Bài giảng Network+ Certification - Chapter 1, Networking Basics

Chapter 1, Networking Basics The outline presents only the key points from the course textbook. It’s not intended to be a complete recap of the textbook content presented in outline form. Where demonstrations are suggested or recommended, it’s assumed that the instructor will know the procedures for the demonstration or will find them in the course textbook. Some of the demonstrations require other equipment or network setup in addition to your class presentation computer. You should review each chapter outline before class to ensure that you have the proper equipment and connections in the classroom and that you know the correct procedure to perform the suggested demonstrations. The outlines are not included on the Student CD-ROM for this course. However, you can certainly make them available to your students, as a study aid, if you wish. If you do so, you might want to edit the file to remove some of the Instructor Notes before giving the outline to your students. |1| Chapter Overview A. Network Communications B. The OSI Reference Model Chapter 1, Lesson 1 Network Communications |2| 1. Signals and Protocols A. A data network is a group of computers connected by a network medium. 1. Network media: cables of various types or wireless technologies B. The network medium carries signals between computers, including the following types: 1. Electric currents 2. Light pulses 3. Infrared 4. Radio waves C. Signals reduce complex information to the simplest possible form. D. Computers communicate by using a language called a protocol. |3| E. Protocols can provide the following services: 1. Packet acknowledgment. The transmission of a return message by the recipient to verify the receipt of a packet or packets a. A packet is the fundamental unit of data transmitted over a local area network (LAN). 2. Segmentation. The division of a lengthy data stream into segments small enough to transmit over the network inside packets 3. Flow control. Messages sent by a receiving system that instruct the sending system to speed up or slow down its transmission rate 2 Outline, Chapter 1 Network+ Certification, Second Edition 4. Error detection. The inclusion of special codes in a packet that the receiving system uses to verify that the content of the packet was not damaged in transit 5. Error correction. Messages sent by a receiving system that inform the sender that specific packets were damaged and must be retransmitted 6. Data compression. A mechanism for reducing the amount of data transmitted over a network by eliminating redundant information 7. Data encryption. A mechanism for protecting the data transmitted over a network by encoding it with a key already known by the receiving system 2. Protocol Interaction A. Computers on a network use many different protocols. |4| B. The protocols on a networked computer are arranged in a stack. 1. The protocol stack ranges from the application running on the computer to the network medium (the network interface adapter providing the connection to the network). 2. The protocols at each layer of the stack provide services to the layers above and below. C. Direction of data flow 1. Complex information originating from the transmitting computer at the top of the stack is reduced to simple signals by the time it reaches the bottom. 2. The process by which data travels down the protocol stack on a transmitting computer is reversed on the receiving computer. |5| D. The protocols at the same layer of the stack on different computers communicate with each other. 3. Local Area Networks and Wide Area Networks |6| A. A local area network (LAN) is a collection of computers located in a relatively small area and connected by a common medium. 1. Typically located in the same room, floor, or building 2. Each computer or communicating device on the LAN is called a node. B. The pattern in which the computers in a LAN are connected is called the topology. C. Types of LAN topologies 1. Bus 2. Star 3. Ring D. The defining protocols for a LAN are the data-link layer protocols, such as Ethernet. |7| E. Wide area networks (WANs) are long-distance connections that nearly always use an external network provider (such as a telephone company). 1. Are usually point-to-point connections, whereas LANs can connect many systems Outline, Chapter 1 3 Network+ Certification, Second Edition 2. WAN links can connect two LANs, a computer to a LAN, or a computer to a computer. F. Two or more networks connected together are called an internetwork. 4. Broadband and Baseband A. A baseband network transmits a single signal at a time. B. A broadband network simultaneously transmits multiple signals over a single medium. |8| C. Packet switching enables computers to share a baseband medium. 1. In a packet-switching network, data is split into discrete units that are transmitted individually and are reassembled at the destination. D. A circuit-switched network is one in which two communicating systems establish a connection that remains open until all of the data is transmitted. |9| 5. Half-Duplex and Full-Duplex Communications A. Half-duplex communication. Signals travel in one direction only. B. Full-duplex communication. Signals travel in both directions simultaneously. |10| 6. Segments and Backbones A. The term “segment” is typically synonymous with LAN. 1. A cable segment does not necessarily refer to a single length of cable. B. A well-designed internetwork uses a backbone network to connect the LANs. C. When all of the segments are connected to a single backbone, internetwork traffic never has to pass through more than two routers, and no through traffic passes over the segments. |11| 7. Client/Server and Peer-to-Peer Networking A. On a client/server network, computers function as either clients or servers. 1. Server. A computer or an application running on a computer that provides a service to other computers 2. Client. A computer that uses the services provided by servers B. On a peer-to-peer network, computers can function as both clients and servers. C. Most network operating systems used today, including Microsoft Windows and all forms of UNIX, use the peer-to-peer model. 1. Only Novell NetWare is a pure client/server operating system. Chapter 1, Lesson 2 The OSI Reference Model 1. Standards A. The OSI reference model is based on standards published by the International Organization for Standardization (ISO) and the 4 Outline, Chapter 1 Network+ Certification, Second Edition Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T). |12| B. The OSI model divides a computer’s networking functions into seven layers. 1. The top of the model interfaces with the application running on the computer. 2. The bottom of the model represents the interface to the network, such as a network interface adapter (also known as a network interface card, or NIC). C. The protocols used today predate the OSI reference model. D. None of the protocol stacks in common use conform strictly to the layers of the model. 