Operation Manual

Glossary
SIP Software Release 6-0-0
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affecting the other layers. This greatly simplifies the task of designing and
maintaining communication programs.
layer 2 Interface An entity representing the layer 2 interface in the OSI/ISO
network layering model, also referred to as a link layer interface. Examples
are Ethernet, PPP, X.25 and Frame Relay.
LED Light Emitting Diode. A luminous indicator.
local interface A default logical interface for all locally generated IP
packets.
loopback A state in which data transmitted is also received. Normally it is
used to test data links by applying a loopback at various points and
verifying successful reception of the data transmitted.
M
MAC Media Access Control. The lower portion of the data link layer. The
MAC differs for various physical media.
MAC address The hardware address of a device connected to a shared
media. For example, the MAC address of a PC on an Ethernet is its Ethernet
address.
Management information base See MIB.
mask A bit pattern used to ‘‘mask out’’ portions of data.
Mb/s Megabits per Second. Unit of data transmission speed.
MCU Multipoint control unit. Unit that manages conference resources,
negotiates between terminals for the purpose of determining the audio or
video coder/decoder (CODEC) to use, and may handle the media stream.
MIB Management Information Base. The set of parameters an SNMP
management station can query or set in the SNMP agent of a network device
(e.g., router). Standard MIBs have been defined, and vendors can develop
private MIBs. In theory, any SNMP manager can talk to any SNMP agent
with a properly defined MIB. See SNMP.
modem Modulator/demodulator. A device that takes digital data from a
computer and encodes it in analog form for transmission over a phone line.
See NTU.
MTU Maximum Transmission Unit. The largest possible unit of data that can
be sent on a given physical medium. For local area networks (e.g. Ethernet),
the MTU is determined by the network hardware. For wide area networks
using serial lines, the MTU is determined by software. The MTU of Ethernet
is 1500 bytes.
multi-homed gateway A dual homed gateway is a system that has two or
more network interfaces, each of which is connected to a different network.