Control Technologies Ethernet TCP/IP Adapter Module CTI 2572 Installation guide

CTI 2572
ETHERNET TCP/IP ADAPTER MODULE
TECHNICAL OVERVIEW
Version 1.1
CTI Part # 062-00156
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2572 Technical Overview Manual 032698 $25

CTI 2572 Technical Overview Manual
Copyright 1993, 1998 Control Technology Inc.
All rights reserved.
This manual is published by Control Technology Inc., 5734 Middlebrook Pike, Knoxville, TN
37921. This manual contains references to brand and product names which are tradenames,
trademarks, and/or registered trademarks of Control Technology Inc. and Siemens AG. Other
references to brand and product names are tradenames, trademarks, and/or registered trademarks
of their respective holders.
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Every effort has been made to ensure the accuracy of this document; however, errors do
occasionally occur. CTI provides this document on an "as is" basis and assumes no
responsibility for direct or consequential damages resulting from the use of this document. This
document is provided without express or implied warranty of any kind, including but not limited
to the warranties of merchantability or fitness for a particular purpose. This document and the
products it references are subject to change without notice. If you have a comment or discover
an error, please call us toll-free at 1-800-537-8398.

CTI 2572 Technical Overview Manual i
PREFACE
This Technical Overview Manual provides an introduction to CTI 2572 Ethernet TCP/IP
Adapter and to the networking specifications used with the module. The manual is intended for
those individuals who wish to gain a fundamental understanding of the 2572, Ethernet, TCP/IP,
and SIMATIC TI505 PLC command interfaces.
This manual is organized as follows:
Chapter 1 describes the features of the 2572;
Chapter 2 provides an overview of local area network topologies;
Chapter 3 reviews Ethernet physical media and data link formats;
Chapter 4 provides an overview of higher level local area network protocols;
Chapter 5 discusses TCP/IP and related protocols
Chapter 6 covers SIMATIC TI505 command protocols.
Individuals interested in more in-depth information regarding Ethernet and TCP/IP may wish to
read one of the several excellent technical books available on the subject. These include
Internetworking with TCP/IP Vol I, II, and III by Douglas E. Comer (Prentice-Hall, 1991),
TCP/IP and Related Protocols by Uyless Black (McGraw-Hill, 1992), and The Simple Book
Book by Marshall T. Rose (Prentice Hall, 1991).
Please refer to the CTI 2572 Installation and Operation Guide for specifications and additional
information about the 2572 message interface.

CTI 2572 Technical Overview Manual iii
TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION..................................................................................................1
1.1 Description ...........................................................................................................................1
1.2 2572 Functions.....................................................................................................................2
CHAPTER 2. LOCAL AREA NETWORK OVERVIEW ............................................................3
2.1 Master/Slave vs. Local Area Networks................................................................................3
2.2 IEEE 802.5 (Token-Ring) ....................................................................................................4
2.3 Ethernet and IEEE 802.3......................................................................................................5
2.4 IEEE 802.4 (Token Bus) ......................................................................................................6
2.5 Future Technologies.............................................................................................................6
2.6 Summary ..............................................................................................................................7
CHAPTER 3. ETHERNET OVERVIEW......................................................................................9
3.1 ISO Reference Model...........................................................................................................9
3.2 Ethernet Topologies and Media - Physical Layer...............................................................10
3.3 Ethernet Protocol - Data Link Layer ..................................................................................13
3.4 Ethernet Addresses.............................................................................................................15
3.5 Requirement for Higher Level Protocols ...........................................................................15
CHAPTER 4. NETWORK PROTOCOLS ..................................................................................17
4.1 Connectionless vs. Connection Oriented Protocols ...........................................................17
4.2 Common LAN Protocols....................................................................................................18
CHAPTER 5. TCP/IP OVERVIEW ............................................................................................21
5.1 TCP/IP Components...........................................................................................................21
5.2 Internet Protocol.................................................................................................................22
5.3 Address Resolution Protocol (ARP) ..................................................................................24
5.4 User Datagram Protocol (UDP)..........................................................................................24
5.5 Transmission Control Protocol (TCP)................................................................................25
5.6 Berkeley Sockets................................................................................................................27
5.7 2572 TCP/IP Support .........................................................................................................27
CHAPTER 6. PLC COMMAND INTERFACE..........................................................................29
6.1 Non Intelligent Terminal Protocol.......................................................................................29
6.2 Task Codes..........................................................................................................................30

