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LLDP

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LLDP (Link Layer Discovery Protocol) allows Ethernet network devices to receive and/or transmit device-related information to directly connected devices on the network that are also using the protocol, and store the information that is learned about other devices. Information gathered with LLDP is stored in the device as a management information database (MIB) and can be queried with the Simple Network Management Protocol (SNMP) as specified in RFC 2922. LLDP transmits information as packets called LLDP Data Units (LLDPDUs). An LLDPDU consists of a set of Type-Length- Value (TLV) elements, each of which contains a particular type of information about the device or port transmitting it.

Each of the TLV components has the following basic structure:

• LLDP supports advertising the following TLVs:
  

  • Mandatory LLDP TLVs: Chassis ID, Port ID, and Time to Live (TTL) are included in an LLDPDU by default.

  • Optional LLDP TLVs: System Name, System Description and so on, the phone sends the optional TLVs along with the mandatory TLVs in an LLDPDU.

  • Organizationally Specific TLVs: MAC/PHY Configuration/Status and Port VLAN ID, which are defined in IEEE Standard 802.3 and 802.1 respectively. 

  • The LLDP frame ends with a special TLV, named end of LLDPDU in which both the type and length fields are 0.
    

• LLDP -MED

  • LLDP -MED (Media Endpoint Discovery) is published by the Telecommunications Industry Association (TIA). It is an extension to LLDP that operates between endpoint devices and network connectivity devices. LLDP -MED specifically provides support for voice over

  • IP (VoIP) applications and provides the following capabilities:

    • Capabilities Discovery—allows LLDP -MED endpoints to determine the capabilities that the connected device supports and has enabled. It can be used to indicate whether the connected device is a phone, a switch, a repeater, etc.

    • Voice VLAN Configuration—provides a mechanism for a switch to notify a device which VLAN to use, which enables ―plug and play‖ networking.

    • Power Management—provides information related to how the device is powered, power priority, and how much power the device needs.

    • Inventory Management—provides a means to manage device and the attributes of the device such as model number, serial number, software revision, etc.

    • Location Identification Discovery—provides location information from the switch to the device when making an emergency call.
       

• In addition to the TLVs advertised by LLDP, LLDP -MED also supports advertising the following TLVs:

  • It should be noted that either LLDP or LLDP -MED—but not both—can be used at any given time on an interface between two devices

    • LLDP -MED capabilities TLV

    • Network policy TLV

    • Power management TLV

    • Inventory management TLV

    • Location identification TLV (not supported by IP phones)
       

• LLDP Feature on Sangoma IP Phones

  • LLDP provides exceptional interoperability benefits, IP telephony troubleshooting, automatic deployment of policies and advanced PoE (Power over Ethernet). When LLDP feature is enabled on IP phones, the IP phones periodically advertise their own information to the directly connected LLDP -enabled switch. The IP phones can also receive LLDP packets from the connected switch. When the application type is “voice”, IP phones decide whether to update the VLAN configurations obtained from the LLDP packets. When the VLAN configurations on the IP phones are different from the ones sent by the switch, the IP phones perform an update and reboot. This allows IP phones to be plugged into any switch, obtain their VLAN IDs, and then start communications with the call control.
     

• Supported TLVS of IP Phones

  • TLVs supported by IP phones are summarized in the following table:

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