NEC UNIVERGE SV9100 Manual page 33

Part 1: VoIP Reference Manual 33
Compression
Compression is used at anywhere from 1:1 to 12:1 ratios in VOIP applications to consume less
bandwidth and leave more for data or other voice/fax communications. The voice quality may
decrease with increased compression ratios.
Connection-oriented
Mode of communication in which a connection must be established between the transmitter and
receiver before transmission of user data. This can be done by switching a circuit or by setting up a
logical channel. A well- known connection-oriented protocol is TCP. Connection-oriented is the
opposite of connectionless.
Connectionless
Mode of communication in which a connection (circuit or logical channel) does not need to be set up
for data transmission between the transmitter and receiver. It is the underlying protocol for packet-
switched transmission. The individual data packets can go from the transmitter to the receiver via
different paths. A well- known connectionless protocol is UDP.
CRTP
Compressed Real-Time Transmission Protocol- See RTP
CS-ACELP
Conjugate Structure Algebraic Code Excited Linear Prediction. CELP voice compression algorithm
providing 8 Kbps, or 8:1 compression, standardized in ITU-T Recommendation G.729.
CSMA/CD
Carrier Sense Multiple Access/Collision Detection This is the access procedure to the Ethernet in
which the participating stations physically monitor the traffic on the line. If no transmission is taking
place at the time the particular station can transmit. If two stations attempt to transmit
simultaneously this causes a collision which is detected by all participating stations. After a random
time interval the stations that collided attempt to transmit again. If another collision occurs the time
intervals from which the random waiting time is selected are increased step by step. Networks using
the CSMA/CD procedure are simple to implement but do not have deterministic transmission
characteristics. The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO
8802.3.
DID
Direct Inward Dialling; The ability to make a telephone call directly into an internal extension without
having to go through the operator. Called DDI in some territories (Direct Dial In)
Diffserv
Differentiated Services; The Diffserv model divides traffic into a small number of classes to provide
quality of service (QoS).
DTMF
Dual-Tone Multifrequency; The type of audio signals generated when you press the buttons on a
touch-tone telephone.
DSP
Digital Signal Processor
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