TN 103 Lecture1
Content
TN103: INTRODUCTION TO NETWORKING
Instructors:
Mtaho Adam Paschal Charles
Course objective: • To introduce students to computer networks and their classification. • To introduce students to networking media with emphasis on LAN cabling. • To introduce students to Ethernet technologies and their standards. • To introduce to students principles of computer networks communication and devices .
Course objective: • To introduce students to computer networks and their classification. • To introduce students to networking media with emphasis on LAN cabling. • To introduce students to Ethernet technologies and their standards. • To introduce to students principles of computer networks communication and devices .
Course objectives cont.. • To introduce students to the basics of fiber optic cabling. • To introduce and sensitize students on computer networks security.
Recommended References/text books 1. 2. 3. 4. 5. 6.
Computer Networks and Intenets, Douglas E. Conner, PrenticeHall, 1997. Data and Computer Communications, 5/e, William Stallings, Prentice-Hall, 1996. Computer Networks, 3/e, Andrew S. Tanenbaum, PrenticeHall, 1996. Data Communication. Computer Networks and Open Systems, Fourth Edition, Fred Halsall, Addison – Wesley, 1996. Snader, J. C. (2000). Effective TCP/IP programming: 44 tips to improve your network programs. Upper Saddle River, NJ: Addison-Wesley. ISBN 0-201-61589-4. Stevens, W.R. (1998) UNIX network programming, volume 1: Networking APIs - sockets and XTI, 2/e. Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-216987-8.
Course content Introduction
to Networking: networks classification basics, peer-to-peer networks,LANs, Wireless LANs, VLANs and WANs, Intranet, Internet, Extranet, peerto-peer,client server, hybrid models.
• Networking Media fundamentals: evolution of networking media, merits and demerits of different media, UTP,
Course content cont.. • STP, Fibre, wireless; different types of connectors,UTPcable preparation, UTP cable Testing. Ethernet Fundamentals:
Technologies and Protocols, Ethernet old, fast Ethernet, Gigabit Ethernet, NIC, MAC address (unicast, multicast, broadcast);
Course content cont.. Network communication principles :
Configuration (computer name, domains, work groups), Routing, TCP/IP Protocol Suite & IP Addressing (Static or Dynamic).
Internetworking
devices: repeater , hub, switch, router, gateway, bridge.
• Fibre optic cabling: types of fibres, mode of transmission, splicing, connectors and termination, structured cabling;
Course content cont.. Cable
testing: Fibre; LAN technologies: Token ring, ARCnet, Ethernet, FDDI, WLAN;
Media
Access method: CSMA/CD, CSMA/CA, access control, collision, performance limitation, methods to reduce collisions,
Network
security: firewalls, AAA servers.
Computer Networks What is a network? Connection of two or more devices for the purpose of exchanging signal or communication ∗
∗
What is computer network? Computer network is the network where by two or more computers have been connected for the purpose of exchanging data and sharing resources such as ∗
Computer Networks • Printers, Scanners, CD-ROMs, exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.
Communication Networks • What are communication networks and what advantages do they offer? • A network, or a communication network , is a system of interconnected computers, telephones, or other communication devices that can communicate with one another and share applications and data. • It is the tying together of so many communication devices in so many ways that is changing the world we live in. • A network requires various devices, and a network operating software
Advantages of Computer Network • Sharing of resources – Allows sharing of resources such printers, disk storage, scanners, modems and central serves
• Faster data sharing – Transferring files across a network is always faster than other non-network means of data transfer.
Advantages of Computer Network • Efficient communication – Electronic mail, project monitoring, online conferencing, etc, can lead to better communication between workgroups and help improve productivity. • Keeping information reliable and up-to-date – A well managed, centralized data storage system allows multiple users from different locations to access data and limits the access to data when it is being processed. • It saves cost-as application programs can only be installed in central computer and shared by all other connected computers.
Disadvantages of Computer Network • If the central computer shared by other networked computer fail, all other users will be unable to run applications programs • If the operating system of the network stops, hardware and software resources cannot be accessed. • Unless properly designed, as traffic on the network increases, network performance degrades. • Network require high skilled system or network administrator for management of it, otherwise it cannot operate efficiently.
TYPES OF COMPUTER NETWORKS • Networks may be divided into different types and categories according to four different criteria:
.
