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The Importance of Voice VLAN in Network Communication

Posted on May 14, 2024 by
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In the exploration of network architectures, VLANs ensure efficient data flow, where FS PoE switches play a crucial role by transmitting data and powering devices like IP phones, thus simplifying network management. These switches support critical features like VLAN and QoS, ensuring high-quality voice communications and reducing clutter by eliminating the need for separate power sources. This article mainly explains the principle of configuring Voice VLAN and its key role in maintaining the quality of IP phone communication in the network architecture.

What is Voice VLAN?

Voice VLAN is a specialized form of VLAN designed specifically for VoIP traffic. It separates voice calls from other internet traffic, making sure that phone calls get through first on the network. This prioritization is critical in maintaining the quality of voice calls and preventing delays, jitter, and packet loss, which can significantly impact call quality.

Automatic Mode and Manual Mode of Voice VLAN

Ports can work in automatic mode or manual mode. In different working modes, the ports join the Voice VLAN in different ways.

  • Automatic mode: When the user's IP phone is started and the outgoing packet passes through a device that supports Voice Virtual Local Area Networks, the device identifies the source MAC address of the packet and matches the OUI address configured on the device. After the OUI address is successfully matched, the device automatically adds the input port of the voice packet to the Voice VLAN, issues a policy, changes the priority of the voice packet to the priority of the voice stream in the Voice Virtual Local Area Networks configured on the device, and uses the aging mechanism to ensure ports within the VLAN are maintained. During the aging time, if the system does not receive any voice packets from the input port, the system will delete the port from the Voice Virtual Local Area Networks.

  • Manual mode: In manual mode, the process of adding a port to the Voice Virtual Local Area Networks or deleting it is manually configured by the administrator. During user IP phone communication, the device identifies the source MAC address of the packet and matches it with the OUI address configured on the device. After the OUI address is successfully matched, a policy is issued to change the priority of the voice packet to the one configured on the device. The priority of voice flows in the Voice Virtual Local Area Networks.

The automatic mode is suitable for PC-IP phone serial access ports, which can transmit voice data and ordinary business data at the same time.

Manual mode is suitable for networking where IP phones are individually connected to the switch and the port only transmits voice packets. This networking method allows the port to be dedicated to transmitting voice data and avoids the impact of business data on voice data transmission.

How the Voice VLAN Port Works With IP Phones

There are generally 2 types of IP phones according to whether or not they automatically obtain an IP address with Voice Virtual Local Area Networks information:

1. A phone that automatically obtains an IP address and Voice Virtual Local Area Networks number. This type of phone can send untagged or tagged voice streams.

2. Manually set the IP address and Voice Virtual Local Area Networks number of the phone. This type of phone can only send tagged voice streams.

When obtaining an IP address automatically, the IP phone can also request Voice VLAN information from the DHCP server at the same time. If the DHCP server returns Voice Virtual Local Area Networks information, the IP phone can directly send a voice stream with a Voice Virtual Local Area Networks tag; if the DHCP server does not return Voice Virtual Local Area Networks information, the IP phone can only send a voice stream without a VLAN tag.

Voice VLAN Ports

If the IP phone supports manual setting of IP address and Voice Virtual Local Area Networks number, the user can also manually set the IP address and set the Voice Virtual Local Area Networks information on the IP phone, and the IP phone will send out tagged and untagged voice streams according to the user's configuration.

  • Voice VLAN Ports and IP Phones Sending Tagged Voice Streams

When an IP phone sends a tagged voice stream, the IP phone must have already obtained the Voice Virtual Local Area Networks information through automatic acquisition or manual configuration. In this case, different types of ports need to be configured accordingly to enable normal transmission of voice messages in the Voice Virtual Local Area Networks without affecting the switch's forwarding processing of ordinary service data. Unlike IP phones that automatically acquire Voice Virtual Local Area Networks information, IP phones that are manually configured for Voice Virtual Local Area Networks will always send and receive voice streams with Voice Virtual Local Area Networks Tag.

  • Voice VLAN Ports and IP Phones Sending Untagged Voice Streams

IP phones will send and receive untagged voice streams in the following two situations:

1. An IP address is acquired automatically, but no Voice Virtual Local Area Networks information is acquired.

2. The IP address is manually configured, but no Voice Virtual Local Area Networks information is configured.

If the IP phone sends untagged voice streams, the user needs to configure the default VLAN of the receiving port and allow the pass-through of the default VLAN, and must configure the default VLAN of the port as Voice Virtual Local Area Networks in order to transmit the voice streams in the Voice Virtual Local Area Networks, and at this time, the Voice Virtual Local Area Networks working mode of the port can only be manual mode.

Secure Mode for Voice VLAN

To better separate the transmission of user voice streams from data streams, Voice Virtual Local Area Networks provides the secure mode function. When the secure mode is on, Voice Virtual Local Area Networks allows only voice streams to be transmitted, and the device checks the source MAC address of the message and allows the message to be transmitted within Voice Virtual Local Area Networks when the source MAC address of the message is a recognizable Voice Virtual Local Area Networks OUI address; otherwise, the message is discarded. When the security mode is off, the source MAC address of the message is not checked, and all messages are allowed to be transmitted within the Voice Virtual Local Area Networks.

The Principle of Configuring Voice VLAN and Overall Implementation

Devices that support the Voice Virtual Local Area Networks function limit data flows and voice flows to the data VLAN and Voice Virtual Local Area Networks respectively, thereby ensuring that voice calls and business packets do not affect each other. At the same time, a priority policy is issued to increase the priority of the voice stream and ensure call quality. Its basic working method is as follows:

  • In the first step, the user creates a dedicated VLAN for transmitting voice packets on the device, that is, the Voice Virtual Local Area Networks, and enables the Voice Virtual Local Area Networks function of the port connected to the IP phone.

  • The second critical step involves adding the port to the Voice VLAN, which varies by the port's mode—automatic or manual: In automatic mode when the device receives a packet from this port, it will match its source MAC address with the legal OUI address. If the source MAC is an OUI address, the packet is considered to be a voice packet. The device automatically adds the port to the Voice VLAN and learns the MAC address on the port. In manual mode, the user manually configures the port connected to the IP phone to be added to the Voice Virtual Local Area Networks.

  • In the third step, whether in automatic mode or manual mode, when the port joins the Voice Virtual Local Area Networks, the device will deliver a policy to increase the priority of all packets passing the Voice Virtual Local Area Networks whose source MAC matches the OUI. Set the priority of voice packets that can match the OUI address to cos=6, dscp=46.

Conclusion

In conclusion, the article elaborately discusses the critical role of Voice VLANs in maintaining the superior quality of voice communications across network architectures, specifically in the context of IP telephony. The overarching narrative underscores the importance of integrating advanced networking hardware and carefully planning network configurations to uphold high standards of voice communication. This essence of strategic network design and implementation serves as a cornerstone for businesses aiming to leverage Voice VLANs for superior voice communication performance.

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