L2CAP: Logical Link Control and Adaptation Protocol
Logical Link Control and Adaptation Protocol, typically short as L2CAP, is used within the Bluetooth protocol stack at the data link layer. It passes packets to either the Host Controller Interface (HCI) or on a hostless system, directly to the Link Manager.
Standard Organization: IEEE
Reference Document: IEEE 802.15.1

L2F: Layer 2 Forwarding protocol
Layer 2 Forwarding (L2F) protocol, originally developed by Cisco, uses tunneling of PPP over IP to create a virtual extension of a dial-up link across a network, initiated by the dial-up server and transparent to the dial-up user. L2F is used to establish a secure tunnel across a public infrastructure (such as the Internet) that connects an ISP POP to an enterprise home gateway. This tunnel creates a virtual point-to-point connection between the user and the enterprise customer's network.
Standard Organization: Cisco
Reference Document: RFC 2341

L2TP: Layer 2 Tunneling Protocol
The Layer 2 Tunneling Protocol (L2TP), defined by IETF based on the Microsoft Point-to-Point Tunneling Protocol (PPTP) and Cisco Layer 2 Forward Protocol (L2F), is used for integrating multi-protocol dial-up services into Internet Service Provider’s Point of Presence. L2TP defines an encapsulation mechanism for transporting multiprotocol packets across layer 2 point-to-point links and it enables the operation of a virtual private network over the Internet.
Standard Organization: IETF
Reference Document: RFC 2661

LAN NNI: LAN Emulation NNI
The LAN Emulation NNI (LNNI), a protocol in the ATM suite, defines the behavior of these LANE service components as seen by each other, the procedures necessary to provide a distributed and reliable LAN Emulation Service. A single ELAN may be served by multiple LECSs, LESs, BUSs and SMSs. Each LES, BUS and SMS serves a single ELAN, while an LECS may serve multiple ELANs. LANE service components interconnect with multiple VCCs for Configuration, Status, Database Synchronization, Control and Data forwarding. The LNNI specification provides multivendor interoperability among the components serving an ELAN so that consumers may mix and match the LANE Service implementations of different vendors.
Standard Organization: ITU-T

LANE UNI: LAN Emulation UNI
The LAN Emulation UNI (LANE), a protocol in the ATM suite, defines the protocols and interactions between LAN Emulation Clients (LE Clients) and the LAN Emulation Service, including initialization, registration, address resolution, and data transfer procedures. Each LE Client connects across the LUNI to a single LES and BUS, may connect to a single LECS, and may have connections to multiple SMSs.
Standard Organization: ITU-T and ATM Forum

LAPB: Link Access Procedure, Balanced
Link Access Procedure, Balanced (LAPB) is a data link layer protocol used to manage communication and packet framing between data terminal equipment (DTE) and the data circuit-terminating equipment (DCE) devices in the X.25 protocol stack. LAPB, a bit-oriented protocol derived from HDLC, is actually the HDLC in BAC (Balanced Asynchronous Class) mode. LAPB makes sure that frames are error free and properly sequenced.
Standard Organization: ITU-T

LAP-D: Link Access Procedure, D-Channel
Link Access Procedure, D-Channel (LAP-D), a Layer 2 protocol in the ISDN suite, is used to do call setup and other signaling over the D Channel. Data transmissions take place on B channels. LAP-D is almost identical to the X.25 LAP-B protocol. LAPD is defined in the ITU Q.921 protocol.
Standard Organization: ITU-T

LAPF: Link Access Procedure for Frame Mode Services
Link Access Procedure for Frame Mode Services (LAPF), as defined in ITU Q.922, is an enhanced LAPD (Q.921) with congestion control capabilities for Frame Mode Services in the Frame Relay network. LADF is used in the Frame Relay network for end-to-end signaling. LAPF conveys data link service data units between DL-service users in the User Plane for frame mode bearer services across the ISDN user-network interface on B-, D- or H-channels.
Standard Organization: ITU-T
Reference Document: Q.922

LAP-H: Link Access Procedure for H-Channel
Link Access Procedure for H-Channel (LAP-H) performs the same function as B-Channel (LAPB) but operates at rates exceeding DS-0 (64 Kbps). The H-Channel is good for fast facsimile, video, high-speed data, high-quality audio, and multiple info streams at lower data rates.
Standard Organization: ITU-T

