User Guide
Page 38
... with "3" as the next to the last character (like the P-2602HWL-D1A or the P-2602HWL-D7A) denote a device that works over ISDN (Integrated Services Digital Network). Note: Only use firmware for your ISP supports determines the maximum upstream and downstream speeds attainable. ZyXEL Devices which work over T-ISDN (UR-2). Models with "1" or "7" as...
... with "3" as the next to the last character (like the P-2602HWL-D1A or the P-2602HWL-D7A) denote a device that works over ISDN (Integrated Services Digital Network). Note: Only use firmware for your ISP supports determines the maximum upstream and downstream speeds attainable. ZyXEL Devices which work over T-ISDN (UR-2). Models with "1" or "7" as...