Chapter 4 Vocabulary

  1. Access Line
    In Frame Relay, the physical serial link that connects a Frame Relay switch.  The access link uses the same physical layer standards as do point-to-point leased lines.
  2. Back-to-back Link
    A serial link between two routers, created without CSU/DSUs, by connecting a DTE cable to one router and a DCE cable to the other.  Typically used in labs to build serial link without the expense of an actual leased line from the Telco.
  3. Clocking
    The process of supplying a signal over a cable, either on a separate pin on a serial cable or as part of the signal transitions in the transmission signal so that the receiving device can keep synchronization with the sending device.
  4. DTE (layer 1)
    Data terminal equipment.  From a layer 1 perspective, the DTE synchronizes its clock based on the clock sent by the DCE.  From a packet switching perspective, the DTE is the device outside the service providers network, typically a router.
  5. CSU/DSU
    Channel service unit / Data service unit.  A device that understands the Layer 1 details of serial links installed by a telco and how to use a serial cable to communicate with networking equipment such as routers.
  6. DCE (layer 1)
    Data communications equipment.  Froma physical layer perspective, the device providing the clocking on a WAN link, typically a CSU/DSU, is the DCE.  From a packet switching perspective, the service providers switch, to which a router might connect, is considered the DCE.
  7. DS0
    Digial signal level 0.  A 64 kbps line or channel of a faster line inside a telco whose origins are to support a single voice call using the original voice (PCM) codecs.
  8. DS1
    Digital signal level 1.  A 1.544 Mbps line from the telco, with 24 DS0 channels of 64kbps each, plus an 8 kbps management and framing channel.  Also called a T1.
  9. Frame Relay
    An internaational standard data-link protocol that defincs the capabilities to create a frame switched (packet switched) service, allowing DTE devices (typically routers) to send data to many other devices using a single physical connection to the frame relay service.
  10. HDLS
    High Level Datalink Control.  A bit-oriented synchronous datalink layer protocol developed by the International Organization for Standardization.  (ISO).
  11. Leased Line
    A serial communications circuit between two points, provided by some service provider, typicall a telephone company (telco).  Because the telco does not sell a physical cable between two end points, instead charging a montly fee for the ability to send bits between the two sites, the service is considered to be a leased service.
  12. Packet Switching
    A generic reference to network services, typically WAN services, in which the service examines the contents of the transmitted data to make some type of forwarding decision.  This term is mainly used to contrast with the WAN term ciruit switching, in which the provider sets up a (layer 1) circuit between two devices and the provider makes no attempt to interpret the meaning of the bits.
  13. PPP
    Point-to-Point protocol.  A protocol that provides router-to-router and host to network connections over synchronous point-to-point and asynchronous point-to-point circuits.
  14. Serial Cable
    A type of cable with many different styles of connectors used to connect a router to an external CSU/DSU on a leased line installation.
  15. Synchronous
    The imposition of time ordering on a bit stream.  Practically, a device will try to use the same speed as another device on the other end of a serial link.  However by examining transitions between voltage states on the link, the device can notice slight variations in speed on each end and can adjust its speed accordingly.
  16. T1
    A line from the telco that allows transmission of data at 1.544 Mbps, with the ability to treat the lines as 24 different 64 kbps DS0 channels.  (Plus 8kbps of overhead).
  17. Virtual Circuit
    In packet switch services like Frame Relay VC referes to the ability of two DTE devices (typically routers) to send and receive data directly to each other, which supplies the same function as a physical leased line (leased circuit), but doing so without a physical circuit.  This term is meant as a contrast with a leased line or leased circuit.
  18. Clock Source
    The device to which other devices on the link adjust their speed when using synchronous links.
  19. Telco
    Telephone company.
  20. Four Wire dircuit
    A line from the telco with 4 wires, composed of two twisted pair wires.  Each pair is used to send in one direction so a four wire circuit allows full-duplex communication.
Card Set
Chapter 4 Vocabulary
CCNA chapter 4 vocabulary