Avaya Definity TN556B ISDN-BRI 4-Wire Interface (Refurbished)Provides 12 ports connecting to ISDN BRI terminals. Each port uses TXT, TXR, PXT, PXR signal leads and ranges up to 3300 feet maximum from the system to the voice terminal. Key Features: Mfr. Part #: TN556B Ports connection to ISDN BRI terminals: 12 Signal leads: TXT, TXR, PXT, and PXR Up to 8 ports can be used for ASAI links 2 B channels 1 D channel Range up to 3300 ft. Compatible with Definity R7 or late Requires a packet control circuit pack