Glossary
36
SWITCHED VIRTUAL CIRCUIT (SVC)—A virtual circuit (X.25), virtual connection
(Frame Relay) or virtual channel connection (ATM) that has been established
dynamically in response to a signaling request message.
SWITCHED LAN—Emerging technology that replaces the shared bus backplane of
Ethernet hubs and the shared ring backplane of token Ring hubs with a switching
backplane. Connectivity is provided by switching sender traffic directly to the port of the
addressed destination device. Provides potentially higher throughput, scalable capacity,
and simpler configuration support. Does not require any changes to access wiring or
adapter cards.
SYNCHRONOUS OPTICAL NETWORK (SONET)—Also called the Synchronous
Digital Hierarchy (SDH), a set of physical layer definitions for data transmission across
fiber-based high-speed links.
TCP/IP PROTOCOLS—A set of protocols for intercomputer communication, including
network level (Internet Protocol), transport level (Transmission Control Protocol or
TCP) and application level protocols (for example, Telnet terminal emulation). TCP/IP
has been used for many years in two country-wide networks, the ARPANET and
MILNET. Recently, TCP/IP has become very popular with users of a variety of multi-
user computer systems and engineering workstations. Most UNIX computers use TCP/
IP over Ethernet as the main intercomputer networking technology. TCP/IP is also
popular among PC users, particularly as a means of communication with large multi-
user computers.
TELCO CONNECTOR— A 50-pin receptacle that plugs into the front of the hub,
enabling cables from external devices to connect to the hub.
TRUNK CABLE—Coaxial cable used for distribution of signals over long distances
throughout a cable system.
UNSHIELDED TWISTED PAIR (UTP)—A cable used in 10Base-T wiring that
consists of at least two twisted pairs of 22 to 26 AWG wire. The pairs should have at least
3 twists per foot and have an impedance of 100 W. Level 3, Level 4 and Level 5 UTP
cables fit these criteria.
USER-TO-NETWORK INTERFACE (UNI)—The interface between an end device
and a public or private ATM switch.
VIRTUAL CIRCUIT (VC)—A connection between end users that has defined end
points and route but does not have bandwidth dedicated to it. Bandwidth is allocated on
demand by the network as users have traffic to transmit.
VIRTUAL CHANNEL CONNECTION (VCC)—Virtual channels in two or more
sequential physical circuits can be concatenated to create an end-to-end connection
called a VCC. A VCC is a specific instance of a SVC or PVC. A VCC may traverse one
end-to-end VPC or several sequential VPCs.
VIRTUAL CIRCUIT IDENTIFIER (VCI)—Field in an ATM cell that maps the cell’s
route through the ATM network.
VIRTUAL LAN (VLAN)—A user-configured logical workgroup or collection of
Ethernet addresses, as opposed to a physical LAN defined entirely by wiring.
VIRTUAL PATH IDENTIFIER (VPI)—Field in an ATM cell that maps the cell’s
route through the ATM network.
