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Data Communications > ILANs > Flashcards

ILANs Flashcards

1
Q

What are the types of networks that link devices together?

A

LAN: Local Area Network used for DCS or a group of PLCs
WAN: Wide Area Network consists of multiple LANs over a big area

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2
Q

What is the OSI Model?

A

Open Systems Interconnection is a model that breaks down all data communication in a 7 layer hierarchy

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3
Q

What are the 7 layers of the OSI Model?

A

1) Application

2) Presentation

3) Session

4) Transport: Long message ordering fragmentation/ defragmentation, message prioritization

5) Network: specifies how data is routed from sender to receiver through IP addressing

6) Data link: Network access method, device addressing, transmitted data frame structure, low level error detection

7) Physical: Electrical signal types, voltage, media, data speed, topology

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4
Q

Describe the star or hub topology.

A

Star or Hub: every device communicates by sending and receiving data to the central hub. The network interface cards are very simple and is very useful for smaller networks. However, if the hub goes down so does the whole network. This method is also not suited for larger networks.

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5
Q

Describe the ring topology.

A

Ring: every device sends data one direction in series and does not require a central hub. The wiring for this method is very simple but if one device faults the whole network is down. Since data is received by multiple devices the probability of data error rises.

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6
Q

Describe the bus topology.

A

Common drop or Busses: this method allows for communication without needing a hub or an intermediary device. The address of the destination device is included in the message. Devices can be physically added or removed without breaking the network, have simple wiring, and if one device faults the network still works. However, the failure of the bus (medium) brings the network down, and network devices fail in a way that make them continuously stream data.

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7
Q

What is NIU?

A

1) Network Interface Unit: a component that connects a device to the network

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8
Q

What is a hub?

A

A passive device that allows for 2 or more computers connect to a network

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9
Q

What is a switch?

A

Like a hub but they allow directing incoming messages be addressed to it’s connected devices only. This is done by forming “Virtual LANs”, allowing alternate channels for redundant communications, and bandwidth restrictions

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10
Q

What is a router?

A

Connect several LANs together and read IP addresses in order to route information accordingly.

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11
Q

What is a bridge?

A

A type of router that allows networks of the same type to connect

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12
Q

What is a gateway?

A

A router that connects different types of network for example different speeds, electrical signal types and message frame structures.

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13
Q

What is a server?

A

A device that stores data and serves it out when devices on the network request that data.

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14
Q

What are the two main types of electrical signals used with networks?

A

Baseband signaling: data in digital pulse trains

Broadband signaling: data in digital pulse trains is modulated onto high frequency sinusoidal signals.

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15
Q

Give some examples for baseband signaling.

A

1) NRZ-L: Non Return to Zero Level Signal, ensures that the average DC signal is zero, and has 0 as positive voltage and 1 as negative
2) Manchester: uses signal transitions for 1s and 0s, and uses synchronization bytes to extract the clock from the data.
3) Differential Manchester: uses logic 0 as ANY transition and logic 1 as no signal, and are transmitted as bipolar NRZ to ensure the average DC is 0

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16
Q

What are the three commonly used network access methods?

A

1) Master/Slave Polling
2) Token
3) CSMA/CD: Carrier Sense Multiple Access with Collision Detection

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17
Q

What is the advantage and disadvantage to using master/slave method?

A

Adv: simple, versatile, and common

Dis: response sequence can be slow causing delays in responses to alarms

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18
Q

What kind of networks use master/slave method?

A

HART and ModBus communications between field devices and controllers

19
Q

How does master/slave work?

A

The master computer asks the slave computers if they have data to transmit. Slaves only transmit/respond to commands from the master.

20
Q

What is “Report by Exception” used for?

A

Reduces the amount of data that slaves must transmit eg. only if a measurement changes a certain % the network reports the change

21
Q

What is the advantage of using Carrier Sense Multiple Access?

