Hx1-Hx2 Manual-1.4.1 - Telos

TelepHone TerMInoloGy GuIDe | A5
BRI or PRI channels as well. Each combination trunk normally has a telephone number,
although they are frequently part of a hunt group and only one number may be published for
that group. Also called a Both Way Trunk. This is not the same as a Two-way DID trunk. See
DID trunk, Hunt Group and Trunk.
Common Channel Interoffice Signaling- See CCIS.
Competitive Local Exchange Carrier- See CLEC.
Concentration- The basic premise is to share facilities wherever possible. For instance, while
there may be thousands of customers served by a given Central Office, there will be substantially
less than that number of calls which can be handled simultaneously. And, even fewer long
distance calls can be made simultaneously. The art of Traffic Engineering is to have enough
capacity that calls are rarely blocked, but no more than that number. See also Choke Exchange
and Blocking.
CPC- Calling Party Control. Sometimes referred to as “CPC Wink” or “disconnect supervision”.
A call supervision feature on an analog loop start line that provides the ability for a CO
(Central Office) to signal the called party when the calling party hangs up. CPC allows the
PBX, key system, or telephone answering device to reset the line so that it is ready to accept or
initiate another call. CPC is accomplished by either a loop current drop or reversal. With some
CO equipment, it is also provided if the called party drops the call. See also MCLD.
CPE- Customer Premise Equipment- Customer owned equipment located at his/her facility,
such as a CSU or terminal. In the USA and Canada, the ISDN NT1 is part of the CPE.
CPN - Called Party Number - European Term. The number that has been dialed. See Called
Party Address.
CSU- Channel Service Unit. The NCTE used in the USA & Canada to terminate a T1 line.
Typically the CSU must be provided by the end user. See NCTE, NIU and DSX1
CSU/DSU- A device which incorporates the functions of a CSU (Channel Service Unit) and
a DSU (Data Service Unit) Most commonly it interfaces between a Switched-56 or Dedicated
Digital Service circuit and a user’s data equipment such as the Zephyr.
D4- See Superframe. See also Line Format.
DCE- Data Communication Equipment. When using serial communications such RS-232,
V.35, or X.21, the DCE is the device sending/receiving from the Telco line. i.e.: a modem or
CSU/DSU. In contrast to DTE.
Dedicated Circuit- A permanent channel between two locations. As opposed to a Switched
Circuit.
Demarc – the point of “Demarcation”. That is, where the telephone company’s responsibility
ends, and the customers begins. Most often in “the main phone closet” or basement terminal. At
one time, a special block was required for a Demarc, one for each customer with a simple way
to disconnect the customers wiring from the Telco’s wiring at the demarc point. This has been
abandoned. Most often today, when you order service, it will be “to the demarc” only, and they’ll
(usually) provide a tag or “cable and pair” number so that you can locate the circuit in question.
Residential phones still usually have a demarc in the form of a (usually) gray box mounted to the
side of the house. It most often provides remote line disconnection facilities (for remote testing
by the phone company) and a customer accessible modular jack to allow the customer to verify
proper operation of the line at the side of the house, “before” the house wiring.
DID- Direct Inward Dialing. The ability for an outside caller to dial to a PBX extension
without going through an attendant or auto-attendant. See also DID Number and DID Trunk.