Bus

Ring

Star

LAN topologies fall into four types of configurations:

Mesh

Figure 6-1: Star, Bus, Ring, and Mesh Configurations

Figure 6-2: Primary/Secondary Ring Topologies

Figure 6-3: Logical Topologies

Figure 6-4: A Network Switch Connection

Figure 6-5: Segmenting a Network

Figure 6-6: Network Bridges

Copper cabling

Fiber-optic cabling

Infrared light

Basically, four media are used to transmit data between computers:

Wireless radio frequency (RF) signals

Simplex mode - Data is only transmitted in one direction.

Half Duplex mode - Data can be transmitted in both direction, but only in one direction at a time.

There are three basic transmission modes for transmitting data:

Full Duplex mode - Data can be transmitted in both directions at the same time. This effectively doubles the operating speed of a connection using this mode.

Figure 6-7: UTP and STP Cabling

Table 6-1: Tip and Ring Wiring

Table 6-2: UTP Cable Category Ratings

Figure 6-8: UTP Cable Connection Specifications

Figure 6-9: IDC Connection

Figure 6-10: Coaxial Cable

RG-6

Coaxial cables are categorized according to their size (diameter), shielding and core construction, type of dielectric, impedance, velocity factor, fire rating, and attenuation rating.

RG-8

RG-58

RG-59

Figure 6-11: Thicknet Connections

Figure 6-12: Transmitting Over Fiber-Optic Cable

Multimode Fiber-Optic Cable

Two basic types of fiber-optic cabling used in networking applications:

Single-Mode Fiber-Optic Cable

Figure 6-13: Fiber-Optic Cable Connectors

Figure 6-14: Small Form Factor Fiber Connectors

Figure 6-15: IrDA Networking

Figure 6-16: A Wireless LAN

Installation flexibility

The fundamental pros and cons associated with wireless networking:

Services for mobile users

Security issues

Services for mobile users

Multipath problems and signal strength

As a peer-to-peer network where each computer is attached to the network in a ring or bus fashion and is equal to the other units on the network.

11

As a client/server network where dependent workstations, referred to as clients, operate in conjunction with a dedicated master computer (file server).

22

Control of a network can be implemented in two ways:

Figure 6-17: A Peer-to-Peer Network

Figure 6-18: A Client/Server Network

Centralized administration

Data and resource security

The major advantages of the client/server networking arrangement include:

Limitations of Ethernet - The Ethernet Limitations of Ethernet - The Ethernet strategy provides for up to 1024 users to strategy provides for up to 1024 users to share the LAN. From the description of share the LAN. From the description of its collision-recovery technique, however, its collision-recovery technique, however, it should be apparent that with more it should be apparent that with more users on an Ethernet LAN, more users on an Ethernet LAN, more collisions are likely to occur, and the collisions are likely to occur, and the average time to complete an actual data average time to complete an actual data transfer will be longer.transfer will be longer.

A preamble

The frame carries the following six sections of information:

A destination address

An originating address

A type field

The data field

The frame check error-detection and correction information

Figure 6-20: A Typical Ethernet Frame

Coaxial cable

Ethernet is classified as a bus topology that has been implemented across several different network media, including:

Twisted-pair copper cable

Fiber-optic cable

Wireless RF

Figure 6-21: Typical Coax and UTP Connections

Figure 6-22: UTP Network Connectivity Device

Table 6-3: Ethernet Specifications

Figure 6-24: A Typical LAN Card

WARNINGWARNING

Use the user guide - Although some cards may have jumper instructions printed directly on them, the card’s user manual is normally required to configure it for operation. Great care should be taken with the user manual, because its loss might render the card useless. At the very least, the manufacturer would have to be contacted to get a replacement.

Figure 6-26: Connecting the Computer to the LAN

Figure 6-27: Crossover Cabling

MDI (media dependent interface) - This connection requires an external crossover (either the cable or the other hub must perform the crossover function).

