| C | DFCA |
| C/I | Carrier to Interference Ratio |
| C/N | Carrier to Noise |
| C4FM | Constant Envelope 4-level Frequency Modulation |
| C4I | Command, Control, Communications, Computers and Intelligence |
| C4ISR | Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance |
| CA | Call Agent |
| CAC | Call Admission Control |
| CAC | Carrier Access Code |
| CAC | Connection Admission Control |
| CAD | Computer-Aided Design |
| CAGR | Compound Annual Growth Rate |
| CALEA | Communications Assistance to Law Enforcement Act |
| CAM | Computer-Aided Manufacture |
| CAMEL | Customized Application of Mobile Enhanced Logic |
| CAP | Competitive Access Provider |
| CAP | Carrierless Amplitude and Phase Modulation |
| CAPEX | Capital Expenditure |
| CAR | Committed Access Rate |
| CARE | Customer Account Record Exchange |
| CAS | Communications Applications Specification |
| CAS | Channel-Associated Signaling |
| CAT | Conditional Access Table |
| CAT | Computer Aided Telephony |
| CAT-5 | Category 5 |
| CATV | Cable Television |
| C-band | Conventional Band |
| CBC | Cipher Block Chaining |
| CBDS | Connectionless Broadband Data Service |
| CBR | Constant Bit Rate |
| CBT | Core-Based Tree |
| CBUS | Control Bus (Nortel) |
| CC | Control Component |
| CCB | Customer Care and Billing |
| CCD | Charge Coupled Device |
| CCDF | Complementary Cumulative Distribution Function |
| CCF | Call-Control Function |
| CCI | Call Clarity Index |
| CCITT | Consultative Committee on International Telephone and Telegraphy |
| CCK | Complementary Code Keying |
| CCM | Clock and Control Module |
| CCR | Call-Completion Ratio |
| CCRR | Co-Channel Rejection Ratio |
| CCS | Common Channel Signaling |
| CCU | Central Control Unit |
| CD | Chromatic Dispersion |
| CD | Compact Disc |
| CDCF | Conventional Dispersion Compensation Fiber |
| CDD | Content Delivery and Distribution |
| CDDI | Copper-Distributed Data Interface |
| CDMA | Code-Division Multiple Access |
| CDMA2000 | a 3G solution based on IS-95, which is the first CDMA-based digital cellular standard pioneered by Qualcomm |
| CDMP | Cellular Digital Messaging Protocol |
| CDMS | Configuration and Data Management ServerCDN |
| CDN | Control Directory Number |
| CDP | Code Domain Power |
| CDPD | Cellular Digital Packet Data |
| CDR | Call Detail Record |
| CDR | Clock and Data Recovery |
| CD-ROM | Compact Disc-Read-Only Memory |
| CDWDM | Coarse Wavelength Division Multiplexing |
| CE | Customer Edge |
| CEI | Comparable Efficient Interface |
| CENELEC | European Committee for Electrotechnical Standardization |
| CEO | Chief Executive Officer |
| CEPT | Centre for Environmental Planning & Technology (CEPT), Ahmedabad, India and European Conference of Postal and Telecommunications Administrations |
| CER | Customer Edge Router |
| CERT | Computer Emergency Response Team |
| CES | Circuit Emulation Service |
| CESID | Caller Emergency Service Identification |
| CESoP | Circuit Emulation Service over Packet |
| CEV | Controlled Environment Vault |
| cEVM | Composite Error Vector Magnitude |
| CFAR | Constant False Alarm |
| CFB/NA | Call Forward Busy/Not Available |
| CFO | Chief Financial Officer |
| CFP | Contention Free Period |
| CFR | Crest Factor Reduction |
| CGI | Common Gateway Interface |
| CHCS | Composite Health Care System |
| CHN | Centralized Hierarchical Network |
| C-HTML | Compressed HTML |
| CI | Contents Indicator |
| CIC | Cascaded Integrator Comb |
| CIC | Circuit Identification Code |
| CID | Caller Identification |
| CIF | Camera Interface |
| CIM | Common Information Model |
| CIMD2 | Computer Interface Message Distribution 2 |
| CINs | Current Injectors |
| CIO | Chief Information Officer |
| CIP | Classical IP over ATM |
| CIR | Communications Industry Researchers |
| CIR | Committed Information Rate |
| CIT | Computer Integrated Telephone |
| CL | Conversion Loss |
| CLASS | Custom Local-Area Signaling Services |
