Data Link Layer - Layer 2 of the OSI model. The entity, which establishes, maintains, and releases data-link connections between elements in a network. Layer 2 is concerned with the transmission of units of information, or frames, and associated error checking.
DiffServ or DS (Differentiated Services) - QoS method to differentiate and control IP traffic so that the traffic’s relative priority can be determined on a per-hop basis.
DSCP (Differentiated Services Code Point) - A field in the header of IP packets for packet classification purposes.
DS0 (Digital Subscriber Level Zero) - A 64 kbps unit of transmission bandwidth. A worldwide standard speed for digitizing one voice conversation, and more recently, for data transmission. Twenty-four DS0s (24 x 64 kbps) equal one DS1.
DS1 (Digital Signal Level 1) Channel - Framing specification used in transmitting digital signals at 1.544 Mbps on a T1 facility or 2.048 Mbps on an E1 facility.
DS2 Channel - For a T1 line, a 6.312 Mbps channel that consists of four DS1 channels; for an E1 line, an 8.45 Mbps channel that consists of four DS1 channels.
DS3 Channel - A 44.736 Mbps line consisting of seven DS2 channels. A DS3 line is also called a T3 line.
DSL (Digital Subscriber Line) - A modem technology for transmitting information at high speeds on existing copper phone lines to homes and businesses. DSL operates over existing copper telephone lines and requires runs of usually less than 20,000 feet to a central telephone office. Types of DSL include asymmetric DSL (ADSL), symmetric DSL (SDSL), high-bitrate DSL (HDSL) and the latest, symmetric high-bitrate DSL (SHDSL).
E
E1 - A 2.048 Mbps line, common in Europe, that supports thirty-two 64 kbps channels, each of which can transmit and receive data or digitized voice. The line uses framing and signaling to achieve synchronous and reliable transmission. The most common configurations for E1 lines are E1 PRI, and unchannelized E1.
E1 MLPPP (Multilink Point-to-Point Protocol) - Combining (bonding) multiple PPP (Point-to-Point Protocol) links between two systems into one logical data pipe. MLPPP is a standard IETF protocol.
E3 - The European standard for high speed digital transmission, operating at 34 Mbps.
EFM Ethernet in the First Mile (also known as IEEE 802.3ah) - A collection of protocols specified in IEEE 802.3, defining Ethernet in the access networks, i.e. First/Last Mile. EFM also addresses other issues required for mass deployment of Ethernet services, such as operations, administration and maintenance (OAM) and compatibility with existing technologies (e.g. spectral compatibility for copper).
E-LAN (Ethernet Local Area Network) - A Fast Ethernet or Gigabit Ethernet service used for multipoint-to-multipoint transparent Ethernet LAN connectivity, allowing any location to speak with any other location in a customer’s Metro Ethernet network (see MEF).
E-Line (Ethernet Line) - A service providing a point-to-point Ethernet Virtual Connection (EVC) between two customer user interfaces or two locations in a Metro Ethernet network (see MEF).
Encapsulation - Encapsulating data is a technique used by layered protocols in which a low level protocol accepts a message from a higher level protocol, then places it in the data portion of the lower-level frame. The logistics of encapsulation require that packets traveling over a physical network contain a sequence of headers.
Enterprise Network - An information infrastructure, often combining private and public facilities, to cover all of the locations operated by a single company or corporate enterprise with a single communications fabric.
Ethernet - Most popular local area network (LAN) technology in use today. All stations on the LAN share the total bandwidth, which is at speeds of 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet), or 1000 Mbps (Gigabit Ethernet).
Ethernet Converter - Ethernet converters are low-cost and simple devices for connecting Ethernet over E1, T1, E3, T3, STM-1, OC-3 and STM-4, OC-12 access lines.
Ethernet Demarcation- A key element in Carrier Ethernet transport and services, providing a clear separation between the user and the network and allowing carriers to extend network visibility into the user premises.
Ethernet Extender - Ethernet signal degradation typically limits Ethernet cable runs to 100 meters (328 feet). To achieve longer distances, an Ethernet extender is required. These devices can be used to drive Ethernet up to 5.5 kilometers over copper and more than 100 kilometers over fiber.
Ethernet modem - RAD Data Communications has a wide range of Ethernet modems with combined E1/T1 multiplexing capabilities for point-to-point Ethernet extension over any type of infrastructure or media.
Ethernet OAM - Ethernet OAM (Operation, Administration and Maintenance) is a set of functions designed to monitor network operation in order to detect network faults and measure its performance. Carrier-class Ethernet services require automated end-to-end management and monitoring, including OAM capabilities such as connectivity verification, fault detection, performance monitoring, and alarm indication.
Ethernet over PDH - Ethernet over PDH (Plesiochronous Digital Hierarchy) is a method for carrying Ethernet traffic over PDH network lines such as E1/T1 or E3/T3. It is one of several technologies available to service providers who wish to offer new carrier-class Ethernet services over existing legacy infrastructure.
Ethernet over SDH or SONET - Although SDH and SONET networks were originally engineered to transport voice traffic, many carriers are using their ubiquitous SDH and SONET infrastructure to deploy Ethernet services. Recent developments in Next Generation SDH/SONET have made these networks more cost-effective and "user friendly" for Ethernet traffic.
Ethernet QoS - One of the key attributes of Carrier Ethernet services, by which the service provider offers business users bandwidth, delivery, and performance guarantees for selected traffic, and allocates the necessary network resources accordingly.
F
Fiber Media Converter - A fiber media converter connects standard optical interfaces with electrical interfaces; links single mode fibers with multimode fiber cables; adapts dissimilar data rates; and converts different transmission protocols such as TDM E1/T1 and Ethernet.
Fiber Optics - A transmission medium consisting of thin glass or plastic filaments. Light beams (generated by an LED or laser) travel through the fiber optic line, carrying large amounts of data over long distances.
Fiber Optic Modems - Fiber optic modulator/demodulators (modems) enable E1/T1, E3/T3, LAN, and data extension over fiber optic infrastructure.
Fiber Optic Multiplexers- Fiber optic multiplexers are devices that combine multiple signals for transport on a common transmission path. RAD’s fiber optic multiplexers enable transmission of E1 or T1 channels, E3 or T3 tributaries and wire-speed Ethernet over a fiber optic link. A fiber optic multiplexer at the other end reverses the process.
Fractional T1 Line - A T1 line that contains both switched and nailed-up channels. T1 PRI and ISDN BRI lines can also be Fractional T1 lines.
Frame - A logical grouping of information sent as a link layer unit over a transmission medium. The terms packet, datagram, segment and message are also used to describe logical information groupings.
Frame Relay - An efficient packet switching technology providing high speed frame or packet transmission with minimum delay and efficient bandwidth utilization over virtual circuits. The link layer handles much of the network layer functionality. It has less protocol overhead than X.25.
Framing - At the physical and data link layers of the OSI model, bits are fit into units called frames. Frames contain source and destination information, flags to designate the start and end of the frame, plus information about the integrity of the frame. All other information, such as network protocols and the actual payload of data, is encapsulated in a packet, which is encapsulated in the frame.
Full Duplex - A circuit or device permitting transmission in two directions (sending and receiving) at the same time.
Glossary
