# List of information technology initialisms

The table below lists information technology initialisms and acronyms in common and current usage. These acronyms are used to discuss LAN, internet, WAN, routing and switching protocols, and their applicable organizations. The table contains only current, common, non-proprietary initialisms that are specific to information technology. Most of these initialisms appear in IT career certification exams such as CompTIA A+.
| Abbreviation | Meaning | Primary Applicability | Normative Reference |
| ACK | Acknowledgement | Transport and other layers | TCP/IP, for example. RFC 793 |
| ACL | Access control list | Security, application layer | Access control list, Cisco overview |
| ADSL | Asymmetric digital subscriber line | Telecom | ITU-T G.992.5 Annex M, for example |
| AES | Advanced Encryption Standard | Security | U.S. FIPS PUB 197 |
| ANSI | American National Standards Institute | Organization | ANSI |
| API | Application Programming Interface | Software | API |
| ARP | Address Resolution Protocol | Link layer | RFC 1122 |
| ATM | Asynchronous Transfer Mode | Telecom | ATM cell description |
| BGP | Border Gateway Protocol (routing protocol) | Application layer, Routers | RFC 4271 |
| BSS | Basic service set (Wi-Fi) | Wireless | IEEE Std 802.11-2007 |
| CAT | Category (e.g. CAT-5 cable) | Physical layer | ANSI/TIA/EIA-568-B.1-2001 |
| CCITT (obs.) | Standards organization that has been replaced by ITU-T | Organization | ITU-T |
| CHAP | Challenge-Handshake Authentication Protocol (PPP) | Security, telecom | RFC 1994 |
| CIDR | Classless Inter-Domain Routing | Architecture | RFC 1518 RFC 1519 |
| CIR | Committed Information Rate (Frame Relay) | Telecom | RFC 1490 RFC 1973 RFC 2427 |
| CLI | Command line interpreter | Hardware | Catalyst 6500 Series Command Reference, 7.6, for example |
| CPE | Customer premises equipment | Telecom | Telecom Glossary |
| CPU | Central processing Unit | Microprocessor | Wikipedia |
| CRC | Cyclic redundancy check | Link and other layers | 24 References here. |
| CRC-16-CCITT | Cyclic redundancy check (X.25, HDLC) | Link layers | Reference on CRC page. |
| CRT | Cathode Ray Tube | Television set, Computer Monitor | Cathode ray tube |
| CSMA/CA | Carrier sense multiple access / collision avoidance | Wireless | IEEE Std 802.11 Downloads |
| CSMA/CD | Carrier sense multiple access / collision detection | Physical layer | IEEE Std 802.3TM-2002 |
| CSU/DSU | Channel service unit / data service unit | Telecom | Telecom Glossary |
| CMOS | Complementary metal-oxide semiconductor | Utility | CMOS |
| DAM | Database activity monitoring | Security | Database activity monitoring |
| DAM | Digital asset management | Internet Layer | Digital asset management |
| DCE | Data communications equipment | Telecom | Telecom Glossary |
| DEC (obs.) | Digital Equipment Corporation | Organization | Digital Equipment Corporation formally Purchased by Compaq in 1998. Merged with Hewlett-Packard 2002. |
| DES | Data Encryption Standard (obs. See AES) | Security | Federal Information Processing Standard (FIPS) FIPS-46-3 |
| DHCP | Dynamic Host Configuration Protocol | Application layer, Internet Layer | RFC 2131 and others |
| DIMM | Dual In-line Memory Module | Hardware | DIMM |
| DNS | Domain Name System | Application layer | Over 30 RFCs here. |
| DRAM | Dynamic random-access memory | Hardware | Dynamic random-access memory |
| DSL | Digital subscriber line | Telecom | Telecom Glossary |
| DSLAM | Digital subscriber line access multiplexer | Telecom | Telecom Glossary (proposed) |
| DTE | Data Terminal Equipment | Telecom | Telecom Glossary |
| DMI | Desktop Management Interface | Utility | Desktop Management Interface |
| EHA | Ethernet Hardware Address (MAC address) | Link layer | IEEE Std 802 IEEE OUI Assignments |
| EIA | Electronics Industry Alliance | Organization | EIA |
| EIGRP | Enhanced Interior Gateway Routing Protocol | Internet Layer | Cisco Doc ID: 16406 |
| EMAC | Ethernet Media Access Control | Link Layer | |
| EOF | End Of Frame (HDLC, etc.) | Link layer | HDLC framing |
| ESS | Extended service set (Wi-Fi group) | Wireless | IEEE Std 802.11-2007 |
| FCC | Federal Communications Commission (US) | Organization | US FCC |
| FCS | Frame check sequence (Ethernet) | Link layer | Ethernet Frame IEEE Std 802.3 |
| FDDI | Fiber Distributed Data Interface | Link layer | American National Standards Institute X3T9.5 (now X3T12), ISO/IEC 9314-x |
| FTP | File Transfer Protocol | Application layer | RFC 959 and others |
