| 2G | Second Generation |
| 3G | Third Generation |
| 3GPP | Third Generation Parnership Project (ETSI) |
| AAL1 | ATM Adaptation Layer, type 1 |
| AAL2 | ATM adaptation layer type 2 |
| AAL5 | ATM adaptation layer type 5 |
| AALn | ATM Adaptation Layer n. Methods associated with formatting information into ATM cells. AAL1 is used for real-time constant bit rate serices, AAL2 for real-time variable bit rate services and AAL5 for packetized data. |
| ABIS | The interface between the BTS and the BSC within a GSM architecture,
usually configured using a 16kbps slot structure |
| ABR | Available Bit Rate |
| Access Control | Network managers define access control by requiring authentication of the user's identity before permitting or limiting entry to a computer network or server. |
| ACTS | Automated Computer Time System, a NIST service that provides announced time via telephone. |
| ADM | Add-Drop Multiplexer |
| ADSL | Asymmetric Digital Subscriber Line. ADSL delivers more bandwidth downstream (from CO to customer) than upstream and is largely used in cost-sensitive consumer applications. Compare against SHDSL, SDSL, HDSL and VDSL |
| Advanced Encryption Standard (AES) | Developed by NIST and private companies, this standard is 256-bit based and thus presents a strong defense for sensitive material |
| Aging | The systematic change in frequency of an oscillator with time. |
| AIS | Alarm Indication Signal |
| AM | Amplitude modulation (AM) is a meth |