Introduction to Computer Science (I1100) Networks. Chapter 6

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1 Networks Chapter 6 501

2 Outline How does Networks and Internet Work? Networking devices Physical Network topology Types of Network Intranets - extranets Copper Media IP Address 502

3 How does Networks and Internet Work? Most of us know how to use the Internet without actually understanding how it works, sort of like electricity in your home. You use it every day but may not forcibly understand the mechanics behind it. 503

4 How does Networks and Internet Work? Whenever most people think of the Internet, this is what comes in mind. The Internet is not a bubble cloud. The Internet 504

5 How does Networks and Internet Work? This is the Internet: the Internet is like a wire (buried in the ground, fiber optic, copper, satellite, through cellphone networks) 505

6 How does Networks and Internet Work? The Internet is useful: 2 computers connected directly to this wire can communicate. A server is a special computer (software) connected directly to the Internet. Web pages are files on that server s hard drive. 506

7 How does Networks and Internet Work? Every server has a unique Internet Protocol address or IP address (just like a postal address). IP addresses help computers find each others Google.com Facebook.com Krispykreme.com But since it doesn t roll off the tongue, we also give names (called domain names) 507

8 How does Networks and Internet Work? Live.com The computer at home is not a server since it s not connected directly to the Internet. These computers are called CLIENTS. Ogero (ISP) Gmail.com They are connected indirectly to the Internet through ISP (Internet Service Provider) Client 508

9 How does Networks and Internet Work? Looking at live.com web pages Live.com Ogero (ISP) Gmail.com Client 509

10 How does Networks and Internet Work? Live.com Send an to com Ogero (ISP) Gmail.com myfriend 1- Log on to my account and compose a message 2-Click send 3-myfreind retrieves the Client 510

11 How does Networks and Internet Work? Whenever an , picture, or webpage travels across the Internet, computers breaks the information into smaller pieces called packets. When information reaches its destination, the packets are reassembled in their original order. 511

12 512

13 Networking Benefits Linking computers into networks provides benefits in the following areas: Information sharing: ability to share information and data quickly and inexpensively. Direction of transmission: One-way communication: some flows goes in one-way: e.g., television. Information flows in this case in one direction from the transmitter to the receiver. Two-way communication: the information must flow in both directions. In this case there is a dialogue between the two communicating partners. Each partner will be a transmitter and a receiver. E.g., the telephone. Hardware and software sharing: ability to reduce the costs drastically by making it possible for several users to share hardware and software simultaneously. Centralized administration and support: from just a single location, the network administrator can perform administrative tasks on any computer on the network. 513

Networking devices NIC NICs are used to physically connect host devices to the network media. A NIC is a printed circuit board that fits into the expansion slot of a bus on a computer motherboard.

14 Networking devices NIC NICs are used to physically connect host devices to the network media. A NIC is a printed circuit board that fits into the expansion slot of a bus on a computer motherboard. NICs are sometimes called network adapters. Each NIC has a unique 48-bit Media Access Control (MAC) address burned in to its ROM during manufacture. A MAC address is usually shown in hexadecimal format, with each octet separated by a dash or colon, for example: B6-C4. 514

15 Networking devices NIC 515

16 Networking devices Network devices are used to extend cable connections, concentrate connections, convert data formats, and manage data transfers. 516

17 Networking devices Repeater A repeater is a network device used to regenerate a signal. Repeaters regenerate signals that are distorted by transmission loss due to attenuation. 517

18 Networking devices Hub Hubs take a group of hosts and allow the network to see them as a single unit. 518

19 Networking devices Bridge Bridges provide connections between LANs. They also check data to determine if it should cross the bridge. This makes each part of the network more efficient. 519

20 Switches determine if data should remain on a LAN and transfer data only to the connection that needs it. Networking devices Switch 520

Networking devices Router Routers have all the capabilities of

21 Networking devices Router Routers have all the capabilities of the other devices. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers. They can also connect to a WAN, which allows them to connect LANs that are separated by great distances. None of the other devices can provide this type of connection. 521