CTI 2572 Technical Overview Manual v
TABLE OF FIGURES
Figure 1 CTI 2572..........................................................................................................................1
Figure 2 Token Ring Topology.......................................................................................................4
Figure 3 Ethernet Topology (Coax)...............................................................................................5
Figure 4 10Base5 (Thick Coax) Topology ...................................................................................10
Figure 5 10Base2 (Thin Coax) Topology.....................................................................................10
Figure 6 10BaseT (Unshielded Twisted Pair) Topology..............................................................11
Figure 7 Fiber Optic Hub ............................................................................................................12
Figure 8 Ethernet Bridge .............................................................................................................12
Figure 9 Mixed Ethernet Media...................................................................................................13
Figure 10 802.3 Frame w/ SNAP Header....................................................................................14
Figure 11 TCP/IP Data Encapsulation........................................................................................21
Figure 12 Datagram.....................................................................................................................22
Figure 13 UDP Datagram ...........................................................................................................25
Figure 14 TCP Segment...............................................................................................................26
Figure 15 NITP Message Format ................................................................................................29

CTI 2572 Technical Overview Manual 1
CHAPTER 1. INTRODUCTION
1.1 Description
The 2572 Ethernet TCP/IP Adapter is a single wide I/O module
which connects SIMATIC TI505 controllers to Ethernet networks.
Using TCP/IP (Transmission Control Protocol/ Internet Protocol),
other controllers or computers can access registers, counters, timers,
and memory locations in the PLC (Programmable Logic Controller).
Thus, the 2572 enables applications such as supervisory control, data
acquisition, and remote program download to be performed using
SIMATIC TI505 equipment over an industry standard local area
network.
The 2572 attaches to all media specified by IEEE 802.3 including
10Base5 (thick coax), 10BASE2 (thin coax), 10BaseT (unshielded
twisted pair), and FOIRL (fiber optic cable). User supplied 10BaseT
cabling can be attached directly to the 2572 via a RJ-45 connector.
Other media may be attached via the appropriate transceiver attached
to the AUI (Attachment Unit Interface) port. The AUI port may be
powered from the backplane or with an external power supply to
conserve backplane power.
In addition to the Ethernet ports, the 2572 provides two serial ports
which can function as program ports for local or remote PLCs.
Operator interface devices, such as the CTI 5250 Access Module, or
personal computers running programming software, such as TISOFT, can access the PLC
memory via these ports. These ports operate concurrently with the Ethernet ports.
An array of diagnostic LEDs indicate operational status of the module, activity on the Ethernet
and serial ports, and the status of the Ethernet connection (link beat status, AUI active, collisions,
and 10BaseT reversed polarity).
The 2572 requires no user programming of the module. The initial baud rates of the serial ports
may be set by switches. All options are set by switches on the module or via word values set by
PLC logic.
Figure 1 CTI 2572

CTI 2572 Technical Overview Manual
2
1.2 2572 Functions
Server Mode
In Server Mode, the module responds to PLC commands embedded in the TCP/IP packet. The
initiating device (usually a computer or a 2572 operating in client mode) encapsulates the PLC
command in the TCP/IP protocol and transmits it to the IP address of the 2572. The 2572
retrieves the command from TCP/IP and formats a corresponding request to the PLC processor.
When the 2572 receives the response from the PLC processor, it encapsulates the response in the
TCP/IP protocol and transmits it back to the IP address which sent the initial command.
No PLC programming is required to support server mode. However, the initiating device must
encapsulate the proper command in the TCP/IP protocol and must properly process PLC
responses which the 2572 embeds in TCP/IP. Many operating systems contain support for
TCP/IP. Unix contains native TCP/IP support; IBM OS/2 and Microsoft Windows provide
optional TCP/IP support. MS DOS does not directly support TCP/IP, but several companies
offer DOS TCP/IP drivers.
Client Mode
In Client Mode, the 2572 can initiate a TCP/IP message. PLC logic is used to tell the 2572 what
to send, where to send it, and when to send it. Using 2572 Client Mode, the local PLC can read
and write memory in other remote PLCs or it can send messages to supervisory computers based
on events detected by the PLC (alarm detection, data logging, etc.). Since a 2572 can operate as
both a server and a client, multiple PLCs (each with a 2572), can participate in peer to peer
communications.
Serial Redirect
Serial Redirect is a very powerful feature which routes data received at a serial port on the
module to another node on the network. Once the serial port has been configured for the type of
service and a destination address has been established, the 2572 will encapsulate the serial port
data in TCP/IP and send it to the destination. Replies from the destination address will be routed
back to the serial port. Using Serial Redirect, devices which normally communicate with the
programming port of the PLC can access remote PLCs. For example, a PC running TISOFT
could download programs to other PLCs on the network.