TYPES OF COMPUTER NETWORKS
A:
According to geographic area of nodes and hosts
A1-PERSONAL AREA NETWORK(PAN) • Is a computer network organized around an individual person. • A PAN is a network that is used for communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room • It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet. • PAN’s can be wired or wireless
A2-Local Area Network(LAN) • Local Area Network (LAN) is a computer network that connect computers and other devices in a limited geographic area such as home,school,computer lab, office building. Rarely are LAN computers more than a mile apart. • In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations.
A2-Local Area Network(LAN) • The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LANs, cables are used to connect the network interface cards in each computer.
A3-Metropolitan Area Network (MAN) • Metropolitan Area Network (MAN) is a computer network that connect computers and other devices in a limited geographic area such as city or large campus. • Metropolitan Area Networks (MANs) fall between LANs and WANs in geographic area. • Higher speed than LANs (155 Mbps and above) • Cover a larger area (such as a city) • Mostly using fiber as the transmission media
A4-Wide Area Network(WAN) • Wide Area Network (WAN) is a computer network that connect computers and other devices in a limited geographic area such as country. • Used to connect LANs and other types of network together, so that users and computers in one location can communicate with users and computers in other location.
Differences between WAN& LAN FEATURE
LAN
WAN
Scale of sharing
Less and limited
Far greater and worldwide.
Communication media
Use cable such Coaxial and UTP
Satellite, microwaves or telecommunicatio n links
Installation cost
low
high
Network coverageSmall area, about Cities, states and 1Mile range countries
B: according to access restrictions • Private • Public
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B1-Private Networks • Most networks are for the private use of the organizations to which they belong; these are called private networks. Networks maintained by banks, insurance companies, airlines, hospitals, and most other businesses are of this nature.
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B2-Public Networks • Public networks, on the other hand, are generally accessible to the average user, but may require registration and payment of connection fees. • Internet is the most-widely known example of a public network. Technically, both private and public networks may be of LAN, MAN, or WAN type, although public networks, by their size and nature, tend to WANs.
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VPN: Virtual Private Network • From the user’s point-of-view, a VPN looks like a secure, private network • VPNs use public telecom infrastructure, maintaining privacy through security procedures.
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VPN: Virtual Private Network • VPNs provide secure network connections for distance computers without using dedicated, private channels to supply the connection. • Key benefit of VPNs over conventional PNs: Lower cost
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C: According to communication model employed by the nodes. • The communication between the nodes is either based on a point-to-point model or a broadcast model • In the point-to-point model, a message follows a specific route across the network in order to get from one node to another • In the broadcast model, on the other hand, all nodes share the same communication medium and, as a result, a message transmitted by any node can be received by all other nodes
broadcast model • A part of the message (an address) indicates for which node the message is intended. All nodes look at this address and ignore the message if it does not match their own address.
According to communication model employed by the nodes point-to-point model and broadcast model
D: According to switching model employed by the nodes. • Circuit switching Vs Packet switching. • Suppose that a host A wishes to communicate with another host B. In circuit switching, a dedicated communication path is allocated between A and B, via a set of intermediate nodes. The data is sent along the path as a continuous stream of bits. This path is maintained for the duration of communication between A and B, and is then released.
Circuit switching Vs Packet switching • In packet switching, data is divided into packets (chunks of specific length and characteristics) which are sent from A to B via intermediate nodes. • Each intermediate node temporarily stores the packet and waits for the receiving node to become available to receive it. Because data is sent in packets, it is not necessary to reserve a path across the network for the duration of communication between A and B.
Circuit switching Vs Packet switching • Different packets can be routed differently in order to spread the load between the nodes and improve performance. • However, this requires packets to carry additional addressing information.
