6.3.1.1-6.4.1.7

Mb/s

megabits per second

TCP and UDP

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

Internet Appliances

An Internet appliance is also called a Net appliance, a smart appliance, or an information appliance. Examples of Internet appliance devices include televisions, game consoles, Blu-ray players, and streaming media players. The device is designed for the specific function and has built-in hardware for Internet connectivity. The Internet connection is either wired or wireless. Internet appliances include a CPU and RAM that support email, web surfing, gaming, as well as video streaming and social networking, as shown in the figure.

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:

Privite

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

IPv4

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

Hardware Firewalls

Hardware firewalls, such as integrated routers, protect data and equipment on a network from unauthorized access. A hardware firewall is a free-standing unit that resides between two or more networks, as shown in the figure. It does not use the resources of the computers it is protecting, so there is no impact on processing performance. A firewall should be used in addition to security software. A firewall resides between two or more networks and controls the traffic between them as well as helps prevent unauthorized access. Firewalls use various techniques for determining what is permitted or denied access to a network segment. Considerations when selecting a hardware firewall include: Space - Free standing and uses dedicated hardware Cost - Initial cost of hardware and software updates can be costly Number of computers - Multiple computers can be protected Performance requirements - Little impact on computer performance NOTE: On a secure network, if computer performance is not an issue, enable the internal operating system firewall for additional security. Some applications might not operate properly unless the firewall is configured correctly for them.

DHCP Addressing

If more than a few computers are a part of the LAN, manually configuring IP addresses for every host on the network can be time consuming and prone to errors. A Dynamic Host Configuration Protocol (DHCP) server automatically assigns IP addresses, which simplifies the addressing process. Automatically configuring TCP/IP also reduces the possibility of assigning duplicate or invalid IP addresses. The DHCP server maintains a list of IP addresses to assign and manages the process so that every device on the network receives a unique IP address. When the DHCP server receives a request from a host, the server selects IP address information from a set of predefined addresses that are stored in a database. When the IP address information is selected, the DHCP server offers these values to the requesting host on the network. If the host accepts the offer, the DHCP server assigns the IP address for a specific period of time. This is called leasing. When the lease expires, the DHCP server can use this address for another computer that joins the network. A device, however, can renew its lease to retain the IP address. Before a computer on the network can take advantage of the DHCP services, the computer must be able to identify the server on the local network. A computer can be configured to accept an IP address from a DHCP server by selecting the Obtain an IP address automatically option in the NIC configuration window, as shown in Figure 1. When a computer is set to obtain an IP address automatically, all other IP addressing configuration boxes are not available. The DHCP settings are configured the same for a wired or wireless NIC. A computer continually requests an IP address at 5-minute intervals from a DHCP server. If your computer cannot communicate with the DHCP server to obtain an IP address, the Windows OS automatically assigns a link-local IP. If your computer is assigned a link-local IP address, which is in the range of 169.254.0.0 to 169.254.255.255, your computer can only communicate with computers connected to the same network within this IP address range. A DHCP server automatically assigns the following IP address configuration information to a host: IP address Subnet mask Default gateway Optional values, such as a DNS server address, as shown in Figure 2