CTI 2572 Technical Overview Manual 3
CHAPTER 2. LOCAL AREA NETWORK OVERVIEW
Local Area Networks (LANs) grew from the need to interconnect many intelligent devices in a
non-proprietary manner. Today, the most widely used LAN standards are Token-Ring (IEEE
802.5) and Ethernet (IEEE 802.3). Token Bus (IEEE 802.4), was proposed by GM in the late
80’s as a part of the Manufacturing Automation Protocol (MAP). Token Bus has seen limited
use, primarily due to cost and installation difficulty. It is briefly discussed in this document to
provide a more complete perspective of factory networking alternatives.
2.1 Master/Slave vs. Local Area Networks
Master/slave networks are commonly used in factory floor communications. These networks use
a master station (computer or /controller) and multiple slave devices (such as controllers,
terminals, or readers). The master station polls each slave unit on the network in turn, requesting
services or information. After the slave performs the task (or indicates that it cannot), the master
polls the next slave. This scheme works reasonably well when there are few devices on the
network. However, as the size of the network grows, more and more master processor resources
and network bandwidth must be devoted to the "overhead" of polling. This overhead limits
throughput and lengthens response time, especially since most master/slave networks operate at a
data rate of 115 K bits/sec or less.
Local area networks (LANs), on the other hand, do not have a master station. All stations on the
network can initiate a message. Standard rules for media access determine when a given station
may send a message. Media access rules usually involve passing a token or listening for traffic
on the line. As a result, the overhead of a typical local area network is much lower than a
master/slave network. This characteristic, coupled with much higher signalling rates (10 - 16
Mb) provides much higher throughput and allows many more devices to be connected to the
network. Because there is no master station, there is no single point of failure.
Each master/slave network tends to use a different protocol, partially because there is no
generally accepted standard. The protocol is typically determined by the primary equipment
manufacturer and in some cases the protocol may be proprietary, subject to copyright or patent
laws. As a result, most master/slave networks have very poor multi-vendor inter-operability.
Conversely, LANs such as Ethernet and Token-Ring have protocols that are well specified and
documented by standards bodies such as IEEE and are supported by a wide number of vendors.

CTI 2572 Technical Overview Manual
4
2.2 IEEE 802.5 (Token-Ring)
Token Ring (IEEE 802.5) uses a ring topology.
Each station on the network has two
connections - one to the "downstream" station
and one to the "upstream" stations. Each
station receives network data from the
downstream station and passes it to the
upstream station. The data circulates through
the network until it reaches the initiating
station, which validates that it was correctly
sent though the network. In practice, rather
than wire directly between each station, the
stations are wired into a central hub. This
approach allows stations to be added by
plugging them into the hub, where the plug
mechanically inserts the station into the ring.
Token ring operates at 4 or 16 M bits/sec using
shielded twisted pair media. Fiber optic cable
may be used for interconnecting hubs.
Token Ring (802.5) uses a "token" which is passed among the stations on the network. When a
station has a token, it can transmit. When it is through transmitting data, a station sends the
token to the next "upstream" station.
The primary benefit of token ring is that it provides a very consistent level of network
performance, since there is a maximum amount of time a token can be held. Token Ring
response is sometimes referred to as deterministic, meaning that the response time can be
precisely calculated. At higher levels of network loading, Token-Ring may provide greater
sustained throughput than Ethernet or Token-Bus.
On the other hand, token ring is costly (about 4 to 5 times more than Ethernet) and its technology
is closely tied to proprietary IBM technology. In some situations, the ring topology of token-ring
networks may not be as well suited to the factory floor as a bus topology.
PC
PC
PC
Server
PC
PC
Figure 2 Token Ring Topology

