Introduction to Computer Networks

1. Introduction to Computer Networks

2. Agenda Introduction. Types of Networks. Clients and Servers. Network Topologies. Internet and Intranet. Network Hardware and Software. Review.

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

7. Introduction. • Computer networking

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. Types of Networks. • Local area networks (wireless and wired) • Span a small geographic area. • Usually confined to abuilding, 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. 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. 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. 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).

17. 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. 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.

20. 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. Clients and Servers. • The relationship between a client and a server

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:

24. Network Topologies. • 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

27. 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).

28. Information flow RING TOPOLOGY

29. Ring topology on the Toronto Rocket RING TOPOLOGY

30. 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. 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

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

36. Network Topologies. • Hybrid topology A hybrid topology is produced when two, or more different basic network topologies are connected (bus, star, ring).

37. Computer Networks Internet and Intranet

38. 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 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. • http://intranet.int.ttc.ca/Pages/default.aspx

41. 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. 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.

43. 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.

44. 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.

45. Internet and Intranet. • The OSI model – Data flow

46. Computer Networks Network Hardware and software

47. Network Hardware and Software. • Network hardware and software Aside from clients and servers, computer networks may also contain the following components:

48. 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.

49. Network Hardware and Software. • Network interface card (NIC) Ethernet port Network port on the Toronto Rocket Coaxial port

50. 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.