Debating VoIP configurations

Connecting all the dots when installing VoIP service from a provider such as Vonage, can be done in a couple ways. Fellow Computerworld blogger Robert L. Mitchell argues that the telephone adapter provided by Vonage should be connected to your network exactly as instructed, between the broadband modem and the router. I disagree, preferring to use the VoIP box (a V-Portal in the case of Vonage) as just another node on my network, plugged into the router along with all the computers.

My point, as I wrote last time, harps back to the purpose of this blog: Defensive Computing. If the VoIP box is connected between the broadband modem and the router, then a problem with it can impact all the computers connected to the router. I can't take that risk, keeping the computers online is more important to me than the VoIP service.

I thought that was that, and planned on writing about configuring a router to provide the best possible VoIP performance next. But Robert responded that my way was "wrong", so the debate is on.

First, let me note that the debate assumes that the broadband modem and router are two separate boxes, rather than a single integrated unit. And, it points up the big advantage of having two separate units: flexibility. Also, having one box for one job (connecting to the outside world or routing) isolates any problems with the box and lets one be upgraded without impacting the other.


In large part Robert's opinion is shaped by the fact that things didn't work for him when his network was configured my way. Specifically, Vonage tech support told him that his V-Portal box had problems renewing its IP address, which is part of DHCP. Let me explain DHCP.

Every computer on a network needs to have a unique identifier. On a standard TCP/IP based network (as most are) the unique identifier is an IP address, a 32 bit binary number.

The hard way for a network device to get assigned an IP address is for a techie to configure the device to always use a specific number, day after day after day. The easy way to get an IP address is to ask for one when booting up.

DHCP is the protocol used on TCP/IP networks for dynamically assigning (handing out) IP addresses. When a computer starts up, it sends out a DHCP request that amounts to "Help, I don't have an IP address, will someone out there please give me one". Normally, the router responds with an IP address (and other techie information) and a time limit. When the time expires, the computer has to send out another "Help, please give me an IP address" request.

DHCP is ancient, so you would expect it be well debugged, tried and true. Yet, for some reason, Robert's V-Portal had problems getting a new IP address from his Linksys WRT54G router after the old IP address expired. Vonage tech support told Robert that this was a known problem and didn't occur when the V-Portal was connected to a broadband modem rather than a consumer grade router. So, understandably, he connected things in a way that worked.

Robert and I got our V-Portal boxes within a couple months of each other and mine is also connected to a Linksys router, a WRT54GL (firmware version 4.30.7).  

My Vonage V-Portal experience has been fine, but it's only been a week or so, the jury is still out. My router gives out IP addresses with a 24 hour expiration period (this is configurable), so my V-Portal has renewed its IP address a number of times without impacting the service. I checked the log in the V-Portal a few times and, while it has experienced a problem connecting to the router, the problem was both short lived and rare.

If there really is a DHCP problem with the V-Portal and some routers (don't always believe what tech support departments say) then it could be worked around by configuring the V-Portal with a static, unchanging, hard coded IP address. This avoids DHCP entirely.


This blog is about Defensive Computing. Not only does my way make the LAN more reliable (a problem with the VoIP box impacts nothing but VoIP), it also offers better debugging when things go wrong with the VoIP service. And things always go wrong.

The Vonage V-Portal, like my previous VoIP adapter from AT&T, has two Ethernet ports. One connects to the outside world and one to an inside LAN. I can debug a VoIP problem using either Ethernet port.

The outside world port is connected to my router. Thus, I can ask the router if it still sees the VoIP adapter, and if it gave it an IP address or not. If the router thinks the VoIP adapter has an IP address, I can enter that address into a web browser on any computer on my LAN and get into the administrative website of the VoIP adapter. From there, I can check it's error log and more. If I can't get into VoIP box from another machine on the LAN, that tells me something too. I can then tell the router to release the IP address currently assigned to the VoIP box and give it a fresh new one.  

