There are two types of topology: physical and logical. The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Logical topology is the method used to pass the information between workstations. Issues involving logical topologies are discussed in the section on protocols.

Main Types of Physical TopologiesThe following sections discuss the physical topologies used in networks and other related topics.

Linear Bus Star Star-Wired Ring Tree Considerations When Choosing a Topology Summary Chart

Linear BusA linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and LocalTalk networks use a linear bus topology.

Fig. 1. Linear Bus topology

Advantages of a Linear Bus Topology

Easy to connect a computer or peripheral to a linear bus. Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

Entire network shuts down if there is a break in the main cable. Terminators are required at both ends of the backbone cable. Difficult to identify the problem if the entire network shuts down. Not meant to be used as a stand-alone solution in a large building.

Star A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator (See fig. 2).

Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called the star-wired ring.

Fig.2. Star topology

Advantages of a Star Topology

Easy to install and wire.

No disruptions to the network when connecting or removing devices. Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

Requires more cable length than a linear topology. If the hub or concentrator fails, nodes attached are disabled. More expensive than linear bus topologies because of the cost of the

concentrators.

Star-Wired RingA star-wired ring topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring (See fig. 3). The Token Ring protocol uses a star-wired ring topology.

Fig.3. Star-wired ring topology

TreeA tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 4). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Fig.4. Tree topology

Advantages of a Tree Topology

Point-to-point wiring for individual segments. Supported by several hardware and software venders.

Disadvantages of a Tree Topology

Overall length of each segment is limited by the type of cabling used. If the backbone line breaks, the entire segment goes down. More difficult to configure and wire than other topologies.

5-4-3 Rule

A consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule. One aspect of the Ethernet protocol requires that a signal sent out on the network cable reach every part of the network within a specified length of time. Each concentrator or repeater that a signal goes through adds a small amount of time. This leads to the rule that between any two nodes on the network there can only be a maximum of 5 segments, connected through 4 repeaters/concentrators. In addition, only 3 of the segments may be populated (trunk) segments if they are made of coaxial cable. A populated segment is one which has one or more nodes attached to it . In Figure 4, the 5-4-3 rule is adhered to. The furthest two nodes on the network have 4 segments and 3 repeaters/concentrators between them.

This rule does not apply to other network protocols or Ethernet networks where all fiber optic cabling is used.

Considerations When Choosing a Topology:

Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.

Length of cable needed. The linear bus network uses shorter lengths of cable. Future growth. With a star topology, expanding a network is easily done by

adding another concentrator. Cable type. The most common cable in schools is unshielded twisted pair, which

is most often used with star topologies.

Summary Chart:

Physical Topology Common Cable Common Protocol

Linear BusCoaxTwisted PairFiber

EthernetLocalTalk

Star Twisted PairFiber

EthernetLocalTalk

Star-Wired Ring Twisted Pair Token Ring

TreeCoaxTwisted PairFiber

Ethernet

Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.

The following sections discuss the types of cables used in networks and other related topics.

Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable Coaxial Cable Fiber Optic Cable Wireless LANs Installing Cable - Some Guidelines

Unshielded Twisted Pair (UTP) CableTwisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1).

Fig.1. Unshielded twisted pair

The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.

Categories of Unshielded Twisted Pair

Type UseCategory 1 Voice Only (Telephone Wire)Category 2 Data to 4 Mbps (LocalTalk)Category 3 Data to 10 Mbps (Ethernet)Category 4 Data to 20 Mbps (16 Mbps Token Ring)Category 5 Data to 100 Mbps (Fast Ethernet)

One difference between the different categories of UTP is the tightness of the twisting of the copper pairs. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. Buy the best cable you can afford; most schools purchase Category 3 or Category 5. Category 5 cable is highly recommended.

If you are designing a 10 Mbps Ethernet network and are considering the cost savings of buying Category 3 wire instead of Category 5, remember that the Category 5 cable will provide more "room to grow" as transmission technologies increase. Both category 3 and category 5 UTP have a maximum segment length of 100 meters. In Florida, Category 5 cable is required for retrofit grants. 10BaseT refers to the specifications for unshielded twisted pair cable (category 3, 4, or 5) carrying Ethernet signals.

Unshielded Twisted Pair Connector

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

Fig.2. RJ-45 connector

Shielded Twisted Pair (STP) CableA disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology.

Coaxial CableCoaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

Fig.3. Coaxial cable

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are: thick coaxial and thin coaxial.

Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum

segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable is popular in school networks, especially linear bus networks.

Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

Coaxial Cable Connectors

The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather than screw, onto the cable.

Fig.4. BNC connector

Fiber Optic CableFiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals, eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.

Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.

Fig.5. Fiber optic cable

Facts about fiber optic cables:

Outer insulating jacket is made of Teflon or PVC. Kevlar fiber helps to strengthen the cable and prevent breakage. A plastic coating is used to cushion the fiber center. Center (core) is made of glass or plastic fibers.

Fiber Optic Connector

The most common connector used with fiber optic cable is an ST connector. It is barrel shaped, similar to a BNC connector. A newer connector, the SC, is becoming more popular. It has a squared face and is easier to connect in a confined space.

Ethernet Cable Summary

Specification Cable Type Maximum length10BaseT Unshielded Twisted Pair 100 meters10Base2 Thin Coaxial 185 meters10Base5 Thick Coaxial 500 meters10BaseF Fiber Optic 2000 meters

Wireless LANsNot all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals or infrared light beams to communicate between the workstations and the file server. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology or by satellite.

Wireless networks are great for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.

Wireless LANs also have some disadvantages. They are very expensive, provide poor security, and are susceptible to electrical interference from lights and radios. They are also slower than LANs using cabling.

Installing Cable - Some Guidelines

When running cable, it is best to follow a few simple rules:

Always use more cable than you need. Leave plenty of slack. Test every part of a network as you install it. Even if it is brand new, it may have

problems that will be difficult to isolate later. Stay at least 3 feet away from fluorescent light boxes and other sources of

electrical interference. If it is necessary to run cable across the floor, cover the cable with cable

protectors. Label both ends of each cable. Use cable ties (not tape) to keep cables in the same location together.

