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Posted: Wed Nov 14, 2007 5:14 pm Post subject: VoIP design problem

I am currently looking to implement a VoIP solution. As it stands right now I am leaning towards the Nortel solution with the CS1000 and SRG's at our remote locations.

My problem is with the connection design of the phones. Right now I have an old Executone system that is running over Cat3, and 70% of my workstations are running on Hubs. So no matter what I have to run cables. I have ordered enough Cat6 to add enough network drops to remove our current hubs.

My original plan was to also run enough cables for the phones, then take my older Cisco switches and run the phones on their own subnet, using a router, or a layer 3 switch to tie the phones back into the data network at the end (firewall / DMZ). I had originally planned on using my older switches because they are 10/100 and I believe they support POE (I have to check on this to make sure). Even if they don't support QoS, I can always configure the QoS at the router because the only traffic will be the VoIP traffic on that subnet. I would then purchase 10/100/1000 switches to run my data network.

Upon talking with the Nortel system engineer, and a Sales engineer they believed the best solution would be to daisy chain the phones to the computers. Meaning I would have just enough drops for the computers, pluging the computers into the phones, and then the phones into the wall. Using the same switches for the data and VoIP networks and just run them on separate VLANs and enable QoS, setting the phones on P1.

No matter what I have to purchase a couple new switches as I don't have enough ports to handle my current setup. I also have to run several thousand feet of cable to get rid of the hubs. So the costs will be about the same either way. Even though it will cost materials and labor running the cables, I wouldn't have to purchase POE gigabit switches.

My logic behind using the old switches and separating the phones from the data was for latency issues, POE (as POE is expensive for gigabit ports), and for a little redundancy. For example if my one of my data switches die, then I don't lose my phones also. Or if one of my phone switches die, then I don't lose my data network. I also would not have to necessarily enable QoS on my data network, at least not set my data traffic to be second to anything.

I'm not really sure now, I am starting to have doubts about my original design. I am rather frugal with my network bandwidth, so there is a possibility that I have gone over board.

What do you dogs think? Any suggestions?

Posted: Sun Nov 18, 2007 1:12 pm Post subject:

Hmmm let me try rephrasing the question.

In your opinion is it better to "daisy chain" the computers to the phones? Meaning I go from the wall to the phone, and then the phone to the computer, using QoS and VLAN's to seperate the traffic.

Or is it better to put the phones on their own separate network with their own separate network drops? Giving a complete separation of service.

Posted: Sun Nov 18, 2007 1:34 pm Post subject:

Skookum wrote:
Hmmm let me try rephrasing the question.

In your opinion is it better to "daisy chain" the computers to the phones? Meaning I go from the wall to the phone, and then the phone to the computer, using QoS and VLAN's to seperate the traffic.

Or is it better to put the phones on their own separate network with their own separate network drops? Giving a complete separation of service.

We just installed a VoIP phone system in Paris. We chose Avaya, by the way, over Cisco (which I have grave technical issues with).

If you consider your phones to be absolutely critical, don't put them on the same LAN as your computers. Remember 64kB/sec is about the top bandwidth of a single phone, so cat 3 (10mb/sec) can probably do the job, but you're likely to have a lot of dropped packets (meaning you will be blamed for the phones sounding like shit).

Best thing to do is get them their own switch. In Cisco-ese, they want to be on their own VLAN.

Guide Dog Joined: 08 Nov 2003 Posts: 8131 Location: MN

EdisonRex wrote:
Skookum wrote:
Hmmm let me try rephrasing the question.

In your opinion is it better to "daisy chain" the computers to the phones? Meaning I go from the wall to the phone, and then the phone to the computer, using QoS and VLAN's to seperate the traffic.

Or is it better to put the phones on their own separate network with their own separate network drops? Giving a complete separation of service.

We just installed a VoIP phone system in Paris. We chose Avaya, by the way, over Cisco (which I have grave technical issues with).

If you consider your phones to be absolutely critical, don't put them on the same LAN as your computers. Remember 64kB/sec is about the top bandwidth of a single phone, so cat 3 (10mb/sec) can probably do the job, but you're likely to have a lot of dropped packets (meaning you will be blamed for the phones sounding like shit).

Best thing to do is get them their own switch. In Cisco-ese, they want to be on their own VLAN.

having seen it done both ways, I must say I've seen some REALLY REALLY slick systems with amazing features that have the phones on the same network as the computers... stablity however, is not a strong point of the systems I'm thinking of. I forget what system they had there, but it was constantly crapping out, and I could hear the dropped packets on the phones... it was bad.

In every place I've worked that has had stable phone systems they used cat 5 or cat 6 and pulled the phones in a different color cable, with different color terminators, and I assume they ran into their own switches on the back end (because the ones closet I was in was like that, and I'd hope for consistency, Though I've given up on expecting it.)

Posted: Sun Nov 18, 2007 5:01 pm Post subject:

I already know that the dBm of the phones on Cat3 will be too much. Right now I have Cat5 in the building and will be running Cat6 over the next couple of weeks.

I will use the old Cat5 for the phones, and the Cat6 for the PCs.

I feel a lot better now, and quite frankly relieved, I was starting to doubt my judgment there for a while when everyone was so adamant about keeping everything on the same switches.

The only thing I have to figure out now is if my Cisco 4000, Cisco 2900 and Cisco 2948G are POE 802.3AF compatable.

Thanks for the help guys, I feel a lot more comfortable moving forward.

Posted: Thu Jan 31, 2008 2:12 am Post subject:

i've seen networks made and designed by csico connecting PCs to phones which are in turn connected to a single switch port.

i think one of voip's advantages is unifying voip and data networks into one to reduce costs and simplify management. having jittery traffic can be fixed by qos as you know, 64kBps + RTP + IP is the max.

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