Static Addressing

In a network with a small number of hosts, it is easy to manually configure each device with the proper IP address. A network administrator who understands IP addressing should assign the addresses and should know how to choose a valid address for a particular network. The IP address that is assigned is unique for each host within the same network or subnet. This is known as static IP addressing. To configure a static IP address on a host, go to the TCP/IPv4 Properties window of the NIC, as shown in Figure 1. The NIC enables a computer to connect to a network using a MAC address. Whereas the IP address is a logical address that is defined by the network administrator, a MAC address, shown in Figure 2, is permanently programmed (or burned in) into the NIC when it is manufactured. The IP address of a NIC can be changed, but the MAC address never changes. You can assign the following IP address configuration information to a host: IP address - identifies the computer on the network Subnet mask - is used to identify the network on which the computer is connected Default gateway - identifies the device that the computer uses to access the Internet or another network Optional values - such as the preferred Domain Name System (DNS) server address and the alternate DNS server address In Windows 7, use the following path: Start > Control Panel > Network and Sharing Center > Change adapter setting > right-click Local Area Connection > Properties > TCP/IPv4 > Properties > Use the following IP address > Use the following DNS server addresses > OK > OK In Windows Vista, use the following path: Start > Control Panel > Network and Sharing Center > Manage network connections > right-click Local Area Connection > Properties > TCP/IPv4 > Properties > Use the following IP address > Use the following DNS server addresses > OK > OK In Windows XP, use the following path: Start > Control Panel > Network Connections > right-click Local Area Connection > Properties > TCP/IP > Properties > Use the following IP address > Use the following DNS server addresses > OK > OK

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.

ICMP

Internet Control Message Protocol (ICMP) is used by devices on a network to send control and error messages to computers and servers. There are several different uses for ICMP, such as announcing network errors, announcing network congestion, and troubleshooting. Ping is commonly used to test connections between computers. Ping is a simple but highly useful command-line utility used to determine whether a specific IP address is accessible. To see a list of options that you can use with the ping command, type C:\>ping /? in the Command Prompt window. The ipconfig command is another useful command-line utility used to verify that a NIC has a valid IP address. To display full configuration information of all network adapters, type C:\> ipconfig /all in the Command Prompt window. You can ping the IP address obtained from the ipconfig /all command to test IP connectivity. Ping works by sending an ICMP echo request to a destination computer or other network device. The receiving device then sends back an ICMP echo reply message to confirm connectivity. Echo requests and echo replies are test messages that determine if devices can send packets to each other. Four ICMP echo requests (pings) are sent to the destination computer. If it is reachable, the destination computer responds with four ICMP echo replies. The percentage of successful replies can help you to determine the reliability and accessibility of the destination computer. Other ICMP messages report undelivered packets and whether a device is too busy to handle the packet.

NAS

Network-attached storage (NAS) is a device consisting of one or more hard drives, an Ethernet connection, and an embedded operating system rather than a full-featured network operating system. The NAS device connects to the network, allowing users on the network to access and share files, stream media, and back up data to a central location. NAS devices that support multiple hard drives can provide RAID-level data protection. NAS is a client/server design. A single hardware device, often called the NAS head, acts as the interface between the NAS and the network clients. Clients always connect to the NAS head, not the individual storage devices. A NAS device requires no monitor, keyboard, or mouse. NAS systems provide easy administration. They often include built-in features, such as disk space quotas, secure authentication, and automatic sending of email alerts if an error is detected in the equipment.

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.

The figure shows how bandwidth on a network can be compared to a highway. In the highway example, the cars and trucks represent the data. The number of lanes on the highway represents the amount of cars that could travel on the highway at the same time. An eight-lane highway can handle four times the number of cars that a two-lane highway can hold.

The amount of time it takes data to travel from source to destination is called latency. Like a car traveling across town that encounters stop lights or detours, data is delayed by network devices and cable length. Network devices add latency when processing and forwarding data. When surfing the Web or downloading a file, latency does not normally cause problems. Time critical applications, such as Internet telephone calls, video, and gaming, can be significantly affected by latency.

