Numerics G L O S S A R Y
GLOSSARY
Numerics
10BaseT
10-Mbps baseband Ethernet specification using two pairs of twisted-pair cabling (Categories 3, 4, or
5): one pair for sending data and the other for receiving data. 10BASET, which is part of the IEEE 802.3
specification, has a distance limit of approximately 328 feet (100 meters) per segment.
A
A-law
ITU-T companding standard used in the conversion between analog and digital signals in PCM
systems. A-law is used primarily in European phone networks and is similar to the North American
µ-law standard. See also companding and µ-law.
AVT tones
Out-of-bound signaling as defined in RFC 2833.
C
category-3 cable
One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 3 cabling is used
in 10BaseT networks and can send data at speeds up to 10 Mbps.
CED tone detection
Called station identification. A three-second, 2100 Hz tone generated by a fax machine answering a
call, which is used in the hand-shaking used to set the call; the response from a called fax machine to
a CNG tone.
CELP
code excited linear prediction compression. Compression algorithm used in low bit-rate voice
encoding. Used in ITU-T Recommendations G.728, G.729, G.723.1.
CLIP
Calling Line Identification Presentation. Shows your identity to callers with Caller ID.
CLIR
Calling Line Identification Restriction. Hides your identity from callers with Caller ID.
CNG
Comfort Noise Generation
codec
coder decoder. In Voice over IP, Voice over Frame Relay, and Voice over ATM, a DSP software
algorithm used to compress/decompress speech or audio signals.
companding
Contraction derived from the opposite processes of compression and expansion. Part of the PCM
process whereby analog signal values are rounded logically to discrete scale-step values on a nonlinear
scale. The decimal step number then is coded in its binary equivalent prior to transmission. The process
is reversed at the receiving terminal using the same nonlinear scale. Compare with compression and
expansion. See also a-law and µ-law.
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Glossary
compression
The running of a data set through an algorithm that reduces the space required to store or the bandwidth
required to transmit the data set. Compare with companding and expansion.
CoS
Class of service. An indication of how an upper-layer protocol requires a lower-layer protocol to treat
its messages. In SNA subarea routing, CoS definitions are used by subarea nodes to determine the
optimal route to establish a given session. A CoS definition comprises a virtual route number and a
transmission priority field.
D
DHCP
Dynamic Host Configuration Protocol. Provides a mechanism for allocating IP addresses dynamically
so that addresses can be reused when hosts no longer need them.
dial peer
An addressable call endpoint. In Voice over IP (VoIP), there are two types of dial peers: POTS and
VoIP.
DNS
Domain Name System. System used on the Internet for translating names of network nodes into
addresses.
DSP
digital signal processor. A DSP segments the voice signal into frames and stores them in voice packets.
DTMF
dual tone multifrequency. Tones generated when a button is pressed on a phone, primarily used in the
U.S. and Canada.
E
E.164
The international public telecommunications numbering plan. A standard set by the ITU-T which
addresses phone numbers.
endpoint
A SIP terminal or gateway. An endpoint can call and be called. It generates and/or terminates the
information stream.
expansion
The process of running a compressed data set through an algorithm that restores the data set to its
original size. Compare with companding and compression.
F
firewall
Router or access server, or several routers or access servers, designated as a buffer between any
connected public networks and a private network. A firewall router uses access lists and other methods
to ensure the security of the private network.
FoIP
Fax over IP
FQDN
Fully Qualified Domain (FQDN) format “mydomain.com” or “company.mydomain.com.”
FSK
Frequency shift key
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Glossary
FXO
Foreign Exchange Office. An FXO interface connects to the public switched phone network (PSTN)
central office and is the interface offered on a standard phone. Cisco FXO interface is an RJ-11
connector that allows an analog connection at the PSTN central office or to a station interface on a
PBX.
FXS
Foreign Exchange Station. An FXS interface connects directly to a standard phone and supplies ring,
voltage, and dial tone. Cisco's FXS interface is an RJ-11 connector that allows connections to basic
phone service equipment, keysets, and PBXs.
G
G.711
Describes the 64-kbps PCM voice coding technique. In G.711, encoded voice is already in the correct
format for digital voice delivery in the PSTN or through PBXs. Described in the ITU-T standard in its
G-series recommendations.
G.723.1
Describes a compression technique that can be used for compressing speech or audio signal
components at a very low bit rate as part of the H.324 family of standards. This Codec has two bit
rates associated with it: 5.3 and 6.3 kbps. The higher bit rate is based on ML-MLQ technology and
provides a somewhat higher quality of sound. The lower bit rate is based on CELP and provides
system designers with more flexibility. Described in the ITU-T standard in its G-series
recommendations.
G.729A
Describes CELP compression where voice is coded into 8-kbps streams. There are two variations of
this standard (G.729 and G.729 Annex A) that differ mainly in computational complexity; both
provide speech quality similar to 32-kbps ADPCM. Described in the ITU-T standard in its G-series
recommendations.
gateway
A gateway allows SIP or H.323 terminals to communicate with terminals configured to other protocols
by converting protocols. A gateway is the point where a circuit-switched call is encoded and
repackaged into IP packets.
H
H.323
H.323 allows dissimilar communication devices to communicate with each other by using a standard
communication protocol. H.323 defines a common set of CODECs, call setup and negotiating
procedures, and basic data transport methods.
I
ICMP
Internet Control Message Protocol
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IP
Internet Protocol. Network layer protocol in the TCP/IP stack offering a connectionless internetwork
service. IP provides features for addressing, type-of-service specification, fragmentation and
reassembly, and security. Defined in RFC 791.
IVR
Interactive voice response. Term used to describe systems that provide information in the form of
recorded messages over phone lines in response to user input in the form of spoken words or, more
commonly, DTMF signaling.
