Objectives In this session, you will learn to: Identify the types of networks

1. Objectives In this session, you will learn to: • Identify the types of networks • Identify the network topologies • Identify the connectivity devices • Define and identify the types of signals • Identify the LAN transmission techniques • Identify the types of cables • Identify the network problems • Identify the access methods • Identify the layers of the OSI model

2. Objectives (Contd.) • Define protocols • Identify the different protocols in the OSI model • Identify the WAN transmission technologies • Define virtual circuits • Identify the advanced WAN technologies • Identify the IP address classes • Define subnetting and subnet masks • Identify the components of the network operating system

3. Types of Networks • A group of computers connected to each other through a medium to share resources and data is known as a network. • Networks, based on the distance covered by them, can be categorized into the following types: • Local Area Networks (LAN) • Metropolitan Area Networks (MAN) • Wide Area Networks (WAN) • A LAN suits business organizations situated in a single location. LANs are restricted in size. • A MAN covers an area of a state or city and includes two or more LANs.

4. Types of Networks (Contd.) • A WAN covers an area larger than a MAN. WAN uses telephone cables and satellites for communication. • The types of networks based on roles of computers on a network are: • Peer-to-peer- In a peer-to-peer network, all computers are at par with each other. Every computer acts as a client as well as a server. • Server-based- In a server-based network, server computers service the requests of the client computers. • Combination- Combination networks combine the features of peer-to-peer and server-based networks.

5. Network Topologies • A network topology refers to the layout or arrangement of computers and other components on a network. Network topologies are of the following types: • Bus • Star • Ring • Star Bus • Star Ring • Physical Mesh • The bus topology is a linear topology where computers are connected to each other through a common cable called a trunk line.

6. Network Topologies (Contd.) • In a star topology, computers are connected through a central device called hub. Data moves from the source computer to all other computers through the central hub. • In a ring topology, computers are connected in a circle. The ring network is unidirectional. Therefore, data transmitted moves in a single direction. • In the star bus topology, the hubs of more than one star network are connected in a linear manner. • In a star ring topology, a physical star connects two or more logical ring networks to a central hub. • In the physical mesh topology, all computers are directly connected to each other.

7. Connectivity Devices • Connectivity devices help to optimize network performance by segmenting existing networks. • A repeater is a device that amplifies weak data signals during data transmission. • A bridge is a device that connects network segments and also divides a network to isolate traffic problems. A bridge determines the appropriate network segment to which it should pass a signal. • A router is a device that determines the address of each segment and identifies the best path for sending data. A router decides the path a packet will follow by determining the number of hops between internetwork segments. There are two types of routers, static and dynamic.

8. Connectivity Devices (Contd.) • A brouter is a router that can also be used to bridge nonroutable protocols. A brouter routes a packet if it uses a routable protocol and bridges the packet if it uses a nonroutable protocol. • A gateway is a device that enables communication between different architectures and environments.

9. Signals • A signal is an electrical or optical energy that is transmitted over a medium, such as cable. • Signals are of two types, analog and digital. • Analog signals are electronic signals of varying frequency or amplitude. Analog signals constantly change their values within a specified range. • Digital signals are electronic signals that are transmitted or stored as discrete units of 0 or 1. Each unit of digital signal is called a bit. Computers communicate with each other through digital signals.

10. LAN Transmission Techniques • The transmission technique used to transmit signals varies with the type of signals. Signals can be transmitted by using baseband or broadband transmission. • Baseband transmission transmits digital signals over a single frequency and uses the entire bandwidth as a single channel for transmission. Baseband transmission supports bi-directional transmission of digital signals. • Broadband transmission supports unidirectional transmission of analog signals. • Signals are transmitted in a LAN using cables. Cables are of three types: Coaxial, Twisted-pair, and Fiber-optic.