22 Physical Network topology 522

23 Physical Network topology A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone. A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable. A star topology connects all cables to a central point. An extended star topology links individual stars together by connecting the hubs or switches. A hierarchical topology is similar to an extended star. However, instead of linking the hubs or switches together, the system is linked to a computer that controls the traffic on the topology. A mesh topology is implemented to provide as much protection as possible from interruption of service. For example, a nuclear power plant might use a mesh topology in the networked control systems. As seen in the graphic, each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology. 523

Logical Network topology The logical topology of a network determines how the hosts communicate across the medium: broadcast : each host sends its data to all other hosts on the network medium.

24 Logical Network topology The logical topology of a network determines how the hosts communicate across the medium: broadcast : each host sends its data to all other hosts on the network medium. Ethernet works this way. token passing: an electronic token is passed sequentially to each host. When a host receives the token, that host can send data on the network. Token Ring and FDDI networks work that way. 524

25 Types of Network LAN Local Area Network (LAN) : correspond in size to intra-company networks. They are used to transport digital information within a company. The typical size is of a few hundred meters. Wide Area Network (WAN) : this network is to interconnect over long distances. These networks are characterized by a low speed compared with the local networks. The distances can be very important. This can be up to several dozens kilometers in the case of satellite link. WANs are often built on transmission media based on the phone network. Metropolitan Area Network (MAN) : this type of network is used for the interconnection of several buildings in the same city. E.g., the case of a university building. 525

26 Local-area networks (LANs) A network serving a home, building or campus is considered a Local Area Network (LAN) 526

27 Wide-area networks (WANs) 527

28 Wide-area networks (WANs) WANs interconnect LANs. WANs make it possible for businesses to communicate across great distances. WANs are designed to do the following: Operate over a large and geographically separated area Allow users to have real-time communication capabilities with other users Provide full-time remote resources connected to local services 528

29 Metropolitan-area networks (MANs) A MAN usually consists of two or more LANs in a common geographic area. 529

30 Intranets and extranets Intranets are designed to permit users who have access privileges to the internal LAN of the organization. Extranets refer to applications and services that are Intranet based, and use extended, secure access to external users or enterprises. This access is usually accomplished through passwords, user IDs, and other application-level security. 530

31 Internet The internet is defined as a global mesh of interconnected networks The set of all networks interconnected forms what is called the Internet 531

32 Copper Media Cables have different specifications and expectations. Important considerations related to performance are as follows: What speeds for data transmission can be achieved? Will the transmissions be digital or analog? How far can a signal travel before attenuation becomes a concern? 532

33 Copper Media Coaxial cable 533

34 Copper Media STP cable 534

35 Copper Media UTP cable 535

36 Copper Media RJ45 Plug & Jack 536

37 Copper Media UTP cable Pin Color Function 1 White with Green +TD (Transmitting Data) 2 Green -TD (Mirrored Transmitting Data) 3 White with Orange +RD (Receiving Data) 4 Blue Not Used 5 White with Blue Not Used 6 Orange -RD (Mirrored Receiving Data) 7 White with Brown Not Used 8 Brown Not Used Introduction to Computer Science (I1100)

38 Straight-through cables VS crossover cables 538

39 Straight-through cables VS crossover cables 539

40 IP Address An IP address is a 32-bit unique and universal sequence of ones and zeros that To make the IP address easier to work with, it is usually written as four decimal numbers separated by periods. 540

41 IP Address For example, an IP address of one computer is Another computer might have the address This is called the dotted decimal format. Each part of the address is called an octet because it is made up of eight binary digits. For example, the IP address would be in binary notation. 541

42 IPv4 addressing A router uses IP to forward packets from the source network to the destination network. The packets must include an identifier for both the source and destination networks. A router uses the IP address of the destination network to deliver a packet to the correct network. When the packet arrives at a router connected to the destination network, the router uses the IP address to locate the specific computer on the network. 542

43 IPv4 addressing Every IP address has two parts. The first part identifies the network where the system is connected and the second part identifies the system. The second part, called the host part, identifies which particular machine it is on the network. 543

44 IPv4 addressing 544

45 IPv4 addressing Class 545

IPv4 addressing Class IP addresses are divided into classes to define the large, medium, and small networks. Class A addresses are assigned to larger networks.

