User guide

44 MultiModem ZPX User Guide
Host Controller Interface. All transfers on the USB are initiated by
the hostsystem’s host controller. The host controlleris responsible
forcontrolling trafficon the USB and can be appropriately
programmed to transferdata to and from USB devices.This is
typically a PCI device that can be programmed to run a given
schedule of transfers on the USB and busmaster the resultsinto
memory for processingby the hostsoftware. There are currently
two standardsfor host controllers:OpenHCI (OHCI or Open Host
Controller Interface) andUHCI (Universal Host Controller
Interface). Both thesestandardsdefine register level interfaces of
the hostcontroller to PCI bus.Bandwidth allocationover the USB is
softwaremanaged and is done by the programming of the host
controller.
UNIX: An operating system developedby Bell Laboratories that
features multiprogramming in a muti-user environment.
Universal Serial Bus: A collection of Universal Serial Bus devices
and the software and hardware that allow them to connect the
capabilities provided by functions to the host.
Universal Serial Bus Device: Includes hubs and functions. See
device.
Universal Serial Bus Driver: The host resident software entity
responsible forproviding common servicestoclients thatare
manipulating one or more functions on one or more Host
Controllers.
Universal Serial Bus Interface: The hardware interface between
the Universal Serial Bus cable and a Universal Serial Bus device.
This includes the protocol engine required for all Universal Serial
Bus devices to be able to receive and send packets.
Unshielded Twisted Pair (UTP): Telephone-type wiring.
Tansmission media for 10Base-T.
Upstream: The direction of data flow towards the host. An
upstream port is the port on a device electrically closest to the
host that generates upstream data traffic from the hub.
Upstream ports receive downstream data traffic.
USB: See Universal Serial Bus.
USBD: See Universal Serial Bus Driver.
USB Performance categories: Low Speed (Interactive Devices at
10-100 Kb/s); Medium Speed (Phone, Audio, Compressed Video
at 500Kb/s - 10Mbp/s); High Speed (Video, Disk at 25-500 Mb/s)
V
V.25bis: An ITU-T standard for synchronous communications
between a mainframe or host and a modem using HDLC or other
character-oriented protocol.
V.54: The ITU-T standard for local and remote loopback tests in
modems, DCEs and DTEs. The four basic tests are:
• local digital loopback (tests DTE send and receive circuits),
• local analog loopback (tests local modem operation),
• remote analog loopback (tests comm link to the remote
modem), and
• remote digital loopback (tests remote modem operation).
Virtual Circuit: A logical connection. Used in packet switching
wherin a logical connection is established between two devices
at the start of transmission. All information packets follow the
same route and arrive in sequence (but do not necessarily carry a
complete address).
W
Wide Area Network (WAN): 1. A network that provides
communication services to a geographic area larger than that
served by a local area network or a metropolitan area network,
and that may use or provide public communication facilities. 2. A
data communications network designed to serve an area of
hundreds or thousands of miles; for example, public and private
packet-switching networks, and national telephone networks.
Contrast with local area network (LAN).
Wide Area Telecommunications Service (WATS): A low-cost toll
service offered by most long distance and local phone
companies. Incoming (800 call service, or IN-WATS) and outgoing
WATS are subscribed to separately, but over the same line.
X
X.25: ITU-T’s definition of a three-level packet-switching protocol
to be used between packet-mode DTEs and network DCEs. X.25
corresponds with layer 3 of the 7-layer OSI model.
Y
Yellow Alarm: An error indication sent by the T1 device when it
has not gotten a receive signal, or cannot synchronize on the
receive signal received. Contrast “Red Alarm” and “Blue Alarm”.
Z
Zero Byte Time Slot Interchange (ZBTSI): A method for allowing
64 Kbps unrestricted user data (allowing all 0s in the user data).
An alternative to (but not as popular as) B8ZS.
Glossary