A

Enables all devices on the network to transmit at the same time.

22
Q

How does CSMA work?

A

Devices listen to “Carrier Sense”, and if no devices are using it the transmission starts

23
Q

How does collision detection improve CSMA?

A

Collision detection notices any damaged data. All transmitting devices stop and wait a random amount of time to try transmitting again.

24
Q

What limits CSMA-CD efficiency?

A

When network loading is greater than 30% it can take a very long time for a device to get a turn to transmit.

25
Q

How does token passing work?

A

All network devices can transmit data but only the device with a “token” can transmit. A network can only have 1 token and it can be held by one device at a time.

26
Q

How is a token regenerated when it is lost due to electrical noises or forgetful network
devices?

A

A device is designated as the network monitor and can regenerate the token.

27
Q

What is the advantage and a disadvantage to the token method?

A

Adv: less collisions occur as only the device with the token can transmit

Dis: can be slow to react to critical situations as devices have to wait for the token

28
Q

What is a VLAN and what advantage does it provide?

A

A Virtual Localized Area Network that is created by a ‘managed switch’. A VLAN is a segment of a network made from a group of devices and can specify channels, data routes and restrict bandwidth on a port by port basis.

29
Q

What are the 3 main type of IP Address classes?

A

Class A: has a subnet range of 1 to 126. Small number of sub networks (2^7) with a lot of hosts (2^24)

Class B: has a subnet range of 128 to 191.255. 2^14 sub networks with 2^16 hosts.

Class C: has a subnet range of 192 to 223.255.255. Allows for a large number of segments (2^21) with a small number of devices (2^8).

30
Q

The last octet in IP addressing can not be a ______________ or _________

A

0 or 255

31
Q

What class of IP addresses is most commonly used in the industry?

A

Class C

32
Q

What layer of the OSI model does the ethernet define?

A

Physical (first layer) and Data Link (second layer)

33
Q

What is a network?

A

A system that connects 3 or more computers together

34
Q

In networks messages are more complex than in point to point communications therefore data is enclosed in ___________, __________, or a ____________.

A

A message frame, a datagram, a data packet

35
Q

What can you find in a network message?

A

1) Sender’s address
2) Receiver’s address
3) Receiver sync bits
4) Error detection bits
5) Actual data
6) Order of the data ( used for a long message that uses more than one frame)

36
Q

What are the key parts of an ethernet message frame?

A

1) DA: Destination Address, a MAC address of the final destination
2) SA: Source Address, a MAC address of the sender
3) LLC: Logical Link Control frame, contains source and destination IP addresses
4) FCS: Frame Check Sequence, a 32 bit CRC error detection character

37
Q

What are the error check methods and which one is the best?

A

1) Parity bit
2) Longitudinal Redundancy Check
3) Checksum
4) CRC (best)

38
Q

What is the problem with using NRZI/Diff Manchester for ethernet electrical signaling?

A

In NRZI and Differential Manchester electrical signals the 0 bits do not produce an edge which makes the synchronization of receivers and transmitters difficult.

39
Q

What type of electrical signaling does ethernet use?

A

4B/5B data coding

40
Q

What is TCP/IP?

A

Transmission Control Protocol: a transport layer protocol (layer 4) that adds data to the ethernet message to create a link between 2 devices by putting a sequence number.

Internet Protocol: a network level protocol (layer 3) that defines an addressing scheme that allows networks to divide into smaller subnetworks

41
Q

What is a TTL parameter?

A

Time to Live parameter specifies how long a message can take to get from sender to receiver

42
Q

What is the maximum number of data bytes that can be put onto an ethernet data packet?

A

1500 bytes

43
Q

What is the general rule for industrial Ethernet loading?

A

Maintain network loading 30% below the maximum of that network

44
Q

What are the two way to subnet networks?

A

1) Use hardware to physically separate network using a router
2) Establish VLANs using a switch

Data Communications (6 decks)

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