If debugging over the LAN fails, the normally unused Local Area Network port on the V-Portal offers another way into the box to poke around. Since the V-Portal was designed as a DHCP server, I can connect an Ethernet cable to its LAN port and to a computer. The V-Portal adapter will give the computer an IP address and using this new, 2-device network, I can again try to access the administrative website inside the V-Portal.

Once I'm into the V-Portal's internal website, I can review the error log, and, possibly, tell the box to request a new IP address from the router. If that was the problem, I'll see it live. If this fails, I can always power the box off and restart it - without impacting any of the other computers on my network.

And there's more. Your router may have another trick up its sleeve. Some offer a feature that fakes out DHCP. The VoIP adapter can be configured to use DHCP but the router can be instructed to always assign the VoIP adapter the same IP address. Over and over, day after day. D-Link refers to this as static DHCP. My Linksys WRT54GL doesn't offer this feature.

Debugging things when the VoIP adapter is between the broadband modem and the router is much harder. As Robert described it:

The problem was that the V-Portal wasn't picking up an IP address from the cable modem. No IP address, no dial tone. That sounds simple, but it took about an hour before she finally isolated the problem to the V-Portal. Coming to that conclusion involved a lot of swapping around of wires, turning things on and off, a few wild gestures, and finally jamming a pen into a hardware reset slot on the V-Portal and rebooting it.



When I started with AT&T's CallVantage VoIP service, I configured the telephone adapter not to use DHCP. Part of Defensive Computing is being pessimistic and I figured that not using DHCP made for a simpler, more reliable setup. And it did.

But, a year or so later, I went traveling and took the telephone adapter with me. Of course, it didn't work when plugged into a different router and it took me a while to figure out that its static IP address was not compatible with the new network.

So, let me suggest that you write down the configuration information for your VoIP adapter on a piece of paper and tape it to the box. If I had a note on mine that said what it's static IP address was, or even just that it was using a static IP address, I could have saved myself a lot of grief.

Perhaps the most important information to tape to the box is the userid and password to log into the internal web site used for administration and configuration of the device. You may also need a port number to access this website. And, of course, note if its using DHCP or not.


There is no single right answer when it comes to the placement of a VoIP telephone adapter on a network. 

Although Robert had problems with a V-Portal connected to a router, and both Vonage and AT&T don't recommend this setup, it works. I happily used an AT&T CallVantage VoIP adapter this way for a few years. And, so far, my Vonage V-Portal has functioned fine this way.

But since this isn't the recommended configuration, you may not get much tech support from your VoIP provider. Non-techies that are dependent on tech support for help, may have no choice but to configure things as the company suggests.

One advantage for the VoIP companies to their recommended setup is that they don't have to deal with routers. Good for them, perhaps not for you.


Finally, Robert recommended a surge protector to protect the VoIP adapter. Unquestioningly, you are better off with a surge protector than without one. But there's an even better option.

All the computers on a LAN depend on the broadband modem and router (be they one physical box or two). While the router can be replaced fairly quickly (being a techie I have spares on hand) it's still a huge hassle, not to mention beyond the technical abilities of many. A problem with the modem can mean being off-line for days. When that is simply not an option, a UPS is the way to go rather than a surge protector.

A good UPS does surge protection better than a surge protector. When there is a surge, it disconnects the power line and provides power from its battery until the surge has passed. In addition, it does much more.

If there is a little too much power (less than surge) it trims the power back to normal levels. On the flip side, if your power company is having a brown-out to conserve power, a good UPS will boost the weak power levels up to normal. This constant adjusting is done by a "line interactive" UPS. Expect to pay over $100 for such a model. I have been very happy with APC as my UPS vendor.

My broadband modem, router and VoIP telephone adapter are all plugged into a UPS. I probably paid more for the UPS than all three boxes are worth together, but the point is Defensive Computing, preventing problems.

Next time, configuring a router to give priority to VoIP traffic.


Copyright © 2009 IDG Communications, Inc.

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