Lldp-Med Overview - ZyXEL Communications MGS3520 Series User Manual

Chapter 36 Link Layer Discovery Protocol (LLDP)
Figure 179 LLDP Overview

36.2 LLDP-MED Overview

LLDP-MED (Link Layer Discovery Protocol for Media Endpoint Devices) is an extension to the
standard LLDP developed by the Telecommunications Industry Association (TIA) TR-41.4
subcommittee which defines the enhanced discovery capabilities, such as VoIP applications, to
enable network administrators manage their network topology application more efficiently. Unlike
the traditional LLDP, which has some limitations when handling multiple application devices, the
LLDP-MED offers display of accurate physical topology, interoperability of devices, and easy trouble
shooting for misconfigured IP addresses. There are three classes of endpoint devices that the LLDP-
MED supports:
Class I: IP Communications Controllers or other communication related servers
Class II: Voice Gateways, Conference Bridges or Media Servers
Class III: IP-Phones, PC-based Softphones, End user Communication Appliances supporting IP
Media
The following figure shows that with the LLDP-MED, network connectivity devices (NCD) like
Switches and Routers will transmit LLDP TLV to endpoint device (ED) like IP Phone first (1), to get
its device type and capabilities information, then it will receive that information in LLDP-MED TLV
back from endpoint devices (2), after that the network connectivity devices will transmit LLDP-MED
TLV (3) to provision the endpoint device to such that the endpoint device's network policy and
location identification information is updated. Since LLDPDU updates status and configuration
information periodically, network managers may check the result of provision via remote status.
The remote status is updated by receiving LLDP-MED TLVs from endpoint devices.
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