电信专业英英词典C-6（在线收听）

补充：

　　CBR

　　continuous bit rate

　　CCIS

　　common-channel interoffice signaling

　　CCITT

　　CCITT is the International Consultative Committee for Telephone and Telegraph, a consultative committee to the International Telecommunications Union (ITU) which recommend international standards for telephone and telegraph services and facilities to aid international connectivity and interoperability.

　　CCSA

　　common-control switching arrangement

　　CCS

　　centi-call seconds or common-channel signaling

　　CDMA

　　code division multiple access

　　Cell Relay

　　Call relay is the process of transferring data in the form of fixed length packets called cells. Cell relay is used in high-bandwidth, low-delay, packet-like switching and multiplexing techniques. The objective is to develop a single multiplexing/switching mechanism for dividing up usable capacity (bandwidth) in a l-manner that supports its allocation to both isochronous (e.g., voice and video traffic) as well as packet data communications services. Standards groups have debated the optimum cell size. Small cells favor low delay for isochronous applications but involve a higher header to user information overhead penalty than would be needed for most data applications. The current CCITT specification for BISDN is for a 53-byte cell which includes a 5- byte header and a 48-byte payload.

　　Centi Call Seconds (CCS)

　　CCS is a unit of the average traffic intensity of a facility during a period of time, a CCS is 100 call seconds of traffic during one hour. Therefore a single traffic source, e.g., one call that generates traffic 100% of the time produces 36 CCS of traffic per hour, i.e., 3600 seconds of traffic every 3600 seconds. An equivalent amount of traffic could also be generated by 10 sources that only generate traffic 10% of the time. That is, 10 sources of traffic generating 3.6 CCS each, contributes the same total traffic as a single 36 CCS traffic source. An alternative measure for traffic is erlangs where 1 erlang equals 36 CCS.

　　CENTRal EXchange (Centrex)

　　Centrex is a LEC-provided switching service for business customers that permits station-to-station dialing, listed directory number service, direct inward dialing and station number identification on outgoing calls. The switching functions are usually performed in a central office. Digital Centrex offers the advanced features of fourth generation PBXs, without the need to purchase or lease equipment and, in most cases, eliminates the need for floor space, electrical prime power and heating, ventilation and air conditioning.

　　Central Offices (CO)

　　A central office is a telephone company building in which network equipment such as switches are installed.