Civil Engineering Reference
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BAS network itself no matter whether it is connected to the Internet or not.
Nowadays, the use of Internet technologies in BAS is extended to the upper
layers of the OSI reference model. The higher-layer protocols and technolo-
gies, such as HTTP and Internet browsers, are used for network integration
(including the integration of BAS networks themselves and integration of
distant BASs over the Internet) and management software development.
6.5 Use of Internet technologies at automation level
Internet protocols and technologies are used in BAS to varying degrees. The
lowest degree of integration application at automation level is the case when
the protocol itself is not compatible with Internet Protocol and the Internet
is employed as the transmission medium only. Where protocol standards
are concerned, BACnet Annex H.3 is a standard specifying such a method.
This method is a substitute for the old telephone service which a traditional
BAS adopted as a remote access method. Another higher degree of integra-
tion application at automation level is the case where the protocol within
BAS is revised to be compatible with IP, so that devices compatible with the
BAS protocol can be connected directly to IP networks. BACnet Annex J is
a standard specifying such a method. In this case, the BAS networks are in
fact Internet/intranet.
Integrating BAS with the Internet or an extension of Internet protocols
into BAS networks are trends in the development of BAS communication
protocols, such as BACnet and LonWorks. As an ISO standard for BAS, the
latest BACnet has good integration capability with the Internet. The next
section discusses how BACnet allows the integration of BAS protocols with
the Internet.
6.5.1 Internet technologies employed to connect BACnet to an
IP network
For BACnet to utilize the Internet for BAS network communication, it must
speak the language of the Internet known as Internet Protocol. IP by itself is
little more than an envelope with 'from' and 'to' addresses and a place for a
message within. For equipment to communicate on the Internet, a Transport
Layer protocol must also be used. Currently, there are two primary Transport
Layer protocols, Transmission Control Protocol and User Datagram Protocol
(introduced in Section 6.2.2). TCP is a reliable connection-oriented transport
service that provides end-to-end reliability, resequencing and flow control.
The TCP/IP combination works much like a telephone call: a connection is
requested, established, and then bidirectional communication follows. UDP is
a connectionless 'datagram' transport service. It is used by applications that
do not require the level of service of TCP, or that wish to use communication
services not available from TCP, such as multicast and broadcast delivery.
Since the BACnet protocol itself provides for the guaranteed delivery of
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