Hx1-Hx2 Manual-1.4.1 - Telos

A4 | appendix 1
Unless very aggressive contesting is planned, these arrangements should probably best be
avoided. See blocking and concentration.
Circuit- A physical path through which electrical signals can pass. It consists of a network of
conductors and other components, separated by insulators. Technically this term cannot be
applied to fiber optic or other “non-metallic” paths. See also channel.
Circuit Switching- A system where a dedicated channel is allocated to the users of that call
for the duration of that call. That channel is allocated for the duration of the call regardless if
information is being transmitted at any given moment. Bandwidth through the channel is fixed,
at no time may this bandwidth be exceeded. If this bandwidth is not used it is wasted. While
inherently inefficient, the dependable and reliable nature of circuit switching makes it ideally
suited to real-time voice and audio/video conferencing applications. When over loaded Circuit
Switched networks will respond “all circuits are busy… try again later”. This is in stark contrast
to packet switched networks or to systems where statistical multiplexing is used. See statistical
multiplexing and Packet Switching.
CLASS- Custom Local Area Signaling Services. A variety of enhanced features (usually on
analog lines) that take advantage of the ability of modern SS7 technology’s ability to transmit
information about the calling party. CLASS includes such features as Caller ID, Automatic
Callback, Call Trace (initiated by subscriber), Selective Call Screening, etc.
Class 4 switch - A Class 4, or Tandem, telephone switch is a U.S. telephone company central
office switch used to connect local exchange (class 5) central offices for long distance communications
in the Public Switched Telephone Network. See Class 4 or Class 4/5 switches,
Class 4/5 switch – Also called a “Hi/Lo” switch. This is a US telephone company central office
switch that provides both local and long distance service. Many CLEC’s are configured in this
way. See Class 4 or Class 5 switches.
Class 5 switch - A Class 5 telephone switch is a telephone switch or telephone exchange in the
Public Switched Telephone Network located at the local telephone company’s central office,
directly serving subscribers. Services provided include basic dial-tone, calling features, and
additional digital and data services to subscribers using the local loop. It is considered a “local
switch’.
CLEC- Competitive Local Exchange Carrier. Your local telephone service provider who is one
of the new-generation providers rather than a RBOC or Independent. A CLEC is really just an
independent, albeit one formed after the divestiture of AT&T. See LEC and Independent.
CLI - Calling Line Identity. European term for CLID. See CLID.
CLID- Calling Line Identification. This is the ISDN and SS7 equivalent of Caller ID; I.E. the
number of the calling party. See also Caller ID and ANI.
CO- Central Office. The Telco facility to which your local telephone circuits lead. Contains
“Switches” and “Trunks” as well as the local telephone circuits.
Codec- COder/DECoder. A device which takes digitized audio and “codes” it in order to
reduce the transmission bit rate and which can also simultaneously “decode” such coded audio.
Strictly speaking, a codec does not include an ISDN terminal adapter and related equipment.
Simple codecs are also used in digital telephony. These use a simple companding scheme to
reduce channel noise.
COL - COnnected Line number. European Term. The number to which you have connected.
This may not be the number you dialed if call forwarding is used.
Combination Trunk- A trunk (channel) which can both make and receive calls. This generally
refers to analog ground start or loop start trunks, although the term can be applied to ISDN