the digital carrier has failed. The result of the CGA condition varies depending on the equipment function. Voice equipment typically coerces the robbed bits for signaling to a state that will result in the far end properly handling the condition, while applying an often different state to the customer equipment connected to the alarmed equipment. Simultaneously, the customer data is often coerced to a 0x7F pattern, signifying a zero-voltage condition on voice equipment. Data equipment usually passes whatever data may be present, if any, leaving it to the customer equipment to deal with the condition. Inband T1 versus T1 PRI Additionally, for voice T1s there are two main types: so-called "plain" or Inband T1s and PRI (Primary Rate Interface). While both carry voice telephone calls in similar fashion, PRIs are commonly used in call centers and provide not only the 23 actual usable telephone lines (Known as "B" channels for bearer) but also a 24th line (Known as the "D" channel for data) that carries line signaling information. This special "D" channel carries: Caller ID (CID) and automatic number identification (ANI) data, required channel type (usually a B, or Bearer channel), call handle, Dialed Number Identification Service (DNIS) info, requested channel number and a request for response. Inband T1s are also capable of carrying CID and ANI information if they are configured by the carrier by sending DTMF *ANI*DNIS*. However, PRIs handle this more efficiently. While an inband T1 seemingly has a slight advantage due to 24 lines being available to make calls (as opposed to a PRI that has 23), each channel in an inband T1 must perform its own setup and tear-down of each call. A PRI uses the 24th channel as a data channel to perform all the overhead operations of the other 23 channels (including CID and ANI). Although an inband T1 has 24 channels, the 23 channel PRI can set up more calls faster due to the dedicated 24th signalling channel (D Channel). Before T1 PRI existed there was T1 CAS. T1 CAS is not common today but it still exists. CAS is Channel Associated Signaling. It is also referred to as Robbed Bit Signaling. CAS is a technology with roots in the 60's and before. Origin of name The name T1 came from the carrier letter assigned by AT&T to the technology in 1957, when digital systems were first proposed and developed, AT&T decided