CTI 2572 Technical Overview Manual 5
2.3 Ethernet and IEEE 802.3
Officially, "Ethernet" is the name of a CSMA/CD network developed at Xerox. It was jointly
documented by Digital Equipment Corporation (DEC), Intel, and Xerox in a 1982 specification
for Ethernet Version 2. This specification is commonly called Ethernet II or "Blue Book"
Ethernet for the color of the specification cover. Later, the IEEE developed a specification for a
CSMA/CD local area network based on Ethernet II. This specification, called 802.3, is fully
compatible with Ethernet II at the physical layer (e.g. hardware, connectors, and media).
However, there are some formatting differences in the data link packet (discussed in the next
section).
Although the specifications are not totally compatible, the distinction between "Ethernet" and
802.3 have become blurred. Consequently both are commonly referred to as Ethernet. In this
document, except where specifically noted, the term Ethernet will refer to both the "Blue Book"
(Version 2) and the 802.3 specification.
Ethernet stations are connected in
a bus arrangement, all stations
share a common connection.
When a message is transmitted on
the network, all attached devices
receive it. The Ethernet standard
supports a variety of media,
including coaxial cable, twisted
pair, and fiber optics.
Ethernet uses a scheme called
Carrier Sense Multiple Access
with Collision Detection
(abbreviated CSMA/CD) to
control access to the media. A
station listens to the network for a
carrier signal which indicates that
another station is transmitting. If the signal is detected, the station waits until it detects no
carrier, then transmits. It is possible that when there is no carrier (no one is transmitting) more
than one station can attempt to transmit data at the same time. This condition is referred to as a
collision. Ethernet stations can detect this condition (Collision Detection), wait a random
amount of time, then retry.
Ethernet has a number of important benefits. Since it is widely used, Ethernet adapters are very
inexpensive when compared to other alternatives. It has a very flexible topology and media
selection (coaxial cable tap, twisted pair hub, or fiber optic hub). In addition, it provides
excellent response and throughput at typical utilization levels.
PC
PC
PC
Server
PC PC
Ethernet
Figure 3 Ethernet Topology (Coax)

CTI 2572 Technical Overview Manual
6
The primary disadvantage of Ethernet is that the response time is not consistent under widely
varying loads. As the network loading increases above 50% , collisions occur more frequently
and the network response time increases. In practice, most large busy networks use bridges to
reduce the number of collisions. Bridges are discussed in the next chapter.
2.4 IEEE 802.4 (Token Bus)
Token-Bus is a LAN standard developed in conjunction with the General Motors Manufacturing
Automation Protocol (MAP) effort. All Token Bus stations are connected a to a common wire,
in this case coaxial cable. Like Token-Ring, a station can transmit only when it has received the
token. The IEEE 802.4 Token-Bus standard supports both a broadband network and a
carrierband network using RF (Radio Frequency) technology. The broadband network
(envisioned as the factory "backbone") supports multiple channels which could contain different
data types (e.g. analog video and digital data) and operates at 10 Mb. The single channel
carrierband supports up to 32 devices at a 5 Mb data rate.
Token Bus was selected by the MAP committee because it provided a bus topology (which some
consider to be a better plant floor topology) and it offered the consistent, deterministic response
time inherent in token passing schemes. RF technology was selected for noise immunity and
because it provided the opportunity for a single factory cabling system to carry both digital data
and analog video.
The big disadvantage of Token Bus is cost and availability. Not only are the adapters very costly
(up to 30 times the cost of Ethernet) but RF transmission is very sensitive to factors such as cable
length, amplifier alignment and termination impedances - making it expensive to install and
maintain.
2.5 Future Technologies
While both Token-Ring and Ethernet are excellent for transferring typical factory data, none
have the capacity to transmit high bandwidth information such as full motion video. There are a
number of emerging LAN standards which promise to offer this capability. These include FDDI
(Fiber Distributed Data Interface), CDDI (Copper Distributed Data Interface), ATM
(Asynchronous Transfer Method), "Switched" Ethernet, and "Fast" Ethernet. These will offer
signaling rates in the range of 100 Mb.
At this point in time, it is difficult to predict which technology will prevail as the new high
speed standard. Many experts speculate that future networks will incorporate both current
(medium speed) and high speed LAN technology.