L
LDAP
Lightweight Directory Access Protocol
LEC
local exchange carrier
Location Server
A SIP redirect or proxy server uses a location server to get information about a caller’s location.
Location services are offered by location servers.
M
MWI
message waiting indication
µ-law
North American companding standard used in conversion between analog and digital signals in PCM
systems. Similar to the European a-law. See also a-law and companding.
N
NAT
Network Address Translation. Mechanism for reducing the need for globally unique IP addresses.
NAT allows an organization with addresses that are not globally unique to connect to the Internet by
translating those addresses into globally routable address spaces. Also known as Network Address
Translator.
NSE packets
Real-Time Transport Protocol (RTP) digit events are encoded using the Named Signaling Event (NSE)
format specified in RFC 2833, Section 3.0.
NAT Server
Network Address Translation. an Internet standard that enables a local-area network (LAN) to use one
set of IP addresses for internal traffic and a second set of addresses for external traffic.
NTP
Network Time Protocol. Protocol built on top of TCP that assures accurate local time-keeping with
reference to radio and atomic clocks located on the Internet. This protocol is capable of synchronizing
distributed clocks within milliseconds over long time periods.
P
POTS
Plain old phone service. Basic phone service supplying standard single-line phones, phone lines, and
access to the PSTN.
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Glossary
Proxy Server
An intermediary program that acts as both a server and a client for making requests on behalf of other
clients. Requests are serviced internally or by passing them on, possibly after translation, to other
servers. A proxy interprets, and, if necessary, rewrites a request message before forwarding it.
PSTN
Public switched phone network
Q
QoS
Quality of Service. The capability of a network to provide better service to selected network traffic
over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and
802.1 networks, SONET, and IP-routed networks that may use any or all these underlying
technologies. The primary goal of QoS is to provide priority including dedicated bandwidth,
controlled jitter and latency (required by some real-time and interactive traffic), and improved loss
characteristics.
R
Redirect Server
A redirect server is a server that accepts a SIP request, maps the address into zero or more new
addresses, and returns these addresses to the client. It does not initiate its own SIP request nor accept
calls.
Registrar Server
A registrar server is a server that accepts Register requests. A registrar is typically colocated with a
proxy or redirect server and may offer location services.
router
Network layer device that uses one or more metrics to determine the optimal path along which
network traffic should be forwarded. Routers forward packets from one network to another based on
network layer information. Occasionally called a gateway (although this definition of gateway is
becoming increasingly outdated). Compare with gateway.
RTP
Real-Time Transport Protocol. One of the IPv6 protocols. RTP is designed to provide end-to-end
network transport functions for applications transmitting real-time data, such as audio, video, or
simulation data, over multicast or unicast network services. RTP provides services such as payload
type identification, sequence numbering, timestamping, and delivery monitoring to real-time
applications.
S
SDP
Session Definition Protocol. An IETF protocol for the definition of Multimedia Services. SDP
messages can be part of SGCP and MGCP messages.
SIP
Session Initiation Protocol. Protocol developed by the IETF MMUSIC Working Group as an
alternative to H.323. SIP features are compliant with IETF RFC 2543, published in March 1999. SIP
equips platforms to signal the setup of voice and multimedia calls over IP networks.
SIP endpoint
A terminal or gateway that acts as a source or sink of Session Initiation Protocol (SIP) voice data. An
endpoint can call or be called, and it generates or terminates the information stream.
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Glossary
SLIC
Subscriber Line Interface Circuit. An integrated circuit (IC) providing central office-like phone
interface functionality.
SOHO
Small office, home office. Networking solutions and access technologies for offices that are not
directly connected to large corporate networks.
T
T.38
T.38 is an ITU recommendation for allowing transmission of fax over IP networks in real time.
TCP
Transmission Control Protocol. Connection-oriented transport layer protocol that provides reliable
full-duplex data transmission. TCP is part of the TCP/IP protocol stack.
TFTP
Trivial File Transfer Protocol. Simplified version of FTP that allows files to be transferred from one
computer to another over a network, usually without the use of client authentication (for example,
username and password).
TN power systems
A TN power system is a power distribution system with one point connected directly to earth (ground).
The exposed conductive parts of the installation are connected to that point by protective earth
conductors.
TOS
Type of service. See CoS.
U
UAC
User agent client. A client application that initiates the SIP request.
UAS
User agent server (or user agent). A server application that contacts the user when a SIP request is
received, and then returns a response on behalf of the user. The response accepts, rejects, or redirects
the request.
UDP
User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol stack. UDP
is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery,
requiring that error processing and retransmission be handled by other protocols. UDP is defined in
RFC 768.
user agent
See UAS.
V
VAD
Voice activity detection. When enabled on a voice port or a dial peer, silence is not transmitted over
the network, only audible speech. When VAD is enabled, the sound quality is slightly degraded but
the connection monopolizes much less bandwidth.
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Glossary
voice packet
gateway
Gateway platforms that enable Internet telephony service providers to offer residential and
business-class services for Internet telephony.
VoIP
Voice over IP. The capability to carry normal telephony-style voice over an IP-based Internet with
POTS-like functionality, reliability, and voice quality. VoIP enables a router to carry voice traffic (for
example, phone calls and faxes) over an IP network. In VoIP, the DSP segments the voice signal into
frames, which then are coupled in groups of two and stored in voice packets. VoIP is a blanket term,
which generally refers to Cisco’s standard-based (for example H.323) approach to IP voice traffic.
X
XML
eXtensible Markup Language. Designed to enable the use of SGML on the World-Wide Web. XML
allow you to define your own customized markup language.
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