KT-Ch 7-Wide Area Networks

  1. ADSL (Asymmetric DSL)
    A variation of DSL that offers more throughput when data travel downstream, downloading from a local carrier's switching facility to the customer, than when data travel upstream, uploading from the customer to the local carrier's switching facility.
  2. asymmetrical
    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.
  3. asynchronous
    A transmission method in which data being transmitted and received by nodes do not have to conform to any timing scheme. In asynchronous communications, a node can transmit at any time and the destination node must accept the transmission as it comes.
  4. ATM (Asynchronous Transfer Mode)
    A Data Link layer technology originally conceived in the early 1980s at Bell Labs and standardized by the ITU in the mid-1990s. ATM relies on fixed packets, called cells, that each consist of 48 bytes of data plus a 5-byte header. ATM relies on virtual circuits and establishes a connection before sending data. The reliable connection ensured by ATM allows network managers to specify QoS levels for certain types of traffic.
  5. B channel In ISDN
    , the "bearer" channel, so named because it bears traffic from point to point.
  6. bonding
    The process of combining more than one bearer channel of an ISDN line to increase throughput. For example, BRI's two 64-Kbps B channels are bonded to create an effective throughput of 128 Kbps.
  7. BPL (broadband over powerline)
    High-speed Internet access delivered over the electrical grid.
  8. BRI (Basic Rate Interface)
    A variety of ISDN that uses two 64-Kbps bearer channels and one 16-Kbps data channel, as summarized by the notation 2B+D. BRI is the most common form of ISDN employed by home users.
  9. broadband cable
    A method of connecting to the Internet over a cable network. In broadband cable, computers are connected to a cable modem that modulates and demodulates signals to and from the cable company's head-end.
  10. bus topology WAN
    A WAN in which each location is connected to no more than two other locations in a serial fashion.
  11. cable drop
    The fiber-optic or coaxial cable that connects a neighborhood cable node to a customer's house.
  12. cable modem
    A device that modulates and demodulates signals for transmission and reception via cable wiring.
  13. cell
    A packet of a fixed size. In ATM technology, a cell consists of 48 bytes of data plus a 5-byte header.
  14. CIR (committed information rate)
    The guaranteed minimum amount of bandwidth selected when leasing a frame relay circuit. Frame relay costs are partially based on CIR.
  15. CO (central office)
    The location where a local or long-distance telephone service provider terminates and interconnects customer lines.
  16. 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. Typically, a CSU is combined with a DSU in a single device, a CSU/DSU.
  17. CSU/DSU
    A combination of a CSU (channel service unit) and a DSU (data service unit) that serves as the connection point for a T1 line at the customer's site. Most modern CSU/DSUs also contain a multiplexer. A CSU/DSU may be a separate device or an expansion card in another device, such as a router.
  18. D channel
    In ISDN, the "data" channel is used to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals.
  19. dedicated
    A continuously available link or service that is leased through another carrier. Examples of dedicated lines include ADSL, T1, and T3.
  20. dial-up
    A type of connection in which a user connects to a distant network from a computer and stays connected for a finite period of time. Most of the time, the term dial-up refers to a connection that uses a PSTN line.
  21. downstream
    A term used to describe data traffic that flows from a carrier's facility to the customer. In asymmetrical communications, downstream throughput is usually much higher than upstream throughput. In symmetrical communications, downstream and upstream throughputs are equal.
  22. DS0 (digital signal, level 0)
    The equivalent ofone data or voice channel in T-carrier technology, as defined by ANSI Physical layer standards. All other signal levels are multiples ofDS0.
  23. 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. DSL comes in several different varieties, the most common of which is Asymmetric DSL (ADSL).
  24. DSL modem
    A device that demodulates an incoming DSL signal, extracting the information and passing it to the data equipment (such as telephones and computers) and modulates an outgoing DSL signal.
  25. 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.
  26. 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. Typically, a DSU is combined with a CSU in a single device, a CSU/DSU.
  27. E1 A digital carrier standard used in Europe that offers 30 channels and a maximum of 2.048-Mbps throughput.
    • E3
    • A digital carrier standard used in Europe that offers 480 channels and a maximum of 34.368-Mbps throughput.
  28. fractional T1
    An arrangement that allows a customer to lease only some of the channels on a T1 line.
  29. frame relay A digital, packet-switched WAN technology whose protocols operate at the
    Data Link layer. The name is derived from the fact that data is separated into frames, which are then relayed from one node to another without any verification or processing. Frame relay offers throughputs between 64 Kbps and 45 Mbps. A frame relay customer chooses the amount of bandwidth he requires and pays for only that amount.
  30. FTTH
    (fiber to the home) A service in which a residential customer is connected to his carrier's network with fiber-optic cable.
  31. FTTP
    (fiber to the premises) A service in which a residential or business customer is connected to his carrier's network using fiber-optic cable.
  32. full-mesh WAN
    A version of the mesh topology WAN in which every site is directly connected to every other site. Full-mesh WANs are the most fault-tolerant type of WAN.
  33. head-end
    A cable company's central office, which connects cable wiring to many nodes before it reaches customers' sites.
  34. 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. HFC upgrades to existing cable wiring are required before current TV cable systems can provide Internet access.
  35. 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. ISDN lines may carry voice and data signals simultaneously. Two types of ISDN connections are used in North America: BRI (Basic Rate Interface) and PRI (Primary Rate Interface). Both use a combination ofbearer channels (B channels) and data channels (D channels).
  36. LANE
    (LAN Emulation) A method for transporting token ring or Ethernet frames over ATM networks. LANE encapsulates incoming Ethernet or token ring frames, then converts them into ATM cells for transmission over an ATM network.
