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Layer 2 protocol tunneling (L2PT) is used on the service provider's edge devices. L2PT allows edge switches to tunnel layer 2 STP (Spanning Tree Protocol), CDP (Cisco Discovery Protocol) and VTP (VLAN Trunking Protocol) packets between customer switches connected through the service provider's network. The edge switch encapsulates layer 2 protocol packets with a specific MAC address before sending them across the service provider's network to other edge switches.



The Layer 2 Tunneling Protocol (L2TP) works at layer 2 (the data link layer) to tunnel network traffic between two peer devices over another network (like the Internet).



L2TP VPN lets remote users use the L2TP and IPSec client software included with their computers' operating systems to securely connect to the network behind the L2TP IPSec router. The remote users do not need their own IPSec gateways or VPN client software. In L2TP VPN, an IPSec VPN tunnel is established first and then an L2TP tunnel is built inside it. See also IPSec.



The IEEE802.3ad standard describes Link Aggregate Control Protocol (LACP), which is a protocol that dynamically creates and manages trunk groups. When you enable LACP link aggregation on a port, the port can automatically negotiate with the ports at the remote end of a link to establish trunk groups. LACP also allows port redundancy, that is, if an operational port fails, then one of the "standby" ports becomes operational without user intervention.


LAN (Local Area Network)

A shared communication system to which many computers are attached. A LAN, as its name implies, is limited to a local area. LANs have different topologies, the most common being the linear bus and the star configuration. The most common type of LAN is named Ethernet.



The time it takes for a bit to be transmitted from source to destination.


Layer-2 Isolation

Layer-2 isolation prevents wireless clients associated with an AP from communicating with other APs (on the same wired network) and their associated wireless clients.



LDAP (Lightweight Directory Access Protocol) is a protocol over TCP that specifies how clients access directories of certificates and lists of revoked certificates.


LDM test

Loop Diagnostic Mode test. See DELT.



LEAP (Lightweight Extensible Authentication Protocol) is a Cisco implemented authentication protocol of IEEE 802.1x. An authentication method that uses a username and password system.



LEDs are visual indicators that relay information about the status of specific functions to the user by lighting up, turning off or blinking. LEDs are usually found on the front panel of the physical device. Examples include Status, Power and System LEDS.



Loop Emulation Standard is an ATM forum specification for sending voice traffic over ATM Adaptation Layer type 2 (AAL2).


Least Load First Algorithm

In load balancing, the least load first algorithm has the device send traffic through the interface with the lowest traffic loading.



When you display video that is a wider aspect ratio than the television (displaying 16:9 ratio video on a 4:3 ratio television for example), the letterbox aspect ratio displays the wider video with bars at the top and bottom of the screen.


License Key

You purchase a license key in order to activate a service on a hardware product or activate a software product.


Limit PSD Mask

To reduce the impact of interference and attenuation, ITU-T 993.2 specifies a limit PSD mask that limits the VDSL2 PSD of the downstream and upstream transmitters.


Link Layer Ethernet OAM

Link layer Ethernet OAM (Operations, Administration and Maintenance), as described in IEEE 802.3ah, monitors link status between directly connected devices in a layer 2 network. Because Link Layer Ethernet OAM operates at layer 2 of the OSI model, neither IP nor SNMP are necessary to monitor or troubleshoot network connection problems. See OSI Basic Reference Model, SNMP.


Link-local Address

An IPv6 link-local address uniquely identifies a device on the local area network (LAN). It is similar to a “private IP address” in IPv4. You can have the same link-local address on multiple interfaces on a device. A link-local address has a predefined prefix of fe80::/10.


Link State Advertisement

Routers constantly send out Link State Advertisements (LSAs) to update the link state database in an OSPF network.


Link State Database

In OSPF, the link state database contains records of router IDs, their associated links and path costs. Each device can then use the link state database and Dijkstra algorithm to compute the least cost paths to network destinations.


Link Sticking

Link sticking has the system route sessions from one source to one destination through the same interface for a period of time.


Link Trace Test

A Link trace test is similar to the trace route function but provides additional connectivity fault analysis to obtain more information on where the fault is.



Linux is a free, open-source UNIX-type operating system. Because of its robustness and availability, Linux has won popularity in the open source community and among commercial application developers.



One VC (Virtual Circuit) carries multiple protocols with protocol identifying information being contained in each packet header. Despite the extra bandwidth and processing overhead, this method may be advantageous if it is not practical to have a separate VC for each carried protocol, eg., if charging heavily depends on the number of simultaneous VCs.


Load Balancing

Load balancing is the process of dividing traffic loads between interfaces (or ports). This improves quality of services and maximizes bandwidth utilization.


Load Balancing (Wireless)

Wireless load balancing is the process whereby you limit the number of connections allowed on an wireless access point (AP) or you limit the amount of wireless traffic transmitted and received on it.


Local powerline adapter

The local powerline adapter is the powerline device directly connected to a computer running the powerline utility.


Local Loopback Test

A local loopback test is used to check the device's DSL chip. A local loopback test failure indicates an internal device problem.


Locked Volume

Locking an encrypted volume blocks all user access to its shares. For security, the NSA automatically locks an encrypted volume if the disk the volume is on is removed or the NSA restarts, is reset (since a reset includes a restart), or loses power. The administrator can also manually lock a volume. Once a volume is locked, no one can use it until an administrator unlocks it.



Logs are device information that a device is scheduled to send out.


Loop Start

A supervisory signal given by a telephone or PBX in response to completing the loop path.



A data path loop forms when there is more than one path or route between two networked devices. A loop in a network may result in a broadcast storm.


Loop Attenuation

Loop attenuation is the difference between the power transmitted at the near-end and the power received at the far-end. It is measured in decibels (dB). Loop attenuation is affected by the channel characteristics (wire gauge, quality, condition and length.


Loopback Interface

The loopback interface is the IP address that you can ping to check whether your devices network adapter and IP stack are working properly. is the IP address most commonly used for the loopback interface.


Loop guard

Loop guard is a mechanism which protects an Ethernet network against loops forming between switches as well loops between two ports on an Ethernet switch. See also STP.



Loop reach defines speed that can be attained at various distances. This is very important for DSL technology as distance from the CO (Central Office) influences attainable speeds.



Line-of-sight (LOS) refers to a wireless signal (such as beamed microwave) where a transmitter must have an unobstructed, direct signal path to a receiver for data transfer to take place. A line-of-sight signal cannot pass through solid objects such as buildings, mountains or trees. In a WiMAX network, wireless links between base stations must be line-of-sight, whereas wireless links between a base station and its subscriber stations can be non-line-of-sight. See also Signal Absorption and Non-Line-of-Sight (NLOS).



LPCM (Linear Pulse Code Modulation) is a method for digitally encoding audio information. In LPCM an audio waveform is represented by a sequence of amplitude values recorded at a sequence of times. LPCM most commonly supports two audio channels (stereo).