11. Cables • Coaxial cables are made up of core copper wire surrounded by insulation, braided metal shielding, and an outer cover. • Coaxial cables are of two types, thicknet and thinnet • A twisted-pair cable contains two insulated copper wires that are twisted. There are two types of twisted-pair cables: • A UTP (Unshielded twisted-pair) cable consists of a pair of insulated copper wires. UTP cables are used as LAN cables and in telephone systems. UTP cables are exposed to crosstalk. • An STP (Shielded twisted-pair) cable consists of a copper braid jacket and a foil wrap for each cable in the twisted-pair. STP protects signals from crosstalk. • Fiber-optic cables are made up of optical fibers. Fiber-optic cables provide secure transmission of data.

12. Network Problems • EMI (Electromagnetic Interference) is a phenomenon where signals get corrupted due to the electromagnetic waves emitted by adjacent cables during transmission. • Crosstalk occurs when signals of one cable get mixed with signals of an adjacent cable due to EMI. • A broadcast storm is a sudden flood of broadcast messages, which clogs the transmission medium. In the worst case, computers cannot even access the network. A malfunctioning network adapter card often causes a broadcast storm. • When signals travel over cables, the resistance of the cable wire interferes with signal transmission, making the signals weak and distorted. This distortion of signals is called attenuation.

13. Access Methods • An access method is a set of rules that defines how a computer places data on the network cable and retrieves data from the cable. Access methods control traffic on the cable by ensuring that only one computer places data on the cable at a time. • Access methods are of the following types: • Carrier-Sense Access Methods • Token Passing • Demand Priority

14. Access Methods (Contd.) • The access methods in which the computers detect the cable for a transmission and act accordingly are called carrier-sense access methods. There are two types of carrier-sense access methods: • Carrier-Sense Multiple Access with Collision Detection (CSMA/CD) is an access method where the computer senses the cable for transmissions. If no data is being transmitted on the cable, the computer transmits the data. • Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) is an access method where each computer signals its intent to transmit data before actually transmitting the data.

15. Access Methods (Contd.) • In the token passing method, a special packet called token is circulated from one computer to another for transmitting data. A token is an access permission for transmitting data. • In demand priority access method, it is possible to prioritize data. By prioritizing data, the collision and damage of data during transmission can be avoided.

16. OSI Model • The OSI model was developed by International Standards Organization (ISO) to standardize network architecture. The OSI model consists of seven layers. • The seven layers of the OSI model are: • Application - The application layer provides services to support user applications, such as software for e-mail, database access, and file transfers. • Presentation - The presentation layer determines the data exchange format on a computer network. • Session - The session layer enables two applications on different computers to connect, use, and terminate the connection.

17. OSI Model (Contd.) • Transport - The transport layer helps in efficient data transmission. At the sending computer, the transport layer splits the data into small data packets. • Network - The network layer determines the route for transmitting data packets to the receiving computer. • Data Link - The data link layer ensures error-free transmission of data through the physical layer. The data link layer transfers data packets in the form of dataframes to the physical layer. • Physical - The physical layer transmits data to the cable. This layer defines the transmission technique for sending data over the cable.

18. Protocols • Protocols specify the guidelines for interaction between the hardware and software components of networks. • Routable protocols support LAN-to-LAN communication over multiple paths. TCP/IP is an example of a routable protocol. • Nonroutable protocols do not support LAN-to-LAN communication over multiple paths. NetBEUI is an example of a nonroutable protocol.

19. Protocols (Contd.) • On the basis of communication, protocols can be classified as connection-oriented and connectionless protocols. • In connection-oriented protocol, the sending computer establishes a connection with the receiving computer for transmitting data. • In connectionless communication, a connection is not established between the sending and receiving computers for transmitting data. The sending computer has the address of the destination computer and transmits data over the available free paths. • In the process of communication between computers, several protocols work together at different layers of the OSI model to ensure the transmission of data.