MIDX (media independent interface crossover) - This type of connection can be switched so that the port performs the crossover function. This allows a straight-through cable to be used to make the connection when engaged.

The markings that are used to identify straight-through and crossover cables are:

HTTP: The protocol, or service, that will be accessed.

The URL consists of the following parts:

help.com: The server name (also called the host name or domain name) that is accessed for files.

/documents/: The directory path from which one, or many, specific files may be accessed.

security.txt: The name of the file to be accessed.

The World Wide Web (WWW) is a The World Wide Web (WWW) is a menu system that ties together Internet menu system that ties together Internet resources from around the world. These resources from around the world. These resources are scattered across computer resources are scattered across computer systems everywhere. Web servers systems everywhere. Web servers inventory the Web’s resources and store inventory the Web’s resources and store address pointers, referred to as links, to address pointers, referred to as links, to them. them.

The hypertext transfer protocol (HTTP) is used to access linked documents on the World Wide Web. The documents are prepared with the hypertext markup language (HTML).

Typical Internet resources include:

(continued)

The hypertext transfer protocol secure (HTTPS) is used to access linked documents on the World Wide Web that are located on a secure server. A secure server typically requires that a password be entered before access is granted. In some applications, https:// means that documents are encrypted (using the Secure Socket Layer protocol as described in detail later in this chapter) before sending them to a user that connects to the secure site.

Typical Internet resources include: (continued)

(continued)

The file transfer protocol (FTP) is used to copy files to and from a remote server. When a URL has the ftp:// prefix, it means that the user is accessing a site from which files can be downloaded or uploaded.

Typical Internet resources include: (continued)

(continued)

The mailto: prefix is used to access an e-mail server. Once the e-mail server is accessed (usually after entering a username and password), the e-mail application is started, and the user can read or write e-mail.

The news: prefix starts the newsgroup application on the Internet. A newsgroup is a bulletin board arranged by specific discussion group titles such as the Internet, Networking, or Computers. There are thousands of newsgroups on the Internet.

Typical Internet resources include: (continued)

(continued)

The gopher:// prefix is used to access the database area of the Internet. Largely replaced by the World Wide Web, Gopher consists of a series of linked menu items.

The telnet:// prefix is used to connect a user to a remote server. Once the connection is established, the user has access to software or tools located on the server. When telnet is specified, a separate telnet application begins on the user’s workstation. Like Gopher, telnet is being used less and less. Network operating systems like Windows NT and Novell NetWare contain remote access services that have largely replaced telnet.

Typical Internet resources include: (continued)

(continued)

The simple mail transfer protocol (SMTP) is used to send e-mail across the Internet. E-mail uses conventions that are somewhat different than those used with other services.

Typical Internet resources include: (continued)

(continued)

The file:// prefix is used to access a file on a local server that supports Internet applications. For example, assume the URL http://inet.com/document/help.txt is accessed. Once the help.txt file is open, it may include references to other documents on the inet.com server. The file:// prefix can be used to directly connect to one of the other documents.

Typical Internet resources include: (continued)

Figure 6-50:Netscape Navigator Home Page

Memorize the Internet-related abbreviations and acronyms.

Figure 6-51: Internet Explorer Home Page

KEY POINTSKEY POINTS

Local area networks (LANs) are systems designed to connect computers together in a relatively close proximity. These connections allow users attached to the network to share resources, such as printers and modems. LAN connections also allow users to communicate with each other and share data between their computers.

KEY POINTSKEY POINTS

Control of the network can be implemented in two ways: as peer-to-peer networks, in which each computer is equal to the other units on the network, or as client/server networks, in which dependent workstations (referred to as clients) operate in conjunction with a dedicated master computer (server).

KEY POINTSKEY POINTS

In a network, some method must be used to determine which node has use of the network’s communications paths, and for how long it can have it. The network’s protocol handles these functions, and it is necessary to prevent more than one user from accessing the bus at any given time.

