Manual

Layer 2 Tunnel Protocol Version 3
Glossary
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Cisco IOS Releases 12.0(29)S and 12.2(25)S
Glossary
AV P s —attribute-value pairs.
BECN—backward explicit congestion notification. Bit set by a Frame Relay network in frames traveling
in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN
bit set can request that higher-level protocols take flow control action as appropriate.
CE—customer edge (Frame Relay switch or user device).
CIR—committed information rate. Rate at which a Frame Relay network agrees to transfer information
under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second,
is one of the key negotiated tariff metrics.
data-link control layer—Layer 2 in the SNA architectural model. Responsible for the transmission of
data over a particular physical link. Corresponds approximately to the data link layer of the OSI model.
DCE—data circuit-terminating equipment (ITU-T expansion). Devices and connections of a
communications network that comprise the network end of the user-to-network interface.
dCEF—distributed Cisco Express Forwarding.
DLCI—data-link connection identifier. A unique number assigned to a PVC endpoint in a Frame Relay
network. Identifies a particular PVC endpoint within an access channel in a Frame Relay network and
has local significance only to that channel.
DTE—data terminal equipment. Device at the user end of a user-network interface that serves as a data
source, destination, or both.
FECN—forward explicit congestion notification. Bit set by a Frame Relay network to inform DTE
receiving the frame that congestion was experienced in the path from source to destination. DTE
receiving frames with the FECN bit set can request that higher-level protocols take flow-control action
as appropriate.
HDLC—High-Level Data Link Control. A generic link-level communications protocol developed by the
International Organization for Standardization (ISO). HDLC manages synchronous, code-transparent,
serial information transfer over a link connection.
ICMP—Internet Control Message Protocol. A network protocol that handles network errors and error
messages.
IDB—interface descriptor block.
IS-IS—Intermediate System-to-Intermediate System. OSI link-state hierarchical routing protocol based
on DECnet Phase V routing, whereby ISs (routers) exchange routing information based on a single
metric to determine network topology.
L2TP—An extension to PPP merging features of two tunneling protocols: Layer 2 Forwarding (L2F)
from Cisco Systems and Point-to-Point Tunneling (PPTP) from Microsoft. L2TP is an Internet
Engineering Task Force (IETF) standard endorsed by Cisco Systems, and other networking industry
leaders.
L2TPv3—Draft version of L2TP that enhances functionality in RFC 2661 (L2TP).
LMI—Local Management Interface.
MPLS—Multiprotocol Label Switching. Switching method that forwards IP traffic using a label. This
label instructs the routers and the switches in the network where to forward the packets based on
preestablished IP routing information.
MQC—modular quality of service command-line interface.