A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a

network: access method, allowed physical topologies, types of cabling, and speed of data transfer. See the Topology and Cabling sections of this tutorial for more information.

The most common protocols are:

Ethernet LocalTalk Token Ring FDDI

EthernetThe Ethernet protocol is by far the most widely used. Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system where each computer listens to the cable before sending anything through the network. If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computer will wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same instant. When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit. With this access method, it is normal to have collisions. However, the delay caused by collisions and retransmitting is very small and does not normally effect the speed of transmission on the network.

The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted over twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps.

Fast Ethernet

To allow for an increased speed of transmission, the Ethernet protocol has developed a new standard that supports 100 Mbps. This is commonly called Fast Ethernet. Fast Ethernet requires the use of different, more expensive network concentrators/hubs and network interface cards. In addition, category 5 twisted pair or fiber optic cable is necessary.

LocalTalkLocalTalk is a network protocol that was developed by Apple Computer, Inc. for Macintosh computers. The method used by LocalTalk is called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). It is similar to CSMA/CD except that a computer signals its intent to transmit before it actually does so. LocalTalk adapters and special twisted pair cable can be used to connect a series of computers through the serial port. The Macintosh operating system allows the establishment of a peer-to-peer network without the need for additional software. With the addition of the server version of AppleShare software, a client/server network can be established.

The LocalTalk protocol allows for linear bus, star, or tree topologies using twisted pair cable. A primary disadvantage of LocalTalk is speed. Its speed of transmission is only 230 Kbps.

Token RingThe Token Ring protocol was developed by IBM in the mid-1980s. The access method used involves token-passing. In Token Ring, the computers are connected so that the signal travels around the network from one computer to another in a logical ring. A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant. At this point, the data is captured by the receiving computer. The Token Ring protocol requires a star-wired ring using twisted pair or fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to the increasing popularity of Ethernet, the use of Token Ring in school environments has decreased.

FDDIFiber Distributed Data Interface (FDDI) is a network protocol that is used primarily to interconnect two or more local area networks, often over large distances. The access method used by FDDI involves token-passing. FDDI uses a dual ring physical topology. Transmission normally occurs on one of the rings; however, if a break occurs, the system keeps information moving by automatically using portions of the second ring to create a new complete ring. A major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps.

Protocol Summary

Protocol Cable Speed TopologyEthernet Twisted Pair, Coaxial, Fiber 10 Mbps Linear Bus, Star, TreeFast Ethernet Twisted Pair, Fiber 100 Mbps StarLocalTalk Twisted Pair .23 Mbps Linear Bus or StarToken Ring Twisted Pair 4 Mbps - 16 Mbps Star-Wired RingFDDI Fiber 100 Mbps Dual ring

Networking hardware includes all computers, peripherals, interface cards and other equipment needed to perform data-processing and communications within the network.

This section provides information on the following components:

File Servers

Workstations

Network Interface Cards

Concentrators/Hubs

Repeaters

Bridges

Routers

File Servers

A file server stands at the heart of most networks. It is a very fast computer with a large amount of RAM and storage space, along with a fast network interface card. The network operating system software resides on this computer, along with any software applications and data files that need to be shared.

The file server controls the communication of information between the nodes on a network. For example, it may be asked to send a word processor program to one workstation, receive a database file from another workstation, and store an e-mail message during the same time period. This requires a computer that can store a lot of information and share it very quickly. File servers should have at least the following characteristics:

75 megahertz or faster microprocessor (Pentium, PowerPC) A fast hard drive with at least four gigabytes of storage A RAID (Redundant Array of Inexpensive Disks) to preserve data after a disk

casualty A tape back-up unit Numerous expansion slots Fast network interface card At least of 32 MB of RAM

WorkstationsAll of the computers connected to the file server on a network are called workstations. A typical workstation is a computer that is configured with a network interface card, networking software, and the appropriate cables. Workstations do not necessarily need floppy disk drives or hard drives because files can be saved on the file server. Almost any computer can serve as a network workstation.

Network Interface CardsThe network interface card (NIC) provides the physical connection between the network and the computer workstation. Most NICs are internal, with the card fitting into an expansion slot inside the computer. Some computers, such as Mac Classics, use external boxes which are attached to a serial port or a SCSI port. Laptop computers generally use external LAN adapters connected to the parallel port or network cards that slip into a PCMCIA slot.

Network interface cards are a major factor in determining the speed and performance of a network. It is a good idea to use the fastest network card available for the type of workstation you are using.

The three most common network interface connections are Ethernet cards, LocalTalk connectors, and Token Ring cards. According to a International Data Corporation study, Ethernet is the most popular, followed by Token Ring and LocalTalk (Sant'Angelo, R. (1995). NetWare Unleashed, Indianapolis, IN: Sams Publishing).

Ethernet Cards

Ethernet cards are usually purchased separately from a computer, although many computers (such as the Macintosh) now include an option for a pre-installed Ethernet card. Ethernet cards contain connections for either coaxial or twisted pair cables (or both) (See fig. 1). If it is designed for coaxial cable, the connection will be BNC. If it is designed for twisted pair, it will have a RJ-45 connection. Some Ethernet cards also contain an AUI connector. This can be used to attach coaxial, twisted pair, or fiber optics cable to an Ethernet card. When this method is used there is always an external transceiver attached to the workstation. (See the Cabling section for more information on connectors.)

Fig. 1. Ethernet card.From top to bottom:

RJ-45, AUI, and BNC connectors

LocalTalk Connectors

LocalTalk is Apple's built-in solution for networking Macintosh computers. It utilizes a special adapter box and a cable that plugs into the printer port of a Macintosh (See fig. 2). A major disadvantage of LocalTalk is that it is slow in comparison to Ethernet. Most Ethernet connections operate at 10 Mbps (Megabits per second). In contrast, LocalTalk operates at only 230 Kbps (or .23 Mbps).

