VOIP bandwidth and latency requirement?

[PandaBear]

How's fax over VOIP line via companies like vonage or Comcast? Inlaw is thinking about dumping landline but they have a fax machine. Also how's VOIP quality (of skype, for example) over a wifi that connects to cable modem?

 

[SuperDave456]

Right now my provider is VERIZON and I have FIOS. I also have a Magic Jack, and it rocks. However, if you play games online or work from home via a VPN, and all your bandwidth is taken up by these activities, then your VIOP has nothing to work with. I only have 1 computer in the house, so this might not be the case if you have your VPN running on one machine and your VOIP running on the other. That being said, my Father has a Magic Jack and he uses it has his business line. He has experimented with it and likes it that much. My office runs nothing but VOIP and it works great. I think alot of it depends on your setup.

 

[ctc]

I just got Ooma which is like magic jack but it is a standalone system and you don't need to plug it into your computer (it plugs in between your cable modem and your router or computer). I currently have Comcast Digital Voice but I'm looking to switch completely over to Ooma. The Ooma system cost $220 at costco.com but there are no montly or yearly fees unless you want their premium offerings (which I don't). Anyway Comcast Digital Voice works well. I just setup ooma yesterday so I'm going to test it for at least 30 days before canceling Comcast Digital Voice and porting my # over.

 

[uc50ic4more]

 Originally Posted By: PandaBear

How's fax over VOIP line via companies like vonage or Comcast? Inlaw is thinking about dumping landline but they have a fax machine. Also how's VOIP quality (of skype, for example) over a wifi that connects to cable modem?

My family ditched the land line over a year ago. We use Skype, and a cell phone as Skype cannot issue numbers in Canada. We pay ~$40USD/ year for unlimited calling in North America. If we could get a phone number through Skype, I think it'd be ~$35USD per year for incoming calls. I videoconferenced with a friend in China for a year; it was like he was around the corner. My parents videoconference with us daily to say howdy to the kids. It works very, very well, especially considering that we're doing this across Mac, Ubuntu and Windows boxen. Try to use port 1720 if possible, as that is the standard VOIP port used by ISP's and third parties that provide VOIP services. A tech fella from my cable ISP tells me they prioritize port 1720 for their own VOIP services, so I use that for Skype.

 

[uc50ic4more]

 Originally Posted By: SuperDave456

However, if you play games online or work from home via a VPN, and all your bandwidth is taken up by these activities, then your VIOP has nothing to work with.

The DD-WRT firmware I use with my router supports QoS (Quality of Service) that prioritizes bandwidth based on the port or IP. I have port 1720, for VOIP, set for higher priority than those used for P2P activity.

 

[PandaBear]

Guys, I know voice is good, but how about if the connection is through a wifi for voice and how's the fax connection reliability? I was told by someone on the net that most voip protocol doesn't do well with data signals like fax, and that wifi add some extra latency over the voip latency.

 

[StevieC]

I fax through my Magic Jack and I have faxed through Vonage when we used to have that... It works fine. Check on your VOIP choice though because it may not support it due to the compression it uses for the voice signals. I have done faxing and talking on Light DSL packages where it's 128K down /64K up and it works but it sometimes would loose packets and the call would be distorted. I would recommend more bandwidth than this, but you could get away with it.

 

[brianl703]

I've done some tests with fax and modems over VOIP. I'm using an Asterisk box with a TDM (analog) card as one endpoint and a PAP2 as another. All the VOIP stuff is on it's own network with only a switch between the PAP2 and the Asterisk box, which has it's own Ethernet interface for the VOIP stuff. Latency-wise, this is as good as it gets. (I also set the PAP2 to use 10mS packets instead of the 30mS default, and of course using the G.711u codec). I cannot get modems to connect at any speed with that configuration. (I tried forcing the speed to 9600bps or less but that still didn't allow a connect). Fax works, but occasionally some pages get garbled (could be due to clock slip?) Incidentally, I have Comcast Digital Voice. I connected a modem to the Arris device that Comcast installed, dialed an ISP, and got a 53k connect. I believe that is because the clock (which controls the PCM sampling) in the Arris device is synchronized with that of the rest of the telephone network, which is a requirement for V.90/V.92 to work. There is no PCM clock synchronization with regular VOIP.

 

[brianl703]

http://www.freepatentsonline.com/6956873.html Arrangement for deriving a local clock in a packet cable telephony modem

 Quote:

In prior art arrangements, the clock signal used for timing the collection of PCM samples of both inbound (downstream) and outbound (upstream) audio signals (e.g., voice signals) is derived from a “national” clock transmitted downstream by the cable modem termination system (CMTS). This signal is recovered by the local cable modem and divided down to the rate used within the modem (for example, 4.096 MHz). The use of a “national” signal thus provides system-wide synchronization. There is a clear advantage in using a single clock source for synchronizing the sampling at both ends of the telephone connection. For example, the common clock prevents clock slip or drift. Without a common clock, the sampling clocks at each customer's cable modem will drift apart and this drift will empty the “jitter buffer” at one end of a connection and overflow the jitter buffer on the other end of the connection. The one direction delay of the connection will change and audio samples may be lost. As a result, fax and modem calls may fail after a long period of time.

 

[brianl703]

 Quote:

There is no PCM clock synchronization with regular VOIP.

If I hadn't made it clear--that's why faxing with VOIP is iffy at best, and why it works with Comcast (or any cable telephony provider), because cable telephony DOES have PCM clock synchronization.