Operation Manual

AT-RG213 Residential VoIP Gateway - SIP Software Reference Manual
SIP Software Release 6-0-0
J613-M0524-00
112
In firewall configurations, a multi homed gateway usually acts to block or
filter some or all of the traffic trying to pass between the networks.
multicast A special form of broadcast where copies of the packet are
delivered to only a subset of all possible destinations. See broadcast, directed
broadcast, unicast.
N
NAK Negative acknowledgement. A response sent to indicate unsuccessful
reception of information. Usually, a NAK triggers retransmission of the lost
data. See ACK.
name resolution The process of mapping a name into the corresponding
address. See DNS.
NCP Network Control Protocol. A protocol forming part of the Point-to-Point
Protocol, used to establish and configure different network layer protocols
running over point-to-point links. Each network layer protocol (e.g. IP, IPX,
DECnet) has it’s own associated NCP.
network A computer network is a data communications system which
interconnects computer systems at various different sites. A network may be
composed of any combination of LANs, MANs or WANs.
network address The network portion of an IP address. For a class A
network, the network address is the first byte of the IP address. For a class B
network, the network address is the first two bytes of the IP address. For a
class C network, the network address is the first three bytes of the IP
address. In each case, the remainder is the host address. In the Internet,
assigned network addresses are globally unique. See IP address.
network number See network address.
network-level firewall A firewall in which traffic is examined at the
network protocol packet level.
NIC Network Information Center. A group at SRI International, Menlo Park,
CA, responsible for providing users with information about TCP/IP and the
connected Internet. The machine named NIC.DDN.MIL is an online archive
of RFCs and other documents related to TCP/IP.
NSAP Network Service Access Point. The point at which network services
are provided by a network entity to a transport entity according to the OSI
reference model. NSAP addresses are assigned by a hierarchy of registration
authorities so that each valid NSAP address provides a globally
unambiguous identification of one system. One system may have multiple
NSAP addresses
NTU Network Terminating Unit. A device that takes digital data from a
computer and encodes it for transmission over digital telecommunication
lines. It is the equivalent of a modem for modern digital links. See modem.