Question : Advice for new company network with DSL, VoIP, QoS

I am designing a network for a small company that wants to use a hosted IP Centrex solution.  There will be five Polycom or Cisco SIP phones growing to fifteen in two years.  Computers will be doing word processing other office apps.  Basic email; nothing consistently bandwidth intensive.

My plan was to use a managed switch to prioritize the voice packets over others to improve QoS.  I have been advised that Edgewater Technologies has devices created specifically for this task.  What I wonder is whether I can accomplish the same thing with a managed switch or Sonicwall.

The internet connection will be a Verizon Business DSL with 4mbps down and 768K up.  I would upgrade to a T1 when the office has ten people, since I need 60K per phone.

Having never done this, I would appreciate advice from any of you who have installed a hosted VoIP installation.

Thanks.

Answer : Advice for new company network with DSL, VoIP, QoS

First and foremost you need to define which codec you will be using. The codec is the compresion method that the VoIP protocol is using. Depending on codec choice and other factors such as VPN, encryption methods and QoS, the packet size per phone call can be as high as 120K.

Here is a few links to help understand

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml
http://www.packetizer.com/voip/diagnostics/bandcalc.html

As grblades mentioned the contention point is the WAN not the LAN. There is one product that I have used often called Packeteer that does a great job of traffic shapping.

Few things on the DSL, DSL lines depending on the area and such can have probelms staying active. Yes you may have an SLA but I am sure it is not 100 percent uptime. So what I would recommend is check to see you distance from the Central Office, if you are in the marginal range of the flavor of DSl being provided, I would consider an addtional Internet connection as backup. Also you want to make sure the Internet connection is capable of supporting good voice quality (jitter is the main culprit of poor voice quality)

http://www.testyourvoip.com/

Another route to take if the Internet connection is not up to par, is use a local IP PBX (Asterisk Business Class Version such as www.convergencecenter.com) and use a VoIP provider such as Packet8, Iconnecthere, Broadvoice to deliver the cost savings of VoIP and a single network for Voice and Data.

Kindest reagrds,

Joel_Sisko