In a

telecommunication network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, mes ...

Transcoder free operation, or TrFO, also known as Out of band transcoder control is the concept of removing

transcoding Transcoding is the direct digital-to-digital conversion of one encoding to another, such as for video data files, audio files (e.g., MP3, WAV), or character encoding (e.g., UTF-8, ISO/IEC 8859). This is usually done in cases where a target ...

function in a call path. In legacy

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...

networks a call between two mobile stations involved two transcoding functions, one at each

BSC A Bachelor of Science (BS, BSc, SB, or ScB; from the Latin ') is a bachelor's degree awarded for programs that generally last three to five years. The first university to admit a student to the degree of Bachelor of Science was the University of ...

. This transcoding functionality was generally implemented in a separate Transcoder and Rate Adaptation Unit, or TRAU. TRAU was connected to BSC and MSC through TDM E1 or

STM-1 The STM-1 (Synchronous Transport Module level-1) is the SDH ITU-T fiber optic network transmission standard. It has a bit rate of 155.52 Mbit/s. Higher levels go up by a factor of 4 at a time: the other currently supported levels are STM-4, STM ...

. With the introduction of NGN and 3G networks the

Radio Network Controller The Radio Network Controller (RNC) is a governing element in the UMTS radio access network ( UTRAN) and is responsible for controlling the Node Bs that are connected to it. The RNC carries out radio resource management, some of the mobility manag ...

was connected to MGW through

ATM ATM or atm often refers to: * Atmosphere (unit) or atm, a unit of atmospheric pressure * Automated teller machine, a cash dispenser or cash machine ATM or atm may also refer to: Computing * ATM (computer), a ZX Spectrum clone developed in Mo ...

or IP instead of TDM. Therefore, this external transcoder was removed and transcoding function was moved up to the MGW. NGN also introduced Nb interface over IP such that it became possible to carry compressed voice codecs such as AMR in the Nb interface. In a call scenario such as this the transcoding functionality in the MGW could be eliminated such that voice quality can be improved and resources in MGW also could be saved. Concept of TrFO became applicable for 2G networks also with the "A interface over IP" implementation.

References

* Mobile telecommunications {{Telecomm-stub