KEY POINTSKEY POINTS

The Ethernet strategy allows up to 1024 users to share the LAN. However, from the description of its collision-recovery technique, it should be clear that with more users on an Ethernet LAN, more collisions are likely to occur, and the average time to complete an actual data transfer will be longer.

KEY POINTSKEY POINTS

Ethernet is classified as a bus topology. The original Ethernet scheme was classified as a 10 Mbps transmission protocol. The maximum length specified for Ethernet is 1.55 miles (2.5 km), with a maximum segment length between nodes of 500 meters. This type of LAN is referred to as a 10Base-5 LAN by the IEEE organization.

KEY POINTSKEY POINTS

In a LAN, each computer on the net requires a network adapter card (also referred to as a NIC), and every unit is connected to the network by some type of cabling. These cables are typically either twisted-pair wires, thick or thin coaxial cable, or fiber-optic cable.

KEY POINTSKEY POINTS

In its simplest form, a modem consists of two major blocks, a modulator and a demodulator. The modulator is a transmitter that converts the parallel/digital computer data into a serial/analog format for transmission. The demodulator is the receiver that accepts the serial/analog transmission format and converts it into a parallel/digital format usable by the computer, or peripheral.

KEY POINTSKEY POINTS

The standard telephone system accommodates a range of frequencies between 300 and 3300 Hz, or a bandwidth of 3000 Hz. This is quite adequate to transmit voice, but severely distorts digital data. In order to use the audio characteristics of the phone lines to their best advantage, the modem encodes the digital 1s and 0s into analog signals within this bandwidth.

KEY POINTSKEY POINTS

In order to maintain an orderly flow of information between the computer and the modem, and between the modem and another modem, a protocol, or set of rules governing the transfer of information, must be in place. All of the participants in the “conversation” must use the same protocols to communicate.

KEY POINTSKEY POINTS

A wide area network is similar in concept to a widely distributed client/server LAN. In a wide area network, computers are typically separated by distances that must be serviced via modems instead of network cards.

KEY POINTSKEY POINTS

The most famous wide area network is the Internet. The Internet is actually a network of networks working together. The main communication path for the Internet is a series of networks, established by the U.S. government, to link supercomputers together at key research sites.

KEY POINTSKEY POINTS

Connecting all of the users and individual networks together are Internet service providers (ISPs). ISPs are companies that provide the technical gateway to the Internet. These companies own blocks of access addresses that they assign to their customers to give them an identity on the network.

KEY POINTSKEY POINTS

The IP addresses of all the computers attached to the Internet are tracked using a listing system called the Domain Name Service (DNS). This system evolved as a method of organizing the members of the Internet into a hierarchical management structure.

KEY POINTSKEY POINTS

The TCP/IP protocol divides the transmission into packets of information, suitable for retransmission across the Internet. Along the way, the information passes through different networks that are organized at different levels. Depending on the routing scheme, the packets may move through the Internet using different routes to get to the intended address. At the destination, however, the packets are reassembled into the original transmission.

KEY POINTSKEY POINTS

ISDN service offers high-speed access to the public telephone system. However, ISDN service requires digital modems, also referred to as terminal adapters. Not only does the end user require a digital modem, the telephone company’s switch gear equipment must be updated to handle digital switching. This fact has slowed implementation of ISDN services until recently.

KEY POINTSKEY POINTS

A special application, called the file transfer protocol (FTP), is used to upload and download information to, and from, the Internet.

KEY POINTSKEY POINTS

One of the most widely used functions of wide area networks is the electronic mail (e-mail) feature. This feature allows Internet users to send, and receive, electronic messages to and from each other over the Internet.

KEY POINTSKEY POINTS

The World Wide Web (WWW) is a menu system that ties together Internet resources from around the world. These resources are scattered across computer systems everywhere. Web servers inventory the Web’s resources and store address pointers, referred to as links, to them.

KEY POINTSKEY POINTS

As the Internet has grown, service providers have continued to provide more user-friendly software for exploring the World Wide Web. These software packages are called browsers and are based on hypertext links.