Rockwell Automation 9220-WINTA ControlNet Traffic Analyzer Reference Manual - Manual (Page 12)

Publication 9220-052C-EN-P - August 2002
1-2 Introduction
See the ControlNet International Specification for more information
about information exchange on a ControlNet network link. The
ControlNet International Specification can be purchased from
ControlNet International.
The following illustration describes the ControlNet network’s link
layer services.
ControlNet Messages
The repetitive time interval in which data can be sent on a link is
called the Network Update Time (NUT). The NUT is divided into three
parts containing three defined types of Media Access Control (MAC)
frames:
•
Scheduled
Every scheduled node in sequential order is guaranteed one
opportunity to transmit. Information that is time-critical is sent
during the scheduled part of the interval. The bandwidth is
reserved in advance to support real time data transfers. Real time
data transfers include:
•
real time control data (I/O updates)
•
analog data
•
peer to peer interlocking
•
Unscheduled
All nodes transmit on a rotating basis in sequential order. This
rotation repeats until the time allocated for the unscheduled
portion is used up.
7
8
9.. 8
9
10.. 9
10..
Network Update Time (NUT)
Scheduled
Service
Unscheduled
Service
Network Maintenance
Service the
“Guardband”
41561
0 ... SMAX 0 ... SMAX
Time
Link Layer Services
0 ... SMAX