| GBIC | Gigabit interface converter | Hardware | Seagate Specification |
| gbps | Gigabit per second | Physical layer | Gigabit per second |
| GEPOF | Gigabit Ethernet (over) Plastic Optical Fiber | Physical layer | IEEE P802.3bv |
| GMAC | Gigabit Ethernet Media Access Control | Link Layer | |
| HDLC | High-level Data Link Control | Link layer | ISO 13239 |
| HTTP | HyperText Transfer Protocol | Application layer | W3C Change History for HTTP |
| HTTPS | HyperText Transfer Protocol Secure | Transport and other layers | SSL 3.0 Specification |
| IaaS | Infrastructure as a service | Cloud Services | IaaS Microsoft Docs |
| IANA | Internet Assigned Number Authority | Organization | IANA |
| ICaaS | Integration Capability as a Service | Organization | ICaaS |
| ICMP | Internet Control Message Protocol | Internet Layer | RFC 792 |
| IDF | Intermediate distribution frame | Physical layer | Structured cabling or Telecom Glossary |
| IDS | Intrusion Detection System | Security | Wikipedia |
| IEEE | Institute for Electrical and Electronic Engineers | Organization | IEEE |
| IETF | Internet Engineering Task Force | Organization | IETF |
| IMAP | Internet Message Access Protocol | Application layer | RFC 3501 |
| IP | Internet Protocol | Internet Layer | RFC 791 RFC 1606 |
| IPS | Intrusion prevention system | Security | "NIST - Guide to Intrusion Detection and Prevention Systems (IDPS)". 2007-02. Retrieved 2010-08-24. |
| IS-IS | Intermediate System to Intermediate System (routing protocol) | Internet Layer | ISO/IEC 10589:2002 |
| ISDN | Integrated Services Digital Network | Telecom | IEC Area 716-xx |
| ISP | Internet service provider | Telecom | Telecom Glossary |
| ITU-T | International Telecommunication Union | Organization | http://www.itu.int |
| kbps | Kilobit per second | Physical layer | Kilobit per second |
| LACP | Link Aggregation Control Protocol | Data link layer | |
| LAN | Local area network | Link and other layers | Telecom Glossary |
| LAPB | Link Access Procedure, Balanced (x.25) | Telecom | ITU-T Recommendation X.222 |
| LAPF | Link-access procedure for Frame Relay | Telecom | RFC 1490 |
| LLC | Logical link control | Link layer | Telecom Glossary |
| MAC | Media access control | Link layer | IEEE Std 802.3 and 802.11, for example |
| MAM | Media access management (related to Digital asset management) | Internet layer | Wikipedia |
| MAN | Metropolitan area network | Telecom | Telecom Glossary |
| Mbps | Megabits per second | Physical layer | Megabit_per_second |
| MC | Multiple choice | IT Professional Certification | About certification exams |
| MDF | Main distribution frame | Physical layer | Glossary See also Structured cabling |
| MIB | Management information base (SNMP) | Application layer | RFC 3418 |
| MII | Media-independent Interface | Link layer | |
| MoCA | Multimedia over Coax Alliance | Organization | Multimedia over Coax Alliance |
| MPLS | Multiprotocol Label Switching | network technology | |
| MTU | Maximum Transmission Unit | Multiple layers | |
| NAC | Network access control | Link and other layers | IEEE 802.1x |
| NAS | Network-attached storage | Hardware / Storage | Computer data storage |
| NAT | Network Address Translation | Internet Layer | Cisco Internet Protocol Journal: A look Inside Network Address Translators |
| NBMA | Non-Broadcast Multiple Access (e.g. Frame Relay ATM) | Telecom | See ATM, Frame Relay and X.25, for examples. |
| NIC | Network Interface Card | Physical layer | Telecom Glossary |
| NRZ | Non-return-to-zero | Physical layer | Federal Standard 1037C |
| NRZI | Non-return to zero inverted | Physical layer | Federal Standard 1037C |
| NVRAM | Non-volatile RAM | Hardware | Sample vendor data here |
| OSI | Open System Interconnect (joint ISO and ITU standard) | Organization | ISO/IEC 9594-5:2005 Open Systems Interconnection Protocol Specifications |
| OSPF | Open Shortest Path First (routing protocol) | Internet Layer | RFC 2238 |
| OUI | Organization Unique Identifier | Link and other layers | IEEE OUI Assignments |
| PAP | Password authentication protocol | Security | RFC 1334 |
| PAT | Port address translation | Internet Layer | RFC 1918 |
| PaaS | Platform as a service | Cloud Computing/Service | Platform as a service |
| PC | Personal computer (host) | Hardware | |
| PIM | Personal information manager | Software category | |
| PCM | Pulse-code modulation | Physical layer | ITU-T G.711 |
| PDU | Protocol data unit (such as segment, packet, frame, etc.) | Multiple layers | Fed Std 1037C |
