Voice VLAN Configuration Guidelines on Ethernet Switches | ||||||||||||||||||||||||||||||||||||||||
24 Aug 2018 In the IP based Ethernet networks, data and voice services are often transmitted simultaneously over the network. Voice traffic, in particular, requires a higher forwarding priority than data traffic. This can be achieved by configuring a voice VLAN on the data switch to transmit voice packets, and setting QoS (Quality of Service) parameters in the voice VLAN so that voice traffic is given priority when network congestion occurs. This post takes a look at why it makes sense to go for voice VLAN and gives voice VLAN configuration guidelines on Ethernet switches. What Is VLAN and Voice VLAN?VLAN (Virtual Local Area Network) is a switched network that logically segments the network into different broadcast domains so that packets are only switched between ports that are designated for the same VLAN. Voice VLAN is an ingenious feature of VLAN that enables access ports to carry voice traffic from an IP phone. By placing IP phones in one VLAN and the PCs connected to phones in another VLAN, you can more easily manage the IP address space, apply QoS, and provide better security by isolating the data and voice traffic. In voice VLAN, the voice traffic is sensitive to delay and jitter, thus it requires a higher priority than data traffic to reduce the delay and packet loss during transmission. Voice VLAN enables access port of the Ethernet switch to affect the connected devices to a separated logical group. As shown in the figure above, the IP phone tags its own packets with the voice VLAN (VLAN 5). The Ethernet switch reads the tags and then assigns the untagged packets to data VLAN (VLAN 15) you have configured on the switchport for data traffic, which is the so called switchport voice VLAN. How Can We Benefit From Voice VLAN?One main advantage of using voice VLAN is that your VoIP (Voice over Internet Phone) devices do not have to contend directly with all the broadcasts and other traffic from data VLAN. This is especially effective if you can afford dedicated hardware for the voice devices. But usually, multiple VLANs will be configured on a given data switch, and trunked on the uplinks with 802.1Q. In this case, voice VLAN can be used for QoS guarantee on IP networks. Another advantage is that in some circumstances, using voice VLAN can simplify network configuration. Specifically, marking packets for QoS is easier, because you don’t have to specify the various ranges of TCP and UDP ports. All packets from the subnet get priority. Similarly, TFTP and the special DHCP services for VoIP phones are easier to configure when all VoIP phones are in the same subnet. Furthermore, the 802.1p Class of Service (CoS) priority and DSCP (Differentiated Services Code Point) priority is supported in voice VLAN to plan priorities for different voice services. Many vendors on the market supply Ethernet switches for DSCP classification. For instance, FS 48 port Gigabit PoE switch supports adding voice VLAN. This PoE switch is embedded with 802.1p CoS and DSCP classification functions and is widely implemented for VoIP infrastructures. Voice VLAN Configuration Steps on Ethernet SwitchesVoice VLAN configuration can be accomplished either in CLI interface or in Web user interface. Here we take FS S5800-8TF12S 10gbe switch as an example to configure voice VLAN. To create a voice VLAN via CLI interface, just perform the voice VLAN configuration command in the chart below:
Note: Keep in mind that the most vital step of transporting voice traffic across a switched network is to maintain the proper Quality of Service level. Voice packets must be delivered in the most timely manner possible, with minimum jitter, loss, and delay. FS Voice VLAN Enabled Ethernet Switches ListFS provides several types of Ethernet switches supported for voice VLAN. These high performance Ethernet switches are able to configure a dedicated voice VLAN, allowing you to configure separated VLANs on the same port. When the Ethernet switch is connected to an IP phone, the IP phone sends voice traffic and the voice traffic’s COS values is set to 5 by default. As listed in the chart below, voice VLAN can be added on all of FS S5800/S5850 series switches and Gigabit PoE switches.
ConclusionIt is undoubtedly that voice VLAN is a lightspot for VoIP infrastructures and IP based Ethernet networks. Before configuring voice VLAN on your Ethernet switches, remember to figure out whether your core network is Layer 2 or Lay 3. If your VLANs are trunked all over your premises, then the voice VLAN can be pretty attractive because your voice end-points can potentially be on the same subnet as gateways, proxies, and other voice infrastructure. However, if your VLANs are small and Layer 3 switching is deployed in the core and distribution layers, then the voice VLAN may not be worth the effort. |
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