Hubs, Bridges, and Switches

To make data transmission more extensible and efficient than a simple peer-to-peer network, network designers use specialized network devices, such as hubs, bridges and switches, routers, and wireless access points, to send data between devices. Hubs Hubs, shown in Figure 1, extend the range of a network by receiving data on one port and then regenerating the data and sending it out to all other ports. A hub can also function as a repeater. A repeater extends the reach of a network because it rebuilds the signal, which overcomes the effects of data degradation over distance. The hub can also connect to another networking device, like a switch or router that connects to other sections of the network. Hubs are used less often today because of the effectiveness and low cost of switches. Hubs do not segment network traffic, so they decrease the amount of available bandwidth for all devices connected to them. In addition, because hubs cannot filter data, a lot of unnecessary network traffic constantly moves between all the devices connected to it. Bridges and Switches Files are broken up into small pieces of data, called packets, before they are transmitted over a network. This process allows for error checking and easier retransmission if the packet is lost or corrupted. Address information is added to the beginning and end of packets before they are transmitted. The packet, along with the address information, is called a frame. LANs are often divided into sections called segments, similar to the way a company is divided into departments, or a school is divided into classes. The boundaries of segments can be defined using a bridge. A bridge filters network traffic between LAN segments. Bridges keep a record of all the devices on each segment to which the bridge is connected. When the bridge receives a frame, the bridge examines the destination address to determine if the frame is to be sent to a different segment or dropped. The bridge also helps to improve the flow of data by keeping frames confined to only the segment to which the frame belongs. Switches, shown in Figure 2, are sometimes called multiport bridges. A typical bridge has two ports, linking two segments of the same network. A switch has several ports, depending on how many network segments are to be linked. A switch is a more sophisticated device than a bridge. In modern networks, switches have replaced hubs as the central point of connectivity. Like a hub, the speed of the switch determines the maximum speed of the network. However, switches filter and segment network traffic by sending data only to the device to which it is sent. This provides higher dedicated bandwidth to each device on the network. Switches maintain a switching table. The switching table contains a list of all MAC addresses on the network, and a list of which switch port can be used to reach a device with a given MAC address. The switching table records MAC addresses by inspecting the source MAC address of every incoming frame, as well as the port on which the frame arrives. The switch then creates a switching table that maps MAC addresses to outgoing ports. When a frame arrives that is destined for a particular MAC address, the switch uses the switching table to determine which port to use to reach the MAC address. The frame is forwarded from the port to the destination. By sending frames out of only one port to the destination, other ports are not affected. Power over Ethernet (PoE) A PoE switch transfers small amounts of DC current over Ethernet cable, along with data, to power PoE devices. Low voltage devices that support PoE, such as Wi-Fi access points, surveillance video devices, and NICs, can be powered from remote locations. Devices that support PoE can receive power over an Ethernet connection at distances up to 330 ft (100 m) away.

Modems

To support the immediate delivery of the millions of messages being exchanged between people all over the world, we rely on a web of interconnected networks. The standardization of the various elements of the network enables equipment and devices created by different companies to work together. It is important that IT technicians understand the purpose and function of different network equipment used to support personal and business operations. A modem is an electronic device that connects to the Internet via an ISP. The modem converts digital data to analog signals for transmission over a phone line. Because the analog signals change gradually and continuously, they can be drawn as waves. In this system, the digital signals are represented as binary bits. The digital signals must be converted to a waveform to travel across telephone lines. They are converted back to bits by the receiving modem so that the receiving computer can process the data. The modem at the receiving end reconverts the analog signals back to digital data to be interpreted by the computer. The process of converting analog signals to digital and back again is called modulation/demodulation. The accuracy of modem-based transmission has increased with the development of error detection and correction protocols, which has reduced or eliminated the effects of noise and interference on telephone lines. An internal modem plugs into an expansion slot on the motherboard. External modems connect to a computer through the serial and USB ports. Software drivers must be installed and connection ports configured for the modem to work properly. When computers use the public telephone system to communicate, it is called Dialup Networking (DUN). Modems communicate with each other using audio tone signals. This means that modems are able to duplicate the dialing characteristics of a telephone. DUN creates a Point-to-Point Protocol (PPP). A PPP is simply a connection between two computers over a phone line.

