Image Processing Reference
In-Depth Information
Client
(e.g., Web browser)
Client
(e.g., Web browser)
Internet
Protocol servers
Config.
Address translation
Gateway logic
Services, data processing
Database
Address translation
Fieldbus drivers
Config.
Fieldbus
drivers
d rivers
Fieldbus
Field device
Field device
FIGURE .
Network topology for a gateway-based interconnection and general architecture of a gateway.
Internet (Figure .). What is different, though, is the way the information exchange is handled.
In the IP tunneling approach, the client connects directly to the server running on the field device.
The access point just forwards the IP traffic, but is not further involved in the data transfer. In the
gateway approach, the access point takes the role of a proxy representing the fieldbus and its data to
the outside world. It fetches the data from the field devices using the usual fieldbus communication
methods and is the communication partner addressed by the client.
There is no best or most suitable architecture for a gateway. It can act as an abstract interface to
an automation system, independent of both the fieldbus protocol (because it operates on application
level) and the fieldbus-specific coding of the data. This way, it can provide unified access to even
morethanoneieldbussimultaneously.hesotwarestructureofthegatewayimplementationcan
reflect this demand for versatility and exhibit a modular structure [,]. [,].The three-level approach
shown in Figure . is one possibility to achieve modularity. Alternatively, the architecture can as
well be monolithic and tailored to one specific case. his high degree of flexibility may be the reason
that gateways are the preferred interconnection concept in practice, especially for remote monitoring
applications [,]. Another reason is that gateways are an ideal point to implement access control
[,,]. In Web-based integration scenarios, the gateway is usually described and implemented
as a Web portal [,].
Unlike the tunneling approach, where each field device has to provide and maintain its data on
an individual basis, information processing for the client in the Internet can be centralized. This
enables the gateway to set up a comprehensive and consistent view of the automation system, a kind
