Basic VoIP network design

For small business VoIP installations a good basic network design can help prevent unwanted VoIP quality issues.  Voice traffic starts on the local VoIP network and any steps that can be taken at the start to make a better VoIP LAN network can have a positive impact on your overall satisfaction.  The following suggestions are good standard practices when deploying a VoIP network.  The basic structure of your Local Area Network will go a long way in eliminating potential issues that will affect both voice quality and other signaling issues that could result from a poorly thought out design. 

Good VoIP network rules

Look at the following:

• Make sure your cabling and infrastructure are up to standards.  Old problematic cabling will be a disaster for VoIP.  If new cables are being run, the best installations would be to have a totally separate physical line for each IP phone.
• Eliminate any additional hops by removing extra pieces of hardware between the phones and the outbound gateway.  These would include any additional switches and/or routers, etc.
• Setting up a VLAN for the voice side will keep it segregated and away from the data traffic.  VLANs make allocating bandwidth to voice more manageable. 
• Set QoS for VoIP, including both the signaling SIP protocols and the RTP voice ports.

Along with good basic network design for VoIP, equipment (hardware) should be robust enough to handle the capacity.  Capacity is most often thought of as bandwidth, and although having sufficient bandwidth is essential, any limiting point on the LAN can add latency and jitter, both of which can quickly degrade voice quality.  If a router or firewall cannot pass the number of packets presented without delay, latency will be added to the voice traffic which can result is quality issues, especially if packet discards result. 

• Deploy hardware (switches, firewalls and routers) that have capacities (packets per second) that exceed your LANs needs.  Bottlenecks can quickly become problem sources if pushed beyond their capacity and packet discards occur.
• Hardware should be in good condition.  Faulty hardware can cause periodic packet loss.
• Faulty routing and other mis-configurations can impact VoIP.
• Use a UPS for equipment, especially routers and switches, and make sure that proper grounding is in place.

The Local Area Network (LAN) needs to maintain good throughput because any delay caused by congestion within the LAN will cause call quality issues such as choppy voice or dropped audio.  Given that a majority of call quality issues are caused by existing issues in the LAN it is important to verify that all switches, routers, firewalls and cabling be able to support the amount of voice traffic without additional latency.