Voice VLAN Configuration Guidelines on Ethernet Switches
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Voice VLAN Configuration Guidelines on Ethernet Switches

Posted on by FS.COM

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?

The 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. The 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.

voice vlan configuration example

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. The voice VLAN enables the 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 the 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 a 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 the data VLAN. This is especially effective if you can afford dedicated hardware for the voice devices. However usually, multiple VLANs will be configured on a given data switch, and trunked on the uplinks with 802.1Q. In this case, the voice VLAN can be used for QoS guarantee on IP networks.

Another advantage is that in some circumstances, using a voice VLAN can simplify network configuration. Specifically, marking packets for QoS is easier, as 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 the 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 Switches

Voice 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, perform the voice VLAN configuration command in the chart below:

Command Purpose
Switch#configure terminal Enter the Configure mode
Switch(config)# QoS enable Enable QoS
Switch(config)# vlan database Enter the VLAN database mode
Switch(config-vlan)# vlan 2 Create VLAN 2
Switch(config-vlan)# exit Exit VLAN database mode
Switch(config)# voice vlan 2 Set VLAN 2 as Voice VLAN
Switch(config)# voice vlan mac-address 0055.0000.0000 ffff.ff00.0000 description test Add an OUI entry for Voice VLAN
Switch(config)# interface eth-0-1 Enter the interface mode
Switch(config-if)# switchport mode trunk Set the switching characteristics of this interface to trunk mode
Switch(config-if)# switchport trunk allowed vlan all Set this trunk to allow all VLANs on this interface
Switch(config-if)# voice vlan enable Enable Voice VLAN on eth-0-1
Switch(config-if)# interface eth-0-2 Enter the interface mode
Switch(config-if)# switchport mode trunk Set the switching characteristics of this interface to trunk mode
Switch(config-if)# switchport trunk allowed vlan all Set this trunk allow all VLANs on this interface
Switch(config-if)# replace cos Replace the COS (enabled by default)

Note: 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 List

FS 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.

Switch FS P/N
Gigabit PoE Switches S1130-8T2F, S1250-8T2F, S1400-24T4F, S1600-24T4F, S1600-48T4S
S5800 Series Switches S5800-48F4S, S5800-8TF12S
S5850 Series Switches S5850-48T4Q, S5850-32S2Q, S5850-48S6Q, S5850-48S2Q4C

Conclusion

It is without doubt that voice VLAN is a great feature 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 Layer 3. If your VLANs are trunked all over your premises, then the voice VLAN can be very useful as your voice end-points can potentially be on the same subnet as gateways, proxies, and other voice infrastructures. However, if your VLANs are small and your Layer 3 switching is deployed in the core and distribution layers, then the voice VLAN may not be worth the effort so this needs to be considered.

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