AT&T AT&T manual Host Computer Endpoint, Analog Data Endpoint, DCE Devices, 108

Data Terminal Dialing mode, or to enter the Setup mode on calls originating from a voice terminal or on auto-answered calls.

In the case of most personal computers, a communications program must be executed in order for it to communicate with its own RS-232 port or built-in modem. Once the communications software is running, further operation will be similar to that of the basic terminal.

c. Host Computer Endpoint

A host computer endpoint is very similar to a data endpoint with keyboard except that the host has many ports and the interface is usually capable of supporting multiple speeds and more of the RS-232 control signals. Front-end communication software running in the host is typically supplied by the computer vendor and is not designed tO support the Data Terminal Dialing feature. Such software typically supports call origination through Automatic Calling Units (ACUs), which are not compatible with Data Terminal Dialing. Thus, the primary means of communicating with the host is by calling from data terminals or personal computers. Groups of host ports with matching characteristics may be members of hunt groups (referred to as host port groups).

d. Analog Data Endpoint

Data endpoints with modems are referred to as analog data endpoints. Modems connected via tip ring lines use PDCs as extension numbers rather than Data Dial Codes (DDCs). Station-to-station data calls to (or from ) this endpoint from (or to) digital endpoints require a modem conversion resource to convert the endpoint’s analog data to digital format. Calls from a digital endpoint to an analog data endpoint (i.e., calls to a PDC), will automatically have a conversion resource inserted in the calling path. If the called (analog) endpoint should then invoke Transfer To Data, the conversion resource will be released. Data calls originating from an analog data endpoint must first enter a Modem Request Code before addressing a digital data endpoint. This is required because the system assumes that a call originating from a voice terminal will invoke Transfer To Data. If the analog data endpoint is not going to transfer to data, they must indicate this so that a conversion resource will be included in the connection.

2.DCE Devices

This group of data endpoints consists primarily of modems. The modems are connected to a data port from their RS-232 side. The data module must be configured as a DTE interface to provide connectivity between the modem and a data port. It is possible to simulate a DTE interface from an ADU data module with a cross-over (“null modem”) cable. This group of endpoints is important for users who provide their own modems, connected to dedicated trunks or private lines, for internal modem pooling.

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