1. Introduction to Computer Networks

2. Agenda Introduction. Types of Networks. Clients and Servers.
13 April 2017
Agenda
Introduction.
Types of Networks.
Clients and Servers.
Network Topologies.
Internet and Intranet.
Network Hardware and Software.
Review.
VRM & RVT Training Program - Vehicle Familiarization

3. Purpose
As part of the job you may be required to use a TTC network to perform duties such as:
Remotely monitor a system.
Work with data.
Run diagnostics.
The purpose of this course is to introduce and familiarize you with the basic aspects of computer networks and how they relate to the TTC networks.

4. Computer Networks
Introduction

5. Introduction.
Networks
Two or more computers connected together in a way that allows resource sharing.
A network contains any combination of computers, computer terminals, printers, display devices, cables, or wireless connections.
A network is a collection of computers or other hardware devices that are connected together using special hardware and software. This allows them to share information and cooperate.

6. Resources Resources may be: Files. Folders. Printers. Memory.
Introduction.
Resources
Resources may be:
Files.
Folders.
Printers.
Memory.
Applications.

7. Computer networking Advantages Disadvantages
Introduction.
Computer networking
Advantages
Disadvantages
Communication between computer processing units (CPUs)
Access restrictions
Data sharing
Server failures
Hardware sharing
Privacy concerns
Internet access
Security threats
Data management
Redundancy

8. Computer Networks
Types of networks

9. Types of Networks.
Network types
Computer networks vary in shape (topology) and size depending on their application.
Some of the major types are:
Local area networks (LANs).
Wide area networks (WANs).

10. Local area networks (wireless and wired)
Types of Networks.
Local area networks (wireless and wired)
Span a small geographic area.
Usually confined to a building, a group of buildings, or a vehicle, for example a train or a streetcar.
Data travels between network devices via network cables (LANs) or wireless signals (WLANs).
The most common types are Ethernet and Wi-Fi.

11. Wide area networks (WAN)
Types of Networks.
Wide area networks (WAN)
A WAN is a computer network that covers a large area (any network whose communication links across metropolitan, regional, or national boundaries).
A network that uses routers, modems, and public communication links.
The world’s largest WAN is the Internet.
WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations.

12. Types of Networks.
WAN

13. Computer Networks
Clients and servers

14. Clients and Servers.
Servers
A server is a core component of the network, providing access to the resources.
The access it provides could be to a resource existing on the server itself or a resource on a client computer.
The server assigns IP addresses to each resource.

15. IP addresses IP stands for Internet Protocol.
Clients and Servers.
IP addresses
IP stands for Internet Protocol.
IP addresses serve as the location of websites on the Internet as well as workstations that are connected to the network.
IP addresses are made up of four sets of numbers called “octets.”
There are two types of IP addresses:
Static IP addresses.
Temporary IP addresses.

16. Static IP addresses Located on servers and do not change.
13 April 2017
Clients and Servers.
Static IP addresses
Located on servers and do not change.
Example: The HVAC units on the Toronto Rocket have a static IP address on the Train Information Network (TIN).
Car Number
HVAC position
IP address 1 2 3 4 5 6
The table displays the IP addresses of each HVAC on each car.
These do not change.
Sometimes, the IP addresses must be entered manually in order to connect to a specific HVAC unit.
i.e. by an SVT
VRM & RVT Training Program - Vehicle Familiarization

17. Temporary IP addresses
Clients and Servers.
Temporary IP addresses
A device connected to the network is assigned a new IP address each time it is logged on.
Assigned by an Internet Service Provider (ISP) each time a computer is logged on to the network.
On the TIN, the Train Information Management System (TIMS) assigns a temporary IP to laptops connected to the Ethernet.

18. Clients and Servers.
Client
Clients are computers/devices that request and receive information over a network.
Client computers can also depend on the central server for processing activities.
For example a laptop running diagnostics on trains.

