Chapter 11 - Communications

Question 1

Baud

Answer 1

The rate at which characters can be transmitted along a communication line. Measured in bits per second.

Question 2

LAN communication conductors

Answer 2

Twisted Pair, Coaxial Cable, Fiber Optics

Question 3

LAN protocols

Answer 3

Token Passing: Whichever node carrying the token has exclusive, temporary use of the system to send data.

Carrier Sense Multiple Access/Collision Detection: Nodes listen for data being sent, collision occurs when data is submitted simultaneously.

Question 4

LAN topologies

Answer 4

Ring, Star and Bus

Question 5

Ring Topology

Answer 5

Nodes are connected in series to form a loop. Popular for token-passing protocols. If any node fails the system crashes. A reamplifier or repeater may be needed if there is a significant distance in cable length

Question 6

Star Topology

Answer 6

Robots are connected to a central control node, either a computer or another robot. Routing of traffic is done by the control node. Best used for remote robots with a main controller.

Question 7

Bus Topology

Answer 7

Nodes are linked to a single main communication line. Data is broadcast in either direction and multiple nodes can tap into the bus and communicate with each other. Common for ethernet. If cable is damaged the whole segment is inoperable.
Master/Slave network- uses two pairs of conductors, one for the master to send to slaves and the other for the slaves to send to master.

Question 8

Broadband

Answer 8

One cable carries several frequencies that are assigned to specific devices connected to the cable, bidirectional

Question 9

Baseband

Answer 9

Several devices are connected to one cable using time-sharing. Each device has a time slot for data transmission. One directional.

Question 10

Twisted Pair Cables

Answer 10

Type of transmission media. UTP (unshielded), STP (shielded). UTP is used widely in Ethernet. Capable of transmitting 100 megabaud over distances up to 100m. Low noise immunity.

Question 11

Coaxial Cables

Answer 11

Tranmission media. Copper conductor wiring. Can be baseband (1in, 10 megabits per second) or broadband (1/2 in, 100 megabaud over 40km). Also can be LAN cables: ThickNet or ThinNet. Very good noise immunity.

Question 12

Fiber Optic Cables

Answer 12

Use LED or injection lasers to transmit data. Received at the other end at PIN diode and avalanche detector. Can carry 1000 megabaud over 10km. Difficult to install and costly. Excellent noise immunity.

Question 13

RS-232-C/RS-422

Answer 13

Used to interconnect data terminal equipment, robots, computers, PLCs and peripherals. Transmits 19.2 kilobaud over 10m and <10megabaud over 1000m.

Question 14

OSI Model

Answer 14

Physical - physical connection between communicating devices
Data Link - breaks data being transmitted into groups or frames
Network - traffic control and routing of data packets (IP)
Transport - error free transmission of data from source to destination (TCP)
Session - provides name/address, allows user access, security
Presentation - data is restructured to allow non-proprietary devices to communicate
Application - provides all services directly comprehensible to application program

Question 15

Controller Area Network (CAN)

Answer 15

Comprises the first two layers of the OSI model (data and physical). Used to control a robot, lets you connect devices directly to plant floor controllers without hardwiring each device into an I/O module

Question 16

Communications and Information Protocol (CIP)

Answer 16

Used for transferring automation data between two devices

Question 17

DeviceNet

Answer 17

A combo of the CIP and CAN physical layer and covers all 7 layers of the OSI model. Plug and play (add or remove devices while power is on.

Question 18

ControlNet

Answer 18

A real-time control layer network used for conveying info such as robot program modifications, P2P messages and communications data.
Designed for fast transfer of I/O data (5 Mbps/sec)
The CIP used by ControlNet can bridge/route data to DeviceNet and Ethernet/IP.
Ideal for systems with multiple robots operating in the same environment.

Question 19

Ethernet

Answer 19

Corresponds to the first two layers of the OSI model. Can carry traffic at 100 Mbps, wireless ethernet can carry 10 Mbps.
Used for PLCs, robots, PCs, mainframes.
Bridges and switches are used to minimize data collisions by segmenting the network into different pieces.

Question 20

Ethernet/IP

Answer 20

Ethernet Industrial Protocol - contains layer 3 and 4, Internet Protocol (IP) and Transport Control Protocol (TCP), transmits between 10Mbps and 100Mbps and up to 1500 bytes per packet.

Question 21

Network Interface Card (NIC)

Answer 21

Connects a robots controller to an ethernet network via transmission media (twisted pair or fiber optics)

Question 22

Routers and Switches

Answer 22

Routers are a layer 3 device. Switches - contain the intelligence to inspect data packers, determine the source and destination for each packet and forward the packet based on this info, layer 2 device.