Fig.2. LocalTalk connectors

Ethernet Cards vs. LocalTalk ConnectionsEthernet LocalTalk

Fast data transfer (10 Mbps) Slow data transfer (.23 Mbps) Expensive - purchased separately Built into Macintosh computers Requires computer slot No computer slot necessary Available for most computers Works only on Macintosh computers

Token Ring Cards

Token Ring network cards look similar to Ethernet cards. One visible difference is the type of connector on the back end of the card. Token Ring cards generally have a nine pin DIN type connector to attach the card to the network cable.

Concentrators/HubsA concentrator is a device that provides a central connection point for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central concentrator. Hubs are multislot concentrators into which can be plugged a number of multi-port cards to provide additional access as the network grows in size. Some concentrators are passive, that is they allow the signal to pass from one computer to another without any change. Most concentrators are active, that is they electrically amplify the signal as it moves from one device to another. Active concentrators are used like repeaters to extend the length of a network. Concentrators are:

Usually configured with 8, 12, or 24 RJ-45 ports Often used in a star or star-wired ring topology Sold with specialized software for port management Also called hubs Usually installed in a standardized metal rack that also may store netmodems,

bridges, or routers

RepeatersWhen a signal travels along a cable, it tends to lose strength. A repeater is a device that boosts a network's signal as it passes through. The repeater does this by electrically amplifying the signal it receives and rebroadcasting it. Repeaters can be separate devices or they can be incorporated into a concentrator. They are used when the total length of your network cable exceeds the standards set for the type of cable being used.

A good example of the use of repeaters would be in a local area network using a star topology with unshielded twisted-pair cabling. The length limit for unshielded twisted-pair cable is 100 meters. The most common configuration is for each workstation to be connected by twisted-pair cable to a multi-port active concentrator. The concentrator regenerates all the signals that pass through it allowing for the total length of cable on the network to exceed the 100 meter limit.

BridgesA bridge is a device that allows you to segment a large network into two smaller, more efficient networks. If you are adding to an older wiring scheme and want the new network to be up-to-date, a bridge can connect the two.

A bridge monitors the information traffic on both sides of the network so that it can pass packets of information to the correct location. Most bridges can "listen" to the network and automatically figure out the address of each computer on both sides of the bridge. The bridge can inspect each message and, if necessary, broadcast it on the other side of the network.

The bridge manages the traffic to maintain optimum performance on both sides of the network. You might say that the bridge is like a traffic cop at a busy intersection during rush hour. It keeps information flowing on both sides of the network, but it does not allow unnecessary traffic through. Bridges can be used to connect different types of cabling, or physical topologies. They must, however, be used between networks with the same protocol.

RoutersA router translates information from one network to another; it is similar to a superintelligent bridge. Routers select the best path to route a message, based on the destination address and origin. The router can direct traffic to prevent head-on collisions, and is smart enough to know when to direct traffic along back roads and shortcuts.

While bridges know the addresses of all computers on each side of the network, routers know the addresses of computers, bridges, and other routers on the network. Routers can

even "listen" to the entire network to determine which sections are busiest -- they can then redirect data around those sections until they clear up.

If you have a school LAN that you want to connect to the Internet, you will need to purchase a router. In this case, the router serves as the translator between the information on your LAN and the Internet. It also determines the best route to send the data over the Internet. Routers can:

Direct signal traffic efficiently Route messages between any two protocols Route messages between linear bus, star, and star-wired ring topologies Route messages across fiber optic, coaxial, and twisted-pair cabling

Summary

Click on the thumbnail picture for a review of the hardware components of a network.

Network Operating Systems

Unlike operating systems, such as DOS and Windows95, that are designed for single users to control one computer, network operating systems (NOS) coordinate the activities of multiple computers across a network. The network operating system acts as a director to keep the network running smoothly.

The two major types of network operating systems are:

Peer-to-Peer Client/Server

Peer-to-Peer

Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source (See fig. 1). In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Peer-to-peer networks are designed primarily for small to medium local area networks. AppleShare and Windows for Workgroups are examples of programs that can function as peer-to-peer network operating systems.

Fig.1. Peer-to-peer network

Advantages of a peer-to-peer network:

Less initial expense - No need for a dedicated server. Setup - An operating system (such as Windows 95) already in place may only

need to be reconfigured for peer-to-peer operations.

Disadvantages of a peer-to-peer network:

Decentralized - No central repository for files and applications. Security - Does not provide the security available on a client/server network.

Client/ServerClient/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers (See fig. 2). The file servers become the heart of the system, providing access to resources and providing security. Individual workstations (clients) have access to the resources available on the file servers. The network operating system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location. Novell Netware and Windows NT Server are examples of client/server network operating systems.

Fig.2. Client/server network

Advantages of a client/server network:

Centralized - Resources and data security are controlled through the server. Scalability - Any or all elements can be replaced individually as needs increase. Flexibility - New technology can be easily integrated into system. Interoperability - All components (client/network/server) work together. Accessibility - Server can be accessed remotely and across multiple platforms.

Disadvantages of a client/server network:

Expense - Requires initial investment in dedicated server. Maintenance - Large networks will require a staff to ensure efficient operation. Dependence - When server goes down, operations will cease across the network.

Examples of network operating systemsThe following list includes some of the more popular peer-to-peer and client/server network operating systems.

Microsoft Windows 95 / 98 Microsoft Windows NT Server Microsoft Windows NT Work Station

 

10Base2 - Ethernet specification for thin coaxial cable, transmits signals at 10 Mbps (megabits per second) with a distance limit of 185 meters per segment.

10Base5 - Ethernet specification for thick coaxial cable, transmits signals at 10 Mbps (megabits per second) with a distance limit of 500 meters per segment.

10BaseF - Ethernet specification for fiber optic cable, transmits signals at 10 Mbps (megabits per second) with a distance limit of 1000 meters per segment.

10BaseT - Ethernet specification for unshielded twisted pair cable (category 3, 4, or 5), transmits signals at 10 Mbps (megabits per second) with a distance limit of 100 meters per segment.

Access Method - Rules that govern how nodes on a network access the cable.

AppleTalk - Apple Computer's network protocol originally designed to run over LocalTalk networks, but can also run on Ethernet and Token Ring.