VoIP Phones

Voice over IP (VoIP) is a method to carry telephone calls over the data networks and Internet. VoIP converts the analog signals of voices into digital information that is transported in IP packets. VoIP can also use an existing IP network to provide access to the public switched telephone network (PSTN). VoIP phones look like normal phones, but instead of using the standard RJ-11 phone connector, they use an RJ-45 Ethernet connector. VoIP phones connect directly to a network and have all the hardware and software necessary to handle the IP communications. When using VoIP to connect to the PSTN, you might be dependent on an Internet connection. This can be a disadvantage if the Internet connection experiences an interruption in service. When a service interruption occurs, the user cannot make phone calls. There are several ways to use VoIP: IP phone - A device that connects to an IP network using an RJ-45 Ethernet connector or a wireless connection. Analog Telephone Adapter (ATA) - A device that connects standard analog devices, such as telephones, facsimile machines, or answering machines, to an IP network. IP phone software - This application connects by using a microphone, speakers, and a sound card to emulate the IP phone functionality.

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. A telephone conversation is an example of full-duplex communication. Both people can talk and be heard at the same time. Full-duplex networking technology increases network performance because data can be sent and received at the same time. Broadband technologies, such as digital subscriber line (DSL) and cable, operate in full-duplex mode. Broadband technology allows multiple signals to travel on the same wire simultaneously. With a DSL connection, for example, users can download data to the computer and talk on the telephone at the same time.

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.

Routers and Wireless Access Points

When subscribing to an ISP, determine what type of equipment is available to select the most appropriate device. An ISP is a company that provides Internet services to individuals and businesses. An ISP usually provides a connection to the Internet, email accounts, and web pages, for a monthly service fee. Some ISPs rent equipment on a month-to-month basis. This could be more attractive than purchasing the equipment because the ISP supports the equipment if there is a failure, change, or upgrade to the technology. Equipment that can be used to connect to an ISP is shown in Figure 1. Wireless Access Points Wireless access points, shown in Figure 2, provide network access to wireless devices, such as laptops and tablets. The wireless access point uses radio waves to communicate with the wireless NIC in the devices and other wireless access points. An access point has a limited range of coverage. Large networks require several access points to provide adequate wireless coverage. A wireless access point provides connectivity only to the network, while a wireless router provides additional features, such as assigning IP addresses. Routers Routers connect networks to each other. Switches use MAC addresses to forward a frame within a single network. Routers use IP addresses to forward packets to other networks. A router can be a computer with special network software installed or a device built by network equipment manufacturers. On a corporate network, one router port connects to the WAN connection and the other ports connect to the corporate LANs. The router becomes the gateway, or path to the outside, for the LAN. Multipurpose Devices Multipurpose devices, shown in Figure 3, are network devices that perform more than one function. It is more convenient to purchase and configure one device that serves all your needs than to purchase a separate device for each function. This is especially true for the home user. In a home network, the router connects the computers and network devices in the home to the Internet. The router serves as a home gateway and a switch. The wireless router serves as a home gateway, wireless access point, and a switch. Multipurpose devices may also include a modem.

IPv6

Working with 128-bit numbers is difficult, so the IPv6 address notation represents the 128 bits as 32 hexadecimal values. The 32 hexadecimal values are further subdivided into eight fields of four hexadecimal values, using colons as delimiters. Each field of four hexadecimal values is called a block. The IPv6 address has a three-part hierarchy, as shown in Figure 1. The global prefix, also called a site prefix, is the first three blocks of the address and is assigned to an organization by an Internet names registry. The subnet ID includes the fourth block of the address, and the interface ID includes the last four blocks of the address. The network administrator controls both the subnet and interface ID. As an example, if a host has an IPv6 address 3ffe:6a88:85a3:08d3:1319:8a2e:0370:7344, the global prefix address is 3ffe:6a88:85a3, the subnet ID address is 08d3, and the interface ID address is 1319:8a2e:0370:7344. An IPv6 address can be abbreviated with the following rules: Omit leading zeroes in a 16-bit value. Replace one group of consecutive zeroes by a double colon. Figure 2 is an example of how these rules are applied.

kb/s

kilobits per second

b/s

bits per second

Gb/s

gigabits per second