2. Data Encapsulation A. Protocols at the various layers provide services to the layer above. |13| B. Data encapsulation is the process by which a protocol adds a header (and possibly a footer) to data received from the layer above. 1. The header consists of fields containing information specific to the protocol functions. 2. The footer contains error detection information. 3. Data encapsulated at one layer becomes the payload for the layer below. |14| C. The protocol data units (PDUs) created at the various OSI model layers have different names at different layers. 1. Application layer: message 2. Transport layer: segment or datagram 3. Network layer: datagram 4. Data-link layer: frame 5. Any layer: packet a. Packet is a generic term for the data unit created at any layer. 3. The Physical Layer A. Defines the hardware elements of the network, including 1. The network medium 2. How the network is installed 3. The type of signaling the devices use |15| B. Physical layer elements 1. Cables 2. Network interface adapters (also called network interface cards, or NICs) 3. Hubs C. The physical layer elements are usually dictated by which data-link layer protocol you select. D. Most physical layer installations should conform to the Commercial Building Telecommunications Cabling Standard, also known as EIA/TIA 568A. Outline, Chapter 1 5 Network+ Certification, Second Edition 1. Published jointly by the American National Standards Institute (ANSI), the Electronics Industry Association (EIA) and the Telecommunications Industry Association (TIA) 4. The Data-Link Layer |16| A. Data-link layer protocols 1. Ethernet 2. Token Ring 3. Fiber Distributed Data Interface (FDDI) 4. Serial Line Internet Protocol (SLIP) 5. Point-to-Point Protocol (PPP) |17| B. Data-link layer protocol components 1. Frame format 2. Media Access Control (MAC) mechanism 3. Physical layer specifications C. Data-link layer protocols are implemented on a computer in its network interface adapter and the adapter driver. D. Data-link layer functions 1. Hardware addressing (also called MAC addressing) 2. Error detection and correction 3. Network-layer protocol identification E. Data-link layer protocols are only capable of carrying traffic to other computers on the same network. 5. The Network Layer |18| A. Network layer protocols 1. Internet Protocol (IP) 2. Internetwork Packet Exchange (IPX) 3. NetBIOS Extended User Interface (NetBEUI) 4. AppleTalk B. Responsible for end-to-end communications C. Network layer functions 1. Addressing a. Network layer addresses and data-link layer addresses may identify different computers. b. Network layer addresses can be self-contained (like IP addresses) or borrowed (like IPX node addresses). 2. Fragmenting a. Different networks support different packet sizes. b. The network layer protocol splits the datagram into pieces small enough for the data-link layer protocol to transmit. 3. Routing a. Is the process of using the most efficient path possible to direct a datagram from its source to its destination 4. Transport layer protocol identification 6 Outline, Chapter 1 Network+ Certification, Second Edition 6. The Transport Layer |19| A. Transport layer protocols 1. Transmission Control Protocol (TCP) 2. User Datagram Protocol (UDP) 3. NetWare Core Protocol (NCP) 4. Sequenced Packet Exchange (SPX) B. Transport layer functions 1. Packet acknowledgment 2. Data segmentation 3. Flow control 4. Error detection 5. Application layer protocol identification |20| C. Some transport-layer protocols are connection-oriented (CO) and others are connectionless (CL). 1. CO protocols require a preliminary exchange of control messages, called a handshake; CL protocols do not. 2. CO protocols have larger headers and more overhead than CL protocols do. 3. CO protocols provide additional services, such as packet acknowledgment, data segmentation, flow control, and end-to-end error detection and correction. 4. CO protocols acknowledge transmitted packets and are therefore called reliable protocols. a. CL protocols do not use acknowledgments and are therefore technically described as not reliable. 7. The Session Layer |21| A. The two most important services at this layer are dialog control and dialog separation. B. Dialog control 1. Selects the mode that systems will use to exchange messages 2. Systems can choose between two-way alternate (TWA) and two-way simultaneous (TWS) mode. C. Dialog separation is the process of creating checkpoints in a data stream to enable systems to synchronize their functions. 8. The Presentation Layer |22| A. Has only one function: translating syntax between different systems 1. Enables systems to negotiate a common syntax for network communications B. The transmitting system converts its abstract syntax to transfer syntax. 1. Abstract syntax. Native form of communication 2. Transfer syntax. Alternative syntax that the two systems have in common C. The presentation layer translation process Outline, Chapter 1 7 Network+ Certification, Second Edition 1. The sender translates its abstract syntax to transfer syntax. 2. The sender transmits data to the receiver. 3. The receiver translates the transfer syntax to its own abstract syntax. 9. The Application Layer A. Is the layer that programs use to access the OSI model and use network resources |23| B. Application layer protocols 1. File Transfer Protocol (FTP) 2. Hypertext Transfer Protocol (HTTP) 3. Simple Mail Transfer Protocol (SMTP) 4. Post Office Protocol, Version 3 (POP3) 5. Internet Mail Access Protocol (IMAP) 6. Simple Network Management Protocol (SNMP) 7. Domain Name System (DNS) 8. Dynamic Host Configuration Protocol (DHCP) |24| Chapter Summary A. Lesson 1: Network Communications 1. Computers communicate by using languages called protocols. 2. Protocols provide services to other protocols operating above and below them. 3. A LAN uses a common network medium to connect computers in a relatively small area. 4. A WAN uses an external network provider to connect LANs. 5. Broadband networks carry multiple signals at once, while baseband networks carry only one signal. 6. A backbone network connects segments together, forming an internetwork. 7. Most operating systems today use the peer-to-peer model, which allows computers to function as both clients and servers. |25| B. Lesson 2: The OSI Reference Model 1. The physical layer defines the hardware elements and structure of the network installation. 2. The data-link layer provides addressing, data encapsulation, and media access control. 3. The network layer provides end-to-end routing and addressing. 4. The transport layer provides packet acknowledgment, flow control, and error detection. 5. The session layer provides dialog control and dialog separation. 6. The presentation layer translates syntaxes between different systems. 7. The application layer provides an interface to applications running on the computer.