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Basic Advanced TCP/IP Wireless
VT2400/VT2500 Series Voice Gateway User Guide
137
Q
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port mirroring
A feature that enables one port (source) on the VT2500 to be copied to another port (destination) to be
studied. The destination mirrors the transmitted (from) or received (to) data on the source port to
enable the person managing the network to monitor activity.
port triggering
A mechanism that allows incoming communication with specified applications. Primarily used for
gaming applications.
PPP
Point-to-Point Protocol is used to transport other protocols, typically for simple links over serial lines. It
is most commonly used to access the Internet with a dial-up modem.
PPPoE
Point-to-Point Protocol over Ethernet. A specification for connecting to the Internet with DSL modems.
PPTP
Point-to-Point Tunneling Protocol encapsulates other protocols. It is a new technology to create VPNs
developed jointly by several vendors.
private IP
address
An IP address assigned to a computer on the VT2500 LAN by the DHCP server on the VT2500 for a
specified lease time. Private IP addresses are used by the VT2500 LAN only; they are invisible to
devices on the Internet. See also
public IP address
.
protocol
A formal set of rules and conventions for exchanging data. Different computer types (for example PC,
UNIX, or mainframe) can communicate if they support common protocols.
provisioning
The process of autodiscovery or manually configuring a cable modem on the CMTS.
PSTN
The public switched telephone network is the traditional circuit-switched, voice-oriented telephone
network. See also
POTS
.
public IP
address
The IP address assigned to the VT2500 by the cable provider. A public IP address is visible to devices
on the Internet. See also
private IP address
.
QAM
Quadrature Amplitude Modulation uses amplitude and phase modulation to encode multiple bits of
data in one signaling element. QAM achieves faster data transfer than amplitude or phase modulation
alone, but the signal is more prone to errors caused by noise. QAM requires a transmission circuit with
a higher CNR than alternate modulation formats such as QPSK. Two types of QAM are:
•
16 QAM encodes four bits per symbol as one of 16 possible amplitude and phase combinations.
•
64 QAM encodes six bits per symbol as one of 64 possible amplitude and phase combinations.
QPSK
Quadrature Phase Shift Key (QPSK) modulation sends two bits of information per symbol period with
one symbol 90 degrees out of phase with other symbols. The four constellation points represented by
the coordinates (0,0 - 0,1 - 1,0 - 1,1) represent the four possible combinations.
QoS
Quality of service describes the priority, delay, throughput, and bandwidth of a connection.
