Integrated Services Digital Network. A fixed narrowband (www.practicallaw.com/A35683) technology offering speeds of up to 128 kbps (128,000 bits of data per second). ISDN technology requires both the telecommunications service provider and the end customer to install equipment at each end of the copper pair of wires telephone line running from the local exchange to the customer’s premises. Once this equipment is installed, data can be sent and received over the copper pair in digital rather than analog form, thus enabling faster data transmission speeds.