Components and Architecture - Networking Basics Reference
22 HC900 Hybrid Controller Installation and User Guide Revision 5
9/03
See also
Refer to Communications Installation on page 85 for details on communications.
Networking Basics Reference
The following information provides a basic reference for identifying and applying networking concepts,
components, and methods. It is intended primarily as a language bridge between users who have a limited
knowledge of networking, but who need to incorporate networking mechanisms in process control systems,
and Information Technology (IT) professionals who are adept in network implementation.
Networking topics are many and broad. To be useful, the networking language bridge given here includes
topics that apply to HC900 Controllers and to closely related computer and networking devices.
Ethernet
Ethernet is a networking standard (IEEE 802.3) that features:
• Local Area Network (LAN), which means that networked devices are near to each other (usually in the
same building)
• "bus" or "star" topology. Bus topology means that all networked devices (also called nodes) connect to
a common cable at different locations. Star topology means that a networking device (called a hub or
"concentrator") provides interconnections for cables from network nodes.
• Transmission speed of 10 Mbps or 100 Mbps
• CSMA/CD access. CSMA/CD stands for Carrier Sense Multiple Access/Collision Detection. All
devices on the LAN are free to transmit at will. If two nodes that are inter-connected at Hubs transmit
simultaneously, the collision of the multiple access is detected by the hardware devices associated with
the nodes. Each device will wait a random time, and will attempt to re-transmit. If the device detects
another collision, it will double wait time before transmitting again. Doubling the wait time is called
"exponential back-off".
Node Addressing
Every node on a network has a unique number and or name that is used by transmission protocols to
identify it as the Source or the Destination of a message. When it is manufactured, every node is given a
hard-coded Media Access Control (MAC) address that can be sensed by other nodes on the network. When
it is placed on an Ethernet network, each node is also given an Internet Protocol (IP) address, which is
stored in non-volatile memory, and which identifies it uniquely on that network.
Open Systems Interconnection Reference Model (OSI)
The OSI Model provides a reference source of all the methods and protocols needed to connect one
computer to another over a network. Although details of networking systems often differ from those
specified in the OSI Model, this model is used widely for design and manufacture of networking
components as well as networking systems from networks are constructed. The Features of the OSI Model
are summarized in Table 3.
Networking Protocols
A network protocol is a set of rules, or syntax, for exchanging data between nodes. In a very simple
system, a single protocol is required. For most networking systems used in commercial and industrial
applications, several protocols are required. Some protocols operate in one layer of the OSI model, while
others operate in more than one layer. For example, Transport Control Protocol/Internet Protocol (TCP/IP)
is commonly on the Internet and is used in private networks such as an HC900 Controller LAN. TCP
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