AT&T AT&T manual Starlan Interface ZTN84, Network

STARLAN Interface (ZTN84) (V2)

The STARLAN Interface (ZTN84) is a System 25 circuit pack (CP) designed to function as either a gateway or a bridge between the PBX and the AT&T STARLAN NETWORK. The ZTN84 contains much of the circuitry common to the other CPS in the system, that is a Sanity and Control Interface (SAKI), a Network Processing Element (NPE), and a 8031 microprocessor. The CP also contains the circuitry required to perform the protocol conversion on the data as it travels from one system to the other. These devices include a 80186 microprocessor, 82586 coprocessor, four Octal Asynchronous Terminal Mode 2 to EIA Asynchronous LSI (OATMEAL) devices, and a logic sequencer. The 80186, the 82586, and the logic sequencer (PLS105N) work together to add and delete the protocol used by the Local Area Network (LAN), while the 80186 and the OATMEALS work together to add and delete the protocol used by the PBX.

The ZTN84 can support up to four circuit switch connections between the Private Branch Exchange (PBX) and the Local Area Network (LAN); this capability is provided by the four OATMEALS and the NPE, the latter being a four channel device. In providing a connection between the PBX and the LAN, capabilities such as file sharing, printer services, connections to hosts, and modem pooling may be accessible across systems.

The OATMEAL devices on the ZTN84 are used in such a way as to support asynchronous data communication at any of the standard rates ranging from 300 bps to 19.2 Kbps. The asynchronous protocol that is used is a subset of Digital Communications Protocol (DCP) Mode 2, as only “I” channel information is transmitted, where the data is formatted in High-Level Data Link Control (HDLC) frames.

The ZTN84	has	been designed with a hardware interface that allows the CP to be connected
to a STARLAN		NETWORK as an OUT connection.	This	can be connected to a STARLAN
NETWORK	Extension Unit (NEU) IN connection, in		a star	configuration.

The design of the ZTN84 is not fully compatible with the daisy-chain arrangement of the STARLAN NETWORK, since much of the daisy-chain circuitry was left off of the card. For testing purposes, the card can be used in a limited daisy-chain arrangement, where the ZTN84 is connected to a personal computer (PC) that possesses an Network Access Unit (NAU). The ZTN84 and the PC should be the only two devices forming the LAN. The daisy-chain circuitry was omitted in order to reduce cost and save board space. It is also the architectural design of the system that the PBX be connected to the LAN by a NEU. The NEU can either be local, in the telephone room with the switch, or in a remote office.

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