Crestron e-Control, Справочное руководство

Страница: 11 / 74

Crestron e-Control
®
Software
IP Communication
The Ethernet standard supports numerous communication protocols that determine
how data is transferred from one network node to another. Different protocols work
together at different levels, or
layers , as outlined by the OSI reference model , to
enable communication on a network. The OSI reference model separates node-to-
node communications into seven layers, each building upon the standards contained
in the levels below it. The lowest of the seven layers deals solely with hardware
links; the highest deals with software interactions at the application-program level.
(The OSI model is explained more in detail in “Appendix B: The OSI Reference
Model” on page 55.)
TCP/IP is the suite (or stack) of networking protocols that make up the Internet and
most LANs. The TCP/IP name is taken from two of the core protocols in the suite, IP
(
I nternet P rotocol) and TCP ( T ransport C ontrol P rotocol. Another core protocol in
the suite is UDP ( U ser D atagram P rotocol).
Crestron equipment communicates over Ethernet using a proprietary protocol called
CIP (
C restron over I nternet P rotocol), which is an implementation of UDP. Crestron
also provides hardware and software gateways that convert data received over TCP
into CIP, and vice-versa.
Both UDP and TCP are transport-layer (layer 3) protocols that run over IP networks.
UDP has several characteristics that make it convenient and useful for e-Control.
First, UDP is
connectionless , meaning that Crestron equipment can transfer data over
Ethernet without prior advertising or need to negotiate a connection. UDP has
minimal overhead; each datagram on the network is composed of just a small header
and the control data. In addition, UDP allows data to be broadcast to multiple
devices. UDP thus provides simple, fast, and efficient transfer of data.
In contrast, TCP is a connection-oriented protocol. Before data transfer can take
place, a connection must first be established; after data transfer, the connection must
be torn down. TCP incurs much more overhead than UDP because it provides
extensive error checking and flow control. This makes TCP a more reliable, yet
slower transmission.
IP Addressing
Both UDP and TCP use the same addressing scheme; that is, they use IP addresses
to identify devices (hosts) connected via Ethernet to other hosts. Every host on an IP
network must have a unique IP address to identify its “location,” or address, on the
network. This applies to both the WAN and LAN connections.
The IP address is a 32-bit binary number that is expressed in “dotted quad” format,
consisting of the decimal values of its four octets (bytes) separated by periods. For
example, the IP address 192.168.123.132 is the decimal equivalent of the binary
number 11000000.10101000.01111011.10000100.
The decimal numbers separated by periods are the octets converted from binary to
decimal notation.
The first part of an IP address identifies the network; the last part identifies the host,
or node. If you take the example 192.168.123.132 and divide it into these two parts
you get 192.168.123.0 as the
network address ; and 0.0.0.132 as the host address .
Reference Guide – DOC. 6052 Crestron e-Control®
•
7