Can I VoIP? Should I VoIP?

June 29, 2005 7:07 PM

What do I need for enterprise VoIP, and do you think the technology's mature enough?

I'm about to sign to get a T-1 dragged into my new office. We're at the point where my little IT company is overloading our DSL line continuously, and we can't even get that good of a DSL line at the new location.

To keep costs reasonable, I can either choose to get a fractional T-1 with four voice trunks running into an asterisk box (VOiP SIP phones in the office, of course, but that's just LAN) and a fractional T-1 for data, or I can get a VOiP provider and get a full T-1, just routing phone over it via VOip.

One of the sales reps I talked to said that if I was going to do VOiP to the world, I'd probably want to get a more robust router that could "split the packets" ... what was she talking about? She couldn't explain it to me satisfactorily in geek, and I don't know enough of the buzzwords to google it.

In a broader sense (because I have a couple of clients that are interested in this if I can pull it off myself...) what kind of considerations should I be looking at before doing a VoIP installation, either VOiP over intranet and trunk to world or VOiP to world, especially in the technical sense, and what are good resources to explore for easy bedtime reading?*

Also, in the general opinion, sense, could I get some comments from the peanut gallery on VOiP in general? Do you think it's mature enough?

* Note: Easy Bedtime Reading(tm) for me usually includes technical manuals and o'Reilly Bookshelf.

posted by SpecialK to Technology (2 answers total)

Best answer: VoIP's ready. The big question is whether your network is.

The big issue in the VoIP world is QoS -- quality of service. Instead of just being a nebulous concept, QoS has a definite meaning in the VoIP world -- that voice packets always get priority over data packets. Without QoS, VoIP can be a major pain -- if you saturate your network (even with a short burst of data), you end up losing your voice connection momentarily. Talking over VoIP on a network without QoS can be likened to listening to someone underwater, as you hear only rapid bits and pieces of the conversation when your data is clogging the network.

Assuming everything on the network and your provider fully support QoS? Not a problem. I use VoIP at the office every day, and it never sounds like anything other than a normal phone -- but that's because we have a well-managed VoIP network, with care and consideration taken to prioritization.

The question is, how are you and your provider prioritizing data? It's something to ask a sales engineer first. Are they using separate ATM PVCs on that T1? Separate frame DLCIs? MPLS with IP? Nothing at all? If they can't tell you how they're prioritizing voice over that pipe and on their network, that's a red flag.

Your router will indeed need to support the termination of multiple PVCs (one for data, one for voice), DLCIs (one for data, or one for voice), or support MPLS (voice packets tagged as such) -- depending on what technique they're using to prioritize the voice packets. The thing is, you'll need a router that supports the right one. If she can't tell you the specific way they're doing it, it's a red flag -- you need to use an end-point device that will respect the particular form of prioritization, otherwise the data packets are likely to "stomp on" the voice packets on the way out. It doesn't help much if the provider prioritizes on their network but you don't at the router.

Then, there's the issue of your existing network. If you expect to have a single Ethernet cable linking your phones and workstations to the rest of your network, you're going to need to prioritize voice over data all the way to the phone. You can do this with VLANs, setting priority for your voice VLAN over the other -- assuming your internal switches and routers can do this. Otherwise, you'll need to run separate Ethernet connections for the phones (time consuming and can be expensive) or ignore priority at the switch (a recipe, again, for problems with the voice being overtaken by the data traffic). You'll want to make sure the IP phones support prioritization as well -- some cheaper ones do not. Keep in mind that this will be an issue whether you go with Asterisk or if you go with a solution hosted by your provider. But you're in IT company -- you guys should eat and breathe this stuff.

To make things really slick, your switches and phones should support power over ethernet, so that you don't have to plug the phones both into the switch and into AC.

Can you pull this off? There's no question. The gear is out there, and a well-designed network can work brilliantly. On the other hand, if you try to shoehorn VoIP on an older network without priority, it can be a disaster. My advice is to continue down the VoIP path -- there are clear advantages in terms of features and price -- but make sure that you're using best practices regarding prioritization and network design.

Also, talk with your provider about the features available on their hosted offer. All VoIP services aren't alike when it comes to available features, and the provider should be able to outline to you exactly what you'll be able to do -- and you should shop around to make sure that either Asterisk or the provider's system will truly fulfill your needs.

Disclaimer: I do VoIP product development for a living, so I'm biased. But I also haven't used a plain-old-telephone-service line at home or the office in over a year, so I eat my own dogfood

Good luck!
posted by eschatfische at 8:16 PM on June 29, 2005

Response by poster: eschatfische: WOW! Thanks. That was an awesome answer, and the reason I love AskMetafilter.

I'm a PHB; we're a small-company-IT services company. We mostly write web-based software for small companies but my clients have been asking me to expand my services into areas that I'm not fully up to speed in. Firewalls, PXE booting thin client linux workstations on PC hardware, DHCP, and DNS caching I can do in my sleep; VoIP and complex networking I'm going to need a few weeks to read on.
posted by SpecialK at 10:21 PM on June 29, 2005