The IEEE 802.1AB standard defines the Link Layer Discovery Protocol
(LLDP). This protocol allows stations residing on an 802 LAN to advertise
major capabilities, physical descriptions, and management information to
physically adjacent devices, allowing a network management system (NMS)
to access and display this information.
The standard is designed to be extensible, providing for the optional
exchange of organizational specific information and data related to other
IEEE standards. The base implementation supports only the required basic
management set of type length values (TLVs).
LLDP is a one-way protocol; there are no request/response sequences.
Information is advertised by stations implementing the transmit function.
The information is received and processed by stations implementing the
receive function. Devices are not required to implement both transmit and
receive functions and each function can be enabled or disabled separately by
the network manager. PowerConnect supports both the transmit and receive
functions in order to support device discovery.
The LLDP component transmit and receive functions can be
enabled/disabled separately per physical port. By default, both transmit and
receive functions are disabled on all ports. The application starts each
transmit and receive state machine appropriately based on the configured
status and operational state of the port.
The transmit function is configurable with respect to packet construction and
timing parameters. The required Chassis ID, Port ID, and Time to Live
(TTL) TLVs are always included in the Link Layer Discovery Protocol Data
Unit (LLDPDU). However, inclusion of the optional TLVs in the
management set is configurable by the administrator. By default, they are not
included. The transmit function extracts the local system information and
builds the LLDPDU based on the specified configuration for the port. In
addition, the administrator has control over timing parameters affecting the
TTL of LLDPDUs and the interval in which they are transmitted.