Brother International FAX 275 Service Manual - Page 187

INTRODUCTION 3 When your fax machine answers in FAX/TEL Mode, the fax machine listens for CNG tones and then responds with receiving tones. The fax "handshake" is the time in which the sending machine's CNG tones and the receiving machines "chirps" overlap. This must be for at least 2 to 4 seconds, so the machines can understand how each is sending and receiving the fax. The handshake cannot begin until the call is answered, and the CNG tones only last for about 40 seconds after the number is dialed. Therefore, it's important for the receiving machine to answer the call in as few rings as possible. When you have an external telephone answering device (TAD) on your fax line, your TAD will determine the number of rings before the call is answered. Pay special attention to the directions in the Installation chapter for connecting a TAD to your fax machine.