How to Use a VLAN For Awesome VoIP Packet Prioritization

As use of Voice over Internet Protocol (VoIP) continues to grow at a frenetic pace, new users are frequently surprised by the frequency of problems. Unless the user has more bandwidth than his needs could ever consume, users of Vonage, Skype, Google Voice, as well as users of business-type services like Hosted PBX, Virtual PBX and Hosted VoIP will experience trouble. Experienced and successful VoIP users have learned that with proper planning and care, VoIP does live up to its hype.

Voice prioritization is one of many areas that require a network administrator's attention. Voice prioritization can be handled by the Differentiated Service Code Point (DSCP) field in the network's packets or by segmenting VoIP equipment into a separate VLAN. This article discusses the set-up of VLANs for successful VoIP transmission.

VLANs have several advantages over using only the DSCP field, although they are somewhat more difficult to construct. They can effectively prioritize all of the mission critical VoIP traffic including call signaling. They will also exclude packets generated on computers that use the Expedited Forward (EF) Per Hop Behavior (PHB) of the DSCP field that may compete with mission critical VoIP. Additional advantages include the reduction of broadcast network traffic as well as higher security as other computers in other VLANs will not be able to monitor phone calls.

The network needs a managed Ethernet switch and an Internet router capable of manipulating the DSCP field to successfully implement a VLAN for voice prioritization. In addition, the computer and VoIP endpoint cannot share an IP address which means no softphones. The computer can use the small Ethernet switch on the back of most IP Telephones and share a single Ethernet cable back to the managed switch.

In setting up the VLAN, all computers and non-telephony devices are programmed as members of the default data VLAN. All VoIP telephones should be members of the voice VLAN.

The router is on the edge between the Local Area Network (LAN) and the Internet. Its LAN interface does know which packets are in which VLAN but its Wide Area Network (WAN) interface to the Internet does not. Thus, the edge router must set to 'yes' the EF bits of the DSCP field for all packets in the voice VLAN. It sets all the bits of the DSCP field to 'no' for all traffic in the default or data VLAN.

The edge router's Quality of Service (QoS) capabilities should be enabled for traffic going out to the Internet on its WAN interface. Packets are sent to it with the EF field set to 'yes' for only those that were originally in the voice VLAN. The QoS settings recognize the EF field and prioritizes the voice packets out to the Internet.

For successful implementation of business VoIP services like Hosted PBX and Hosted VoIP, prioritization of voice packets out to the Internet is crucial. Of the two methods for establishing voice priority, VLANs require some extra hardware (managed Ethernet Switches) and a extra programming. However, they can do a superior job by including call signaling in the prioritization queues and excluding any non-mission critical traffic.

Voice prioritization is only one of many areas that require attention. For more information, read "Top 7 Common Causes of VoIP voice Quality Problems." Visit my website to learn how Hosted PBX and Hosted VoIP providers can help your business. You can contact my knowledgeable sales engineers at 866-242-6161.