A network that traverses some distance and usually connects LANs, whether across the city or across the nation. The Internet is the largest WAN.
NSPs (Network Service Providers)
A carrier that provides long-distance (and often global) connectivity between major data-switching centers across the Internet.
Continuously available communications channels, from a telecommunications provider, such as a local telephone company or ISP. They come in a variety of types that are distinguished by their capacity and transmission characteristics.
A connection between one WAN site (or point) and another site (or point). Most are point-to-point, connecting one site to only one other site.
Bus Topology WAN
A WAN in which each location is connected to no more than two other locations in a serial fashion.
Ring Topology WAN
A type of WAN in which each site is connected to two other sites so that the entire WAN forms a ring pattern.
Star Topology WAN
A type of WAN in which a single site acts as the central connection point for several other points. this arrangement provides separate routes for data between any two sites; however, if the central connection point fails, the entire WAN fails.
Mesh Topology WAN
A type of WAN in which several sites are directly interconnected. These are highly fault tolerant because they provide multiple routes for data to follow between any two points.
Full Mesh WAN
A version of the mesh topology WAN in which every site is directly connected to every other site. It is the most fault-tolerant type of WAN. One drawback is cost.
Partial Mesh WAN
A version of a mesh topology WAN in which only critical sites are directly interconnected and secondary sites are connected through star or ring topologies. These are less expensive to implement than full mesh WANs.
Tiered Topology WAN
A type of WAN in which sites that are connected in stat or ring formations are interconnected at different levels, with the interconnection points being organized into layers to form hierarchical groupings.
PSTN (Public Switched Telephone Network)
The network of lines and carrier equipment that provides telephone service to most homes and businesses. Encompasses the entire telephone system, from the wires that enter homes and businesses to the network centers that connect different regions of a country.
A connection in which a user connects her computer, via a modem, to a distant network and stays connected for a finite period of time.
The place where a telephone company terminates lines and switches calls between different locations.
Local Loop or Last Mile
The part of a phone system that connects a customer site with a telecommunications carrier's switching facility.
An analog, packet-switched technology designed for long-distance data transmission and standardized by the ITU in the mid-1970's. Specifies protocols at the Physical, Data Link, and Network layers of the OSI Model.
An updated, digital version of the X.25 that also relies on packet switching. Operates at the Data Link layer of the OSI Model and can support multiple different Network and Transport layer protocols.
Connections between network nodes that, although based on potentially disparate physical links, logically appear to be direct, dedicated links between those nodes.
Connections that are established when parties need to transmit, then terminated after the transmission is complete.
Connections that are established before data needs to be transmitted and maintained after the transmission is complete. NOTE: the connection is established only between the two points (the sender and receiver); the connection does not specify the exact route the data will travel.
CIR (Committed Information Rate)
The guaranteed minimum amount of bandwidth selected when leasing a frame relay circuit. Frame relay costs are partially based on this.
ISDN (Integrated Services Digital Network)
An international standard that uses PSTN lines to carry digital signals. It specifies protocols at the Physical, Data Link, and Transport Layers of the OSI Model. These lines may carry voice and data signals simultaneously.
The "bearer" channel, employing circuit-switching techniques to carry voice, video, audio, and other types of data over the ISDN connection. Has a maximum throughput of 64 Kbps.
The "data" channel, employing packet-switching techniques to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals. Has a maximum througghput of 16 or 64 Kbps.
BRI (Basic Rate Interface)
A variety of ISDN that uses two 64-Kbps bearer channels and one 16-Kbps data channel, as indicated by the notation 2B+D. ** Is the most common form of ISDN employed by home users.
The process of combining more than one bearer channel of an ISDN line to increase throughput.
NT1 (Network Termination 1)
A device used on ISDN networks that connects the incoming twisted pair wiring with the customer's ISDN terminal equipment.
NT2 (Network Termination 2)
An additional connection device required on PRI to handle the multiple ISDN lines between the customer's network termination connection and the local phone company's wires.
PRI (Primary Rate Interface)
A type of ISDN that uses 23 bearer channels and one 64-Kbps data channel, represented by the notation 23B+D. It is less commonly used by individual subscribers than BRI, but it may be used by businesses and other organizations needing more throughput.
