315-4PN33

coaxial Ethernet networks are based on a bus topology the twisted-
pair network is based on a point-to-point scheme. The network that
may be established by means of this cable has a star topology. Every
station is connected to the star coupler (hub/switch) by means of a
separate cable. The hub/switch provides the interface to the Ethernet.
The hub is the central element that is required to implement a twisted-
pair Ethernet network. It is the job of the hub to regenerate and to
amplify the signals in both directions. At the same time it must have
the facility to detect and process segment wide collisions and to relay
this information. The hub is not accessible by means of a separate
network address since it is not visible to the stations on the network.
A hub has provisions to interface to Ethernet or to another hub res.
switch.
A switch also is a central element for realizing Ethernet on Twisted
Pair. Several stations res. hubs are connected via a switch. After-
wards they are able to communicate with each other via the switch
without interfering the network. An intelligent hardware analyses the
incoming telegrams of every port of the switch and passes them colli-
sion free on to the destination stations of the switch. A switch opti-
mizes the bandwidth in every connected segment of a network.
Switches enable exclusive connections between the segments of a
network changing at request.
7.4
Basics - Protocols
Protocols define a set of instructions or standards that enable com-
puter to establish communication connections and exchange informa-
tion as error free as possible. A commonly established protocol for
the standardization of the complete computer communication is the
so called ISO/OSI layer model, a model based upon seven layers
with rules for the usage of hardware and software
Ä Chapter 7.2
‘Basics - ISO/OSI reference model’ on page 108
The following protocols are used:
n Siemens S7 connections
n Open communication
–
TCP native according to RFC 793
– ISO on TCP according to RFC 1006
– UDP according to RFC 768
With the Siemens S7 connection large data sets may be transferred
between PLC systems based on Siemens
STEP
®
7. Here the stations
are connected via Ethernet. Precondition for the Siemens S7 commu-
nication is a configured connection table, which contains the defined
connections for communication. Here NetPro from Siemens may be
used.
Properties:
n A communication connection is specified by a connection ID for
each connection partner.
n The acknowledgement of the data transfer is established from the
partner station at level 7 of the ISO/OSI reference model.
n At the PLC side FB/SFB VIPA handling blocks are necessary for
data transfer for the Siemens S7 connections.
Hub (repeater)
Switch
Overview
Siemens S7 connec-
tions
VIPA System 300SDeployment Ethernet communication - productive
Basics - Protocols
HB140 | CPU | 315-4PN33 | GB | 14-43 110