  37. local loop
    The part of a phone system that connects a customer site with a telecommunications carrier's switching facility.
  38. mesh topology WAN
    A type of WAN in which several sites are directly interconnected. Mesh WANs are highly fault tolerant because they provide multiple routes for data to follow between any two points.
  39. NIU (network interface unit)
    The point at which PSTN-owned lines terminate at a customer's premises. The NIU is usually located at the demarc.
  40. NSP (network service provider)
    A carrier that provides long-distance (and often global) connectivity between major data-switching centers across the Internet. AT&T, Verizon, and Sprint are all examples of network service providers in the United States. Customers, including ISPs, can lease dedicated private or public Internet connections from an NSP.
  41. NT1 (Network Termination 1 )
    A device used on ISDN networks that connects the incoming twisted pair wiring with the customer's ISDN terminal equipment.
  42. 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.
  43. OC (Optical Carrier)
    An internationally recognized rating that indicates throughput rates for SONET connections.
  44. OLT (optical line terminal)
    A device located at the carrier's endpoint of a passive optical network. An OLT contains multiple optical ports, or PON interfaces and a splitter that subdivides the capacity of each port into up to 32 logical channels, one per subscriber.
  45. ONU (optical network unit)
    In a passive optical network, the device near the customer premises that terminates a carrier's fiber-optic cable connection and distributes signals to multiple endpoints via fiber-optic cable, in the case of FTTP, or via copper or coax cable.
  46. 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. Partial-mesh WANs are less expensive to implement than full-mesh WANs.
  47. PON (passive optical network)
    A network in which a carrier uses fiber-optic cabling to connect with multiple endpoints—for example, many businesses on a city block. The word passive applies because in a PON no repeaters or other connectivity devices intervene between a carrier and its customer.
  48. PRI (Primary Rate Interface)
    A type ofISDN that uses 23 bearer channels and one 64-Kbps data channel, represented bythe notation 23B+D. PRI is less commonly used by individual subscribers than BRI, but it may be used by businesses and other organizations needing more throughput.
  49. PSTN (Public Switched Telephone Network)
    The network of lines and carrier equipment that provides telephone service to most homes and businesses. Now, except for the local loop, nearly all of the PSTN uses digital transmission. Its traffic is carried by fiber-optic or copper twisted pair cable, microwave, and satellite connections.
  50. PVC (permanent virtual circuit)
    A point-to-point connection over which data may follow any number of different paths, as opposed to a dedicated line that follows a predefined path. X.25, frame relay, and some forms of ATM use PVCs.
  51. 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.
  52. RJ-48 (registered jack 48)
    A standard for terminating wires in an eight-pin connector. RJ-48 is the preferred connector type for T1 connections that rely on twisted pair wiring.
  53. SDH (Synchronous Digital Hierarchy)
    The international equivalent of SONET.
  54. self-healing
    A characteristic of dual-ring topologies that allows them to automatically reroute traffic along the backup ring if the primary ring becomes severed.
  55. signal level
    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.
  56. smart jack
    A termination for T-carrier wire pairs that is located at the customer demark and which functions as a connection protection and monitoring point.
  57. SONET (Synchronous Optical Network)
    A high-bandwidth WAN signaling technique that specifies framing and multiplexing techniques at the Physical layer of the 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.
  58. 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.
  59. SVC (switched virtual circuit)
    A logical, point-to-point connection that relies on switches to determine the optimal path between sender and receiver. ATM technology uses SVCs. switched virtual circuit See SVC.
  60. symmetrical
    A characteristic of 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.
  61. symmetrical DSL
    A variation of DSL that provides equal throughput both upstream and downstream between the customer and the carrier.
  62. synchronous
    A transmission method in which data being transmitted and received by nodes must conform to a timing scheme.
  63. T1
    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.
  64. T3
    • A digital carrier standard used in North America and most of Asia that can carry the equivalent of 672 channels T3s rely on time division multiplexing and require either fiber-optic or microwave transmission media.
    • 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).
  65. T-carrier
    The term for any kind of leased line that follows the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4s.
  66. TA (terminal adapter)
    A device used to convert digital signals into analog signals for use with ISDN phones and other analog devices. TAs are sometimes called ISDN modems.
  67. TE (terminal equipment)
    The end nodes (such as computers and printers) served by the same connection (such as an ISDN, DSL, or T1 link).
  68. tiered topology
    WAN A type of WAN in which sites that are connected in star or ring formations are interconnected at different levels, with the interconnection points being organized into layers to form hierarchical groupings.
  69. upstream
    A term used to describe data traffic that flows from a customer's site to a carrier's facility. In asymmetrical communications, upstream throughput is usually much lower than downstream throughput. In symmetrical communications, upstream and downstream throughputs are equal.
  70. virtual circuit
    A connection between network nodes that, although based on potentially disparate physical links, logically appears to be a direct, dedicated link between those nodes.
  71. WAN link
    A point-to-point connection between two nodes on a WAN.
  72. X.25
    An analog, packet-switched WAN technology optimized for reliable, long-distance data transmission and standardized by the ITU in the mid-1970s. The X.25 standard specifies protocols at the Physical, Data Link, and Network layers of the OSI model. It provides excellent flow control and ensures data reliability over long distances by verifying the transmission at every node. X.25 can support a maximum of only 2-Mbps throughput.
  73. xDSL
    The term used to refer to all varieties of DSL
Card Set
KT-Ch 7-Wide Area Networks
Network + Guide to Networks Sixth Edition Tamara Dean