AUI Connector (Attachment Unit Interface) - A 15 pin connector found on Ethernet cards that can be used for attaching coaxial, fiber optic, or twisted pair cable.

Backbone - A cable to which multiple nodes or workstations are attached.

Bit - Binary digit in the binary numbering system. Its value can be 0 or 1. In an 8-bit character scheme, it takes 8 bits to make a byte (character) of data.

BNC Connector (Bayone-Neill-Concelman) - Standard connector used to connect 10Base2 coaxial cable.

Bridge - Devices that connect and pass packets between two network segments that use the same communications protocol.

Cable - Transmission medium of copper wire or optical fiber wrapped in a protective cover.

Client/Server - A networking system in which one or more file servers (Server) provide services; such as network management, application and centralized data storage for workstations (Clients).

CSMA/CA - Carrier Sense Multiple Access Collision Avoidance is a network access method in which each device signals its intent to transmit before it actually does so. This prevents other devices from sending information, thus preventing collisions from occurring between signals from two or more devices. This is the access method used by LocalTalk.

CSMA/CD - Carrier Sense Multiple Access Collision Detection is a network access method in which devices that are ready to transmit data first check the channel for a carrier. If no carrier is sensed, a device can transmit. If two devices transmit at once, a

collision occurs and each computer backs off and waits a random amount of time before attempting to retransmit. This is the access method used by Ethernet.

Coaxial Cable - Cable consisting of a single copper conductor in the center surrounded by a plastic layer for insulation and a braided metal outer shield.

Concentrator - A device that provides a central connection point for cables from workstations, servers, and peripherals. Most concentrators contain the ability to amplify the electrical signal they receive.

Dumb Terminal - Refers to devices that are designed to communicate exclusively with a host (main frame) computer. It receives all screen layouts from the host computer and sends all keyboard entry to the host. It cannot function without the host computer.

E-Mail - An electronic mail message sent from a host computer to a remote computer.

End User - Refers to the human executing applications on the workstation.

Ethernet - A network protocol invented by Xerox Corporation and developed jointly by Xerox, Intel and Digital Equipment Corporation. Ethernet networks use CSMA/CD and run over a variety of cable types at 10 Mbps (megabits per second).

Expansion Slot - Area in a computer that accepts additional input/output boards to increase the capability of the computer.

Fast Ethernet - A new Ethernet standard that supports 100 Mbps using category 5 twisted pair or fiber optic cable.

Fiber Optic Cable - A cable, consisting of a center glass core surrounded by layers of plastic, that transmits data using light rather than electricity. It has the ability to carry more information over much longer distances.

File Server - A computer connected to the network that contains primary files/applications and shares them as requested with the other computers on the network. If the file server is dedicated for that purpose only, it is connected to a client/server network. An example of a client/server network is Novell Netware. All the computers connected to a peer-to-peer network are capable of being the file server. Two examples of peer-to-peer networks are LANtastic and Windows for Workgroups.

Gigabyte (GB) - One billion bytes of information. One thousand megabytes.

Hub - A hardware device that contains multiple independent but connected modules of network and internetwork equipment. Hubs can be active (where they repeat signals sent through them) or passive (where they do not repeat but merely split signals sent through them).

Infrared - Electromagnetic waves whose frequency range is above that of microwaves, but below that of the visible spectrum.

Internet - A global network of networks used to exchange information using the TCP/IP protocol. It allows for electronic mail and the accessing and retrieval of information from remote sources.

LAN (Local Area Network) - A network connecting computers in a relatively small area such as a building.

Linear Bus - A network topology in which each node attaches directly to a common cable.

LocalTalk - Apple Corporation proprietary protocol that uses CSMA/CA media access scheme and supports transmissions at speeds of 230 Kbps (Kilobits per second).

MAN (Metropolitan Area Network) - A network connecting computers over a large geographical area, such as a city or school district.

MAU (Multistation Access Unit) - A Token Ring wiring hub.

Modem (Modulator/Demodulator) - Devices that convert digital and analog signals. Modems allow computer data (digital) to be transmitted over voice-grade telephone lines (analog).

Multiplexer - A device that allows multiple logical signals to be transmitted simultaneously across a single physical channel.

Network Modem - A modem connected to a Local Area Network (LAN) that is accessible from any workstation on the network.

Network Interface Card (NIC) - A board that provides network communication capabilities to and from a computer.

Network Operating System (NOS) - Operating system designed to pass information and communicate between more than one computer. Examples include AppleShare, Novell NetWare, and Windows NT Server.

Node - End point of a network connection. Nodes include any device attached to a network such as file servers, printers, or workstations.

Node Devices - Any computer or peripheral that is connected to the network.

PCMCIA - An expansion slot found in many laptop computers.

Peer-to-Peer Network - A network in which resources and files are shared without a centralized management source.

Physical Topology - The physical layout of the network; how the cables are arranged; and how the computers are connected.

Point-to-Point - A direct link between two objects in a network.

Ports - A connection point for a cable.

Protocol -A formal description of a set of rules and conventions that govern how devices on a network exchange information.

RAID (Redundant Array of Inexpensive Disks) - A configuration of multiple disks designed to preserve data after a disk casualty.

RAM (Random Access Memory) - The working memory of a computer where data and programs are temporarily stored. RAM only holds information when the computer is on.

Repeater - A device used in a network to strengthen a signal as it is passed along the network cable.

RJ-45 - Standard connectors used for unshielded twisted-pair cable.

Router -A device that routes information between interconnected networks. It can select the best path to route a message, as well as translate information from one network to another. It is similar to a superintelligent bridge.

Segment - Refers to a section of cable on a network. In Ethernet networks, two types of segments are defined. A populated or trunk segment is a network cable that has one or more nodes attached to it. A link segment is a cable that connects a computer to an interconnecting device, such as a repeater or concentrator, or connects a interconnecting device to another interconnecting device.

Sneaker-Net - Refers to a manual method of sharing files in which a file is copied from a computer to a floppy disk, transported to a second computer by a person physically walking (apparently wearing sneakers) to the second computer, and manually transferring the file from floppy disk to the second computer.