| POP3 | Post Office Protocol, version 3 | Application layer | RFC 1939 |
| POP | Point of presence | Telecom | Telecom Glossary |
| POST | Power-on self test | Hardware | Cisco Catalyst 2800 User Guide, for example |
| POTS | Plain old telephone service | Telecom | Telecom Glossary |
| PPP | Point-to-point Protocol | Telecom | RFC 1661 |
| PPTP | Point-to-Point Tunneling Protocol | Telecom | RFC 2637 |
| PTT | Public Telephone and Telegraph | Telecom | Telecom Glossary or Free Dictionary |
| PVST | Per-VLAN Spanning Tree | Link layer | Cisco's introduction to Spanning Tree Protocol |
| RADIUS | Remote Authentication Dial-In User Service | Security | RFC 2865 |
| RAM | Random Access Memory | Physical layer | Telecom Glossary |
| RARP | Reverse ARP | Link layer | RFC 903 |
| RIMM | Rambus In-line Memory Module | Hardware | Wikipedia |
| RFC | Request for Comments | Multiple layers | IETF's RFC Index |
| RIP | Routing Information Protocol | Internet Layer | RFC 2453, for RIP version 2 |
| RLL | Run-Length Limited | Physical layer | RLL is used in a wide range of encodings. |
| ROM | Read-Only Memory | Hardware | Telecom Glossary |
| RSTP | Rapid Spanning Tree Protocol | Link layer | IEEE 802.1w - Rapid Reconfiguration of Spanning Tree |
| RTP | Real-time Transport Protocol | Application layer | RFC 3550 |
| SaaS | Software as a service | Cloud Computing/Service | Software as a service Microsoft Docs |
| SDLC | Synchronous Data Link Control | Link layer | Cisco Technology Handbook: SDLC and Derivatives |
| SDN | Software-defined networking | Architecture | Software-defined networking |
| SFD | Start-of-frame delimiter (Ethernet, HDLC, etc.) | Link layer | IEEE 802.3 (Ethernet), or RFC 2687 (HDLC), for examples |
| SFP | Small form-factor pluggable | Hardware | Seagate Specification |
| S-HTTP | Secure HTTP (rarely used) | Transport and other layers | RFC 2660 See also https |
| SLARP | Serial Line ARP (Address Resolution Protocol) | Link and other layers | Archived Cisco Serial Line Encapsulation extension |
| SLIP | Serial Line Internet Protocol (obs.) | Telecom | RFC 1055 |
| SIMM | Single In-line Memory Module | Hardware | Wikipedia |
| SMTP | Simple Mail Transfer Protocol | Application layer | RFC 5321 |
| SNA | Systems Network Architecture (IBM) | Multiple layers | SNA Protocol Suite |
| SNAP | SubNet Access Protocol | Link layer | IEEE 802 Overview and Architecture |
| SNMP | Simple Network Management Protocol | Application layer | RFC 1155, RFC 3410 thru RFC 3418 and others |
| SOF | Start of frame | Link layer | IEEE 802.3 (Ethernet), or RFC 2687 (HDLC), for examples |
| SRAM | Static random access memory | Hardware | PC Guide's Definition |
| SSH | Secure shell | Application layer | RFC 4252 |
| SSID | Service set identifier (Wi-Fi) | Wireless | IEEE 802.11 |
| STP | Spanning Tree Protocol | Link layer | Cisco's Introduction to Spanning Tree Protocol |
| SYN (TCP) | Synchronization | Link and other layers | RFC 793 and many others |
| TCP/IP | Transmission Control Protocol/Internet Protocol | Transport layer | RFC 793 and many others |
| TDM | Time-division multiplexing | Physical layer | Fed Std 1037C |
| TFTP | Trivial File Transfer Protocol | Application layer | RFC 1350 |
| TIA | Telecommunications Industry Alliance | Organization | Telecommunications Industry Association |
| TOFU | Trust On First Use | Security | Improving SSH-style Host Authentication with Multi-Path Probing |
| UDP | User Datagram Protocol | Transport layer | RFC 768 |
| URL | Uniform Resource Locator | Web address | URL spec (1994) |
| USB | Universal Serial Bus | Physical and other layers | USB 3.0 Specification |
| UTP | Unshielded twisted pair | Physical | Many versions are defined by TIA, such as: TIA-568-B |
| VC | Virtual circuit | Transport and other layers | Telecom Glossary |
| VLAN | Virtual local area network | Link layer | IEEE 802.1Q |
| VLSM | Variable-length subnet masking | Architecture | RFC 1518 RFC 1519 |
| VM | Virtual machine | virtualization/emulation | Virtual machine |
| VPN | Virtual private network | Application layer | Virtual Private Network Consortium |
| W3C | World Wide Web Consortium | Organization | W3C |
| WAN | Wide-area network | Telecom | Telecom Glossary |
| WEP | Wired Equivalent Privacy | Wireless | IEEE 802.11 |
| Wi-Fi | An implementation of IEEE wireless communication standard 802.11 | Wireless | Wi-Fi Alliance |
| WLC | Wireless LAN Controller | Wireless | Cisco |
| WPA | Wi-Fi Protected Access | Security | IEEE 802.11i |
| www | World Wide Web | Architecture | W3C Consortium |