19. Client/server networking
13 April 2017
Clients and Servers.
Client/server networking
A client/server network is a system where one or more computer called a client connects to a central computer called a server to share or use resources.
A computer network is referred to as a client/server if, at least, one of the computers is used to “serve” other computers referred to as “clients.”
Many types of devices can be part of the network; e.g., scanners, printers, laptops–portable test equipment (PTE), and desktop computers.
Sometimes, like in the case with TIMS, the operating system on the clients must be compatible with that on network.
VRM & RVT Training Program - Vehicle Familiarization

20. Client/server networking
Clients and Servers.
Client/server networking
In a client/server network, each computer can store resources and files. Clients can also access resources stored on other clients.
Most files and resources are centralized. This means that one computer (the server) stores them and other computers (the clients) access them.
The server is always on, allowing any client to access files and resources even if the other clients (computers) are off.

21. The relationship between a client and a server
13 April 2017
Clients and Servers.
The relationship between a client and a server
In order to gain access to the network and other resources the client sends a request to the servers and the server will respond with a path/access to the requested resources
VRM & RVT Training Program - Vehicle Familiarization

22. Computer Networks
Network Topologies

23. Network Topologies.
Network topologies
Network topology refers to the shape of a network, or the network’s layout. A network’s topology determines how different devices in a network are connected to each other and how they communicate.
The different network topologies are as follows:
Bus.
Hybrid.
Star.
Mesh.
Ring.

24. Network topologies Physical topology
The physical structure of the network. The layout of the cables and connections between the network components.
Logical topology
Defined by the network protocols and explains how data travels across the cables.

25. Network Topologies.
Bus topology
All devices are connected to a central cable, called a bus or a backbone.
The simplest physical topology–least amount of cables–but also covers the shortest distance.
There are terminators at each end of the bus that stop the signals and keep them from travelling backwards.
All computers share the same data and address path. Messages pass through the central cable and each computer checks to see if the message is addressed to itself. If the address of the message matches the computer’s address, the network adapter copies the message to the card’s on-board memory.

26. Information flow BUS TOPOLOGY 13 April 2017
The signal (yellow) leaves its source and as it travels through the central cable it passes through each connected device, however, only the addressed device is the one that will ‘accept’ the message (let the message through).
Pro: Easy to set up
Any break in the network central cable or either terminal will result in a total break in the network.
Information flow
BUS TOPOLOGY
VRM & RVT Training Program - Vehicle Familiarization

27. 13 April 2017
Network Topologies.
Ring topology
All devices are connected to one another in the shape of a closed loop.
Each device is connected directly to two other devices, one on either side of it.
An equivalent system exists on the trains (TIN) and on streetcars (the Streetcar Network).
VRM & RVT Training Program - Vehicle Familiarization

28. Information flow RING TOPOLOGY 13 April 2017
A break in one of the components won’t prevent the signals from going through.
The signal can flow in the other direction to reach its destination.
Information flow
RING TOPOLOGY
VRM & RVT Training Program - Vehicle Familiarization

29. Ring topology on the Toronto Rocket
13 April 2017
Example on the TR.
Data/signals flow both in the clockwise and counterclockwise directions
Ring topology on the Toronto Rocket
RING TOPOLOGY
VRM & RVT Training Program - Vehicle Familiarization

30. On the train: ring switch
Network Topologies.
On the train: ring switch
Contains the network software.
Assigns IP addresses.
Enables communication over the TIN.
Routes the signals to the TIMS for monitoring.

31. On the streetcar: ring switch
Network Topologies.
On the streetcar: ring switch
Contains the network software.
Assigns IP addresses.
Enables communication over the streetcar network.

32. Network Topologies.
Star topology
Devices are not directly connected to each other, rather through a central hub.
Devices communicate across the network by passing data through the hub or switch.

