Vswitch voice vlan Analysis

The so-called voice vlan identifies a packet as a voice packet, and the packet carries the voice data. In networks where voice messages and data packets coexist, vlan-based voice packets are identified to distinguish voice messages and data packets, and a higher priority is given to voice packets to ensure that voice data is preferentially served, low latency and low packet loss rate.

Networking scenario:

Generally, a voice device (usually an ip Phone) has two Ethernet interfaces. An Ethernet interface of an ip Phone connects to the Ethernet interface of the access switch, another Ethernet interface of the ip Phone connects to the computer's Ethernet interface. In this way, the same interface of the vswitch has both the voice packets of the ip phone and the data packets of the computer.

In another case, the ip phone and computer are connected to the same hub, and the hub is connected to the switch. But now the interactive Ethernet switch is very cheap. You can buy 20 or 30 vswitches with five ports. There is no need to use a hub to expand Ethernet. Basically, no hub is available on the market.

If the computer and ip phone are connected to different interfaces of the switch, in principle, the voice packet can be identified based on the port, and the PVID of the port is used to tag the packet and mark it with a higher priority. However, the voice tag method described below is flexible. At the same time, ip phones and computers are often together (on the office space), while switches are at a certain distance from the office space, which is a waste of wiring resources and switch interface resources.

How to determine the voice vlan:

Currently, there are two methods to tag voice.

1. Voice devices supporting tags, such

Tags are supported for packets sent/received by ip phones, so that the voice device attaches a voice tag to the packets when sending messages. After the switch receives the packet, it compares the vlan configured by the packet with the voice vlan configured by the interface. If the packet vlan is a voice vlan, the packet is given a higher priority and then forwarded. So how does the ip phone know what tag should be added to the sent packet so that the vlan of the packet is the voice vlan configured for the interface connected to it? This is achieved through the LLDP protocol. The ip phone communicates with the switch through LLDP. The switch sends the voice vlan of the interface to the ip Phone through LLDP protocol.

2. Speech devices that do not support tags, such as Huawei's EchoLife ET65

The packets sent/received by the ip Phone do not contain tags. In this case, the OUI field of the mac address of the ip phone is used to identify the packets. In fact, vlan is divided based on the mac address. Because the mac address of the device is determined when the device leaves the factory, the OUI field is allocated to a vendor, then, based on the OUI field of the source MAC address of the packet, we can know that the packet is generated by the ip phone of the vendor. After the switch receives the packet, based on the OUI of the MAC address of the source packet, vlan the packet and a higher priority is assigned to it.

Default voice vlan OUI address configured on the H3C Switch

Serial number

OUI address

Manufacturer

1

0003-6b00-0000

Cisco phone

2

000f-e200-0000

H3C aolympus NK phone

3

00d0-1e00-0000

Pingtel phone

4

00e0-7500-0000

Polycom phone

5

00e0-bb00-0000

3Com phone