TA (Terminal Adapter)
A device used to convert digital signals into analog signals for use with ISDN phones and other analog devices. These are sometimes called ISDN modems.
TE (Terminal Equipment)
The end nodes (such as computers and printers) served by the same connection (such as an ISDN, DSL, or T1 Link)
The term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s.
A digital carrier standard used in North America and most of Asia that provides 1.544-Mbps throughput and 24 channels for voice, data, video, or audio signals. T1s rely on time division multiplexing and may use shielded or unshielded twisted pair, coaxial cable, fiber optics, or microwave links.
A digital carrier standard used in North America and most of Asia that can carry the equivalent of 672 channels for voice, data, video, or audio, with a maximum data throughput of 44.736 Mbps (typically rounded up to 45 Mbps for purposes of discussion). It relies on time division multiplexing and requires either fiber-optic or microwave transmission media.
An ANSI standard for T-carrier technology that refers to its Physical layer electrical signaling characteristics. DS0 is the equivalent of one data or voice channel. All other signal levels are multiples of DS0.
DS0 (Digital Signal, Level 0)
The equivalent of one data or voice channel. All other signal levels are multiples of DS0
An arrangement that allows a customer to lease only some of the channels on a T1 line.
A termination for T-carrier wire pairs that is located at the customer demark and which functions as a connection protection and monitoring point. Not capable of interpreting data.
CSU/DSU (Channel Service Unit/Data Service Unit)
A combination of a CSU and a DSU that serves as the connection point for a T1 line at the customer's site. Most modern ones contain a multiplexer.
CSU (Channel Service Unit)
A device used with T-carrier technology that provides termination for the digital signal and ensures connection integrity through error correction and line monitoring.
DSU (Data Service Unit)
A device used in T-carrier technology that converts the digital signal used by bridges, routers, and multiplexers into the digital signal used on cabling.
DSL (Digital Subscriber Line)
A dedicated WAN technology that uses advanced data modulation techniques at the Physical layer to achieve extraordinary throughput over regular phone lines. It comes in several different varieties, the most common of which is asymmetric DSL (ADSL)
A term used to describe data traffic that flows froma carrier's facility to the customer. In asymmetrical communications, _________ throughput is usually much higher than upstream throughput. In symmetrical communications, _________ and upstream throughputs are equal.
A term used to describe data traffic that flows from a customer's site to a carrier's facility. In asymmetrical communications, _________ throughput is usually much lower than downstream throughput. In symmetrical communications, _________ and downstream throughputs are equal.
The characteristic of a transmission technology that affords greater bandwidth in one direction (either from the customer to the carrier, or vice versa) than in the other direction.
A variation of DSL that offers more throughput when data travels downstream, downloading from a local carrier's switching facility to the customer, than when it travels upstream, uploading from the customer to the local carrier's switching facility.
A characteristic of a transmission technology that provides equal throughput for data traveling both upstream and downstream and is suited to users who both upload and download significant amounts of data.
A variation of DSL that provides equal throughput both upstream and downstream between the customer and the carrier.
DSLAM (DSL Access Multiplexer)
A connectivity device located at a telecommunications carrier's office that aggregates multiple DSL subscriber lines and connects them to a larger carrier or to the Internet backbone.
Broadband Cable (Cable Modem Acces)
A method of connecting to the internet over a cable network. With this, computers are connected to a cable modem that modulates and demodulates signals to and from the cable company's head-end.
A device that modulates and demodulates signals for transmission and reception via cable wiring. These operate at the Physical and Data Link layer of the OSI Model.
HFC (Hybrid Fiber-Coax)
A link that consists of fiber cable connecting the cable company's offices to a node location near the customer and coaxial cable connecting the node to the customer's house. ________ upgrades to existing cable wiring are required before current TV cable systems can provide Internet access.
The fiber-optic or coaxial cable that connects a neighborhood cable node to a customer's house.
A cable company's central office, which connects cable wiring to many nodes before it reaches customers' sites.
