formed) reflects the underlying metaphor of subma-
rine sonar. Just as the sonar operator sends out a sig-
nal and waits to hear it echo ("ping") back from a
submerged object, the network user can ping another
node on the network and wait to see if it responds.
being embedded within the signal as in synchronous
transmissions.
that is part of the X.25 stack.
for the calculation of paths through the network,
among switches and groups of switches. It is based on
well-known link-state routing procedures and allows
for automatic configuration in networks whose
addressing scheme is determined by the topology.
gle system at the starting point, called the "root node,"
to systems at multiple points of destination, called
"leaves." See also: point-to-point connection.
two ways between two ATM end systems. See also:
point-to-multipoint connection.
ignoring the split-horizon rule) after route poisoning
has occurred. Typically used with DV routing proto-
cols in order to overcome large routing loops and offer
explicit information when a subnet or network is not
accessible (instead of merely suggesting that the net-
work is unreachable by not including it in updates).
See also: route poisoning.
ary devices have data to transmit. A message is sent to
each secondary, granting the secondary the right to
transmit.
to interconnect with a local exchange carrier. (2) Post
Office Protocol (currently at version 3): A protocol
used by client e-mail applications for recovery of mail
from a mail server.
because it is difficult to manage. Allows only certain
frames to traverse administrator-assigned segments.
Transport layer are called segments; PDUs at the Net-
work layer are called packets or datagrams; and PDUs
at the Data-Link layer are called frames. The Physical
layer uses bits.
ing the earlier SLIP. Its features include address notifi-
cation, authentication via CHAP or PAP, support for
multiple protocols, and link monitoring. PPP has two
layers: the Link Control Protocol (LCP) establishes,
configures, and tests a link; and then any of various
Network Control Programs (NCPs) transport traffic
for a specific protocol suite, such as IPX. See also:
CHAP, PAP, and SLIP.
encoded, and converted for use by software at the
Application layer. See also: Application layer, Data-
Link layer, Network layer, Physical layer, Session
layer, and Transport layer.
is made up of a single 64Kbps D channel in addition to
23 (T1) or 30 (E1) B channels. See also: ISDN.
for link management, such as link setup and tear-
down.
Cisco TAC.