Wireless LANs: • Wireless LANs: – Are used to connect LAN's without the additional cost or inconvenience of wiring a building. – LAN radio uses radio transmissions to interconnect LAN components. – Infrared uses beams of infrared light to establish network links between LAN components. – Wireless LAN technology makes LANs easy to set up, relocate, and maintain. • Disadvantages: – High initial costs
Wireless LANs… • Not all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs • 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…
Wireless LANs have several disadvantages. They provide poor security, and are susceptible to interference from lights and electronic devices. They are also slower than LANs using cabling
INTERNET • WAN & IP (Internet Protocol) • A collection of networks interconnected and function as a single worldwide network is known as INTERNET • WAN is used for interconnection;
INTRANET
• Network within organization
Components of a LAN….. • LANs are made up of several standard components/ hardware, software and other accessories • Connection or cabling system: wired (twisted-pair cable, coaxial or fiber optic cable) or wireless (infrared and radio-wave transmission). • Microcomputers/workstations with interface cards
COMPONENTS OF LAN…
– Network operating system-software – Network Interface Cards ,Routers – Switch, Bridges – Repeater, Hubs – Gateways, Modems
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Components of a LAN • Network operating system-software that manages the activity of the network-providing multi-user and multitasking capabilities • Unlike operating systems, such as DOS and Windows, 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. • Other shared devices can be printers, fax machines, scanners, storage devices and other peripherals
Components of a LAN • A repeater is a device that regenerates and amplifies signals to create long-distance networks • A switch is a high-speed multi-port bridge. Today, switches are replacing multi-port repeaters or concentrators in a UTP environment. • An intelligent hub that maintains a bridging table, keeping track of which hardware addresses are located on which network segment • Server- a computer with higher hard disk and higher speed than any other computer on the network.
Components of a LAN • There are various types of servers which can be connected in LANs, such as File server, Printer server, etc.
A File Server • A File server is a high capacity computer that provides various resources to the network. • A file server has the following characteristics – Needs a very fast computer with a large amount of RAM and storage space, a fast network interface card, and a tape back-up device – Needs network operating system such as Novell Netware, Windows NT server, or Apple Share – Controls the communication of information between the nodes on a network
Network Interface Cards (NICs)
• Network Interface Card-NIC provides the link between your computer and your network. • provide the physical connection between the network and the workstation.
Network Interface Cards • The 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. • Laptop computers can now be purchased with a network interface card built-in • 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.
Switch • A concentrator is a device that provides a central connection point for cables from workstations, servers, and peripherals. So, a switch is a concentrator. • In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. • Switches no longer broadcast network packets as hubs did in the past, they memorize addressing of computers and send the information to the correct location directly. Switches 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
Repeaters • Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts 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 Metroporitan area network using a star topology with unshielded twisted-pair cabling. The length limit for unshielded twisted-pair cable is 100 meters.
Repeaters • The most common configuration is for each workstation to be connected by twisted-pair cable to a multi-port active concentrator. The concentrator amplifies all the signals that pass through it allowing for the total length of cable on the network to exceed the 100 meter limit.
Bridges • A 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.
Bridges • 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 • Used to form a connection between two separate, but similar networks
Routers • A router translates information from one network to another; it is similar to a super intelligent 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 head-on collisions, and is smart enough to know when to direct traffic along back back roads roads and and shortc shortcuts. uts. • 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 • 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 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.
Router • A special-purpose computer that directs data traffic when several paths are available • A router examines the destination info in each arriving packet and then routes it through the most efficient path available • The router either delivers the packet to the destination computer across a local network or forwards or forwards the packet to another router that router that is closer to the final destination
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Gateway • Device sitting at the network node for interfacing with another network that uses different protocol. • LAN’s may use a gateway (or router) to connect to the Internet.
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Workstations • All of the user computers connected to 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 because files can be saved on the file server. Almost any computer can serve as a network workstation.
Network Hardware/Components
Communication Channels/Media • What is communication channel/Media? – Is a path-the physical medium- over which data travels in a telecommunication systems from its source to its destination. Channels are also called links, lines or media • Types of communication channels • Physical channel • transmit data through the cable or wire. – Use solid medium to connect sending and receiving devices. • Wireless media
Twisted pair Cable • Consist of two insulated copper wires arranged in a regular spiral pattern to minimize interference. • Advantages – low cost, small size, and ease of installation • Disadvantages – Suffers from electromagnetic interference(EMI) between adjacent pairs – low frequency transmission medium – limited distance, usually less than 100 meters • Uses: the most popular and is generally the best option for school networks
Twisted Cable
• Twisted pair cabling comes in two varieties: Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP)
Unshielded twisted pair (UTP) • Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks • 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 tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.
Unshielded twisted pair (UTP) • The standard connector for unshielded twisted pair cabling is an RJ-45 connector
• A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference
Shielded Twisted Pair (STP)
• 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 Cable • Coaxial cable resembles the wire used to connect a TV or VCR • Has an inner conductor surrounded by a braided mesh • Both conductors share a common center axial, hence the term "co-axial" • Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers .
