ZyXEL Communications omni series user manual Digital Data, Determining the Packet Length

∙V.110

∙X.75

or the call may be initiated by an analog device (non-data).

This section will provide some general guidelines for setting up the device for call answer handling. Be aware that the TA will not automatically answer a call unless S-register S0 is set to a value greater than 0 (zero). If S-register S0=0, the TA will only report “RING” to your terminal program. It can also respond with an audible tone (external) that will allow you to decide whether or not you should take any action.

When an ISDN data call comes in, the TA will try to negotiate a connection using the proper ISDN protocol.

When an analog call comes in, the TA will send the call to the analog port as the factory default, Phone 1 and then Phone 2 (non-data).

Digital Data

The omni currently supports Circuit Switched Data (CSD) for ISDN data applications. The CSD protocols supported by the TA include: PPP, MPPP, V.120, X.75, and V.110. PPP is the most popular protocol used in North America; it is used by most Internet service providers. Once the TA answers a call, it will examine the incoming data to determine which protocol to use, and automatically switch to this mode. The TA is able to auto-switch for PPP, MPPP, V.120, X.75, V.110, and above protocols over the speech channel. In most cases, you can rely on the auto-switching feature for your applications. If you need more specific settings for answering calls, refer to the section entitled “Answering a Call using MSN” found later in this chapter.

Determining the Packet Length

The user’s information is sent on a frame-by-frame basis for V.120 and X.75. Sometimes we call it “packetized.” The maximum frame length on the sending side should not exceed the maximum frame

30 ISDN Communication Basics