Speed of Data Transfer - The rate at which information travels through a network, usually measured in megabits per second.

Star Topology - LAN topology in which each node on a network is connected directly to a central network hub or concentrator.

Star-Wired Ring - Network topology that connects network devices (such as computers and printers) in a complete circle.

Tape Back-Up - Copying all the data and programs of a computer system on magnetic tape. On tape, data is stored sequentially. When retrieving data, the tape is searched from the beginning of tape until the data is found.

Terminator - A device that provides electrical resistance at the end of a transmission line. Its function is to absorb signals on the line, thereby keeping them from bouncing back and being received again by the network.

Token - A special packet that contains data and acts as a messenger or carrier between each computer and device on a ring topology. Each computer must wait for the messenger to stop at its node before it can send data over the network.

Token Ring - A network protocol developed by IBM in which computers access the network through token-passing. Usually uses a star-wired ring topology.

Transceiver (Transmitter/Receiver) - A Device that receives and sends signals over a medium. In networks, it is generally used to allow for the connection between two different types of cable connectors, such as AUI and RJ-45.

Tree Topology - LAN topology similar to linear bus topology, except that tree networks can contain branches with multiple nodes.

Twisted Pair - Network cabling that consists of four pairs of wires that are manufactured with the wires twisted to certain specifications. Available in shielded and unshielded versions.

WAN (Wide Area Network) - A network connecting computers within very large areas, such as states, countries, and the world.

Workgroup - A collection of workstations and servers on a LAN that are designated to communicate and exchange data with one another.

Workstation - A computer connected to a network at which users interact with software stored on the network.

Computer Networking Tutorials Overview

In this section you will learn about basic networking tutorials, lan, wan, ethernet, wireless technology, basic topologies, internet, intranet, extranet and VLAN technology. Computer networking is the engineering concerned with communication between computers. A general definition of the computer networking is that two or more computers connected together to share data and resources. Two devices or computers are connected together and are separated by a distance of few meters like Bluetooth technology or unlimited such as internet.

Examples of the computer network are LAN, MAN, WAN and internet. Internet is the largest computer network.

Ethernet

Ethernet is a large frame based computer network technology for the local area networks. The name Ethernet comes from physical concept of Ether which defines a number of wiring and signaling standards for the physical layer. Ethernet has been standardized as IEEE 802.3 and its star-topology twisted pair wiring became the most wide spread network type till present. Ethernet technology replaced the old networking technologies such as coaxial cable Ethernet, token ring, ARCNET and FDDI.

 

How to Build a Computer Network

A Simple Network

A simple computer network may be developed from two or more computers. Each computer will require a NIC card and a special cable known as a cross over cable. If the computers are more than two then a specialized networking device known as hub or switch will be required and all the computers in a network will be connected with the hub or switch. A simple network is useful for home networking. Additionally, a network between the two computers can be established by using a standard connection such as Rs-232 serial port on both computers connecting with each other by a special cross lined null modem cable.

Practical Networks

Practical networks generally consist of more than two computers and require specialized devices along with the NIC cards and these devices can be hubs, modems, switches, routers and others.

Common Types of Networks:

Following is the list of the common computer networking types.

 

LAN (Local Area Network):

A network that is limited to a relatively small geographical area such as a room, building, school network, ship, aircraft or a small office. LANs are also known as single location networks. The large LANs may be divided into the smaller logical segments known as workgroups.

CAN (Campus Area Network):

A network that connects two or more small LANs and is limited to a specific geographical area, such as a school, college, university campus or a military base, is known as a CAN. A CAN is generally confined to an area that is smaller than a Metropolitan area network.

MAN (Metropolitan Area Network):

A network that connects two or more LANs or CANs within a geographical area in a town, city or a metropolitan area is known as a MAN. A number or communication devices are required to create a MAN such as routers, switches, hubs and modems etc.

WAN (Wide Area Networks):

A WAN is a data communication network type that covers a very large geographical area. WAN networks can be privately owned such as a multi national company network or publically own such as internet. WAN technology generally functions at the lower three layers of the OSI model. Internet is the best example of WAN. There are two main types of WAN centralized and distributed WAN. The centralized WAN consists of a central computer that is connected to the dumb terminal or other types of the communication devices, such as a bank and post office networks. The distributed WAN consists of two or more computers that are physically placed at different locations and may also include connections to dumb terminal and other connecting devices.

Internetwork:

Two or more networks or connecting together using communication devices such as router. Any interconnection between private, commercial, public or government network may also be defined as internetwork. A specific internetwork consists of international interconnection of government, public and private networks.

Intranet:

An internetwork or a network that is limited to a single organization and uses TCP/IP protocol suite, HTTP, FTP and other protocols. Intranet can be categorized into LAN, MAN, CAN and WAN. Intranet is a company’s private network that is only accessible to the authorized users.

Extranet:

Extranet is a combination of intranet and some other trusted networks. For example a company’s customer may be provided access to the intranet, creating an intranet and while at the same time the customer may not be considered trusted with regards to the security of the company. An extranet can also be categorized into CAN, MAN and WAN and by definition extranet cannot be considered to consist of only a single LAN. An extranet must have at least one connection the extra network. Intranet and extranet may also have the connections to the internet. But only the authorized users can enter into the extranet internet plays a role only of a portal.

VLAN

A virtual LAN commonly known as VLAN is a method of creating independent logical networks within a physically network. Many Vlans can consist in a physical network. Vans help in reducing the broadcast domain and aids in network administration by separating the logical segments of a LAN. VLANS behaves as if connected to the same wire even though they may actually be physically connected to the different segments of a LAN. VLANs can be configured with software rather than hardware. One main advantage of the VLAN is that when computers are physically moved from one location to another, they can stay on the same VLAN without the reconfiguration of the hardware and software.

TYPES OF TOPOLOGY

Linear Bus

Ethernet and local talk networks use linear bus topology. In Linear Bus topology, each device is directly connected to the linear cable.