20. Protocols in the OSI Model • Based on the layers of the OSI model, you can classify protocols as application protocols, transport protocols, and network protocols. • Application protocols provide the functionality of the application, presentation, and session layers of the OSI model. These protocols provide application-to-application interaction and data exchange. SNMP and SMTP are examples of application protocols. • Transport protocols provide the functionality of the transport layer of the OSI model. These protocols establish a communication session between computers and ensure that data move reliably between computers. SPX and NetBEUI are examples of transport protocols.

21. Protocols in the OSI Model (Contd.) • Network protocols provide the functionality of the network, data link, and physical layers of the OSI model. These protocols handle addressing and routing information, error checking, and retransmission requests. Network protocols also define the rules for communicating in a particular networking environment. IP and IPX are examples of network protocols.

22. TCP/IP Protocol • TCP/IP is Transmission Control Protocol and Internet Protocol. TCP of TCP/IP is a transport protocol. IP of TCP/IP is a network protocol. TCP provides interoperability among dissimilar operating systems by linking two types of networks. Some protocols are written for the TCP/IP suite: • Simple Mail Transfer Protocol (SMTP) is an electronic mail routing standard that uses TCP/IP to route mail messages between networks. • File Transfer Protocol (FTP) is a protocol that enables users to transfer files between computers by using TCP/IP. • Simple Network Management Protocol (SNMP) is a network management protocol used to control network communications by using TCP/IP.

23. Other Protocols • Standard bodies such as International Standards Organization (ISO) and Institute of Electrical and Electronics Engineers (IEEE) have developed protocols that map to a few layers in the OSI model. Examples of IEEE protocols are Ethernet, Token Passing Bus, and Token Ring. • Microsoft products use Net BIOS Extended User Interface ( NETBEUI), TCP/IP, and NWLink. • Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX), Apple Talk, Advanced Program to Program Communication (APPC), X.25, and Network File System (NFS) are some of the commonly used protocols.

24. WAN Transmission Technologies • There are three types of WAN transmission techniques: • Analog • Digital • Switched • Analog lines are of two types, dial-up and dedicated. • Analog connectivity uses the same lines as used by the telephone network. This worldwide network is known as Public Switched Telephone Network (PSTN). • Digital lines are of three types: Digital Data Service, T-Carriers, and Switched 56.

25. WAN Transmission Technologies (Contd.) • Switching is a technique that helps you determine how connections are made and how data is transmitted on a WAN. • Switching is of three types: circuit switching, message switching, and packet switching. • Circuit switching connects the sending computer and the receiving computer by a single physical connection for the entire duration of the communication session. • Message switching does not establish a dedicated connection between the sending computer and the receiving computer. • Packet switching breaks long messages into small parts called packets. Packet switching is enabled by virtual circuits.

26. Virtual Circuits • Virtual circuits are a series of logical connections between the sending computer and the receiving computer. • Virtual circuits are of two types, Switched Virtual Circuits(SVC) and Permanent Virtual Circuits(PVC). • SVCs are similar to dial-up lines where network resources are dedicated to a circuit for as long as the connection is maintained. • PVCs are similar to leased lines that are dedicated and virtual.

27. Advanced WAN Technologies • Transmission technologies, such as analog, digital, and packet switching, may not fulfill the speed and bandwidth requirements of an organization. In such a situation, you need to consider using some advanced WAN technologies that meet the requirements of an organization. • Asynchronous Transfer Mode (ATM), X.25, Frame Relay, Integrated Services Digital Network (ISDN), and Fiber Distributed Data Interface (FDDI) are some of the advanced WAN technologies.

28. IP Address • All communication protocols identify individual computers by using their IP addresses. • An IP address is a 4-byte (32-bit) address, and each byte is separated by a dot. • An IP address has two components, network id and host id. • The IP addresses are categorized into five address classes: Class A, Class B, Class C, Class D, and Class E. • Class A IP addresses are used by large organizations that have few networks and a large number of hosts. In a class A IP address, only the first byte denotes the network id. The remaining three bytes specify the host id. The network ids supported by class A IP addresses range between 1 and 126.

