Specifications

24 Rockwell Automation Publication AG-SG001G-EN-P - April 2015
Chapter 2 Choosing a Telemetry Network
Choosing a Transmission
Mode
The transmission mode defines the way information is sent and received between
and/or among devices on a network. For SCADA systems, your network
topology generally determines your data transmission mode.
Choosing a Link Media
When choosing link media, consider the following:
• Data transmission needs of the application
• Remote site and control center locations
• Distance between sites
• Available link media services
• Project budget
Several types of link media are available, including public transmission media,
atmospheric media, and dedicated line media.
The following sections outline the advantages, disadvantages, and requirements
of each link medium.
If you have chosen this
topology
Then your transmission mode is Which means
Point-to-multipoint Half-duplex Information is sent in one direction at a time over the link.
Point-to-point Full-duplex Information is simultaneously sent and received over the link.
Multipoint-to-multipoint Full-duplex (between station and
modem)
Half-duplex (between modems)
Information is simultaneously sent and received over the
station to modem link, whereas information is sent in only
one direction at a time over the modem to modem link.
Station
A
Station
B
transmit
receive
receive
transmit
Station
A
Station
B
transmit
receive
receive
transmit
Station
A
Modem
A
transmit
receive
receive
transmit
Modem
B
transmit
receive
receive
transmit
Station
B
receive
receive
transmit
Media Category Type
Public transmission
media
• Public-switched telephone network (PSTN);
Internationally: general switched telephone network (GSTN)
• Private leased line (PLL)
• Digital data service (DDS)
• Internet via ISP
Atmospheric media • Microwave radio
• VHF/UHF radio
• Geosynchronous satellite
• Cellular network
Dedicated line • Dedicated wire
• Power line