AAL
ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs consist of two sublayers: CS and SAR. AALs differ on the basis of the source-destination timing used (CBR or VBR) and whether they are used for connection-oriented or connectionless mode data transfer. At present, the four types of AAL recommended by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5.

AAL5
ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented VBR services and is used predominantly for the transfer of classical IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability. See also AAL.

ADSL
Asymmetric digital subscriber line. ADSL is designed to deliver more bandwidth downstream (from the central office to the customer site) than upstream. Downstream rates range from 1.5 to 9 Mbps; upstream bandwidth ranges from 16 kbps to 1 Mbps. ADSL transmissions work at distances up to 18,000 feet over a single copper wire twisted pair. See also DSL.

Agent
Generally, software that processes queries and returns replies on behalf of an application. In the context of network management, an agent is a process that resides in all managed devices, and stores management data and responds to the manager’s data requests.

ATM
Asynchronous Transfer Mode. A cell-based data transfer technique in which channel demand determines packet allocation. ATM offers fast packet technology, real times; demand led switching for efficient use of network resources. This is an International standard for cell relay in which multiple service types (such as voice, video or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media such as E3, SONET, and T3.

ATU-C
ADSL Transmission Unit—central office.

ATU-R
ADSL Transmission Unit—remote.

BAS
Broadband Access Server. Device within the ADSL POP terminating PPP sessions providing access to routing or service selection. Can be the same hardware platform as the LAC.

BRAS
Broadband Remote Access Server. Device that terminates remote users at the corporate network or Internet users at the Internet Service Provider (ISP) network, such as the NetSpeed FireRunner product that provides firewall, authentication, and routing services for remote users.

Community Name
An identification used by an SNMP manager to grant an SNMP server access rights to a MIB.

CPE
Customer premises equipment. Terminating equipment at the subscriber's side of the local telephone loop. CPE is often supplied by the telephone company and is always connected to the telephone company's network. Examples of CPE include telephones, POTS splitters, terminals, modems, and the Cisco 676 router.

DSL
Digital subscriber line. A public network technology that delivers high bandwidth over conventional copper wiring (such as telephone lines) at limited distances. There are five types of DSL: ADSL, HDSL, IDSL, SDSL, and VDSL. All are provisioned through modem pairs, with one modem located at a central office and the other at the customer site. Because most DSL technologies do not use the whole bandwidth of the twisted pair, there is room left for a voice channel. See also ADSL.

DSLAM
Digital Subscriber Line Access Multiplexer. A device that concentrates traffic in DSL implementations through a process of time-division multiplexing (TDM) at the CO or remote line shelf. This device is usually located in the CO for termination of multiple customer DSL devices.

ESS (Error Seconds)
ESS is a generic term with various meanings depending on the signal standards domain in which it’s being used.

Ethernet
One of the most popular baseband LANs in widespread use. It is a carrier service multiple access collision detect (CSMA/CD) system using coaxial cable and developed by Xerox, Intel, and Digital Equipment Corporation. Introduced in 1979. Ethernet Version II is compatible with the IEEE 802.3 CSMA/CD standard.

G.SHDSL
G.SHDSL is a standards-based, multirate version of HDSL-2 and offers symmetrical service. The advantage of HDSL-2, which was developed to serve as a standard by which different vendors' equipment could interoperate, is that it is designed not to interfere with other services. However, the HDSL-2 standard addresses only services at 1.5 Mbps. Multirate HDSL-2 is part of Issue 2 of the standard known as G.SHDSL, and is ratified by the ITU. G.SHDSL builds upon the benefits of HDSL-2 by offering symmetrical rates of 2.3 Mbps.

IGMP
(Internet Group Management Protocol) snooping-as implied by the name, is a feature that allows SmartDSLAM to "listen in" on the IGMP conversation between hosts and routers.
GVRP
:Generic Attribute Registration Protocol (GARP) VLAN Registration Protocol (GVRP)-With GVRP, SmartDSLAM can exchange VLAN configuration information with other GVRP switches, prune unnecessary broadcast and unknown unicast traffic, and dynamically create and manage VLANs on switches connected through 802.1Q trunk ports.

IP
Internet Protocol. Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Defined in RFC 791.

ISP
Internet Service Provider. A company that offers individual customers or corporations dialup or leased-line connections to the Internet for a fee.

LAN (Local Area Network)
A non-public data network in which serial transmission is used without store and forward techniques for direct data communication among data stations located on the user's premises.

Lofs (Loss of Frames)
Lofs is a generic term with various meanings depending on the signal standards domain in which it’s being used.

Lols (Loss of Links)
Lols is a generic term with various meanings depending on the signal standards domain in which it’s being used.

Loss (Loss of Signals)
A loss of signal occurs when n consecutive zeros is detected on an incoming signal.

Lprs (Loss of Power failures)
Lprs is a generic term with various meanings depending on the signal standards domain in which it’s being used.

MDF (Main Distribution Frame)
Hardware component in the CO, which provides an interface between outside lines (subscriber lines and trunks) and the switching equipment. The vertical side of the mainframe where the outside plant cables are terminated on connectors/protectors. Also known as mainframe.

MTU/MHU
MTU is Multi-Tenant Unit whereas MHU is Multi-Hotel Unit.

PPP (Point to Point Protocol)
A successor to Serial Line IP (SLIP), PPP provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.

PPPoE
PPP over Ethernet. The transport of PPP frames over Ethernet.

PSTN (Public Switched Telephone Network)
General term referring to the variety of telephone networks and services in place worldwide. Sometimes called POTS.

PVC( Permanent Virtual Circuit, or connection)
Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. In ATM terminology, called a permanent virtual connection.

Rack mount
A structure that houses shelves (usually a maximum of four). The unit or container that houses the internal modular circuitry. The shelf consists of slots that hold each module and a backplane that interconnects all modules.

SAR
Segmentation and reassembly. One of the two sub-layers of the AAL CPCS, responsible for dividing (at the source) and reassembling (at the destination) the PDUs passed from the CS. The SAR sub-layer takes the PDUs processed by the CS and, after dividing them into 48-byte pieces of payload data, passes them to the ATM layer for further processing. See also AAL and ATM.
SDU (Service Data Unit)
Unit of information from an upper-layer protocol that defines a service request to a lower-layer protocol.

Signal Noise Ratio (SNR)
This is a DSL transmission parameter, measured in dB, which indicates the Signal-to-Noise (S/N) ratio at a receiver point.

SNAP
Subnetwork Access Protocol. Internet protocol that operates between a network entity in the subnetwork and a network entity in the end system. SNAP specifies a standard method of encapsulating IP datagrams and ARP messages on IEEE networks. The SNAP entity in the end system makes use of the services of the subnetwork and performs three key functions: data transfer, connection management, and QoS selection.

SNMP (Simple Network Management Protocol)
Simple Network Management Protocol. The network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, and to manage configurations, statistics collection, performance, and security.

VC
Logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a VPI/VCI pair, and can be either permanent (PVC) or switched (SVC). Virtual circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel.

VID
VLAN ID. The identification of the VLAN, which is used by the standard 802.1Q. Being on 12 bits, it allows the identification of 4096 VLANs.

VLAN Virtual LAN. Group of devices on one or more LANs that are configured (using management software) so that they can communicate as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. Because VLANs are based on logical instead of physical connections, they are extremely flexible.