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.
Coaxial Cable • Advantages: • bandw bandwidth idth of up to 400 400 Mhz Mhz – highly resistant to signal interference – Transfer voice and data faster than twisted pair cable • Disadvantage – quite bulky and sometimes difficult to install • Uses: used for connecting parts of LAN over long distance (300-600 meters)
Fiber Optic Cable • Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. 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. • 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 possibili possibilities ties to inclu include de servic services es such such as as video video conferencing and interactive services
Fiber Optic Cable • The most common connector used with fiber optic cable is an ST ST connector. It is barrel shaped, similar to a BNC connector
Fiber Optic Cable • Consists of a center glass core surrounded by several layers of protective materials • Advantages – immunity to environmental interference – greater capacity (bandwidth of up to 2 Gbps) – carry information at vastly greater speeds
Fiber Optic Cable • Disadvantages – very expensive – small size and lighter weight – difficult to install and modify, require highly skilled installers – adding additional nodes is difficult • 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals • Uses: used for distances up to 100 kilometers
LANs Topology • Network can be laid out in different ways . The physical layout, or shape, of a network is called a topology. • Network topology can be physical or logical design • Physical topology refer to physical design of network which includes devices, cables, location and installation of network. • Logical topology refer to the amount of data to be transferred within the network.
LANs Topology • There are Six basic network topologies: star, ring, bus, Mesh, tree, Hybrid (hierarchical)
Star topology
• Most commonly used network topology design you will come across in LAN computer network. • In star, all computers are connected to central device
Star topology • In star we require more connecting devices • • • •
cables, hub/switch, etc Each node connected directly to a central network hub or concentrator a separate cable connects to each computer, and if one cable breaks, only a single computer should be affected. When the central communicating device i.e hub/router fails, the entire network will collapse Used in homes, offices, in buildings because of its commercial success.
Star topology • Advantages: • easy to install and wire • no disruptions to the network when connecting or removing devices • easy to detect network problems • Disadvantages: • more expensive, requires a hub and more cable length than a linear bus topology • all nodes shut down if the hub or concentrator fails • The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow.
Bus topology
•Uses one common cable(backbone) to connect all devices in the network in linear shape. •Consist of a main run of cable with a terminator at each end. • NIC of all network devices are attached to a single backbone cable.
Bus topology
hen any computer sends out message in the network, it is broadcasted in the entire network but only intended computer accepts the message and process it. hen the backbone cable get damaged, it will shunt down the entire network, and no computer will run on the network, and no network can be made between computers until the backbone is replaced. he file server, workstations, and peripherals are
Bus topology
he easiest topology to install oes not require a lot of cables thernet cables are used in this type of topology
Bus topology
isadvantages
ntire network shuts down if there is a break in the backbone cable ifficult to identify the problem if the entire network shuts down dvantages
Ring topology • A ring network is much like a bus network, except the length of wire, cable, or optical fiber connects to form a loop • Local computer processors are tied together sequentially in a ring; with each device being connected to two other devices. • Computers and other networking devices are attached to each other in such a way that they form a ring shape, i.e all messages(data) will travel either clockwise or counter-clockwise.
Ring topology • • • • • • • •
Disadvantages: Relatively expensive and difficult to install Adding/or removing computer disturbs the networks Failure of one computer on the ring affect the whole network Advantages: Ring networks do not require a central computer to control activity nor does it need a file server. Each computer can communicate directly with the other computers in the network Offers high bandwidth and can span larger distance.
Mesh topology • In mesh topology , computers are connected to each other by point-to-point circuits. • It uses router to choose the shortest distance for the destination. • In star, bus, ring: the message is broadcasted to the entire network and only intended computer accepts the message, but in mesh, the message is only sent to the destination computer after finding its route it self with the help of the router.
Mesh topology • In mesh topology one or more computers usually become switching centers, interlinking computers with each other. • Advantage: • The damage of on or several cables or computers may not affect the entire network. • Disadvantage • Very expensive
Hybrid/ Hierarchical topology • In hybrid/ hierarchical topology, computers are arranged in hierarchy where the host computer at the top is mainframe computers. Low levels in the hierarch could consist of minicomputers and microcomputers. • This system combine star, bus and ring network. • This topology is most effective in a centralized corporation like banking companies .
