Chapter 6 (Networking)

Chapter 6 (Networking)

1. Computer Networks

   • Networks are systems that are formed by links. For example, roads that connect groups of people together create a physical network. Connections with your friends create your personal network. Websites that allow individuals to link to each other’s pages are called social networking sites.
     • People use the following networks every day: Mail delivery system Telephone system Public transportation system Corporate computer network The Internet
       • A host is any device that sends and receives information on the network. Some devices can serve either as hosts or peripherals. For example, a printer connected to your laptop that is on a network is acting as a peripheral. If the printer is connected directly to a network, it is acting as a host.
         • Many different types of devices can connect to a network: Desktop computers Laptop computers Tablet computers Smartphones Printers File and print servers Game consoles Home appliances
           • Computer networks are used globally in businesses, homes, schools, and government agencies. Many of the networks are connected to each other through the Internet. A network can share many different types of resources and data:
             • Services, such as printing or scanning Storage space on removable devices, such as hard drives or optical drives Applications, such as databases Information, stored on other computers Documents Calendars, synchronizing between a computer and a smartphone
   • Require Fewer Peripherals The figure shows that many devices can be connected on a network. Each computer on the network does not need to have its own printer or backup device. Multiple printers can be set up in a central location and shared among the network users. All network users send print jobs to a central print server that manages the print requests. The print server can distribute print jobs over multiple printers or queue jobs that require a specific printer.
     • Increase Communication Capabilities Networks provide several different collaboration tools that can be used to communicate between network users. Online collaboration tools include email, forums and chats, voice and video, and instant messaging. With these tools, users can communicate with friends, family, and colleagues.
       • Avoid File Duplication and Corruption A server manages network resources. Servers store data and share it with users on a network. Confidential or sensitive data can be protected and shared with the users who have permission to access that data. Document tracking software can be used to prevent users from overwriting files or changing files that others are accessing at the same time.
         • Avoid File Duplication and Corruption A server manages network resources. Servers store data and share it with users on a network. Confidential or sensitive data can be protected and shared with the users who have permission to access that data. Document tracking software can be used to prevent users from overwriting files or changing files that others are accessing at the same time.
           • Lower Cost Licensing Application licensing can be expensive for individual computers. Many software vendors offer site licenses for networks, which can dramatically reduce the cost of software. The site license allows a group of people or an entire organization to use the application for a single fee.

2. Types of Networks

   • A Wireless LAN (WLAN) is a LAN that uses radio waves to transmit data between wireless devices. In a traditional LAN, devices are connected together using copper cabling. In some environments, installing copper cabling might not be practical, desirable, or even possible. In these situations, wireless devices are used to transmit and receive data using radio waves. As with LANs, on a WLAN you can share resources, such as files and printers, and access the Internet.
     • In a WLAN, wireless devices connect to access points within a specified area. Access points are typically connected to the network using copper cabling. Instead of providing copper cabling to every network host, only the wireless access point is connected to the network with copper cabling. The range (radius of coverage) for typical WLAN systems varies from under 98.4 ft (30 m) indoors to much greater distances outdoors, depending on the technology used.
       • A personal area network (PAN) is a network that connects devices, such as mice, keyboards, printers, smartphone, and tablets within the range of an individual person. All of these devices are dedicated to a single host and are most often connected with Bluetooth technology.
         • A metropolitan area network (MAN) is a network that spans across a large campus or a city. The network consists of various buildings interconnected through wireless or fiber optic backbones. The communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users. A MAN can act as a high-speed network to allow sharing of regional resources.
           • A wide area network (WAN) connects multiple smaller networks such as LANs that are in geographically separated locations. The most common example of a WAN is the Internet. The Internet is a large WAN that is composed of millions of interconnected LANs. WAN technology is also used to connect corporate or research networks. Telecommunications service providers are used to interconnect these LANs at different locations.
   • In a peer-to-peer network, there is no hierarchy among the computers, nor are there any dedicated servers. Each device, also called a client, has equivalent capabilities and responsibilities. Individual users are responsible for their own resources and can decide which data and devices to share or install. Because individual users are responsible for the resources on their own computers, the network has no central point of control or administration.
     • Peer-to-peer networks have several disadvantages: There is no centralized network administration, which makes it difficult to determine who controls resources on the network. There is no centralized security. Each computer must use separate security measures for data protection. The network becomes more complex and difficult to manage as the number of computers on the network increases. There might not be any centralized data storage. Separate data backups must be maintained. This responsibility falls on the individual users.
       • Servers have software installed that enables them to provide services, such as email or web pages, to clients. Each service requires separate server software. For example, a server requires web server software to provide web services to the network.
         • In a client/server network, the client requests information or services from the server. The server provides the requested information or service to the client. Servers on a client/server network commonly perform some of the processing work for client machines, for example, sorting through a database before delivering only the records requested by the client. This provides for centralized network administration, which makes it easy to determine who controls resources on the network. Resources are controlled by a centralized network administration.