33. Information flow STAR TOPOLOGY 13 April 2017
The information flow in the star topology goes through one central point to which all devices are connected.
A break in the connection between the hub and one of the components will isolate only that component, but will not affect the rest of the network.
Issues with the hub itself, however, will affect the entire network.
Information flow
STAR TOPOLOGY
VRM & RVT Training Program - Vehicle Familiarization

34. Network Topologies.
Mesh topology
The simplest logical topology in terms of data flow, and the most complex topology in terms of physical design.
Each device is connected to every other device.
This topology is rarely found in LANs, mainly because of the complexity of the cabling.
Because of its design, the physical mesh topology is very expensive to install and maintain.
The advantage you get from mesh topology is that it has a high fault tolerance.

35. Information flow MESH TOPOLOGY 13 April 2017
PRO: A break in the system won’t prevent the signal from getting through, as it will find alternate routes to reach its destination.
CON: However, setting up cables, connecting devices, and shouldering the costs renders the topology impractical.
Information flow
MESH TOPOLOGY
VRM & RVT Training Program - Vehicle Familiarization

36. 13 April 2017
Network Topologies.
Hybrid topology
A hybrid topology is produced when two, or more different basic network topologies are connected (bus, star, ring).
This topology is used when a new section is added to an already existing network.
PRO: Highly reliable
CON: But hard design and very costly to set up (cables and specialized hubs)
VRM & RVT Training Program - Vehicle Familiarization

37. Internet and Intranet Computer Networks 13 April 2017
VRM & RVT Training Program - Vehicle Familiarization

38. Transmission Control Protocol
Internet and Intranet.
Internet vs. intranet
Internet
A worldwide system of computer networks. A network of networks in which users at any one computer, with the necessary permissions, can get information from any other computer.
The most commonly used protocol is TCP/IP, it stands for:
Transmission Control Protocol
Internet Protocol
TCP
/IP

39. Internet and Intranet.
Internet protocol
The most common network protocol in public use is the IP.
The basic protocol that enables home computing devices and LANs across the Internet to communicate with each other.
Works well for moving individual messages from one network to another.
TCP allows continuous transmission of data (streaming).
The two protocols are almost always paired together and are known as TCP/IP.

40. Internet vs. intranet Intranet A self-contained private network.
13 April 2017
Internet and Intranet.
Internet vs. intranet
Intranet
A self-contained private network.
It may consist of many interlinked local area networks and also use leased lines in a wide area network.
Uses TCP/IP, hypertext transfer protocol (HTTP) and other Internet protocols.
Companies can send messages through the public network, using encryption/decryption and other security safeguards to connect one part of the intranet to another.
VRM & RVT Training Program - Vehicle Familiarization

41. Network/communication protocols
Internet and Intranet.
Network/communication protocols
A protocol is simply an agreed on set of rules and procedures for transmitting data between two or more devices. Hundreds of different protocols have been developed, each designed for specific purposes and environments.
The protocol defines:
How the sending device indicates it has finished sending the message.
How the receiving device indicates it has received the message.
How data is transmitted from source to destination.
The type of error checking to be used.

42. Network/communication protocols
Internet and Intranet.
Network/communication protocols
Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into messages, sent, and received.
Hundreds of different computer protocols have been developed, each designed for specific purposes and environments.

43. 13 April 2017
Internet and Intranet.
Network protocols
Network protocols are layered such that each one relies on the protocols that underlie it. Sometimes referred to as the protocol stack.
Both TCP and IP operate somewhere in the middle of a network protocol stack.
VRM & RVT Training Program - Vehicle Familiarization

44. The Open System Interconnection (OSI) model
Internet and Intranet.
The Open System Interconnection (OSI) model
A logical representation of the path data must travel in order to go through the network.
Upper layers: Represent software that implements network services like encryption and connection management.
Lower layers: Implement hardware-oriented functions like routing, addressing, and flow control.

45. Internet and Intranet.
The OSI model
Data communication starts with the top layer of the stack at the sending side.
Travels down the stack to the sender’s lowest (bottom) layer.
Then traverses the physical network connection to the bottom layer on the receiving side, and up its OSI model stack.

