Industrial Networks & Databases. Protocols and Networks - Device Bus - - Field Bus -

(1)

Protocols and Networks - Device Bus -

- Field Bus -

- Data Bus -

(2)

Recall

 MODBUS protocol is a messaging structure used to set up

master/client type communications with slaves/servers between intelligent devices

 It is a protocol with one master and no direct communication from slave to slave

slave to slave

 MODBUS PLUS is an industrial networking system that uses token- passing peer-to-peer communications at data transfer rates of one megabits per second;

megabits per second;

 It uses the MODBUS messaging structure to establish multi-master communication.

communication.

(3)

Modbus TCP/IP

MODBUS TCP/IP uses TCP/IP and Ethernet up to 1 Gbits/s to carry the MODBUS messaging structure.

the MODBUS messaging structure.

APPLICATION

7 Modbus

PRESENTATION

SESSION 6

5

EMPTY

EMPTY SESSION

TRANSPORT 5

4

EMPTY

TCP

NETWORK

LINK = LLC + MAC 3

2 CSMA/CD

IP

LINK = LLC + MAC

PHYSICAL 2

1

CSMA/CD

Ethernet V2 or 802.3

(4)

OSI Correspondence to the TCP/IP Layer Model

 Few working networks are implemented on the OSI Model

 TCP/IP Layer Model – Developed

OSI Model Application

 TCP/IP Layer Model – Developed before the OSI

 It’s simpler and has fewer layers

Application Service Layer

TCP/IP Model Application

Presentation Session

The TCP/IP Layer model:

 Application Service Layer – Provides the functionality of the

Service Layer Service Provider Layer (Host-to-Host)

Internetwork Layer

Session Transport

Network

Provides the functionality of the

Application, Presentation and Session layers

 Service Provider – Matches the Transport Layer. Called “Transport

Layer

Subnetwork Layer

(Network Access Layer)

Data-Link Physical Physical

Transport Layer. Called “Transport Layer.”

 Internetwork Layer – Matches the OSI Network Layer. Called the

“Network Layer”.

 Subnetwork Layer – Includes the OSI Data Link and Physical Layers

(5)

Data Movement

 User application requests information from a PLC

 A Modbus message is formed

 A Modbus message is formed in the “Modbus” layer

 Starting register, block length ….

 Message is encoded, sent

Application PLC

 Message is encoded, sent

received and passed to the PLC

 Information is sent back to application following the same

Modbus

Service Provider

TCP

Modbus

Service Provider application following the same procedure

Service Provider Layer (Host-to-Host)

TCP IP

Service Provider Layer (Host-to-Host)

Subnetwork Layer Subnetwork Layer

Modbus TCP/IP

(6)

Modbus TCP/IP Network Media - Coaxial Cable

Coaxial Cable - Two types used

 Coaxial Cable - Two types used

 Thin – 10Base2 networks

 Thick 10Base5 networks

 Point to Point - If a single connection

 Point to Point - If a single connection fails, the entire network fails

Thin coaxial cable is known as RG58 It is used in thin ethernet (10Base2) installations 185 metres maximum segment length

50 centimetres minimum distance between connection points

Thin Coax 185 metres maximum segment length between connection points

Maximum 30 connections per segment 5 centimetres minimum bend radius Uses BNC (Bayonet-Neil Concelman)

connectors External diameter of +/- 4.9 millimetres

Thick coaxial cable is known as RG8 It is used in thick ethernet (10Base5) installations 2.5 metres minimum distance between

Thin Coax

500 metres maximum segment length

2.5 metres minimum distance between connection points

Maximum 100 connections per segment 25 centimetres minimum bend radius Uses a viper tap to connect backbone to

network interface card External diameter of +/- 10.29 millimetres

Thick Coax

(7)

Modbus TCP/IP Network Media - Twisted Pair

Used increasingly, even at 100 Mbps

UTP - Insulated pairs of copper wires twisted together Multiple colour-coded pairs enclosed in a plastic sleeve Faster than coaxial cable

STP - Indivisible pairs enclosed in a shielding with aluminium foil

Category 5 (Cat 5) – The most common for IT networks Cat 5 = 100 Mbps (specification pending)

Cat 3 = 10 Mbps Uses RJ45 connector

Unshielded twisted pair is known as UTP It is currently available in 5 different categories (Cat 1 to 5) Cat 5 UTP is used in 10BaseT, 100BaseT,