Tree network topology • A tree topology combines many star topology by using bus topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.
Tree network topology
Advantages of a Tree Topology • Point-to-point wiring for individual segments. • Supported by several hardware and software venders • Very simple to design if you have better understanding of star and bus topologies.
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
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.
LAN ARCHITECTURES • Networks are all about sharing resources of computers, servers, scanners, etc to each other. • This type of LAN architecture depend on the requirement of the network and needs before you choose any type. • There are types of networks in LAN architecture:
client/server
peer to peer
Client/Server • Has one or more dedicated computers called server(s) • All computers connected to other connecting devices is connected to the server. • The server is responsible to perform according to the request sent to it by clients, eg. Server can act a print server, if the client request a print of document, the server will send print command to print and it will be printed. The same way to all files that are stored on the server and not on the client server, the same client can retrieve data on other computer on the same network. And this concept is called centralization
Client/Server
• Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers . 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
Client/Server
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
Peer-to-Peer(p2p) • Is the most commonly used computer networks • Is very coast effective • 10-15 computers can be connected each other using p2p networking model without problem • All computers possesses the same status within the network and no computer controls any other computer but itself. • This network does not have a server to control and monitor
Peer-to-Peer(p2p)
• The security level is not high and each computer is itself responsible for security. • File can be shared among computers, files like videos,audios,pictures,spreadsheet can be sent and received within the network. • Printers, scanners and can be shared within all computers.
Peer-to-Peer(p2p) • 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. 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(p2p)
Advantages of a peer-to-peer network: • Less initial expense - No need for a dedicated server. • Setup - An operating system (such as Windows XP) 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
LAN TECHNOLOGIES • ETHERNET • LOCAL TALK • FDDI • TOKEN RING
•
The 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 wireless access points, twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps up to 1000 Mbps.
LocalTalk •
LocalTalk 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.
Token Ring •
• •
•
The 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.
FDDI •
Fiber 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.
Instructors:
Mtaho Adam Paschal Charles
Course objective: • To introduce students to computer networks and their classification. • To introduce students to networking media with emphasis on LAN cabling. • To introduce students to Ethernet technologies and their standards. • To introduce to students principles of computer networks communication and devices .
Course objective: • To introduce students to computer networks and their classification. • To introduce students to networking media with emphasis on LAN cabling. • To introduce students to Ethernet technologies and their standards. • To introduce to students principles of computer networks communication and devices .
Course objectives cont.. • To introduce students to the basics of fiber optic cabling. • To introduce and sensitize students on computer networks security.
Recommended References/text books 1. 2. 3. 4. 5. 6.
Computer Networks and Intenets, Douglas E. Conner, PrenticeHall, 1997. Data and Computer Communications, 5/e, William Stallings, Prentice-Hall, 1996. Computer Networks, 3/e, Andrew S. Tanenbaum, PrenticeHall, 1996. Data Communication. Computer Networks and Open Systems, Fourth Edition, Fred Halsall, Addison – Wesley, 1996. Snader, J. C. (2000). Effective TCP/IP programming: 44 tips to improve your network programs. Upper Saddle River, NJ: Addison-Wesley. ISBN 0-201-61589-4. Stevens, W.R. (1998) UNIX network programming, volume 1: Networking APIs - sockets and XTI, 2/e. Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-216987-8.
Course content Introduction
to Networking: networks classification basics, peer-to-peer networks,LANs, Wireless LANs, VLANs and WANs, Intranet, Internet, Extranet, peerto-peer,client server, hybrid models.
• Networking Media fundamentals: evolution of networking media, merits and demerits of different media, UTP,
Course content cont.. • STP, Fibre, wireless; different types of connectors,UTPcable preparation, UTP cable Testing. Ethernet Fundamentals:
Technologies and Protocols, Ethernet old, fast Ethernet, Gigabit Ethernet, NIC, MAC address (unicast, multicast, broadcast);
Course content cont.. Network communication principles :
Configuration (computer name, domains, work groups), Routing, TCP/IP Protocol Suite & IP Addressing (Static or Dynamic).
Internetworking
devices: repeater , hub, switch, router, gateway, bridge.