LAP-M: Link Access Procedure for Modems
Link Access Procedure for Modems (LAP-M) is the data link protocol used by V.32 error- correcting modems. When two LAPM modems establish a session, they transmit data in frames using bit-oriented synchronous techniques. An attached computer still sends data to the LAPM modems as standard asynchronous input, but the modem transmits it as frames.
Standard Organization: ITU-T

LAPS: Link Access Procedure-SDH
Link Access Procedure - SDH (LAPS), a variant of the original LAP protocol, is an encapsulation scheme for Ethernet over SONET/SDH. LAPS includes data link service and protocol specification used in transporting IP packets over SDH networks. LAPS provides a point-to-point unacknowledged connectionless service over SONET/SDH. LAPS enables the encapsulation of IPv6, IPv4, PPP, and other higher-layer protocols. X.86 Defines Ethernet over LAPS.
Standard Organization: ITU-T

LAT: Local Area Transport protocol
Local Area Transport (LAT) protocol, a protocol in the DECnet, is designed to handle multiplexed terminal traffic to/from timesharing hosts. Local Area Transport is a non-routable networking technology to provide connection between the DECserver 90, 100, 200, 300, 700 and DECserver 900 Terminal Servers and Digital's VAX and Alpha host computers via Ethernet, giving communication between those hosts and serial devices such as video terminals and printers. The protocol itself was designed in such a manner as to maximize packet efficiency over ethernet by bundling multiple characters from multiple ports into a single packet for Ethernet transport. Over time, other host implementations of the LAT protocol appeared allowing communications to a wide range of Unix and other non-DECnet operating systems using the LAT protocol.
Standard Organization: DEC/HP

LAVC: Local Area VAX Cluster protocol
Local Area VAX Cluster protocol (LAVC) belongs to the DECnet protocol suite for communications between DEC VAX computers in a cluster.
Standard Organization: DEC/HP

LCAS: Link Capacity Adjustment Scheme
Link Capacity Adjustment Scheme (LCAS) is a method of using SONET/SDH overhead to communicate the status of a Virtually Concatenation (VC) connections. LCAS allows re-adjust of link capacity without traffic loss or network error. LCAS is a key enabler of Ethernet over SONET/SDH (EoS) networks. The LCAS mechanism can also automatically decrease the capacity if a VC/SPE in a VCG experiences a failure in the network, and increase the capacity when the fault is repaired.
Standard Organization: ITU-T

LCP: Link Control Protocol
The Link Control Protocol (LCP), a protocol in the Point-to-Point protocol (PPP) suite, is used to automatically agree upon the encapsulation format options, handle varying limits on sizes of packets, detect a looped-back link and other common misconfiguration errors and terminate the link. Other optional facilities provided are authentication of the identity of its peer on the link and determination when a link is functioning properly and when it is failing. LCP is versatile and portable to a wide variety of environments.
Standard Organization: IETF
Reference Document: RFC 1570

LDAP: Lightweight Directory Access Protocol
Lightweight Directory Access Protocol (LDAP) is designed to provide access to the X.500 Directory while not incurring the resource requirements of the Directory Access Protocol (DAP). LDAP is specifically targeted at simple management applications and browser applications that provide simple read/write interactive access to the X.500 Directory and is intended to be a complement to the DAP itself.
Standard Organization: IETF
Reference Document: RFC 3377

LDCELP : Low-delay CELP
Low-delay CELP (LSCELP) is a CELP voice compression algorithm providing 16 kbps, or 4:1 compression. LSCELP has been standardized in ITU-T Recommendation G.728.
Standard Organization: ITU-T
Reference Document: G.728

LDP: Label Distribution Protocol
Label Distribution Protocol(LDP) is a signaling protocol in the MPLS (Multi Protocol Label Switching) architecture. In the MPLS network, 2 label switching routers (LSR) must agree on the meaning of the labels used to forward traffic between and through them. LDP defines a set of procedures and messages by which one LSR (Label Switched Router) informs another of the label bindings it has made.
Standard Organization: IETF
Reference Document: RFC 3036