Uses RJ45 connector

Cat 5 UTP is used in 10BaseT, 100BaseT,

gigabit and token ring Cat5 is the most popular installation choice presently Cat6 is being developed for the next

generation of installations 100 meteres maximum segment length Uses RJ45 plugs and sockets

Overbending the cable increases cross-talk between the 8 wires

Uses RJ45 plugs and sockets the 8 wires

(8)

Modbus TCP/IP Network Media - Optical Fibres

Three component parts:

Core

– Carries the light beam (glass or plastic)

Cladding

– Glass tube which reflects any interference light in the core

Cladding

– Glass tube which reflects any interference light in the core

Coating –

Protects the core and the optical cladding

Multimode fibre is the most popular type as it is the least expensive and easier to use.

(9)

Optical Fibres

Single-mode fiber is a higher performance, longer distance and more expensive technology than multimode fiber.

Multi-mode fiber is generally limited to one or two kilometers in length, depending on the application.

(10)

Fibre Optic Connectors

ST Connector

• Industrial equipment uses both ST an SC type

both ST an SC type connectors

• ST connectors have a bayonet type lock

SC Connector SC Connector

(11)

Transmission media

Ethernet is available on three types of medium:

Name Description Speed Max. Max. no. of Name Description Speed Max.

length

Max. no. of stations/segment 10 base 5 Thick Ethernet 10 Mbps 500 m 100

Coaxial cable cable

10 base 2 Thin Ethernet 10 Mbps 185 m 30 10 base T Twisted pair 10 Mbps 100 m 1024 Shielded

twisted twisted

pair 100 base TX Twisted pair cat. 5 100 Mbps 100 m ? ? ? 10 base F 2 fibres 10 Mbps 2000 m 1024 Optical

fibre fibre

100 base FX 2 fibres 100 Mbps 2000 m ? ? ? Radio wireless

(12)

Modbus TCP/IP Physical Layer

Topology: Free

Bus, star, tree or ring Bus, star, tree or ring

Maximum distance : Depends on medium and speed Minimum: 200 m on 100 base TX

Maximum: 40,000 m on 10 base F

Speed: 10 Mbps - 100 Mbps - 10 Gbps 10 Gbps in office automation

Max. no. of devices: Depends on medium

Minimum: 30 per segment on 10 base 2

Maximum: 1024 on 10 base T or 10 base F

(13)

Transport network link layers

Medium access method: CSMA/CD

(Carrier Sense Multiple Access with Collision Detection)

Collision Detection)

The stations listen to the transmission medium and wait until it is free to send.

If a collision is detected, each station continues to send in order that the collision is If a collision is detected, each station continues to send in order that the collision is seen by the entire network.

The stations resend their message after a random period of time has elapsed.

(14)

Modbus TCP Application Layer - Frame

ADU (Application Data Unit)

Address Function Data Checksum Modbus frame

PDU (Protocol Data Unit)

Address Function Data Checksum

Modbus TCP frame

ADU (Application Data Unit)

MBAP Function Data

PDU (Protocol Data Unit) MODBUS Application Protocol Header

Frame Identifier Protocol Identifier Size Unit Identifier

2 bytes 2 bytes 2 bytes 1 byte

Modbus = 0 Modbus Address

(15)

Modbus TCP Application Layer - Conformance Class

Class 0

 read multiple registers (#03)

 write multiple registers (#16)

Machine/vendor/network specific functions

 write multiple registers (#16)

Class 1

 read coils (#01)

 diagnostics (#08)

 program (484) (#09)

 poll (484) (#10)

 get comm event counters (Modbus) (#11)

 read input discretes (#02)

 read input registers (#04)

 write coil (#05)

 write single register (#06)

 get comm event counters (Modbus) (#11)

 get comm event log (Modbus) (#12)

 program (584/984) (#13)

 poll (584/984) (#14) report slave ID (f#17)

 write single register (#06)

 read exception status (#07)

Class 2

 force multiple coils (#15)

 report slave ID (f#17)

 program (884/u84) (#18)

 reset comm link (884/u84) (#19)

 program (ConCept) (#40)

 force multiple coils (#15)

 read general reference (#020)

 write general reference (#021)

 mask write register (#022)

 program (ConCept) (#40)

 firmware replacement (#125)

 program (584/984) (#126)

 report local address (Modbus) (#127)

 mask write register (#022)

 read/write registers (#023)

(16)

Modbus TCP/IP-ETHERNET DATA PACKET

(17)

