1         Overview

As the voice over IP (VoIP) service becomes more popular, voice data and non-voice data are usually transmitted on the same network. Voice data must have a higher priority than other service data to minimize the delay and jitter during transmission.

2         Concepts

2.1         VoIP

Voice over Internet Protocol (VoIP) compresses and encapsulates ***og signals into packets, and then transmits packets over the IP network. Voice data can be transmitted over the Internet, enterprise intranet, and local area networks using VoIP.

Compared with transmitting voice data over the point-to-point connections on ISPs' networks, using VoIP is more cost-effective.

2.2         OUI Address

An Organizationally Unique Identifier (OUI) is the first 24 bits of a MAC address. It is a unique identifier assigned by Institute of Electrical and Electronics Engineers (IEEE) to a device vendor. 

Generally, IEEE allocates the first 24 bits, that is, a MAC address segment, to each vendor. Then the vendor allocates MAC addresses from the MAC address segment to their devices. Therefore, the IP phones can be identified by OUIs. That is, network devices know which packets are sent from IP phones based on the MAC address segments allocated to the IP phone vendors. These packets from IP phones are voice packets.

The operators can manually set OUIs using masks and specify the mask length.

OUIs commonly used by IP phone vendors are:

2.3         802.1Q

802.1Q defined the format of a VLAN tag:

A VLAN tag contains two bytes (16 bits). The VLAN ID occupies 12 bits, PRI occupies 3 bits (PRI is also called COS or 802.1p field), and CFI occupies 1 bit. Depending on the usage of VLAN tags, packets are classified into three types.

The IP phones may send tagged packets, untagged packets, and tagged packets with VLAN ID 0. The CoS value of voice packets should be higher than the priorities of other packets to ensure preferred forwarding of voice packets. Generally, voice packets have a CoS value of 5. The CoS value of tagged packets sent by the IP phones from most mainstream vendors is 5 by default. However, some IP phones set CoS values in voice packets to other values, for example, 0. IP phones may send the following five types of packets. When a Huawei switch receives a tagged packet with priority 0, it treats it as an untagged packet. That is, the interface that receives the packet adds a VLAN tag containing the PVID to the packet.

2.4      DSCP

Differentiated Services Code Point (DSCP) is a QoS standard released by IETF in December, 1998. DSCP occupies 6 bits, and its value ranges from 0 to 63.

DSCP uses the 6 bits in the ToS field of IP headers to allocate service classes and priorities, thus ensuring quality of communication, as shown in the figure:

2.5         Voice VLAN

A VLAN assigned to voice packets is called voice VLAN.

Huawei switches can only specify VLANs as voice VLANs, but cannot assign voice VLANs to IP phones unless the switches use the protocols such as LLDP and DHCP.

3         IP Phone Deployment

An IP phone provides two ports, one connected to the upstream switch and the other connected to PCs. There are two methods to deploy IP phones:

l  Connect a PC to an IP phone.

Advantage: Only one port on the switch is occupied. That is, one network port provides both voice and data services.

l  An IP phone and a PC connect to the switch independently.

Advantage: The voice flows and data flows are separated, facilitating service management and maintenance.

A Huawei switch provides the following deployment methods.

Example for Connecting an S Series Switch to an IP Phone Using LLDP

3.1         LLDP Overview

The Link Layer Discovery Protocol (LLDP) is a standard data link discovery protocol defined in IEEE 802.1ab.

If an IP phone (for example, from Huawei or Polycom) supports LLDP, the switch assigns a VLAN ID to the IP phone using the MED TLV field.

3.2         Applicable Version and Model

In this document, V200R006C00 is used as an example. The version differences will be described in section 3.8 Summary.

3.3         Networking Requirement

Data flows of the High Speed Internet (HSI), Voice over IP (VoIP), and Internet Protocol Television (IPTV) services are transmitted on a network. Users require high quality of the VoIP service. Therefore, voice flows must be transmitted with a high priority. If the IP phone supports LLDP and has a high 802.1p priority (for example, 5), you can configure LLDP and voice VLAN on the switch. Then the switch uses the LLDP protocol to deliver the voice VLAN ID to the IP phone and does not change the packet priority.

As shown in the following figure, the IP phone obtains voice VLAN ID using LLDP. In this example, a port on the switch needs to transmit both voice and data flows.

3.4         Data Plan

VLAN plan: Voice flows (VoIP) are transmitted in VLAN 300 and data flows (HIS and IPTV) are transmitted in VLAN 500.

3.5         Configuration Roadmap

The configuration roadmap is as follows:

l  Create VLANs for voice and data flows.

l  Enable LLDP globally to assign voice VLAN to the IP phone.

l  Configure the interface to trust the packet priority.

3.6         Procedure

Step 1: Create VLANs for voice and data flows.

Step 2: Set the interface type and PVID to forward data flows. Add the interface to voice VLAN 300.

Step 3: Enable LLDP globally to assign voice VLAN ID to the IP phone.

Step 4: Set the trusted 802.1p value so that the interface does not change the 802.1p value in packets.

(Optional) Step 5: Configure the switch to be compatible with Cisco IP phones so that the switch can assign voice VLAN ID to Cisco IP phones. If you use the IP phones from other vendors, skip this step.

Step 6: Specify the VLANs from which the voice and data packets are transparently transmitted by the upstream interface.

Step 7: Verify the configuration.

l  Run the display lldp local interface GigabitEthernet 0/0/1 | include Media policy VlanID command to check whether the voice VLAN ID obtained using LLDP is correct.

l  The IP phone can connect to the switch. The VLAN ID in the MAC address entry of the IP phone is 300. This indicates that the IP phone communicates with the switch through VLAN 300.

3.7         Configuration Files

3.8         Summary

l  The lldp tlv-enable med-tlv network-policy voice-vlan vlan 300 and lldp compliance cdp txrx commands apply to V200R001C00 and later versions. In the versions earlier than V200R001C00, use voice VLAN.

l  Set the link type of the interface. The default value varies depending on switch's software versions. It is recommended that you set it to Hybrid manually.

l  Enable the forwarding of BPDU packets using the bpdu enable command because the LLDP packets are BPDU packets. In V100R006 and later versions, the forwarding of BPDU is enabled by default.

★★★Summary★★★ All About Huawei Switch Features and Configurations