Star

In the star topology each node such as computers, file server, workstations and peripheral devices are directly connected to the centralized device known as hub or switch. Data in the star topology passes through the hub or switch before it reaches to the destination. Hub or concentrators also act as repeaters for the data flow. Twisted pair cable, coaxial cable, and fiber optic cables can be used. Star wired topology appears to the same as star topology. The Token Ring protocol uses star-wired ring topology.

Tree

Tree topology is the combination of the linear bus and star topology. Linear Bus consists of the star configured workstations connected to the Linear Bus backbone cable.

Token Ring

Token Ring was developed by several manufactures and it is used for high traffic network loadings. Ethernet now has taken the popularity of the Token Rings.

Networking Hardware

Numerous types of the computer networking hardware is used develop a computer network such as Routers, hubs, workstations, NIC cards, servers, firewall, switches, bridges, modems, local talk connectors, UTP/STP cables and many other types of basic and advance communication hardware.

An Overview of Computer Network Topology

Here you will learn network topology introduction, how computers get connected, bus, star, hub, hybrid, mesh, tree topologies and network physical design. In Computer Networking “topology” refers to the layout or design of the connected devices. Network Topologies can be physical or logical. In this section I will illustrate on the different types of the topologies.

 

 

Physical Topology means the physical design of a network including the devices, location and cable installation.

Logical Topology refers to the fact that how data actually transfers in a network as opposed to its design.

Topology can be considered as a virtual shape or structure of a network. This shape actually does not correspond to the actual physical design of the devices on the computer network. The computers on the home network can be arranged in a circle shape but it does not necessarily mean that it presents a ring topology.

 

Computer network topologies can be categorized in the following categories.• bus • star • ring• mesh • Tree.Hybrid networks are the complex networks, which can be built of two or more above mentioned topologies.

Bus Topology

Bus topology uses a common backbone to connect all the network devices in a network in a linear shape. A single cable functions as the shared communication medium for all the devices attached with this cable with an interface connector. The device, which wants to communicate send the broadcast message to all the devices attached with the shared cable but only the intended recipient actually accepts and process that message.

Ethernet bus topologies are easy to install and don’t require much cabling and only a main shared cable is used for network communication. 10Base-2 and 10BaseT are two popular types of the Ethernet cables used in the Bus topology. Also, Bus network works with very limited devices. Performance issues are likely to occur in the Bus topology if more than 12-15 computers are added in a Bus Network. Additionally, if the Backbone cable fails then all network becomes useless and no communication fails among all the computers. Unlike in the Star topology in which if one computer is detached from a network then there is not effect on the other computers in a network.

Ring Topology

In ring Network, every computer or devices has two adjacent neighbors for communication. In a ring network, all the communication messages travel in the same directory whether clockwise or anti clockwise. Any damage of the cable of any cable or device can result in the breakdown of the whole network. Ring topology now has become almost obsolete. FDDI, SONET or Token Ring Technology can be used to implement Ring Technology. Ring topologies can be found in office, school or small buildings.

Star Topology

In the computer networking world the most commonly used topology in LAN is the star topology. Star topologies can be implemented in home, offices or even in a building. All the computers in the star topologies are connected to central devices like hub, switch or router. The functionality of all these devices is different. I have covered the detail of each networking devices in the separate portion of my website. Computers in a network are usually connected with the hub, switch or router with the Unshielded Twisted Pair (UTP) or Shielded Twisted Pair Cables.

As compared to the bus topology, a star network requires more devices & cables to complete anetwork. The failure of each node or cable in a star network, won’t take down the entire network

as compared to the Bus topology.

However if the central connecting devices such as hub, switch or router fails due to any reason,then ultimately all the network can come down or collapse.

Tree Topology

 

Tree topologies are comprised of the multiple star topologies on a bus. Tree topologies integrate multiple star topologies together onto a bus. Only the hub devices can connect directly with the tree bus and each Hub functions as a root of a tree of the network devices. This bus/star/hybrid combination supports future expandability of the computer networks, much better than a bus or star.

Mesh Topology

Mesh topology work on the concept of routes. In Mesh topology, message sent to the destination can take any possible shortest, easiest route to reach its destination. In the previous topologies star and bus, messages are usually broadcasted to every computer, especially in bus topology. Similarly in the Ring topology message can travel in only one direction i.e clockwise or anticlockwise. Internet employs the Mesh topology and the message finds its route for its destination. Router works in find the routes for the messages and in reaching them to their destinations.The topology in which every devices connects to every other device is called a full Mesh topology unlike in the partial mesh in which every device is indirectly connected to the other devices.

Summary

Topologies are the important part of the network design theory. A better network can be built if you have the knowledge of these topologies and if you know the difference between each topology. Similarly you should have the knowledge of each network device so that you can properly use them according to your network needs. A misconfigured network can result in a waste of time and energy as well as a lots of troubleshooting methods to resolve the issue. So thebasic understanding of the network topologies and network devices is a must to build a good network.

An Overview of the Wireless Networking

Here you will find wireless networking tutorials, what is wifi, general security overview, wlans, wpans, wmans, wep and wireless access control overview. Whether you want to make a phone call from your mobile, received a message on your pager, checked your email from a PDA we have come across a wireless data or voice network.  

If a user or a company wants to make a data portable then Wireless networking is the answer. A wireless networking system can avoid the downtime, which may be caused in the wired network. A wireless network is also save your time and efforts in installing the lot of cables.

Also, if you need to relocate a client machine in your office, you only need to move the computer with wireless network card.

 

Wireless networking is very useful in the public places, libraries, hotels, schools, airports, railway stations where one might find wireless access to the internet. A drawback in the wireless internet is that quality of service (QOS) is not guaranteed if there is any interference then the connection may be dropped.

Wireless Network Types

Wireless Local Area Networks (WLANS)

WLANS allow users in local area, such as in a university or a library to form a network and gain wireless access to the internet. A temporary network can be formed by a small number of users without the need of access point; given that they do not need to access the resources.

Wireless Personal Area Networks (WPANS)

There are two current technologies for wireless personal network Bluetooth and Infra Red. These technologies will allow the connectivity of personal devices within an area of 30 feet. Infra Red requires a direct line and the range is less as compared to Bluetooth technology.