Modbus TCP Application Layer – Frame (example)

Protocol PPP (Point-to-Point Protocol, RFC 1661) can be used to transfer data – other protocol frames - inside the PPP pocket

other protocol frames - inside the PPP pocket

Frame PPP Frame PPP

Frame IP

Frame TCP Frame TCP

Frame Modbus

(18)

Modbus TCP Application Layer – Frame (example)

IP Protocol ID

|0||21|

|45||0||0||34||0||7d||40||0||80||6||40||1d||a||74||11||bb||d9||62||c4||98|

Ver|

IHL TOS

Size ID Flags|o ffset TTL

TCP Protocol

Check-

sum Source Addres

Dest.

Addres

|45||0||0||34||0||7d||40||0||80||6||40||1d||a||74||11||bb||d9||62||c4||98|

Port 502

TOS Protocol

ID

Source Port

Dest.

Port

Sequence no

Ack. no

Header size| Flags

Window

Data index

PPP pocket IP

pocket

TCP

|16||2e||1||f6||c||d||a||c||30||80||4b||be||50||18||ff||ff||49||45||0||0|

Sequence no ^Window_size

Check sum Frame ID

Protocol

Size Start Address

Size

TCP pocket

Modbus pocket

|0||1||0||0||0||6||1||3||0||c7||0||5|

FCS Protocol

ID

Unit ID Function

Address

|cb||9b|

FCS

MBAP First word

address = 199 Function

code = 3

Number of words to read = 5

7 bytes 1 byte 2 bytes 2 bytes

address = 199

code = 3 words to read = 5

(19)

Ports & Sockets

 TCP multiplexes multiple connections to a single host using sockets and ports

Network Device single host using sockets and ports

 Each computer interface is divided into 65536 ports.

 Incoming packets know the address (IP) and the port

Ports

Network Device (IP address: a.b.c.d)

and the port

 Destination port is part of the TCP protocol field

 Ports are numbered and are like a pigeon hole mail

80

502 hole mail

 Mail for a specific person is only delivered to a single hole

 SMTP (Simple Mail Transfer Protocol) goes to port 25

25 goes to port 25

 HTTP goes to port 80

 Modbus TCP -> port 502

 Sockets – The combination of an IP address and a port number

HTTP

25

Modbus TCP

and a port number SMTP

(20)

Ports & Sockets

 21TCP File Transfer - FTP control

 22TCP SSH Remote Login Protocol 22UDP pcAnywhere

 22UDP pcAnywhere

 23TCP Telnet

 25TCP Simple Mail Transfer Protocol (SMTP) RFC 821.

 37TCP UDP Time Protocol RFC 868.

 53TCP UDP Domain Name Server (DNS)

 67TCP UDP Bootstrap Protocol Server

 68TCP UDP Bootstrap Protocol Client (BOOTP) RFC 951.

 80TCP Hypertext Transfer Protocol (HTTP) RFC 2616.

 110TCP UDP Post Office Protocol (POP) Version 3 RFC 1939.

 137TCP UDP NetBIOS Name Service

 138TCP UDP NetBIOS Datagram Service

 139TCP UDP NETBIOS (Session Service) Windows file and printer sharing.

 143TCP UDP Internet Message Access Protocol (IMAP) Mail Server IMAP

 161TCP UDP Simple Network Management Protocol (SNMP)

 162TCP UDP SNMPTRAP

(21)

Modbus TCP/IP - summary

Medium access method: CSMA/CD

Determinism: Resolved using segmentation Load factor < 10%

Transmission method: In packets

or IP datagrams, 64 to 1500 bytes

Max. size of useful data: 1442 bytes per packet (APDU) Transmission security: CRC32 at link layer level

Transmission security: CRC32 at link layer level

Acknowledgement at TCP link level

Response at application level

^(Modbus)

(22)

Example of Architecture

Redundant optical ring 200 Mbps full duplex

Switch Switch Switch

Premium Transceiver

Quantum

Optical loop

Hub Transceiver

Optical fibre

Optical loop

Hub

Quantum Momentum Magelis Momentum Altivar 58 Altistart 48 Altivar 38 Momentum Altivar 58

(23)

Example of Architecture

I/O scanning on Momentum CPU

16 distributed I/O modules I/O modules

(24)

Example of Architecture

Modbus TCP/ Modbus RTU Brigde (Gateway)

About 250 power meters and controllers on modbus RTU