LAN (Local Area Network) - A network that interconnects devices over a geographically small area, typically in one building or part of a building. The most popular LAN type is Ethernet, a 10 Mbps standard that works with 10BaseT, 10Base2, or 10Base5 cables.
Last Mile - (Sometimes referred to as Local Loop). The final leg of delivering communications connectivity to a resident or customer. Typically seen as an expensive challenge because “fanning out” wires and cables is a considerably expensive and physically difficult task.
Latency - The time between initiating a request for data and the beginning of the actual data transfer. Network latency is the delay introduced when a packet is momentarily stored, analyzed and then forwarded.
LCAS (Link Capacity Adjustment Scheme) - A method to dynamically increase or decrease the bandwidth of virtual concatenated containers in SDH. The LCAS protocol is specified in ITU-T G.7042. It allows on-demand increase or decrease of the bandwidth of the virtual concatenated group in a hitless manner. This brings bandwidth-on-demand capability for data clients like Ethernet when mapped into SDH containers.
Leased Line - A permanent telephone connection between two points that is rented for exclusive use from a telecommunications common carrier. In contrast to a normal dial-up connection, a leased line is always active. Typically, the highest speed data connections require a leased line connection. For example, a T1 channel is a type of leased line that provides a maximum transmission speed of 1.544 Mbps.
Local Loop - (Sometimes referred to as Last Mile). The physical wires that run from the subscriber’s telephone set, PBX, or key telephone system to the telephone company’s central office. Increasingly, the Local Loop now goes from the main distribution frame at the customer premises to the telephone company. The subscriber is responsible for connecting his wires from the box at the customer’s premises to his phone, PBX, or key system.
Loopback - A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through all or part of a communications link or network.
M
MAC (Media Access Control) - A protocol that defines the way workstations gain access to transmission media, most widely used in reference to LANs. For IEEE LANs, the MAC layer is the lower sublayer of the data link layer protocol.
MAC-in-MAC - An IEEE 802.1ah standard for layering the Ethernet network into customer and provider domains with complete isolation among their MAC addresses. It enables service providers to separate customer traffic from management traffic and also save on VLAN IDs.
MAN (Metropolitan Area Network) - A network that provides regional connectivity within a metropolitan area (such as a city).
MEF (Metro Ethernet Forum) - A non-profit organization chartered with the mission of accelerating the adoption of optical Ethernet as the technology of choice in future metro networks worldwide. Ethernet was chosen for its relative simplicity and popularity with end-users, as well as for lowering costs of Ethernet equipment.
MIB (Management Information Base) - A directory listing the logical names of all information resources residing in a network and pertinent to the network’s management. A key element of SNMP management systems.
MLPPP (Multilink PPP) - Connects multiple links between two systems as needed to provide extra bandwidth. Remotely accessing resources through MLPPP allows for an increase in overall throughput by combining the bandwidth of two or more physical communication links, such as analog modems, ISDN and other analog/digital links.
Modem (Modulator-Demodulator) - A device used to convert serial digital data from a transmitting DTE to a signal suitable for transmission over extended distances. It also reconverts the transmitted signal to serial digital data for acceptance by a receiving DTE.
MPLS (Multiprotocol Label Switching) - A standards-approved technology that allows core network routers to operate at higher speeds without needing to examine each packet in detail, allows more complex services to be developed, enabling discrimination on a QoS basis. MPLS speeds up network traffic flow by bringing Layer 2 information to Layer 3 (IP) and facilitating network management. It forwards traffic using a label that instructs the routers and the switches in the network where to forward the packets based on pre-established IP routing information. MPLS is called multiprotocol because it works with the IP, ATM, and Frame Relay network protocols.
Multimode Fiber - A fiber with a large core diameter. 50-200 microns compared with the wavelength of light. It therefore propagates more than one mode. With multimode fiber, light traverses multiple paths, some longer than others. This leads to dispersion, which reduces optical range at high bit rates.
Multiplexer - At one end of a communications link, a device that combines several lower speed transmission channels into a single high speed channel. A multiplexer at the other end reverses the process. Sometimes called a mux. See Bit Interleaving/Multiplexer.
Multiplexer (Mux) - A device allowing two or more signals to pass over and share a common transmission path simultaneously.
N
Network - (1) An interconnected group of nodes. (2) A series of points, nodes, or stations connected by communications channels; the collection of equipment through which connections are made between data stations.
Network Layer - A layer in the OSI reference model. The network layer provides address resolution and routing protocols. Address resolution enables the network layer to determine a unique network address for a node. Routing protocols allow data to flow between networks and reach their proper destination. Examples of network layer protocols are Address Resolution Protocol (ARP), Datagram Delivery Protocol (DDP), Internet Control Message Protocol (ICMP), Interior Gateway Protocol (IGP), Internet Protocol (IP), Internetwork Packet Exchange (IPX) and Packet Layer Protocol (PLP).
NMS (Network Management System) - The system that controls the network configuration, fault and performance management, and diagnostic analysis.
NNI (Network Node Interface or Network-to-Network Interface) - ITU-T standard interface between nodes within the same network. The ATM forum distinguishes between two standards, one for private networks called PNNI and one for public networks known as public NNI.
Node - A point of interconnection to a network.
O
OAM (Operation Administration and Maintenance) - A set of network management functions that provide for network fault and performance management, analysis and fault isolation. OAM functions exist in carrierclass TDM and ATM networks, but are now also being implemented in MPLS and Ethernet networks. These capabilities will provide the basic tools for carriers to monitor, diagnose, and troubleshoot first-mile Ethernet access links.
OSI (Open Systems Interconnection) Model - A seven-layer model of network communications developed by the International Organization for Standardization (ISO).
Out-of-Band Connection - A remote link, or a link outside connected networks, established over a modem. It is useful when network communications are not available.
Out-of-Band Signaling - The transmission of signaling information over a different path from data and/or voice information. CCS7 uses out-ofband signaling.
Glossary