29. IP Address (Contd.) • Class B IP addresses are used by universities and large companies. In a class B IP address, the first two bytes identify the network and the last two bytes identify the host. The value in the first byte of the network id in a class B IP address ranges between 128 and 191. • The Class C IP addresses are used by networks that have very few hosts. In a class C IP address, the first three bytes constitute the network id and the last byte identifies the host. The value in the first byte of a network id in a class C IP address ranges between 192 and 223.

30. IP Address (Contd.) • Class D IP addresses are used for multicast transmissions. A multicast transmission enables a host to broadcast to multiple destinations. You cannot use a class D address for communicating to a single host. The IP addresses supported by class D range from 224.0.0.0 through 239.255.255.255. • Class E IP addresses are reserved for experimental use. The IP addresses supported by class E range between from 240.0.0.0 through and 255.255.255.255.

31. Subnetting • With an increase in the number of hosts accessing the Internet, IP addresses are getting exhausted. In addition, the classes A and B support few networks but a large number of hosts per network. Therefore, many host ids are wasted. Using subnets can solve these problems. • A subnet is a small logical network with a limited number of hosts. You create a subnet by dividing a large physical network into smaller logical networks. • A subnet mask consists of 32 bits and distinguishes a network address from a host address. The bits that correspond to the network address are all set to 1, and the bits that correspond to the host address are all set to 0.

32. Subnetting (Contd.) • To derive a subnet mask, you need to: • Determine the number of bits for the subnet ID • Assign the value 1 to subnet ID bits • Convert the resultant binary to decimal

33. Network Operating System • In a network, the network operating system is the foundation of all hardware and software activities. • A network operating system is a specialized software that controls allocation of tasks to the displayed hardware resources. • The network operating system has two components. These are the client software and the server software. • The client software is installed on the client computer. This software helps the client computer to connect to the server and communicate with the server software. • Server software is installed on the server and enables the client computers to access the data on the server. Server software also allows client computers to connect to peripherals.

34. Summary In this lesson, you learned that: • Computer networks are two or more computers connected to each other through a medium to share resources. • Networks, based on the distance covered by them, can be categorized into LAN, MAN, and WAN. • Networks, based on the roles of computers on a network, can be categorized into Peer-to-peer, server-based, and combination. • A network topology refers to the layout or arrangement of computers and other components on a network. • There are different kinds of topologies, such as bus, star, ring, star bus, star ring, and physical mesh.

35. Summary (Contd.) • Repeater, hub, bridge, router, brouter, and gateway are types of connectivity devices. • A signal is electrical or optical energy that is transmitted over a medium, such as cable. Signals are of two types, analog and digital. • There are three major types of cables: coaxial, twisted-pair, and fiber-optic. • EMI, crosstalk, and attenuation are the major types of problems faced during signal transmission in a network. • An access method is a set of rules that defines how a computer places data on the network cable and retrieves data from the cable.

36. Summary (Contd.) • The three types of access methods are CSMA, token passing, and demand priority. • The OSI model was developed by International Standards Organization (ISO) to standardize network architecture. The OSI model consists of seven layers. • Protocols are rules that govern communication between computers are called protocols. • Protocols can be categorized into routable or nonroutable protocol depending on whether the protocol is supported by a router or not. • Based on the layers of the OSI model, you can classify protocols as application protocols, transport protocols, and network protocols.

37. Summary (Contd.) • There are three types of WAN transmission techniques: analog, digital, and packet switched. • An IP address is a 4-byte (32-bit) address, and each byte is separated by a dot. An IP address has two components, network id and host id. • The IP addresses are categorized into five address classes, Class A, Class B, Class C, Class D, and Class E. • A subnet is a small logical network with a limited number of hosts. You create a subnet by dividing a large physical network into smaller logical networks. • A network operating system is a specialized software that controls allocation of tasks to the displayed hardware resources. The network operating system has two components, the client software and the server software.