• Fibre optic cabling: types of fibres, mode of transmission, splicing, connectors and termination, structured cabling;
Course content cont.. Cable
testing: Fibre; LAN technologies: Token ring, ARCnet, Ethernet, FDDI, WLAN;
Media
Access method: CSMA/CD, CSMA/CA, access control, collision, performance limitation, methods to reduce collisions,
Network
security: firewalls, AAA servers.
Computer Networks What is a network? Connection of two or more devices for the purpose of exchanging signal or communication ∗
∗
What is computer network? Computer network is the network where by two or more computers have been connected for the purpose of exchanging data and sharing resources such as ∗
Computer Networks • Printers, Scanners, CD-ROMs, exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.
Communication Networks • What are communication networks and what advantages do they offer? • A network, or a communication network , is a system of interconnected computers, telephones, or other communication devices that can communicate with one another and share applications and data. • It is the tying together of so many communication devices in so many ways that is changing the world we live in. • A network requires various devices, and a network operating software
Advantages of Computer Network • Sharing of resources – Allows sharing of resources such printers, disk storage, scanners, modems and central serves
• Faster data sharing – Transferring files across a network is always faster than other non-network means of data transfer.
Advantages of Computer Network • Efficient communication – Electronic mail, project monitoring, online conferencing, etc, can lead to better communication between workgroups and help improve productivity. • Keeping information reliable and up-to-date – A well managed, centralized data storage system allows multiple users from different locations to access data and limits the access to data when it is being processed. • It saves cost-as application programs can only be installed in central computer and shared by all other connected computers.
Disadvantages of Computer Network • If the central computer shared by other networked computer fail, all other users will be unable to run applications programs • If the operating system of the network stops, hardware and software resources cannot be accessed. • Unless properly designed, as traffic on the network increases, network performance degrades. • Network require high skilled system or network administrator for management of it, otherwise it cannot operate efficiently.
TYPES OF COMPUTER NETWORKS • Networks may be divided into different types and categories according to four different criteria:
.
TYPES OF COMPUTER NETWORKS
A:
According to geographic area of nodes and hosts
A1-PERSONAL AREA NETWORK(PAN) • Is a computer network organized around an individual person. • A PAN is a network that is used for communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room • It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet. • PAN’s can be wired or wireless
A2-Local Area Network(LAN) • Local Area Network (LAN) is a computer network that connect computers and other devices in a limited geographic area such as home,school,computer lab, office building. Rarely are LAN computers more than a mile apart. • In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations.
A2-Local Area Network(LAN) • The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LANs, cables are used to connect the network interface cards in each computer.
A3-Metropolitan Area Network (MAN) • Metropolitan Area Network (MAN) is a computer network that connect computers and other devices in a limited geographic area such as city or large campus. • Metropolitan Area Networks (MANs) fall between LANs and WANs in geographic area. • Higher speed than LANs (155 Mbps and above) • Cover a larger area (such as a city) • Mostly using fiber as the transmission media
A4-Wide Area Network(WAN) • Wide Area Network (WAN) is a computer network that connect computers and other devices in a limited geographic area such as country. • Used to connect LANs and other types of network together, so that users and computers in one location can communicate with users and computers in other location.
Differences between WAN& LAN FEATURE
LAN
WAN
Scale of sharing
Less and limited
Far greater and worldwide.
Communication media
Use cable such Coaxial and UTP
Satellite, microwaves or telecommunicatio n links
Installation cost
low
high
Network coverageSmall area, about Cities, states and 1Mile range countries
B: according to access restrictions • Private • Public
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B1-Private Networks • Most networks are for the private use of the organizations to which they belong; these are called private networks. Networks maintained by banks, insurance companies, airlines, hospitals, and most other businesses are of this nature.
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B2-Public Networks • Public networks, on the other hand, are generally accessible to the average user, but may require registration and payment of connection fees. • Internet is the most-widely known example of a public network. Technically, both private and public networks may be of LAN, MAN, or WAN type, although public networks, by their size and nature, tend to WANs.
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VPN: Virtual Private Network • From the user’s point-of-view, a VPN looks like a secure, private network • VPNs use public telecom infrastructure, maintaining privacy through security procedures.