Wireless Metropolitan Area Networks (WMANS)

WMANS allow the connectivity of multiple networks in a metropolitan area such as building in a city. The network connectivity is the alternative of copper or fiber cabling.

Wireless Wide Area Networks (WWANS)

WWANS or Wireless Area Networks can be maintained over large areas such as in different cities or between different countries, via multiple satellite systems or antenna sites. The types of system are called 2G systems. The following table shows the range those different types of wireless network covers.Network Meter Personal Area Network 0-10Local Area Network 0-100Wide Are Network 0-10000Security in Wireless NetworkingThe following different types of security methods are available in the wireless networking.

Wired Equivalent Privacy (WEP)

Wired Equivalent Privacy is intended to stop the interference of radio frequency that is signaled by unauthorized users and this security measure is most suitable for the small networks. There is not key management protocol and each key is entered manually into the clients that’s why this is very time consuming administrative task. The WEP security

 

method is based on the RC4 encryption algorithm. In the WEP all the client computers and Access points are configured with the same encryption and decryption keys.

Service Set Identifier (SSID)

Service Set Identifier (SSID) acts a simple password by allowing WLAN network to be split up into different networks and each having a unique identifier. These identifiers are configured in the multiple access points. To access any of any networks, a computer is configured in such a way that each is having a corresponding SSID identifier for that network. If the SSID match between the two computers or networks then access is granted to each other.

Media Access Control filtering (MAC Access Control)

A list of the MAC addresses of the client computers can be inputted into an Access point and only those computers are granted to give the access to the network. When a computer makes a request, its MAC address is compared to the list of the MAC addresses to the Access point and based on this access permission granted to deny.This is a good security method but it is mainly involved in the small wireless networks because there is more manual work is involved of entering the MAC address into the Access point.

Bluetooth

Bluetooth is a simple type of the wireless networking that operates in the digital devices, like mobiles phones, personal computers, PDA, Laptops, digital camera, MP3 players and other Bluetooth enabled devices to form a small network. In the Bluetooth technology eight devices can be connected to each other at the same time. Bluetooth can also be found in the headsets, hands-free kits, wireless keyboards and mouse. Bluetooth technology was invented by Ericsson in 1994 and after four years in 1998 some major mobile phone companies such as Nokia, Ericsson, Intel and Toshiba formed a group to promote this technology.

Bluetooth technology falls in the category of personal area networking because it operates in the range of 30 to 300 feet. Bluetooth uses the radio waves technology, which is not very expensive and has low power consumption. Many different companies are intended to add the Bluetooth chip in their digital devices. Bluetooth technology is getting very popularity because of its low cost and portability.

The Future of Wireless Networking

WLANS wireless networking type is very popular in home networking and more than 20 percent homes with broadband internet are using WLANS and this number is increasing. In a general estimate worldwide hotspots have now reached more than 30,000 and will grow about 210,000 in the next few years. Most large hotels already offer Wi-Fi and the business travelers are willing to pay wireless access. 802.11 is the next Wi-Fi speed

standard is set to offer bandwidth around 108Mbps and is still under development. With the speed of 70 Mbps and a range up to 30 miles, the 80216 standard, known as WiMAX is sure to get boost.

Some Tips & Tricks

• When purchasing a wireless NIC card try to get one that is having external antenna. When you are out and using Wi-Fi enabled laptop, disable Microsoft file and sharing, which enables other computers in a network to access data and resources on your computer. In this way, your computer or laptop will be saved from hackers.• If you are concerned about the interference from the other wireless access point set the AP and wireless computers to use a non-overlapping channel.• Change the configuration interface password of the access point before you enable it. • Only buy an access point that is having upgradeable capabilities. By this way you can take the advantage of security enhancements. • Keep the access point up to date.

What is a Web Server?

Learn Web server software overview, how to configure, how it works, apache, tomcat. Web server is a computer including a software package that provides the specific services to the client computers. Web server delivers the web pages. Every web server has an IP address and a domain name. If you sends a request through your browser for this website http://www.networktutorials.info, the request goes to the server whose domain name is networktutorials.info.  

The server fetches the index or main page of the website and sends it to your browser. Web-based servers are used for hosting the websites. One web server can hosts thousands for one sites. But in the hosting companies there are number of the web servers for load balancing and sharing the other services.

A computer can be act as a web server by installing and configuring the server software and connecting the computer to the Internet. Normally, web server computers have to be turn on (online) for almost all the day.

 

There are many software applications that are used as the web server like IIS, Apache web server, Tom Cat web server. A web server typically accepts thousands of the concurrent incoming requests for the specific domain, that it hosts.

In case if the server is down for any reason, the websites that are hosted on this server cannot be accessed. So the downtime is a biggest negative thing for the web hosting companies. Many hosting companies have to mention the uptime of their servers for the client’s satisfactions like 99.9 % uptime. You may have seen this percentage on many hosting companies’ websites.

The web servers serves the objects in the form of html documents, plain text, images, sounds, video and some other form of the data. Many of the data types may not be placed in the static form but they are shown on the run time by the software programs, that are installed on the web server and the CGI scripts are the most common form of these programs.

Web servers and the browsers such as internet explorer, Firefox, Netscape, Opera etc communicate with the web server by using the HTTP protocols (Hypertext Transfer Protocol). This is very effective method of requesting the data over the Internet. Web servers are in various shapes and sized and run under different operating systems like Windows, Linux, and Unix etc. They are also range differently in prices and working.

Apache Web Server

The Apache web server is the most popular and most commonly used web server today. Apache web server has many features and good functionality that appeals to the users and that’s major cause of its popularity. On the other end, Microsoft’s IIS still is struggling to complete fully with apache web server. IIS is a very good server on the NT platforms and Apache is compatible with the Linux/Unix platforms.

Another big reason for the worldwide acceptance of the Apache web server is its stability. Many big websites on the Internet has chosen Apache web server for their hosting needs. Additionally, Apache web server is a relatively fast. If your website contents are static then Apache’s working is very efficient and fast and on the other end, if you are using scripts like CGI scripts or others, it usually slows down the speed of the Apache web server.A Web server is simply a little piece of the software, it takes the file name sent in the GET command, retrieves that files and send it back to the browser.

