Training:Verify Network

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Confirming the network is optimized for voice

Voice over IP is already widespread in enterprise networks and is growing in public switched voice networks as carriers migrate from TDM to VoIP.

A network that appears to function adequately without voice can give the impression that there are no underlying network problems. Users become accustomed to using what they have and assume that the network is functioning well. In reality there can be issues that are unknown until packet transmission of voice is introduced. For instance if an email arrives a few seconds late it is not obvious to users that there is a delay in the network. However a few seconds in a voice transmission is unacceptable. It stands to reason that the cause of the delay in email may go unresolved without raising any noticeable performance lag to users. However, such a condition must be resolved in a voice network.

Quality of Service (QOS) is a mechanism to assure that voice packets have priority over other data packets.

There are basic steps that should be taken to optimize a network for voice traffic.

  1. The Switches should be managed switches that support QOS. Recommendations:
    1. QOS capable data switches (QOS settings are configured in the Smart Switch)
    2. POE data switches are highly recommended in VoIP applications
    3. UPS is highly recommended
      Note: backing up the POE extends power to telephones during a power outage.
  2. The entire network infrastructure should be at minimum Certified CAT 5e
  3. If item 2 is not met upon inspection, you should consider to be prepared to quote for wiring and equipment to get the infrastructure of the network to this status.
  4. Make certain that your quote covers your costs and expenses and labor. It is always best to do this before any new IP PBX is placed on the network so that you can be confident of the network and its ability to carry voice traffic.
  5. Consider a network analysis to analyze the Network for possible pitfalls. MicroConvergent is a good option.
  6. If you are not the manager of this DATA network then you should develop a good relationship with the IT management team for this network as their assistance will prove invaluable to you.
  7. After the network is certified for voice, you should test it.
    1. Certified Category 5 cabling
    2. Smart Data Switches with QOS enabled and configured
    3. Recommended use of POE
    4. For applications for Remote Phones the Router must be capable of supporting multiple NAT sessions (see IPitomy’s list of known performing routers) 
  8. It is also recommended that you certify the bandwidth is appropriate for what is required for remote users and SIP Trunks. Technically using the standard G.711 CODEC each voice conversation uses 64kbs send 64kbs receive. With SIP overhead this is increased to approximately 80kbs. To simplify calculations we recommend using a round number of 200Kb (kilo bits) of symmetrical bandwidth for each concurrent voice call. (100Kb Send/100Kb Receive)
    1. Most data connections are asymmetrical – meaning that there is a difference in speed upload versus download. Usually expressed as 10Dn/5Up… the VoIP connection can be no greater than the lesser bandwidth rate.
    2. Keep in mind that some connections fluctuate at times during the day and your connection will only ever be as good as the weakest link.
    3. Always recommend proper equipment for the job to avoid the pitfalls and traps of old existing Networks with aging performance issues.
    4. If the DATA Network is managed by another team you should provide them with a checklist and a proof of assurance document that they may sign off on which provides you with verification that your requirements for the Voice network are in fact being met. Any changes to meet the requirements must be completed before the day of installation without incurring additional labors costs.


  1. IP Address of the IP PBX is identified and verified available (Ping IP PBX IP Address to assure that no device is using the address.)
  2. Establish IP Address range for DHCP use
  3. Disclose any Static IP Addresses currently in use.
  4. POE capable, QOS capable Switch(es)
  5. For applications with Remote Phones - Router capable of multiple NAT sessions (use).
  6. Ports in router forwarded to PBX for remote phones (5060, 10,000 – 20,000)
  7. Ports in router forwarded to the PBX for remote maintenance (Port 80)
  8. Ports in router forwarded to the PBX for Branch Office use (Port 4569)
  9. Ports in router forwarded to the PBX for Factory support access (Port 22)

The prior analysis provided in the outline above will best assure that you have a successful and prosperous IPitomy install. It also outlines a means of successful integration and a continuing good working relationship with existing IT personnel.