Indicates the frame/slot/port. 24 0 0011000 | xxxxxxxx | xxxxxx | xxxxxxx | 0000 port frame slot port 0 type The highest 7 bits indicate the type of port, for PSTN port, must be 0x18 the next 8 bits indicate the frame ID, the next 6 bits indicate the slot ID, the next 7 bits indicate the port ID, the last 4 bits must be 0. The type of port include: E1 port = 0x16 PSTN port = 0x18 BRA port = 0x19 AT0 port = 0x1b