Most servers implement some level of security on the serving process. For example login/password accessible page requires the proper login and password from the users to accept that page. Web servers have the database and login information of the entire subscriber and only a subscriber of that typical service will be able to see that page. Additionally, while doing secure transactions the web pages allows encrypted transactions between the browsers and the servers such as on the E-commerce websites and other websites where a transaction through a credit card is required.

Basic Overview How Web Server Works

A web server performs various tasks on the request from the clients. To understand the working of the web server, it is necessary to first understand that what is client and server and what is their relationship with each other. A client is a program that sends request to a server and server responds to the requests of the clients.

 

This generic definition covers many types of relationships between client and servers like database server & web server etc. Web server have to be connected to the internet because client computers need to access them for various needs like data, files, graphics, video and html documents access.

The client program such as browsers and typically designed for the purpose of communicating with the web servers. A browser itself has different levels of features and security. To start the communication between the client (browser) and the server, a set of rules or agreed upon way is required and that is called a protocol. To access the web pages from the server HTTP protocol is required and for the file sharing access FTP protocol is required. There are a large number of the web protocols.

A web server is configured and designed in such a way that it responds to the thousands of the concurrent incoming requests from the clients for different things like html documents, graphics, images or video etc.

Internet Protocol Tutorial

IP Address Notation - What Is An IP Address?

IPv4 and IPv6

Internet Protocol (IP) technology was developed in the 1970s to support some of the first research computer networks. Today, IP has become a worldwide standard for home and business networking as well. Our network routers, Web browsers, email programs, instant messaging software - all rely on IP or other network protocols layered on top of IP.

Two versions of IP technology exist today. Essentially all home computer networks use IP version 4 (IPv4), but an increasing number of educational and research institutions have adopted the next generation IP version 6 (IPv6).

IPv4 Addressing Notation

An IPv4 address consists of four bytes (32 bits). These bytes are also known as octets.

For readability purposes, humans typically work with IP addresses in a notation called dotted decimal. This notation places periods between each of the four numbers (octets) that comprise an IP address. For example, an IP address that computers see as

00001010 00000000 00000000 00000001 is written in dotted decimal as

10.0.0.1 Because each byte contains 8 bits, each octet in an IP address ranges in value from a minimum of 0 to a maximum of 255. Therefore, the full range of IP addresses is from

0.0.0.0 through 255.255.255.255. That represents a total of 4,294,967,296 possible IP addreses.

IPv6 Addressing Notation

IP addresses change significantly with IPv6. IPv6 addresses are 16 bytes (128 bits) long rather than four bytes (32 bits). This larger size means that IPv6 supports more than

300,000,000,000,000,000,000,000,000,000,000,000,000 possible addresses! In the coming years, as an increasing number of cell phones, PDAs, and other consumer electronics expand their networking capability, the smaller IPv4 address space will likely run out and IPv6 address become necessary.

IPv6 addresses are generally written in the following form:

hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh In this full notation, pairs of IPv6 bytes are separated by a colon and each byte in turns is represented as a pair of hexadecimal numbers, like in the following example:

E3D7:0000:0000:0000:51F4:9BC8:C0A8:6420 As shown above, IPv6 addresses commonly contain many bytes with a zero value.Shorthand notation in IPv6 removes these values from the text representation (though the bytes are still present in the actual network address) as follows:

E3D7::51F4:9BC8:C0A8:6420 Finally, many IPv6 addresses are extensions of IPv4 addresses. In these cases, the rightmost four bytes of an IPv6 address (the rightmost two byte pairs) may be rewritten in the IPv4 notation. Converting the above example to mixed notation yields

E3D7::51F4:9BC8:192.168.100.32 IPv6 addresses may be written in any of the full, shorthand or mixed notation illustrated above.Internet Protocol Tutorial Classes of IP Addresses, IP Broadcast and IP Multicast

IPv4 Address ClassesThe IPv4 address space can be subdivided into 5 classes - Class A, B, C, D and E. Each class consists of a contiguous subset of the overall IPv4 address range.

With a few special exceptions explained further below, the values of the leftmost four bits of an IPv4 address determine its class as follows:

Class Leftmost bits Start address Finish addressA 0xxx 0.0.0.0 127.255.255.255B 10xx 128.0.0.0 191.255.255.255C 110x 192.0.0.0 223.255.255.255D 1110 224.0.0.0 239.255.255.255E 1111 240.0.0.0 255.255.255.255

All Class C addresses, for example, have the leftmost three bits set to '110', but each of the remaining 29 bits may be set to either '0' or '1' independently (as represented by an x in these bit positions):

110xxxxx xxxxxxxx xxxxxxxx xxxxxxxx Converting the above to dotted decimal notation, it follows that all Class C addresses fall in the range from 192.0.0.0 through 223.255.255.255.

IP Address Class E and Limited BroadcastThe IPv4 networking standard defines Class E addresses as reserved, meaning that they should not be used on IP networks. Some research organizations use Class E addresses for experimental purposes. However, nodes that try to use these addresses on the Internet will be unable to communicate properly.

A special type of IP address is the limited broadcast address 255.255.255.255. A broadcast involves delivering a message from one sender to many recipients. Senders direct an IP broadcast to 255.255.255.255 to indicate all other nodes on the local network (LAN) should pick up that message. This broadcast is 'limited' in that it does not reach every node on the Internet, only nodes on the LAN.

Technically, IP reserves the entire range of addresses from 255.0.0.0 through 255.255.255.255 for broadcast, and this range should not be considered part of the normal Class E range.

IP Address Class D and MulticastThe IPv4 networking standard defines Class D addresses as reserved for multicast. Multicast is a mechanism for defining groups of nodes and sending IP messages to that group rather than to every node on the LAN (broadcast) or just one other node (unicast).

Multicast is mainly used on research networks. As with Class E, Class D addresses should not be used by ordinary nodes on the Internet.

IP Address Class A, Class B, and Class CClass A, Class B, and Class C are the three classes of addresses used on IP networks in common practice, with three exceptions as explained next.