ATM (Asynchronous Transfer Mode)
A Data Link layer technology originally conceived in the early 1980s at Bell Labs and standardized by the ITU in mid-1990s. _______ relies on fixed packets, called cells, that each consist of 48 bytes of data plus a 5-byte header. _____ relies on virtual circuits and establishes a connection before sending a. The reliable connection ensured by ATM allows network managers to specify QoS levels for certain types of traffic.
A transmission method in which data being transmitted and received by nodes does not have to conform to any timing scheme. In _________ communications, a node can transmit at any time and the destination node must accept the transmission as it comes.
LANE (LAN Emulation)
A method for transporting token ring or Ethernet frames over ATM network. ______ encapsulates incoming Ethernet or token ring frames, then converts them into ATM cells for transmission over an ATM network.
SONET (Synchronous Optical Network)
A high-bandwidth WAN signaling technique that specifies framing and multiplexing techniques at the Physical layer of OSI model. It can integrate many other WAN technologies (for example, T-carriers, ISDN, and ATM technology) and allows for simple link additions and removals. SONET's topology includes a double ring of fiber-optic cable, which results in very high fault tolerance.
A characteristic of dual-ring topologies that allows them to automatically reroute traffic along the backup ring if the primary ring becomes severed.
OC (Optical Carrier)
An internationally recognized rating that indicates throughput rates for SONET connections.
The process of dialing into a remote access server to connect with a network, be it private or public.
A user's unique identifying characteristics that enable him to authenticate with a server and gain access to network resources. The most common type of credentials are a user name and password.
The process of comparing and matching a client's credentials with the credentials in the NOS user database to enable the client to log on to the network.
RAS (Remote Access Service)
The dial-up networking software provided with Microsoft Windows 95, 98, NT, and 2000. RAS requires software installed on both the client and server, a server configured to accept incoming clients, and a client with sufficient privileges on the server to access its resources.
RRAS (Routing and Remote Access Service)
The software included with Win2000 Server, XP, Vista, Server 2003, and Server 2008 that enables a server to act as a router, firewall, and remote access server. Using ______, a server can provide network access to multiple remote clients.
SLIP (Serial Line Internet Protocol)
A communications protocol that enables a workstation to connect to a server using a serial connection. _____ can support only asynchronous communications and IP traffic and requires some configuration on the client workstation.
PPP (Point to Point Protocol)
A communications protocol that enables a workstation to connect to a server using a serial connection. _____ can support multiple Network layer protocols and can use both asynchronous and synchronous communications. it performs compression and error correction and requires little configuration on the client workstation.
PPPoE (PPP over Ethernet)
PPP running over an Ethernet network. The standard for connecting home computers to an ISP via DSL or broadband cable.
RDP (Remote Desktop Protocol)
An Application layer protocol that uses TCP/IP to transmit graphics and text quickly over a remote client-host connection. _____ also carries session, licensing, and encryption information.
VNC (Virtual Network Computing)
An open source system designed to allow one workstation to remotely manipulate and receive screen updates from another workstation.
The term for software that is developed and packaged by individuals and made available to anyone for free. No licensing fee required to use it.
ICA (Independent Computing Architecture)
The software from Citrix Systems, that, when installed on a client, enables the client to connect with a host computer and exchange keystrokes, mouse clicks, and screen updates. Can work with virtually any operating system.
VPNs (Virtual Private Networks)
Wide area networks that are logically defined over public transmission systems. ______ can be created through the use of software or combined software and hardware solutions. This type of network allows an organization to carve out a private WAN through the internet, serving only its offices, while keeping the data secure and isolated from other (public) traffic.
The process of encapsulating one type of protocol in another. ______ is the way in which higher-layer data is transported over VPNs by Layer 2 protocols.
PPTP (Point-to-Point Tunneling)
A Layer 2 protocol developed by Microsoft that encapsulates PPP data for transmission over VPN connections. _____ operates with Windows RRAS access services and can accept connections from multiple different clients It is simple, but less secure than other modern tunneling protocols.
L2TP (Layer 2 Tunneling Protocol)
A protocol that encapsulates PPP data, for use on VPNs. _____ is based on Cisco technology and is standardised by the IETF. It is distinguished by its compatibility among different manufacturers' equipment; its ability to connect between clients, routers, and servers alike; and also by the fact that it can connect nodes longing to different Layer 3 networks.