-0-63-89.chcgilgm.covad.net                  2      1101      1082      0      41      203      16                        2      1101      1083      0      59      1094      93                        1      1101      1090      0      64      984      94
chc2il1lrs1-gige2-2.wcg.newt                  2      1101      1086      0      57      890      93
brvwil1wcx2-pos6-3.wcg.net                  2      1101      1083      0      58      891      93
chcgil9lch1-pos4-1-oc48.wcg.net                  2      1100      1088      0      63      890      94
aer1-ge-4-1.chicagoequinix.savvis.net            2      1100      1081      0      65      843      93
bpr2-ae2.ChicagoEquinix.savvis.net            8      1100      1014      0      59      922      94
dcr2-so-6-3-0.Chicago.savvis.net                  2      1100      1084      0      59      922      78
dcr2-so-2-0-0.Denver.savvis.net                  2      1100      1086      15      70      891      94
dcr2-so-2-0-0.Denver.savvis.net                  3      1100      1071      31      83      843      94
dcr1-as0-0.Denver.savvis.net                  5      1100      1053      31      98      813      93
bpr3-so-0-0-0.SeattleSwitchDesign.savvis.net      2      1100      1081      62      117      844      94
bpr3-so-0-0-0.SeattleSwitchDesign.savvis.net      2      1100      1082      62      112      875      94
border5.ge5-1-bbnet1.sef.pnap.net            2      1100      1083      62      113      938      78                        2      1100      1082      62      129      875      266
WinMTR      0.8. Copyleft @2000-2002 Vasile Laurentiu Stanimir  ( stanimir@cr.nivis.com )

I'm hoping that I shouldn't simply sum the Loss % column, but I'm thinking that, "Yes, we're losing 30% of our conversations."  Is that correct?  The voice quality is poor enough for that to be believable particularly hop 9 which is 8% all by its lonesome.  Furthermore, it looks like the destination is somewhere in Washington state.  Perhaps there's another service provider somewhere closer?   Anyone know of an outfit in Chicago.

Author Comment

ID: 16700488
This page simply won't let me post formatted data :(
LVL 36

Accepted Solution

grblades earned 1400 total points
ID: 16701431
The loss is the amount of loss between you and that destination.
So if you started getting loss at  you would expect points later in the trace to be the same or perhaps even greater loss.
The exception to this is where a router has been set to respond to pings at very low priority and in this case you would expect a higher loss to this router but subsquent ones would be better (as in the case with 8% loss).

In your case the loss starts between the router you have and the ISP which is basically the SDSL line itself. I would contact them and complain as 2% loss is unacceptible and will be noticeable.

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