Motorola 68P02958C00-B - Manual (Page 24)

System Overview
2-4
MDLC Over IP
MOSCAD RTUs and IP Gateways can use IP (Internet Protocol) technology to interface to
advanced radio infrastructure (e.g. digital ASTRO IP conventional systems) and to standard
private IP networks. Most benefits of the MDLC protocol are preserved. MDLC and IP
networks can be integrated in the same system, as networking properties are preserved.
MOSCAD MDLC applications need not be modified as the lower layers of the protocol
support IP.
MDLC packets to be transmitted are enveloped inside IP datagrams and sent between remote
RTUs or between an IP Gateway and an RTU.
An IP Gateway can act as a gateway between the field and the SCADA Central to extract the
enveloped frames from the IP message. A ToolBox can be connected to one of the RTUs or to
the IP Gateway, either locally or over IP network.
Each RTU/IP Gateway is assigned a Site ID. In addition, each RTU/IP Gateway with an IP
interface is assigned an IP address. An IP conversion table which maps Site IDs to IP
addresses is created in the ToolBox and downloaded to the RTUs and IP Gateway. This
enables routing over the IP network to the proper destination.
Two variations of MDLC over IP exist, MDLC via Terminal Server and MDLC via Astro IP.
MDLC via Terminal Server
If the RTUs are on a Local Area Network (LAN), each can be connected to a Terminal Server
attached to the Ethernet. The Terminal Server converts the RS232 to the Ethernet LAN and
enables communication with an IP Gateway, or between RTUs.
In the diagram below, a typical configuration is shown, with RTUs attached via SLIP (Serial
Line IP) port to a Terminal Server, which is in turn attached to Ethernet.