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VPN: Virtual Private Network • VPNs provide secure network connections for distance computers without using dedicated, private channels to supply the connection. • Key benefit of VPNs over conventional PNs: Lower cost
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C: According to communication model employed by the nodes. • The communication between the nodes is either based on a point-to-point model or a broadcast model • In the point-to-point model, a message follows a specific route across the network in order to get from one node to another • In the broadcast model, on the other hand, all nodes share the same communication medium and, as a result, a message transmitted by any node can be received by all other nodes
broadcast model • A part of the message (an address) indicates for which node the message is intended. All nodes look at this address and ignore the message if it does not match their own address.
According to communication model employed by the nodes point-to-point model and broadcast model
D: According to switching model employed by the nodes. • Circuit switching Vs Packet switching. • Suppose that a host A wishes to communicate with another host B. In circuit switching, a dedicated communication path is allocated between A and B, via a set of intermediate nodes. The data is sent along the path as a continuous stream of bits. This path is maintained for the duration of communication between A and B, and is then released.
Circuit switching Vs Packet switching • In packet switching, data is divided into packets (chunks of specific length and characteristics) which are sent from A to B via intermediate nodes. • Each intermediate node temporarily stores the packet and waits for the receiving node to become available to receive it. Because data is sent in packets, it is not necessary to reserve a path across the network for the duration of communication between A and B.
Circuit switching Vs Packet switching • Different packets can be routed differently in order to spread the load between the nodes and improve performance. • However, this requires packets to carry additional addressing information.
Wireless LANs: • Wireless LANs: – Are used to connect LAN's without the additional cost or inconvenience of wiring a building. – LAN radio uses radio transmissions to interconnect LAN components. – Infrared uses beams of infrared light to establish network links between LAN components. – Wireless LAN technology makes LANs easy to set up, relocate, and maintain. • Disadvantages: – High initial costs
Wireless LANs… • Not all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs • 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…
Wireless LANs have several disadvantages. They provide poor security, and are susceptible to interference from lights and electronic devices. They are also slower than LANs using cabling
INTERNET • WAN & IP (Internet Protocol) • A collection of networks interconnected and function as a single worldwide network is known as INTERNET • WAN is used for interconnection;
INTRANET
• Network within organization
Components of a LAN….. • LANs are made up of several standard components/ hardware, software and other accessories • Connection or cabling system: wired (twisted-pair cable, coaxial or fiber optic cable) or wireless (infrared and radio-wave transmission). • Microcomputers/workstations with interface cards
COMPONENTS OF LAN…
– Network operating system-software – Network Interface Cards ,Routers – Switch, Bridges – Repeater, Hubs – Gateways, Modems
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Components of a LAN • Network operating system-software that manages the activity of the network-providing multi-user and multitasking capabilities • Unlike operating systems, such as DOS and Windows, 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. • Other shared devices can be printers, fax machines, scanners, storage devices and other peripherals
Components of a LAN • A repeater is a device that regenerates and amplifies signals to create long-distance networks • A switch is a high-speed multi-port bridge. Today, switches are replacing multi-port repeaters or concentrators in a UTP environment. • An intelligent hub that maintains a bridging table, keeping track of which hardware addresses are located on which network segment • Server- a computer with higher hard disk and higher speed than any other computer on the network.
Components of a LAN • There are various types of servers which can be connected in LANs, such as File server, Printer server, etc.
A File Server • A File server is a high capacity computer that provides various resources to the network. • A file server has the following characteristics – Needs a very fast computer with a large amount of RAM and storage space, a fast network interface card, and a tape back-up device – Needs network operating system such as Novell Netware, Windows NT server, or Apple Share – Controls the communication of information between the nodes on a network
Network Interface Cards (NICs)
• Network Interface Card-NIC provides the link between your computer and your network. • provide the physical connection between the network and the workstation.
Network Interface Cards • The 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. • Laptop computers can now be purchased with a network interface card built-in • 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.
Switch • A concentrator is a device that provides a central connection point for cables from workstations, servers, and peripherals. So, a switch is a concentrator. • In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. • Switches no longer broadcast network packets as hubs did in the past, they memorize addressing of computers and send the information to the correct location directly. Switches 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
Repeaters • Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts 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 Metroporitan area network using a star topology with unshielded twisted-pair cabling. The length limit for unshielded twisted-pair cable is 100 meters.
Repeaters • The most common configuration is for each workstation to be connected by twisted-pair cable to a multi-port active concentrator. The concentrator amplifies all the signals that pass through it allowing for the total length of cable on the network to exceed the 100 meter limit.