46. The OSI model – Data flow
13 April 2017
Internet and Intranet.
The OSI model – Data flow
An is sent from one user to another on the network.
The passes through all seven layers on the sender’s computer (upper to lower) then go up all seven layers (lower to upper) on the receiving computer, until the is displayed on the screen of the addressed computer/user.
VRM & RVT Training Program - Vehicle Familiarization

47. Network Hardware and software
Computer Networks
Network Hardware and software

48. Network Hardware and Software.
Aside from clients and servers, computer networks may also contain the following components:
Network interface card (NIC).
Hub.
Bridge.
Router.
Modem.
Gateway.
Switch.
Firewall.
Operating System.

49. Network Hardware and Software.
Network interface card (NIC)
Provides the physical interface between computer and cabling.
In the computer, data moves along buses in parallel, as on a four-lane highway. But on a network cable, data travels in a single stream as on a one lane highway.
The NIC’s job is to translate the data from the computer into signals that can flow easily along the cable. It does this by converting digital signals into analog signals.

50. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Network interface card (NIC)
Ethernet port
Network port on the Toronto Rocket
Coaxial port
VRM & RVT Training Program - Vehicle Familiarization

51. Network Hardware and Software.
Hub
Hubs are devices used to link several computers together.
A hub repeats any signal that comes in on one device and copies it to all other devices connected to the hub.
There are two types of hubs:
Passive hubs (not powered): connect all devices together.
Active hubs (powered): use electronics to amplify and clean up the signal before it is broadcast to the other devices.

52. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Hub
HUB
VRM & RVT Training Program - Vehicle Familiarization

53. Network Hardware and Software.
Bridge
Joins similar topologies and is used to divide LANs into segments.
If a bridge knows the destination address, it is able to forward packets to that address, otherwise a bridge will forward the packets to all devices.
Filters out noise.
The main disadvantage of bridges is that they can’t connect dissimilar network types or perform intelligent path selection. For that function you require a router.

54. Network Hardware and Software.
Bridge: an example
With 200 clients on one Ethernet segment, the performance will be slower because of the design of the Ethernet and the number of workstations that are fighting to transmit information.
By dividing the 200 clients into two segments of 100 clients each, the traffic will be much lower on either side, and speed will increase.

55. Network Hardware and Software.
Router
Routers are important devices that let messages flow between networks, rather than within networks.
Home networks use a wireless or wired Internet Protocol router. An IP router, such as a digital subscriber line (DSL) or a cable modem broadband router, joins the home’s LAN to the WAN of the Internet.
Broadband routers combine the functions of a router with those of a network switch and a firewall in a single unit.

56. Network Hardware and Software.
Router
When you connect to a website through an ISP and exchange information, there is no fixed connection between your computer and the Web server computer hosting the website. Routers find the best possible path, these paths avoid slow links and favour fast ones.

57. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Modem
Stands for MODulator- DEModulator.
Modern modems, such as cable TV and DSL modems, no longer modulate and demodulate the signals.
Routers provide access to a LAN, however, in order for the router to connect to the Internet, it must be connected to a modem.
The modern modem no longer works in the same way: converting digital to analog – electronic signals with audible freq (Modulating) and the converting that back to digital (Demodulating)
However, the device that connects to the user to the Internet (WAN) is still referred to as a modem.
VRM & RVT Training Program - Vehicle Familiarization

58. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Gateway
Gateways are routers that rout between networks, however, they also perform protocol conversions so that different networks can work together.
A gateway is an essential feature of most routers. A gateway may contain devices such as protocol translator, impedance matching devices, rate converters, fault isolators, or signal translators as necessary to provide system interoperability.
VRM & RVT Training Program - Vehicle Familiarization

59. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
On the train: gateway example
On the TIN there is a Mobile Communications Gateway (MCG), which provides wireless communication between a train and the yard maintenance system.
VRM & RVT Training Program - Vehicle Familiarization

60. WLAN communication via the MCGs
TIN DIAGRAM

61. Network Hardware and Software.
Switch
A switch is a computer network device that connects network segments.
Network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately.
By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth allowing for better system performance.

62. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Switch
Computers 1 and 5 transmit first and then 2 and 3.
Simultaneous signals are sent by #1 and #5, and the switch directs them straight to their respective destination, without going through the rest of the connected devices.
Same is repeated for #2 and #3.
SWITCH
VRM & RVT Training Program - Vehicle Familiarization

63. Network Hardware and Software.
Ethernet protocol
Ethernet uses a protocol called CSMA/CD, this stands for:
Carrier Sense
Multiple Access
with Collision Detection CS MA
/CD

64. Network Hardware and Software.
Ethernet protocol
Carrier Sense
When a device connected to an Ethernet network wants to send data, it first checks to make sure it has a carrier on which to send its data (usually copper cable connected to a hub).
Multiple Access
All machines on the network are free to use the network.
Collision Detection
Ensures that if two computers transmit data simultaneously, data re-transmissions are generated at differing time intervals.

65. Network Hardware and Software.
Ethernet
The basic bus topology:
The computers are daisy chained together.
Each packet of data contains the destination address, the sender’s address and the data.

66. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Ethernet
Computer 2 wants to send a message to computer 4.
Computer 2 checks to make sure the network is not in use. If all clear, it will transmit the data onto the network.
Signal is sent to every computer on the network but only addressed to computer 4, the other computers ignore it.
Computer 4 sends a message back to computer 2 acknowledging receipt of data.
VRM & RVT Training Program - Vehicle Familiarization

67. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Ethernet
What happens if two computers try to transmit at the same time?
A COLLISION occurs and each computer has to back off for a random period of time before retrying.
On small networks, this goes unnoticed. On larger networks, the more collisions you have, the slower the network functions.
Computer 2 and 5 both try to transmit simultaneously causing a collision which destroys the signals. After a random period of time, they retransmit.
VRM & RVT Training Program - Vehicle Familiarization

68. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Hub vs. switch
An Ethernet hub changes the topology from a bus to a star network.
Collisions are still possible, however, hubs have centralized wiring, and can automatically bypass any ports that are disconnected or have cabling faults.
VRM & RVT Training Program - Vehicle Familiarization

69. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Hub vs. switch
Switches are used to overcome the problem of collisions.
With a switch, computers can transmit simultaneously.
Switches read the destination address and switch the signal directly to the recipient without broadcasting to all the computers on the network.
VRM & RVT Training Program - Vehicle Familiarization

70. Network Hardware and Software.
13 April 2017
Network Hardware and Software.
Hub vs. switch
A vital difference between a hub and a switch is that all the devices connected to a hub share the bandwidth among themselves, while a device connected to a switch has the full bandwidth to itself.
Example: If 10 devices are communicating using a hub on a 10 Megabits per second (Mbps) network, then each device may only get a portion of the 10 Mbps if other devices on the hub want to communicate as well. With a switch, each device can communicate at the full 10 Mbps.
VRM & RVT Training Program - Vehicle Familiarization

71. Network Hardware and Software.
Firewall
Firewall is a software loaded onto a network that serves as a barrier to keep destructive forces away from a network of computers.
Firewall can block information from entering a network or from getting out of a network, they can permit different users to perform different kinds of operations, according to the user’s permissions.
Packets of data are analyzed against a set of standards called filters. Filters block certain designated IP addresses.

72. Filtering signals before allowing them to access the network
FIREWALL

73. Computer Networks
Review

74. Identify the type of network
Review.
Identify the type of network
Local area network LAN
Wide area network WAN

75. Name the network components
Review.
Name the network components
Server
Client
Resource

76. Name the network components that control the data transmission
13 April 2017
Review.
Name the network components that control the data transmission
Explain again, that the hub only repeats the signal to all the devices, and it’s up to the devices themselves to identify and receive the signals that are addressed to them. Causes delay, but is not noticeable in smaller networks.
The switch reads the packet’s address and directs it accordingly, making the system much more efficient and suitable for large networks.
Hub
Switch
VRM & RVT Training Program - Vehicle Familiarization

77. Which of the following network topologies require terminators?
Review.
Which of the following network topologies require terminators?
Bus
Star
Mesh

78. ?

79. End