Image Processing Reference
In-Depth Information
TABLE .
Performance Indicators for P-NET
Performance Indicator
Profile /
Delivery time
.-. ms
Number of end-stations
Number of switches between end-stations
Throughput RTE
-. M octets/s
Non-RTE bandwidth
%
Time synchronization accuracy
—
Non-time-based synchronization accuracy
. ms
Redundancy recovery time
s
TABLE .
Performance Indicators for Vnet/IP
Performance Indicator
Profile /
a
Profile /
b
Delivery time
ms
ms
Number of end-stations
Number of switches between end-stations
Throughput RTE
M octets/s
M octets/s
Non-RTE bandwidth
%-%
%-%
Time synchronization accuracy
<
ms
<
ms
Non-time-based synchronization accuracy
—
—
Redundancy recovery time
<
ms
<
ms
a
For two end-stations belonging to the same domain.
b
For two end-stations belonging to different domains with one lost frame.
21.4.1.4 Vnet/IP (Profile 10/1)
Vnet/IP
∗
hasbeendevelopedbyYokogawaandisincludedintheIECdocumentasproile/.
The Vnet/IP protocol uses standard TCP/IP protocols for the integration of HTTP or other Internet
protocols over the network and special RT extension protocols called RTP (RT and reliable datagram
protocol).
The Vnet/IP is in fact not an RTE protocol. It just uses the UDP/IP protocol suite to transport the
RTP application protocol. No special measures are taken to get a deterministic or even RT behavior.
A Vnet/IP network consists of one or more domains connected to each other by routers. The
IP unicast and multicast addresses are used as addresses of the data-link protocol and queued
communication relations are used.
The minimum cycle time of scheduling of RT traffic is ms, which fulfills the application
class of process control. This specification does not cover the limiting of other traffic using
the available bandwidth, e.g., HTTP or TCP transfer on the same network, which could slow
down the RT behavior. The performance indicators as indicated in the IEC standard are listed in
Table ..
At the application layer, different objects like variables, events, regions, time and network, and the
corresponding services are defined. As an example, the variable object may be accessed over client-
server relations with read or write services or publisher-subscriber relations with push or pull mode
of operation. In the pull model, the publisher distributes the variable data periodically by multicas-
ting as requested by a remote subscriber. In the push model, the request is generated locally by the
publisher itself.
21.4.2 Realization of the on Top of Ethernet
heseRTErealizationsdonotaltertheEthernetcommunicationhardwareinanyway,butarerealized
by specifying a special protocol type (Ethertype) in the Ethernet frame. he standard protocol type
∗
Vnet/IP is the trade name of Yokogawa Electric Corporation.