| CLE | Customer-Located Equipment |
| CLEC | Competitive Local Exchange Carrier |
| CLI | Command Line Interface |
| CLLI | Common Language Location Identifier |
| CLR | Circuit Layout Record |
| CM | Cable Modem |
| CM&B | Customer Management and Billing |
| CMBS | Collision Mitigation Braking System |
| CMIP | Common Management Information Protocol |
| CMIS | Common Management Information Service Element |
| CMMI | Capability Maturity Model Integration |
| CMOS | Complementary Metal-Oxide Semiconductor |
| CMP | Connection Management Protocol |
| CMRR | Common-Mode Rejection Ratio |
| CMRS | Commercial Mobile Radio Service |
| CMTS | Cable Modem Termination System |
| CNAM | Calling Name (also defined as “caller identification with name” and simply “caller identification”) |
| CNAP | CNAM Presentation |
| CO | Central Office |
| CoB | Chip on Board |
| CODEC | Coder/Decoder |
| COFDM | Coded Orthogonal Frequency Division Multiplexing |
| COGS | Cost of Goods Sold |
| COI | Community Of Interest |
| CompactPCI | Compact Peripheral Component Interconnect |
| COMSEC | Commercial Off The Shelf |
| COO | Chief Operations Officer |
| COP | Common Operational Picture |
| COPS | Common Open Policy Service |
| CORBA | A standard from the Object Management Group (OMG) |
| CORBA | Common Object Request Broker Architecture |
| CORDIC | Coordinate Rotation Digital Computer |
| CORE | Council OF Registrars |
| CoS | Class of Service |
| COT | Central Office Terminal |
| COTS | Commercial Off-of-the-Shelf |
| COW | Cellsite On Wheels |
| CP | Connection Point |
| CPAS | Cellular Priority Access Service |
| CPC | Calling-Party Category |
| CPC | Calling-Party Control |
| CPC | Calling-Party Connected |
| CPE | Customer Premise Equipment |
| CPI | Continual Process Improvement |
| CPL | Call Processing Language |
| CPLD | Complex Programmable Logic Device |
| CPN | Calling-Party Number |
| CPNI | Customer Proprietary Network Information |
| CPRI | Common Public Radio Interface |
| CPU | Central Processing Unit |
| CPW | Coplanar Waveguide |
| CQI | Channel Quality Indicator |
| CRC | Cyclic Redundancy Code |
| CRC | Cyclic Redundancy Check |
| CRM | Customer-Relationship Management |
| CRS | Capacity, Reach, and Speed |
| CRTP | Compressed Real-time Transport Protocol |
| CRV | Call Reference Value |
| CS | Client Signal |
| CS-[x] | Capability Set [x] |
| CS_IWF | Control Signal Interworking Function |
| CSA | Carrier Serving Area |
| CSCE | Converged Service-Creation and Execution |
| CSCF | Call session control function |
| CSCW | Computer Supported Collaborative Work |
| csdm | Community service and data management |
| CSF | Critical Success Factors |
| CSM | Customer-Service Manager |
| CSMA | Collision Sensing Multiple Access |
| CSMA/CA | Carrier Sensed Multiple Access with Collision Avoidance |
| CSMA/CD | Carrier Sensed Multiple Access with Collision Detection |
| CSMA-CA | Carrier Sense Multiple Access with Collision Avoidance |
| CSN | Circuit-Switched Network |
| CSP | Chip Scale Packaging |
| CSP | Communications Service Provider |
| CSP | Content Service Provider |
| CSR | Customer-Service Representative |
| CS-TDMA | Carrier Sense Time Division Multiple Access |
| CSU | Channel Service Unit |
| CSV | Circuit-Switched Voice |
| CT | Computer Telephony |
| CT-2 | Cordless Telephony Generation 2 |
| CTE | Coefficient of Thermal Expansion |
| CTI | Computer Telephony Integration |
| CTIA | Cellular Telecommunications Industry Association |
| CTM | Center for Telecommunications Management |
| CTO | Chief Technology Officer |
| CUG | Closed User Group[ |
| CVD | Chemical Vapor Deposition |
| CVSD | Continously Variable Slope Delta |
| CW | Continuous Wave |
| CWD | Centralized Wavelength Distribution |
| CWDM | Coarse Wavelength Division Multiplexing |
| CWIX | Cable and Wireless Internet Exchange |
| CYTOP | Cyclized Transparent Optical Polymer |