Image Processing Reference
In-Depth Information
TABLE .
Performance Indicators for EPA
Performance Indicator
Profile /
Profile /
Delivery time
ms
µs
Number of end-stations
Number of switches between end-stations
Throughput RTE
. M octets/s
. M octets/s
Non-RTE bandwidth
%
%
Time synchronization accuracy
<
µs
<
µs
Non-time-based synchronization accuracy
—
—
Redundancy recovery time
<
ms
<
ms
It is a distributed approach to realize deterministic communication based on a time slicing mecha-
nism inside the MAC layer. he time to complete a communication procedure is called communica-
tion macrocycle and marked as T. Figure . illustrates that each communication macrocycle (T) is
divided into two phases, periodic-message transferring phase (Tp) and nonperiodic-message trans-
ferring phase (Tn) The last part of each device's periodic message contains a nonperiodic-message
announcement which indicates whether the device also has a nonperiodic message to transmit or
not. Once the periodic-message transferring phase is completed, the nonperiodic-message transfer-
ring phase begins. All devices which announced (during the periodic message transfer phase) that
they have a nonperiodic message to send are allowed to transmit their nonperiodic messages in this
phase. Two sets of consistent performance indicators are listed in Table ..
In EPA systems, there are two kinds of application processes, EPA function block
∗
application
processes and NRT application processes, which may run in parallel in one EPA system. NRT appli-
cation processes are those based on regular Ethernet and TCP/IP. The interoperation between two
function blocks is modeled as connecting the input/output parameters between two function blocks
using EPA application services.
21.4.2.4 PROFINET CBA (Profile 3/3)
PROFINET is defined by several manufacturers (including Siemens) and supported by PROFIBUS
International(seewww.proibus.org)[].heirstversionwasbasedoncomponent-basedautoma-
tion (CBA) and is included in IEC - (type in IEC ) as profile /.
he mechanical, electrical, and functional elements of an automation device are grouped together
into components. Components have inputs and outputs. he values of the input and output variables
of the components are transmitted over the standard TCP/IP connection using the remote procedure
call (RPC)
†
and distributed component object model (DCOM)
‡
protocolfromtheoiceworld.
With this RPC and DCOM protocol it is possible to reach cycle times for what we call the human
control application class. If cycle times of less than ms are required, the RT protocol is used. he
RT protocol is based on a special Ethertype (see Table .) and frame prioritization (see explanation
in Section ...). In this case, the TCP/IP stack is bypassed and cycle times of less than ms
become possible.
With PROFINET CBA, the end user defines his automation components with the traditional pro-
gramming and configuration tool for PLC. These components are represented by one controller in
amachine,aieldbusnetwork,oranydeviceontheieldbusitself.Fortheplanningoftheinstalla-
tion, logical connections between the different components are defined. These connections specify
∗
A function block is an algorithm with its own associated static memory. Function blocks can be instantiated with another
copy of the function block's memory. Function blocks are only accessed via input and output variables.
†
An RPC is a protocol that allows a computer program running on one host to cause code to be executed on another host
without the programmer needing to explicitly code for this (source: wikipedia.org).
‡
DCOM is a Microsoft proprietary technology for software components distributed across several networked computers
(source: wikipedia.org).