CTI 2572 Technical Overview Manual 7
2.6 Summary
Older master/slave networks are rapidly being replaced by standard LANs which provide better
performance, multi-vendor support, and integration with information networks. Of the current
LAN standards, Token-Ring and Ethernet have the significant market share. Token Bus, because
of the cost and complexity, has never become a major contender for the factory LAN market.
In general, Ethernet offers the most cost-effective and flexible factory floor networking solution
available today. In a properly designed factory network, Ethernet provides excellent
performance, reliability, and manageability. Since Ethernet is used with the 2572, it is discussed
in more detail in the following section.

CTI 2572 Technical Overview Manual 9
CHAPTER 3. ETHERNET OVERVIEW
3.1 ISO Reference Model
Modern network implementations separate data communication functions into layers. Each layer
performs a specific set of services and interacts with layers above and below in a well defined
way.
In 1984 the International Standards Organization published the Open Systems Interconnection
(OSI) Reference model. Although there are few, if any, strict implementations of the entire
seven layer model, it is commonly used as a conceptual reference when discussing networking
software. The OSI model is briefly described below:
Layer Function
Layer 7
Application Provides application services such as file transfer, virtual terminal, and directory services.
Layer 6
Presentation Resolves differences in data representation between the communicating applications
Layer 5
Session Synchronizes communications between applications
Layer 4
Transport Provides reliable data transfer from end node to end node.
Layer 3
Network Translates physical addresses into logical addresses and routes packets to the destination node.
Layer 2
Data Link Places messages into data frames and manages access to the media.
Layer 1
Physical Defines the electrical and mechanical characteristics of the transmission media .
The Ethernet specifications describe both the Physical layer (cabling, connectors, and
topology) as well as the Data Link (Medium Access) layer. As a result of this complete
specification, Ethernet equipment from various vendors can be used on the same network.
Ethernet is the most widely used local area network in the world and it is continuing to gain
market share due to its low cost and flexibility. One of the fastest growing areas in Ethernet
installations is the factory floor.

CTI 2572 Technical Overview Manual
10
3.2 Ethernet Topologies and Media - Physical Layer
Ethernet Version 2 and IEEE 802.3 are fully compatible at the physical level. Therefore the
formal IEEE 802.3 specification is used to describe all Ethernet media. The 802.3 specification
provides for a variety of topologies and media. All commonly used media operate at 10 Mb.
Specified media/topology can be used interchangeably and can be intermixed on the same
network. Ethernet media specifications include "thick" coax (10Base5), "thin" coax (10Base2),
twisted pair (10BaseT), and Fiber Optics (FOIRL). The specification provides for a media
independent port on Ethernet adapter cards known as an Attachment Unit Interface (AUI).
Media specific transceivers attach to the AUI. In addition most adapters provide at least one
native media attachment (usually 10Base2 or 10BaseT).
10Base5 "Thick" Coax
10Base5 was the original Ethernet media.
It is capable of cable runs up to 500 meters
(approximately 1500 feet). This distance
may be extended by the use of a repeater.
Ethernet stations (nodes) are attached to
the 10Base5 cable in a tap fashion. The
transceivers are mounted on the cable and
a cable is run from the transceiver to the
AUI port on the adapter. Although there
are numerous installations in place using
10Base5 cabling, new installations tend to
use other, more cost effective, cabling
media.
10Base2 "Thin" Coax
10Base2 coax has been a popular media
for Ethernet installations. It is capable of
cable runs up to 200 meters (about 600
feet). This distance may be extended by
using a repeater. The standard uses a 50
ohm coaxial cable and standard BNC
connectors, both widely available and
relatively inexpensive. In fact 10Base2 is
often referred to as "cheapernet" due to
this low cost. 10Base2 cabling uses a "T"
connector at each tap with a 50 ohm terminator at each end. The "T" connector may be attached
to a 10Base2 transceiver (and the network adapter card via the AUI port). Alternately, the
network adapter may provide a direct attachment for 10BaseT.
Transceiver Transceiver Transceiver
Ethernet
Station
AUI Port
Ethernet
Station
AUI Port
Ethernet
Station
AUI Port
10Base5 (Thick Coax)
Figure 4 10Base5 (Thick Coax) Topology
--
Transceiver
Station
AUI Port
Transceiver
Station
AUI Port
10Base2 Port
Station
10Base2 (Thin Coax)
Figure 5 10Base2 (Thin Coax) Topology