Alkahest my heroes have always died at the end

March 19, 2008

Pros and Cons of VoIP

Filed under: Technical — cec @ 9:45 am

We’ve got voice over IP phones at the office.  For the most part, they are a very smart way to handle our communications.  We’re too large to want to use individual analog lines through the local telephone company – their rates would be prohibitively expensive.  We’re too small to make a private branch exchange (PBX) worthwhile.  So sending our voice data over the internet is a good approach.  When the phones work, the sound quality is excellent, the cost is relatively inexpensive and the system is fairly reliable.  Unfortunately, when the phones don’t work the challenges begin.

The biggest problems with the VoIP system is that the people that sell them, the same company that supports them, don’t really understand them.   Two recent examples of this:

All of the telephones connect to a regular networking switch.  Yesterday, that switch (which we own) died.  No lights, no power, no fan.  It went to silicon heaven (where all the calculators go).   Okay, no problem.  I call our technical support folks and they find us a spare switch – a Cisco Catalyst 2924 which must be about 12 years old now.  The tech brings it out, he and I rack mount it and move all the phones over.  Most, but not all, of the phones refuse to work.  The only phones that seem to work are those which were somewhat isolated from the original switch and didn’t notice it change.  All of the other phones failed to get their software from the network and just sat there trying to connect.

I tested my laptop in the switch.  That worked just fine.  So I punted and called the company that supports sells the phones.  I explained the problems, explained that my laptop worked, etc.  They had me take a phone and bypass the switch (arguably something I should have done myself) and when that worked, they said it was a switch problem and I should try a new switch.  Odd, since my laptop worked, but okay.

I called the other guy in the office who knows something about the phones, he was in Orlando for a conference, and he had seen a similar problem on another “smart” switch.  So we figured we should buy a dumb switch – maybe a netgear unmanaged switch that’s similar to the little 5 port version we had been testing with earlier.  Before I did that, I borrowed the same smart switch we had tried before.  Sure enough, it also didn’t work.  Fortunately, unlike the Cisco, I could get at the management interface without a dumb terminal.

It occurred to me that maybe the problem was that we weren’t passing phone traffic because the phones were on a VLAN.  I got into the interface, turned on the right VLAN on all of the ports and sure enough, phones plugged into the switch worked.  Woo hoo!  We were back online.  Of course, after the fact, I was annoyed that our provider just said “switch problem” without actually suggesting what it could be.  If I had purchased a new switch and it still didn’t work, I’m not certain what they would have said.  It’s like they don’t know how their own products work.

The second example of this has been ongoing for several months.  On a call, you occasionally lose parts of what the other person is saying.  Random half second parts of the conversation are completely lost.  The other person can always hear what you are saying – no trouble there.  It’s only a problem for voice traffic you are receiving.

The provider has been worse than no help on this one.  They first tried blaming it on our using a lot of data.  Well, sure, but we’ve got the quality of service QoS router they required – it limits the bandwidth for data to ensure that you’ve got enough for voice.  So they tried lowering the absolute limit on data from just giving priority to voice to 2.5 Mb/s for data (out of the total of 3).  That didn’t help.  So then, without telling us, they lowered it to 2 Mb/s.  Still didn’t help.  Essentially, our provider can’t understand why the QoS router wasn’t working to prevent the voice loss.

So we started thinking about it and doing some testing.  I spoke to a friend that does networking and he reminded me that the bottleneck for bandwidth is our 3 Mb/s connection to the internet.  On our side of that we’ve got a gigabit on the internet side, the ISP’s router probably has gigabits.  Moreover, our QoS router can only limit our *outbound* traffic with any certainty.  It can *try* to limit inbound traffic by dropping packets and hoping that TCP/IP will negotiate the speed downward.  But that negotiation takes time and is only good for 1 connection.  What we really needed, according to my friend, was QoS on the ISP’s router in order to limit inbound traffic on our 3 Mb/s bottleneck.  So we tried a few things.  We tried saturating the inbound line, and sure enough, the voice got terrible.  We monitored inbound traffic and saw that poor voice correlated to high inbound traffic and that the inbound traffic definitely “burst” over the QoS limits.  Then we tried the same things for outbound.  Sure enough, for outbound traffic, the QoS router did exactly as it should.  Even when we were uploading huge amounts of data, the QoS router ensured that we had enough available for voice.

We contacted the provider about QoS on the upstream router we’re connected to (since this would solve the problems).  Unfortunately, the ISP won’t turn on QoS.  Our VoIP provider suggested that we add a 3rd T1 to our data connection bringing out total bandwidth up to 4.5 Mb/s and that this would help.  WRONG.  The internet, heck CNN, is fully capable of saturating our link, be it 3 Mb/s or 4.5 Mb/s.  What we need is a 3rd T1 that is dedicated to voice only.  Our VoIP provider didn’t (and doesn’t) seem to understand this, and they’ve made it difficult to order, but we finally got through to them and it should be installed in a few weeks.  At that time, we’ll finally have a pretty good, reasonably priced, phone service.  Even if the provider doesn’t understand QoS, VLANs or for that matter VoIP and VoIP management.  Why are we paying these guys again?

1 Comment

  1. […] has an interesting bit on the ‘pros and cons’ (but mainly cons) of Voice over IP in what sounds like a large […]

    Pingback by VoIP-Point » VoIP, QoS and old kit — March 19, 2008 @ 2:53 pm

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