Overview of Interoperation Between Switches and IP Phones

Created Feb 28, 2019 14:19:39 11 0 0 0

Basic Concepts

Currently, the switch identifies voice traffic through MAC addresses or voice VLAN IDs of IP phones. Before introducing the IP phone interoperation solutions, you need to understand the following basic concepts:

  • OUI

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

    Each device vendor needs to request a MAC address from the IEEE. Generally, the IEEE allocates a 24-bit address segment, from which a device vendor allocates addresses. During packet forwarding, a switch can identify voice devices based on OUIs and then can determine voice packets.

  • Voice VLAN

    A voice VLAN is used to forward voice packets. A Huawei switch only allows a VLAN to be specified as a voice VLAN, but cannot allocate the voice VLAN ID to voice devices. Protocols such as LLDP and DHCP need to be used to allocate a specified voice VLAN ID to voice devices.

  • VLAN Tag

    802.1Q defines the format of a VLAN tag.
    imgDownload?uuid=d42b8b26c0dd43ba851abc3

    A VLAN tag consists of 16 bits. The PRI (also called CoS or 802.1p priority) occupies 3 bits, CFI occupies 1 bit, and VID occupies 12 bits.

    Packet types are defined based on VLAN tags as follows:
    1. Untagged packets: Packets do not carry VLAN tags.
    2. Packets tagged with VLAN 0: Packets carry tags with VLAN 0.
    3. Tagged packets: Packets carry non-0 tags.

    A high priority specified by the CoS value (usually 5) needs to be set for voice packets so that they can be forwarded preferentially. Generally, IP phones of mainstream vendors (for example, Cisco 7962) send tagged voice packets in which the default CoS value is 5. There are many types of IP phones, and CoS values of some IP phones cannot be set to 5.

    The method for connecting IP phones to switches varies according to the VLAN tags of packets and the configured CoS values. The following table lists the categories of packets sent by IP phones.Table 2-1  Categories of packets sent by IP phones

    No.

    Packet Characteristics

    Description

    1

    The packets carry VLAN tags in which the CoS value is 5.

    After IP phones connect to a switch, the priority of packets does not need to be increased.

    2

    The packets carry VLAN tags in which the CoS value is 0.

    After IP phones connect to a switch, the switch needs to identify the priority of packets and increase the packet priority.

    3

    The packets carry VLAN tags in which the VLAN ID is 0 and the CoS value is 5.

    After IP phones connect to a switch, the switch needs to identify voice packets based on the OUI, add the voice VLAN ID, and the priority of packets does not need to be increased.

    4

    The packets carry VLAN tags in which the VLAN ID is 0 and the CoS value is 0.

    After IP phones connect to a switch, the switch needs to identify voice packets based on the OUI, add the voice VLAN ID, and set a high priority.

    5

    The packets do not carry VLAN tags.

    After IP phones connect to a switch, the switch needs to identify voice packets based on the OUI, add the voice VLAN ID, and set a high priority.

    imgDownload?uuid=694008b6fa5a449e91d1f4b NOTE:A Huawei switch processes packets tagged with VLAN 0 in the same manner as untagged packets; that is, an interface adds the VLAN tag specified by the PVID to the packets. For voice packets, the switch needs to identify them based on the OUI and add the voice VLAN ID to the voice packets so that the voice packets can be forwarded in the voice VLAN.

Physical Connection of an IP Phone for Interworking

Cisco 7962 is used as an example. Figure 2-1 shows the internal structure of the IP phone. The IP phone integrates a three-port switching chip:

  • P1 port connects to an uplink switch or another data communication device.
  • P2 connects to the internal ASIC to transmit voice traffic.
  • P3 connects to a PC or another data communication device.

Figure 2-1  Internal structure of the IP phone 
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In Figure 2-1, the IP phone provides two interfaces to connect to an uplink switch and a PC, respectively. When the IP phone and PC are deployed simultaneously, there are two methods:

  • The downstream PC connects to the IP phone, as shown in Figure 2-2. Only one interface on a switch is occupied. That is, one network interface provides both voice and data services.Figure 2-2  Connecting a downstream PC to an IP phone 
    imgDownload?uuid=f60fb99e0250445f9e33a1e
  • The PC and IP phone connect to the switch separately, as shown in Figure 2-3. Voice and data flows are deployed separately, facilitating management and maintenance.Figure 2-3  Connecting the PC and IP phone to the switch separately 
    imgDownload?uuid=09123ae382ee4eaaaed69ef

See more please click 

https://support.huawei.com/enterprise/en/doc/EDOC1000069520/9aadccc0/comprehensive-configuration-examples


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