LE_ARP: LAN Emulation Address Resolution Protocol
LAN Emulation Address Resolution Protocol (LE_ARP) provides the ATM address that corresponds to a MAC address.
Standard Organization: ATM Forum

LEAP: Lightweight Extensible Authentication Protocol
Lightweight Extensible Authentication Protocol (LEAP), also known as Cisco-Wireless EAP, is a Cisco security technology that builds on Wi-Fi's WEP encryption. Basically, it changes the WEP key dynamically during a session to make it less likely that a snooper will be able to derive the key. LEAP provides username/password-based authentication between a wireless client and a RADIUS server like Cisco ACS or Interlink AAA. LEAP is one of several protocols used with the IEEE 802.1X standard for LAN port access control.
Standard Organization: Cisco

LLAP: LocalTalk Link Access Protocol
LocalTalk Link Access Protocol (LLAP) is a link-level protocol that manages node-to-node delivery of data on a LocalTalk/AppleTalk network. LLAP manages bus access, provides a node-addressing mechanism, and controls data transmission and reception, ensuring packet length and integrity.
Standard Organization: Apple

LLC: Logic Link Control
Logic Link Control (LLC) is the IEEE 802.2 LAN protocol that specifies an implementation of the LLC sublayer of the data link layer. IEEE 802.2 LLC is used in IEEE802.3 (Ethernet) and IEEE802.5 (Token Ring) LANs to perform some functions.
Standard Organization: IEEE
Reference Document: IEEE 802.2

LLC2: Logical Link Control, type 2
Logical Link Control,type 2 (LLC2) is a connection-oriented LLC-sublayer protocol. LLC2 (IEEE 802.2) is widely used in LAN environments, particularly among IBM communication systems connected by Token Ring.
Standard Organization: IEEE
Reference Document: IEEE 802.2

LMP: Link Manager Protocol
Link Manager Protocol (LMP) is a data link layer protocol in the Bluetooth protocol stack. LMP carries out link setup, authentication, link configuration and other protocols. It discovers other remote Link Manager (LM) and communicates with them via the Link Manager Protocol (LMP). To perform its service provider role, the LM uses the services of the underlying Link Controller (LC).
Standard Organization: IEEE
Reference Document: IEEE 802.15.1

LocalTalk
LocalTalk is a particular implementation of the data link and physical layer of the AppleTalk networking system from Apple Computer. LocalTalk uses CSMA/CD and specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s.
Standard Organization: Apple

LPP: Lightweight Presentation Protocol
Lightweight Presentation Protocol (LPP) describes an approach for providing "streamlined" support of OSI application services on top of TCP/IP-based network for some constrained environments. LPP was initially derived from a requirement to run the ISO Common Management Information Protocol (CMIP) in TCP/IP-based networks.
Standard Organization: IETF
Reference Document: IETF 1085

LQR: Link Quality Report
Link Quality Report (LQR), a protocol in the Point-to-Point Protocol (PPP) suite, specifies the mechanism for link quality monitoring and reporting for PPP communications. Data communications links are rarely perfect. Packets can be dropped or corrupted for various reasons (line noise, equipment failure, buffer overruns, etc.). To determine when, and how often, the link is dropping data. Routers, for example, may want to temporarily allow another route to take precedence. An implementation may also have the option of disconnecting and switching to an alternate link. The process of determining data loss is called "Link Quality Monitoring".
Standard Organization: IETF

LU: Logic Unit
Logical Units (LUs) are functions in the IBM Systems Network Architecture including LU0, LU1, LU2, LU3, LU6.2, for communication session management. Each SNA node contains one or more logical units (LUs). An LU provides a set of functions that are used by Transaction Programs (TPs) and end users to provide access to the network. LUs communicate directly with local TPs and devices. For example, a TP running on a workstation that uses the AIX operating system can communicate with a TP on an AS/400 computer as easily as it can with a TP on another AIX workstation, as long as both TPs use the same LU type.
Standard Organization: IBM

LU 6.2: Logical Unit 6.2
Logical Unit 6.2 (LU 6.2) is a term in the IBM SNA network, which provides peer-to-peer communications between programs in a distributed computing environment. The IBM APPC also runs on LU 6.2 devices.