Setup Network for Voip

Posted on 2014-01-05
Last Modified: 2014-01-15
Hello.  Recently implemented a voip PBX and am having poor performance.  Have not implemented any QoS or VLans.
Have Comcast for out ISP with mid tier which is about 50/20.
Have plenty of switches at my disposal.  several Procurve 2924s and one 5406zl.  All support POE.
I am not an IT professional.  Just manage the best I can.  Have the ability to set Vlan tags and do most configuration changes if I know what to do.  The last time I tried Vlans, I found it cumbersome and problematice with DHCP, DNS and the few locations where the phone shares the same connection for both the phones and the PC.
My Question.
Given that we are a small shop with plenty of hardware.  Can anyone provide me some recommendations that do not require an in-depth study of SIP and networking.  Just want to phones to work.

My only other option is to segment the entire network physically and put the phones on a different subnet.  Do not like the idea of maintaining two DCHP servers.  DNS is not a big problem.  To manage the PBX have planned to configure two NIC.  one to manage it from the regualr network and the other with no gateway for the Voip network.

Any recommendations will be a big help.
Question by:kbettencourt
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LVL 25

Accepted Solution

Ken Boone earned 225 total points
ID: 39758386
So basically you need a vlan for the PCs and a vlan for the PBX and phones.  You only need 1 DHCP server to accommodate that.  DHCP requests are normally sent as broadcast traffic which means it will not pass beyond a router.  So If your DHCP server is on your PC vlan, the PCs send out a broadcast and receive the DHCP info from the server - no problem.  The phones on the other would not normally get the DHCP info from the server because they are on a different layer 3 network (layer 2 vlan with different layer 3 IP network on top)  So to resolve this issue, routers can act as DHCP relay agents.  So when the phone sends out a DHCP request, the router which would not normally do anything with a DHCP broadcast traffic will forward that request on to the DHCP server.  This way the request gets to the DHCP server.  The dhcp server knows who sent the request by the information that was provided from the DHCP relay agent (the router)  Now this is something that you would have to configure, but in most equipment the statement is something like this:  ip helper-address x.x.x.x   On the DHCP server just create a new scope with the appropriate layer 3 information for the phone network.  That takes care of the DHCP issue - 1 server does it all. No problems this is very very standard.

So far what I have described assumes that a PC is in a port with its vlan and the Phone is in a port with its vlan.  Now you have the scenario where you have a PC plugged into the back of a phone.  - Now the port where the phone is connected to needs to be configured as a trunk port carrying both the voice and data vlan, with the data vlan being the native (or untagged) vlan on that port.  That is how the switch port would need to be configured.

Now in order for the phone to know what vlan its in is yet another piece of the puzzle.  There are many different ways that manufacturers do this.  You didn't mention what phone system you were using, but some of the methods include using LLDP to provide information to the phone, hardcoding the vlan and qos tags on the phone, or using DHCP options to provide the vlan and qos tags to the phone.  You will need to check with your phone manufacturer to find out how this needs to be done for your particular phone system.

Now QoS has been addressed partially in that you have separated your voice from your data traffic by putting the voice in a separate vlan.  So if you have a broadcast storm on your data network, the phones are protected - however, if you have trunks between switches, you can still overrun the trunk port.  This is where you will need to configure qos in your switches to give the voice traffic priority.  Again, most manufacturers have the qos settings already set on the phone, and you just need to configure your switch to give priority to the voice packets.  If traffic will be going over an MPLS backbone or something like that then you will need to implement QoS at yet a different level within the routers.  Not sure if that applies to you though.

Hope this rough overview helps.

Author Comment

ID: 39759045
It does actually.  I'll give this a try next weekend.
From what I am gathering it will not be necessary to have a separate subnet because the vlan is already separating the traffic.  Is that correct?
As for the pix we are using 3cx with Yealink phones.  
Having the DHCP server provide the vlan setup for the phones sounds great.  If that works will same a lot of time as opposed to setting each phone up manually.
LVL 25

Expert Comment

by:Ken Boone
ID: 39759505
Each vlan will require its own unique ip subnet.

Author Comment

ID: 39769782
The explanation does explain a few things.  I received this from procurve support.
However, in a much more simple configuration, if you were only going to have phones connected to certain ports, and these would only have phones connected and would not change, then you can simply set the port priority on all those ports to a higher level than the data ports.  The priority is a numeric value from 0 to 7, with seven being the highest.
An example of setting up a single port would be as follows, in this example I used port 10:
HPALF2848-1# configure
HPALF2848-1(config)# int 10
HPALF2848-1(eth-10)# qos priority 7
So at this point port 10 would have a qos priority of 7, which is the highest, and receive the most attention.  Any ports that had the same qos priority setting would receive the highest priority, while any other ports would receive normal priority.
The down side is you would have to individually configure each port manually, rather than setting on a vlan.
This sounds simple and I am trying to implement this now.
Aside from the stated downside of configuring port individually, are there any others?
LVL 25

Expert Comment

by:Ken Boone
ID: 39769869
No thats the main thing.  Static port assignments and the fact that now you need switch ports for all locations 1 for PC and 1 for phone.

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