We are currently looking at VoIP for about 70 users. We're getting a bit confused regarding the choice to run a 'converged' network (VoIP running on the same cables and switches as data) versus 'separate' (separate cabling and switches for data and VoIP traffic). We understand the need to use proper gear so that we can manage QoS, VLANs, supply PoE if necessary, etc., although it's fair to say that we don't understand the related details or implications.
We are not doing this ourselves, we just want to do due diligence on vendor recommendations. Naturally, we have different recommendations from different vendors. The vendors are telling us why they think their recommendation is better, but we're having some difficulty putting it all together so that we can choose what's best for us.
Most of our users are connected to the network via 'direct' Ethernet connections. About 15 users are in a separate building supplied by fiber, but they are ultimately on the same network. There is currently no VLAN, but we understand the benefits of VLAN if we decide to go converged (it allows use to go 'separate' without the need for physically separate switches and cables). About 15 of our users are remote workers in various parts of the country and we have another 10 or so road warriors. I don't know if it matters, but all remote staff, most road warriors, and some 'stationary' workers are on Terminal Services and we expect to eventually have about 2/3 of our staff on Terminal Services.
Most of our current concern regarding this is associated with two factors: soft phones and bandwidth to the desktop. As we understand it, opting to use a large number of soft phones requires that we deal with the various convergence issues even if we do have hard phones on a separate network. Is this true? Is it also true that the only sensible way to keep soft phones on a separate network would be to supply each user with 2 network cards?
As far as bandwidth to the desktop, it's our understanding that the standard approach in converged networks is to connect a hard phone to the network then connect the user's computer to the phone. At present we provide gigabit to each user and the cost of phones that can deliver gigabit to the computer is so much higher than 100 mbit that we'd actually be cheaper to run separate networks (assuming most users get hard phones).
There are some things we already know. We know that losing a switch in any configuration of converged will take down both data and voice, but we also know that having a pre-configured spare will keep our downtime to little more than the length of time it takes to troubleshoot and locate the failed device. We know that we have to do a good job of the network to go converged and that we may have to do more than just replace some switches (replacing switches is not really an issue, because that needs to happen anyway for other reasons). We have looked at articles like this and they're helpful as far as understanding general concepts but a bit light on specifics.
Update 1: We're not running a call centre. Based on our telco's reports, we have no blocked calls with 10 lines. Those 10 lines serve about 50 people at our headquarters. I don't remember the line count recommendations (I'm working from home today), but there was certainly no need to increase the number of lines.
Update 2 – query: I haven't seen anyone comment on the implications of the fiber link we run between two buildings. Is that because it has no bearing on the issue? Is it even possible to run separate networks in this case? As far as I can tell, we are multi-mode capable.
Update 3 – Why I chose plz: Every response was very useful, but ultimately, plz led us to consider things that we had not already considered. We have already some of what we learned here to get more information from our vendors. They're coming back with better articulated reasons for their recommendations, so I think we'll be okay now. As it stands now, converged (with VLAN, etc.) looks most likely given our current infrastructure, call volume, and the preference for softphones.
Best Answer
A lot of this depends on the bandwidth that your phone system is going to use - if it's a call center with hundreds of people on the phone simultaneously you'll have a higher need for a separate network than an office of hundreds who just want phones on their desks but aren't heavy users. A conservative (as in, "way more than is really used") estimate is 128kbps per simultaneous call, or 8 calls per megabit, so gigE can do approximately 8000 simultaneous calls (okay, a little less due to overhead, but that's the right order of magnitude). So it's unlikely to be a bottleneck. And as long as you have QoS so that big downloads won't affect your phone traffic you should be fine.
Something you don't address is the Power Over Ethernet (PoE) angle - PoE switches are a significantly more expensive (both to buy and to run) than their non-PoE counterparts. One nice feature of PoE is that a single UPS on the switch keeps all the phones running during a power outage.
What I've done in the past is: run a PoE and a non-PoE port to everyone's desk. The PoE is labeled 'Phone', the non-PoE is 'data'. This preserves data speeds for the user's computer, gets the aforementioned power redundancy for the phone, and allows me to (eventually, if needed) separate out the networks more.
So I guess what I'm saying is: don't bother with 'software' non-convergence, but do bother with separate networks where the hardware matters. If the hardware's going to be the same though (ie. you're running all PoE or all-non-PoE switches) then a converged network should be fine.