46 IPv4 addressing Class IP addresses are divided into classes to define the large, medium, and small networks. Class A addresses are assigned to larger networks. Class B addresses are used for medium-sized networks and Class C for small networks. The first step in determining which part of the address identifies the network and which part identifies the host is identifying the class of an IP address. 546

47 IPv4 addressing Class A The Class A address was designed to support extremely large networks, with more than 16 million host addresses available. The first bit of a Class A address is always 0. With that first bit a 0, the lowest number that can be represented is , decimal 0. The highest number that can be represented is , decimal

The 127.0.0.0 network is reserved for loopback testing.

48 IPv4 addressing Class A The numbers 0 and 127 are reserved and cannot be used as network addresses. Any address that starts with a value between 1 and 126 in the first octet is a Class A address. The network is reserved for loopback testing. Routers or local machines can use this address to send packets back to themselves. Therefore, this number cannot be assigned to a network. 548

49 IPv4 addressing Class B The Class B address was designed to support the needs of moderate to large-sized networks. The first two bits of the first octet of a Class B address are always 10. The remaining six bits may be populated with either 1s or 0s. Therefore, the lowest number that can be represented with a Class B address is , decimal 128. The highest number that can be represented is , decimal 191. Any address that starts with a value in the range of 128 to 191 in the first octet is a Class B address. 549

IPv4 addressing Class C The Class C address space is the most commonly used of the original address classes. This address space was intended to support small networks with a maximum of 254 hosts.

50 IPv4 addressing Class C The Class C address space is the most commonly used of the original address classes. This address space was intended to support small networks with a maximum of 254 hosts. A Class C address begins with binary 110. Therefore, the lowest number that can be represented is , decimal 192. The highest number that can be represented is , decimal 223. If an address contains a number in the range of 192 to 223 in the first octet, it is a Class C address. 550

51 Public and private IP addresses Address Private IP Class A: to 10,255,255,254, allowing the creation of large private networks with thousands of computers. Private addresses Class B IP: to , to create private networks of medium size. Class C private IP address: to , for the establishment of small private networks. 551

52 References 552

53 Exercises 553

54 Review Questions 1. For n devices in a network, what is the number of cable links required for a mesh, ring, bus, and star topology? 2. For each of the following four networks, discuss the consequences if a connection fails. a. Five devices arranged in a mesh topology b. Five devices arranged in a star topology (not counting the hub) c. Five devices arranged in a bus topology d. Five devices arranged in a ring topology 3. What is the number of bits in an IPv4 address? 4. Explain why most of the addresses in class A are wasted. Explain why a medium-size or large-size corporation does not want a block of class C addresses. 554

55 Review Questions 5. Change the following IP addresses from binary notation to dotted-decimal notation. a b c d Find the class of the following IP addresses. a b c d

56 Review Questions 7. In a block of addresses, we know the IP address of one host is What are: a. the first address (network address) in this block b. the last address (limited broadcast address) in this block c. the total number of usable addresses in this block 556

57 Review Questions 8. Give the topology type of the following network 557

58 Review Questions 9. Give the topology type of the following network 558

59 Review Questions 10. Implement by drawing a local network consisting of 4 hosts using a hub as a connecting device. 11. Implement by drawing a local network consisting of 2 hosts without using any connecting devices. 559

Prepared by Agha Mohammad Haidari Network Manager ICT Directorate Ministry of Communication & IT

Network Basics Prepared by Agha Mohammad Haidari Network Manager ICT Directorate Ministry of Communication & IT E-mail :Agha.m@mcit.gov.af Cell:0700148122 After this lesson,you will be able to : Define