COS2626 Exam Notes 2021.

CHAPTER 1 An Introduction to Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 CHAPTER 2 Networking Standards and the OSI Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 CHAPTER 3 Transmission Basics and Networking Media. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 CHAPTER 4 Introduction to TCP/IP Protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 CHAPTER 5 Topologies and Ethernet Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 CHAPTER 6 Network Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 CHAPTER 7 WANs and Remote Connectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 CHAPTER 8 Wireless Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 CHAPTER 9 Network Operating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 CHAPTER 10 In-Depth TCP/IP Networking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485 CHAPTER 11 Voice and Video Over IP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 CHAPTER 14 Ensuring Integrity and Availability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683 iii COS2626 Exam Notes 2021. 2Chapter 1 • Client – devices and users that connects to the network • Server—A computer on the network that manages shared resources; servers usually have more processing power, memory, and hard disk space than clients. • Workstation—A personal computer (such as a desktop or laptop); most clients are workstation computers. • NIC (network interface card) —The device inside a computer that connects a computer to the network media, thus allowing it to communicate with other computers; many companies (such as 3Com, IBM, Intel, SMC, and Xircom) • NOS (network operating system) —The software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions. Examples Microsoft Windows Server 2003 or Windows Server 2008, and Mac OS X Server. • Host—A computer that enables resource sharing by other computers on the same network • Connectivity device—A specialized device that allows multiple networks or multiple parts of one network to connect and exchange data. A client/server network can operate without connectivity devices. However, medium- and large-sized LANs use them to extend the network and to connect with WANs. • Segment—A part of a network. Usually, a segment is composed of a group of nodes that use the same communications channel for all their traffic. • Backbone—The part of a network to which segments and significant shared devices (such as routers, switches, and servers) connect. A backbone is sometimes referred to as “a network of networks, ” because of its role in interconnecting smaller parts of a LAN or WAN. • Topology—The physical layout of a computer network. Topologies vary according to the needs of the organization and available hardware and expertise. Networks can be arranged in a ring, bus, or star formation, and the star formation is the most common. • Protocol—A standard method or format for communication between networked devices. A protocol is simply a set of instructions written by a programmer to perform a function. • Data packets—The distinct units of data that are exchanged between nodes on a network. Breaking a large stream of data into many packets allows a network to deliver that data more efficiently and reliably. • Transmission media—The means through which data is transmitted and received. Transmission media may be physical, such as wire or cable, or atmospheric (wireless), such as radio waves. Figure 1-8 shows several examples of transmission media. Chapter Summary ■ A network is a group of computers and other devices (such as printers) that are connected by some type of transmission media, such as copper or fibre-optic cable or the atmosphere (wireless transmission). ■ Networks enable multiple users to share devices and data. Sharing resources saves time and money. Networks also allow you to manage, or administer, resources on multiple computers from a central location. ■ In a peer-to-peer network, every computer can communicate directly with every other computer. By default, no computer on a peer-to-peer network has more authority than another. However, each computer can be configured to share only some of its resources and keep other resources inaccessible. ■ Traditional peer-to-peer networks are usually simple and inexpensive to set up. However, they are not necessarily flexible or secure. ■ Client/server networks rely on a centrally administered server (or servers) to manage shared resources for multiple clients. In this scheme, the server has greater authority than the clients, which are typically desktop or laptop workstations. 3■ Client/server networks are more complex and expensive to install than peer-to-peer networks. However, they are more easily managed, more scalable, and typically more secure. They are by far the more popular ■ Servers typically possess more processing power, hard disk space, and memory than client computers. To manage access to and use of shared resources, among other centralized functions, a server requires a network operating system. ■ A LAN (local area network) is a network of computers and other devices that is confined to a relatively small space, such as one building or even one office. ■ LANs can be interconnected to form WANs (wide area networks), which traverse longer distances and, therefore, require slightly different transmission methods and media than LANs. The Internet is the largest example of a WAN. ■ Client/server networks share some common elements, including clients, servers, workstations, transmission media, connectivity devices, protocols, addressing, topology, NICs, data packets, network operating systems, hosts, backbones, segments, and nodes. ■ Although e-mail is the most visible network service, networks also provide services for printing, file sharing, Internet access, remote access capabilities, communicating in multiple forms, and network management. ■ File and print services provide the foundation for networking. They enable multiple users to share data, applications, storage areas, and printers. ■ Networks use access services to allow remote users to connect to the network or network users to connect to machines outside the network. ■ Communications services provided by networks include e-mail, telephone, video, fax, messaging, and voice mail. ■ Mail services (running on mail servers) allow users on a network to exchange and store e-mail. Most mail packages also provide filtering, routing, scheduling, notification, and connectivity with other mail systems. ■ Internet services such as World Wide Web servers and browsers, file transfer capabilities, addressing schemes, and security filters enable organizations to connect to and use the global Internet. 4 The OSI Model OSI (Open Systems Interconnection) model used for understanding and developing computer-to-computer communications over a network. Divides network communications into seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The OSI model is a theoretical representation of what happens between two nodes communicating on a network. Programmers Dare Not Throw Salty Pretzels Away 1 Physical layer • Function: Manages hardware connections • Protocols at the Physical layer accept frames from the Data Link layer and generate signals as changes in voltage at the NIC. (Signals are made of electrical impulses that, when issued in a certain pattern, represent information.) When the network uses copper as its transmission medium, these signals are also issued over the wire as voltage. In the case of fiber-optic cable, signals are issued as light pulses. When a network uses wireless transmission, the signals are sent from antennas as electromagnetic waves. • Physical layer protocols also set the data transmission rate and monitor data error rates. However, even if they recognize an error, they cannot perform error correction. When you install a NIC in your desktop PC and connect it to a cable, you are establishing the foundation that allows the computer to be networked. In other words, you are providing a Physical layer. • Simple connectivity devices such as hubs and repeaters operate at the Physical layer. NICs operate at both the Physical layer and at the Data Link layer. 2 Data Link layer • The primary function is to divide data they receive from the Network layer into distinct frames that can then be transmitted by the Physical layer. • A frame is a structured package for moving data that includes not only the raw data, or “payload,” but also the sender’s and receiver’s network addresses, and error checking and control information. • The Data Link layer protocols find out that information has been dropped and ask the first computer to retransmit its message—through a process called error checking. • Error checking is accomplished by a 4-byte FCS (frame check sequence) field, whose purpose is to ensure that the data at the destination exactly matches the data issued from the source. When the source node transmits the data, it performs an algorithm (or mathematical routine) called a CRC (cyclic redundancy check). CRC takes the values of all of the preceding fields in the frame and generates a unique 4-byte number, the FCS. When the destination node receives the frame, its Data Link layer services unscramble the FCS via the same CRC algorithm and ensure that the frame’s fields match their original form. If this comparison fails, the receiving node assumes that the frame has been damaged in transit and requests that the source node retransmit the data. Note that the receiving node is responsible for detecting errors. • Data Link layer gives instruction to retransmit the information if acknowledgement has not arrived. The Data Link layer never tries to figure out what went wrong. • Another communications mishap that might occur on a busy network is a flood of communication requests. The Data Link layer controls the flow of this information, allowing the NIC to process data without error. • In fact, the IEEE has divided the Data Link layer into two sublayers. The reason for this change was to allow higher layer protocols to interact with Data Link layer protocols without regard for Physical layer specifications. × The upper sublayer of the Data Link layer, called the LLC (Logical Link Control), provides an interface to the Network layer protocols, manages flow control, and issues requests for transmission for data that has suffered errors.