B-30
Appendix B: Glossary
Line The hardware that connects two devices. Materials for lines include fiber
optic, coaxial, and phone-grade twisted pair cables.
LLC/SNAP Logical Link Control/Subnetwork Access Protocol. An 8-byte packet encap-
sulation header added by the WAN router to outgoing Ethernet or ATM traffic.
The LLC/SNAP header enables devices in a connectionless network to send
frames to the devices that can switch them to their destination. The LLC
header is three bytes; it set SNAP as both the Source Service Access Point
(SSAP) and the Destination Service Access Point (DSAP) protocol. The 5-byte
SNAP header follows with a 3-byte organization code and a 2-byte code that
indicates the data type (for example, IP).
LLDP Link Layer Discovery Protocol. LLDP provides a standard method for Ethernet
network devices (such as switches, routers, and wireless LAN access points)
to advertise information about themselves to other nodes on the network and
to store the information they discover from other nodes.
LLQ Low-Latency Queuing. A QoS mechanism that places high-priority traffic in a
special queue that is served first with a set amount of bandwidth.
LMI Local Management Interface. LMI is a set of enhancements to the basic Frame
Relay specifications. It provides global addressing, virtual circuit status
messages, and multicasting capabilities.
LMP Link Management Protocol. In a multilink WAN connection, LMP is a protocol
that allows multiple carrier-lines to be treated as a single data link. Among
other functions, LMP verifies the physical connectivity of lines in the link and
localizes link failures for protection/restoration purposes. For more informa-
tion on LMP, see the IETF Internet draft at http://www.ietf.org/internet-
drafts/draft-ietf-ccamp-lmp-10.txt/.
Local Loop The connection between a subscriber’s premises and the public carrier’s
nearest central office (CO). The local loop includes telecom infrastructure
devices such as repeaters, switches, cable, and connectors.
Loopback A loopback channel is a communications channel with only one endpoint. A
signal sent on the loopback channel simply returns to the interface that sent
it. The loopback function serves to test the line.
LQR Link Quality Report. An LCP link-configuration protocol that monitors how
many frames are being dropped over a link. LQR is part of the PPP suite.
LS Loop Start. A method of signaling a switch that it should start a call. An on-
hook conditions consists of an open circuit. An off-hook phone condition
completes a closed circuit, which informs the switch to provide dial tone. See
also GS.
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