sundance-communications.com/forum Forums VOIP Phones & IP PBX VoIP & Cloud Phones, Hosted PBX, General IP Phones VPN Tunnel and VoIP?

I am trying to assist a new customer troubleshoot poor voice quality on their IP phones at a remote location. Both the main office and remote office have high-speed DSL.

Their IT guy wants to put in new routers to create a VPN tunnel. I always thought a VPN tunnel was simply for security purposes (encryption), so how would this benefit voip traffic? Ability to use QOS settings?

We tried that. Problem is that the routers can have Qos all day long, managed ports on switches, you name it. It's the public Internet that causes inconsistent operation. We found out that in our investigation, the provider of our PRI at the office end doesn't have Qos in any of their network's routers!

We abandoned the VPN tunnel when one of the routers failed. I think that it's the cable TV high speed Internet at our remote end that is inconsistent.

We tried using G711 instead of G729. At first it seemed better, but we recently went back to 729. Although 711's lack of compression sounds great when there's not much traffic out there, it's awful if there is. 729, although sometimes sounds bad, appears to be more consistent.

VPN is to get around NAT also. We have people sign sheets stating we are not responsible for the sound quality over the public internet, before putting in any IP that uses the internet. So far IP has been great money because I get to charge everytime I get a call on VOIP calls not sounding great because it's usually always the network. Packet sniffers are my best friend.

A VPN won't help the voice quality because it actually creates more overhead in the bandwidth, so I don't think it'll help you.

Ditto on what Toner said.

We run a lot of audio across VPN tunnels, and I can tell you just enabling the tunnel by itself, prior to moving any data at all greatly reduces the available bandwidth.

Unlike their IT guy, I didn't think setting up a VPN would help, but what do I know...

As I understand it, you'ld create a VPN primarily for security purposes, essentially using encryption over the internet to create a 'private' link to a remote site.

Am I correct?

That is exactly correct. VPN creates very secure traffic.

VPN tunneling is most desired when SIP is being used rather than H.323. SIP overhead is near nothing compared to the other CODEC's thus the bandwidth requirement still is considerably lower. Also the need for VPN tunneling for SIP is as stated in regards to NAT Traversal. SIP builds a text ASCII format and has to be able for tear down at the receiving end all the while being packetized.

Using VPN technology allows for us to provide access the main offices for remote users and branch offices.

There is more overhead in the VPN tunnels, this overhead is created from the establishment of the tunnel and the constant encryption of data. Depending on the size of your pipe, T-1, DSL, Cable, Fiber and how much traffic you actually have on the wire you may or may not notice a differance in speed.

Many times it not just the pipe though, with the variety of firewalls out ther today...many support VPN, but may cause latency as the traffic passes through. For instance a Cisco 506e passes VPN traffic at 17Mbps, whereas Sonicwall and Watchguard support aproximatly 50-80 Mbps...depending on the model.

Just a note to keep it real, its not always the pipe that is the problem, but also how the VPN is terminating.

-Kruptos

I am curious as to which routers should be used then. I am assuming that the Linksys should be avoided since configuration is limited.

NAT transversal seems to be my downfall, I use a VPN cause I am not as savey at setting up networks as an IT guy. As a consequence I think I might be running everything across VPN. How can one send only VOIP across VPN. Or better yet Send VOIP to a distant router with out VPN?