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LLDP for Media Endpoint Devices (LLDP-MED) is an extension to LLDP that operates between endpoint devices such as IP phones and network devices such as switches. It specifically provides support for voice over IP (VoIP) applications and provides additional TLVs for capabilities discovery, network policy, Power over Ethernet, inventory management and location information. By default, all LLDP-MED TLVs are enabled.

 

LLDP-MED supports these TLVs:

 

LLDP-MED capabilities TLV

Allows LLDP-MED endpoints to determine the capabilities that the connected device supports and has enabled.

 

Network policy TLV

Allows both network connectivity devices and endpoints to advertise VLAN configurations and associated Layer 2 and Layer 3 attributes for the specific application on that port. For example, the switch can notify a phone of the VLAN number that it should use. The phone can connect to any switch, obtain its VLAN number, and then start communicating with the call control.

 

By defining a network-policy profile TLV, you can create a profile for voice and voice-signalling by specifying the values for VLAN, class of service (CoS), differentiated services code point (DSCP), and tagging mode. These profile attributes are then maintained centrally on the switch and propagated to the phone.

 

Power management TLV

Enables advanced power management between LLDP-MED endpoint and network connectivity devices. Allows switches and phones to convey power information, such as how the device is powered, power priority, and how much power the device needs.

 

LLDP-MED also supports an extended power TLV to advertise fine-grained power requirements, end-point power priority, and end-point and network connectivity-device power status. However, it does not provide for power negotiation between the endpoint and the network connectivity devices.

 

Starting with Cisco IOS Release 12.2(52)SE, when LLDP is enabled and power is applied to a port, the power TLV determines the actual power requirement of the endpoint device so that the system power budget can be adjusted accordingly. The switch processes the requests and either grants or denies power based on the current power budget. If the request is granted, the switch updates the power budget. If the request is denied, the switch turns off power to the port, generates a syslog message, and updates the power budget. If LLDP-MED is disabled or if the endpoint does not support the LLDP-MED power TLV, the initial allocation value (15.4 W) is used throughout the duration of the connection.

 

You can change power settings by entering the power inline { auto [ max max-wattage ] | never | static [ max max-wattage ]} interface configuration command. By default the PoE interface is in auto mode; If no value is specified, the maximum is allowed (15.4 W).

 

Inventory management TLV

Allows an endpoint to send detailed inventory information about itself to the switch, including information hardware revision, firmware version, software version, serial number, manufacturer name, model name, and asset ID TLV.

 

Location TLV

Provides location information from the switch to the endpoint device. The location TLV can send this information:

 

– Civic location information

 

Provides the civic address information and postal information. Examples of civic location information are street address, road name, and postal community name information.

 

– ELIN location information

 

Provides the location information of a caller. The location is determined by the Emergency location identifier number (ELIN), which is a phone number that routes an emergency call to the local public safety answering point (PSAP) and which the PSAP can use to call back the emergency caller.This example shows how to enable a TLV on an interface:

 

Switch# configure terminal

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# lldp med-tlv-select inventory-management

Switch(config-if)# end