3. Data Flow

   • When data is sent over a computer network, it is broken up into small chunks called packets. Each packet contains source and destination address information. The packet, along with the address information, is called a frame. It also contains information that describes how to put all of the packets back together again at the destination. The bandwidth determines the number of packets that can be transmitted within a fixed period of time.
     • Bandwidth is measured in bits per second and is usually denoted by any of the following units of measure: b/s - bits per second kb/s - kilobits per second Mb/s - megabits per second Gb/s - gigabits per second
       • Simplex Simplex, also called unidirectional, is a single, one-way transmission. An example of simplex transmission is the signal that is sent from a TV station to your home TV.
         • Half-Duplex When data flows in one direction at a time it is known as half-duplex, as shown in the figure. With half-duplex, the channel of communications allows alternating transmission in two directions, but not in both directions simultaneously. Two-way radios, such as police or emergency communications mobile radios, work with half-duplex transmissions. When you press the button on the microphone to transmit, you cannot hear the person on the other end. If people at both ends try to talk at the same time, neither transmission gets through.
           • Full-Duplex When data flows in both directions at the same time it is known as full-duplex, as shown in the figure. Although the data flows in both directions, the bandwidth is measured in only one direction. A network cable with 100 Mb/s in full-duplex mode has a bandwidth of 100 Mb/s.

4. Networked Equipment Addressing

   • Transmission Control Protocol/Internet Protocol (TCP/IP) defines the rules computers must follow to communicate with each other over the Internet. TCP is the primary Internet protocol for the reliable delivery of data. IP provides an addressing structure that is responsible for delivering data from the source computer to the destination computer.
     • An IP address is a number that is used to identify a device on the network. Each device on a network must have a unique IP address to communicate with other network devices. As noted earlier, a host is a device that sends or receives information on the network. Network devices are devices that move data across the network.
       • IPv4 and IPv6 In the early 1990s there was a concern about running out of IPv4 network addresses, which lead the Internet Engineering Task Force to begin looking for a replacement. This led to the development of what is now known as IPv6. Currently IPv6 is operating alongside and is beginning to replace IPv4.
         • An IPv4 address consists of 32 bits with a potential address space of 2^32. In decimal notation that is approximately a 4 followed by 9 zeroes, an IPv6 address consists of 128 bits with a potential address space of 2^128. In decimal notation, that is approximately a 3 followed by 38 zeroes. With IPv6, the number of addresses available per person is approximately 10^30. If the IPv4 address space is represented by a marble, then the IPv6 address space is represented by a sphere that is almost the size of the planet Saturn.
   • An IPv4 address consists of a series of 32 binary bits (ones and zeros). It is difficult for humans to read a binary IPv4 address. For this reason, the 32 bits are grouped into four segments of 8 bits called octets. An IPv4 address, even in this grouped format, is hard for humans to read, write, and remember. Therefore, each octet is presented as its decimal value, separated by a decimal point or period. This format is referred to as dotted-decimal notation.
     • When a host is configured with an IPv4 address, it is entered as a dotted-decimal number, such as 192.168.1.5. Imagine if you had to enter the 32-bit binary equivalent of this: 11000000101010000000000100000101. If just one bit were mistyped, the address would be different, and the host might not be able to communicate on the network.
       • IPv4 addresses are divided into the following classes: Class A - Large networks implemented by large companies Class B - Medium-sized networks implemented by universities and other similar sized organizations Class C - Small networks implemented by small organizations or Internet service providers (ISPs) for customer subscriptions Class D - Special use for multicasting Class E - Used for experimental testing
         • In addition to creating separate classes, the IETF reserved some Internet address space for private networks. Private networks have no connection to public networks. Private network addresses are not routed across the Internet. This allows networks in different locations to use the same private addressing scheme without creating addressing conflicts. An example of when these private addresses are useful is in a classroom lab where you want to prevent access outside of your network.
           • Each of these classes has a range of private IP addresses: Class A - 10.0.0.0 to 10.255.255.255 Class B - 172.16.0.0 to 172.31.255.255 Class C - 192.168.0.0 to 192.168.255.255

5. Common Ports and Protocols

   • A protocol is a set of rules. Internet protocols are sets of rules governing communication within and between computers on a network. Protocol specifications define the format of the messages that are exchanged. A letter sent through the postal system also uses protocols. Part of the protocol specifies where the delivery address on the envelope needs to be written. If the delivery address is written in the wrong place, the letter cannot be delivered.
     • Timing is crucial for the reliable delivery of packets. Protocols require messages to arrive within certain time intervals so that computers do not wait indefinitely for messages that might have been lost. Systems maintain one or more timers during the transmission of data. Protocols also initiate alternative actions if the network does not meet the timing rules.
       • These are the main functions of protocols: Identifying and handling errors Compressing the data Deciding how data is to be divided and packaged Addressing data packets Deciding how to announce the sending and receiving of data packets
         • Devices and computers connected to the Internet use a protocol suite called TCP/IP to communicate with each other. The information is transmitted most often via two protocols, TCP and UDP, as shown in the figure. In the design of a network, you must determine the protocols that are going to be used. Some protocols are proprietary and only work on specific equipment, while other protocols are open standard and work on a variety of equipment.
           • When the TCP/IP protocol stack is enabled, other protocols can communicate on specific ports. For example, HTTP uses port 80 by default. A port is a numeric identifier used to keep track of specific conversations. Every message that a host sends contains both a source and destination port.
             • Network software applications use these protocols and ports to perform functions over the Internet or over a network. Some network software applications include services to host a web page, send email, and transfer files. These services may be provided by a single server or by several servers. Clients use well-known ports for each service so that the client requests can be identified by using a specific destination port.