FG-D (Feature Group D) is a type of telecommunication trunk used to provide "equal access" capability from telecommunication carriers and central offices (where the switching equipment is located and customer lines are connected and terminated) to the access tandem. Feature Groups (FGs) categorize telco products
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according to services and features. The most commonly mentioned feature groups are FG-A, FG-B, and FG-D (FG-C is used almost exclusively by AT&T). FG-D provides higher quality services than the other Feature Groups. It is sometimes known as equal access because it guarantees that all carriers are processed equally.
The FG-D protocol defines interconnection rules between a local exchange carrier (LEC) and an inter-exchange carrier (IEC) such as MCI or Sprint. FG-D services route inter-LATA calls to the IEC point of termination (POT), route calls with a carrier access code (CAC) to the user's carrier, and pass information to the carrier. Information passed includes the caller's number, through automatic number identification (ANI). Because of its ability to pass on caller information, FG-D is proposed for use with the 911 service.