- G recommendations A series of standards defined by the ITU-TS covering transmission facilities. They are: G.703 2.048Mbit/s - transmission facilities running at 2.048Mbit/s that use the ITU-TS recommended physical and electrical interface specified in G.703; G.703 641K - likewise for transmission facilities running at 64Kbits/s; G.703 - the ITU-TS standard 1984 current version for the physical and logical traits of transmissions over digital circuits. G.703 now includes specifications for the US 1.544Mbit/s as well as the European 2.048Mbit/s, and circuits with larger bandwidths on both continents. G.703 is still generally used to refer to the standard for 2.048Mbit/s; G.821 - ITU-TS Recommendation that specifies performance criteria for digital circuits for ISDN.
- Gateway Network interconnection device and software that operate at OSI Layer Seven. A gateway supports a full stack of the relevant protocol, such as SNA, DecNet, ISO, TCP/IP, and can covert to a non-seven layer protocol, such as async or BSC. It is typically used to provide access to wide area networks over asynchronous or X.25 links from a LAN environment. Examples include pads and protocol converters.
- GFI (Group Format Identifier) (X.25 reference) the first four bits in a packet header, GFl contains the obit, Dbit and modulus value.
- GGP (Gateway-to-Gateway Protocol) The protocol that core gateways use to exchange routing information, GGP implements a distributed shortest path routing computation.
- GMII Gigabit Media Independent Interface
- GOMSFE Generic Object Model for Substation Feeder Equipment; Models and meta data on some 100 substation device models (switch, breaker, transformer, RTU, ...)
- Gosip (Government Open Systems Interconnect Profile) Country specific ISO OSI functional profiles that have been defined as part of national procurement policies. The US has US Gosip which is defined as a Federal Information Processing Standard. The UK has the UK Gosip which is defined by the Central Computer and Telecommunications Agency. The UK Government will not buy equipment unless it supports OSI as specified in Gosip. Unfortunately, the various Gosips as published by the UK, US and Japanese governments are all slightly different.
- Group In the context of network security, a group is a set of users who share common permissions for one or more resources. Individually assigned user permissions take precedence over those assigned through groups.
- GSM (Global System for Mobile communications) A two-way, pan-European digital cellular system. Its specification is in line with ISDN and ITU-TS System 7 signaling and approved by almost all European countries. GSM operates at 900MHz and is a forerunner to the mass-market Personal Communications Networks, based on the same set of standards. GSM services include current digital subscriber services and the unique Short Message Service - a superior form of paging offering up to 160 alphanumeric characters with guaranteed delivery.
- Guard band The unused bandwidth separating channels to prevent crosstalk.
- Guard tone A tone generated by a high speed modem dial-up modem to ensure that there is sufficient bandwidth available on the PSTN circuit for transmission.
- GUI (Graphical User Interface) Often pronounced "goo-ee", it describes the screen display that first greets a user and with which the user interacts during the computer session. A GUI makes use of Windows, Icons, Menus and Pointers - so-called WIMP systems - such as Microsoft Windows, GEM and X-Windows. Apple's GUI is particularly notable and be-spoke GUIs are becoming popular.