FORE Systems ES-2810 Ethernet Switch User's Manual
Glossary - 37
Glossary
Glossary
Virtual Private Data Network (VPDN) - a private data communications network built on public
switching and transport facilities rather than dedicated leased facilities such as T1s.
Virtual Private Network (VPN) - a private voice communications network built on public switch-
ing and transport facilities rather than dedicated leased facilities such as T1s.
Virtual Source/Virtual Destination (VS/VD) - An ABR connection may be divided into two or
more separately controlled ABR segments. Each ABR control segment, except the first, is
sourced by a virtual source. A virtual source implements the behavior of an ABR source end-
point. Backwards RM-cells received by a virtual source are removed from the connection.
Each ABR control segment, except the last, is terminated by a virtual destination. A virtual
destination assumes the behavior of an ABR destination endpoint. Forward RM-cells received
by a virtual destination are turned around and not forwarded to the next segment of the con-
nection.
Virtual Tributary (VT) - a structure used to carry payloads such as DS1s that run at significantly
lower rates than STS-1s.
Warm Start Trap - an SNMP trap which indicates that SNMP alarm messages or agents have
been enabled.
Wide-Area Network (WAN) - a network that covers a large geographic area.
Wideband Channel - Communications channel with more capacity (19.2K bps) than the stan-
dard capacity of a voice grade line.
X.21 - ITU-T standard for serial communications over synchronous digital lines. The X.21 pro-
tocol is used primarily in Europe and Japan.
X.25 - a well-established data switching and transport method that relies on a significant
amount of processing to ensure reliable transport over metallic media.
Yellow Alarm - An alarm signal sent back toward the source of a failed signal due to the pres-
ence of an AIS (may be used by APS equipment to initiate switching).
Zero Byte Time Slot Interchange (ZBTSI) - A technique used with the T carrier extended super-
frame format (ESF) in which an area in the ESF frame carries information about the location of
all-zero bytes (eight consecutive “0”s) within the data stream.
Zero Code Suppression - The insertion of a “1” bit to prevent the transmission of eight or more
consecutive “0” bits. Used primarily with T1 and related digital telephone company facilities,
which require a minimum “1’s density” in order to keep the individual subchannels of a mul-
tiplexed, high speed facility active.
Zero-Bit Insertion - A technique used to achieve transparency in bit-oriented protocols. A zero
is inserted into sequences of one bits that cause false flag direction.
To Next Page
Loading...
