Motorola SURFBOARD SVG2500 - Manual (Page 173)

17 GLOSSARY
158
TERM DEFINITION
TTL The time to live is the number of routers (or hops) a packet can
traverse before being discarded. When a router processes a
packet, it decreases the TTL by 1. When the TTL reaches zero,
the packet is discarded.
tunnel To place packets inside other packets to send over a network.
The protocol of the enclosing packet is understood by each
endpoint, or tunnel interface, where the packet enters and
exits on the network. VPNs rely on tunneling to create a secure
network.
Tunneling requires the following protocol types:
• A carrier protocol, such as TCP, used by the network that
the data travels over
• An encapsulating protocol, such as IPSec, L2F, L2TP, or
PPTP, that is wrapped around the original data
• A passenger protocol, such as IP, for the original data
two-way A cable system that can transmit signals in both directions to
and from the headend and the subscriber.
U-Z
TERM DEFINITION
UDP User Datagram Protocol
unicast A point-to-point data transmission sent from one sender to one
receiver. This is the normal way you access websites. See also
broadcast and multicast
upstream In a cable data network, upstream describes the direction of data
sent from the subscriber’s computer through the cable modem
to the CMTS and the Internet.
USB Universal Serial Bus is a computer interface for add-on devices
such as printers, scanners, mice, modems, or keyboards. USB
supports data transfer rates of 12 Mbps and plug-and-play
installation. You can connect up to 127 devices to a single USB
port.
UTP Unshielded twisted pair (wire)
VLAN A virtual local area network is group of devices on different LAN
segments that are logically configured to communicate as if
they are connected to the same wire.
VoIP Voice over Internet Protocol is a method to exchange voice,
fax, and other information over the Internet. Voice and fax have
traditionally been carried over traditional telephone lines of the
PSTN using a dedicated circuit for each line. VoIP enables calls