Bridges • A 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.
Bridges • 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 • Used to form a connection between two separate, but similar networks
Routers • A router translates information from one network to another; it is similar to a super intelligent 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 head-on collisions, and is smart enough to know when to direct traffic along back back roads roads and and shortc shortcuts. uts. • 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 • 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 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.
Router • A special-purpose computer that directs data traffic when several paths are available • A router examines the destination info in each arriving packet and then routes it through the most efficient path available • The router either delivers the packet to the destination computer across a local network or forwards or forwards the packet to another router that router that is closer to the final destination
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Gateway • Device sitting at the network node for interfacing with another network that uses different protocol. • LAN’s may use a gateway (or router) to connect to the Internet.
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Workstations • All of the user computers connected to 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 because files can be saved on the file server. Almost any computer can serve as a network workstation.
Network Hardware/Components
Communication Channels/Media • What is communication channel/Media? – Is a path-the physical medium- over which data travels in a telecommunication systems from its source to its destination. Channels are also called links, lines or media • Types of communication channels • Physical channel • transmit data through the cable or wire. – Use solid medium to connect sending and receiving devices. • Wireless media
Twisted pair Cable • Consist of two insulated copper wires arranged in a regular spiral pattern to minimize interference. • Advantages – low cost, small size, and ease of installation • Disadvantages – Suffers from electromagnetic interference(EMI) between adjacent pairs – low frequency transmission medium – limited distance, usually less than 100 meters • Uses: the most popular and is generally the best option for school networks
Twisted Cable
• Twisted pair cabling comes in two varieties: Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP)
Unshielded twisted pair (UTP) • Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks • 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 tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.
Unshielded twisted pair (UTP) • The standard connector for unshielded twisted pair cabling is an RJ-45 connector
• A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference
Shielded Twisted Pair (STP)
• 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 Cable • Coaxial cable resembles the wire used to connect a TV or VCR • Has an inner conductor surrounded by a braided mesh • Both conductors share a common center axial, hence the term "co-axial" • Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers .
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.
Coaxial Cable • Advantages: • bandw bandwidth idth of up to 400 400 Mhz Mhz – highly resistant to signal interference – Transfer voice and data faster than twisted pair cable • Disadvantage – quite bulky and sometimes difficult to install • Uses: used for connecting parts of LAN over long distance (300-600 meters)
Fiber Optic Cable • Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. 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. • 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 possibili possibilities ties to inclu include de servic services es such such as as video video conferencing and interactive services
Fiber Optic Cable • The most common connector used with fiber optic cable is an ST ST connector. It is barrel shaped, similar to a BNC connector
Fiber Optic Cable • Consists of a center glass core surrounded by several layers of protective materials • Advantages – immunity to environmental interference – greater capacity (bandwidth of up to 2 Gbps) – carry information at vastly greater speeds
Fiber Optic Cable • Disadvantages – very expensive – small size and lighter weight – difficult to install and modify, require highly skilled installers – adding additional nodes is difficult • 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals • Uses: used for distances up to 100 kilometers
LANs Topology • Network can be laid out in different ways . The physical layout, or shape, of a network is called a topology. • Network topology can be physical or logical design • Physical topology refer to physical design of network which includes devices, cables, location and installation of network. • Logical topology refer to the amount of data to be transferred within the network.
LANs Topology • There are Six basic network topologies: star, ring, bus, Mesh, tree, Hybrid (hierarchical)
Star topology
• Most commonly used network topology design you will come across in LAN computer network. • In star, all computers are connected to central device
Star topology • In star we require more connecting devices • • • •
cables, hub/switch, etc Each node connected directly to a central network hub or concentrator a separate cable connects to each computer, and if one cable breaks, only a single computer should be affected. When the central communicating device i.e hub/router fails, the entire network will collapse Used in homes, offices, in buildings because of its commercial success.
Star topology • Advantages: • easy to install and wire • no disruptions to the network when connecting or removing devices • easy to detect network problems • Disadvantages: • more expensive, requires a hub and more cable length than a linear bus topology • all nodes shut down if the hub or concentrator fails • The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow.
Bus topology
•Uses one common cable(backbone) to connect all devices in the network in linear shape. •Consist of a main run of cable with a terminator at each end. • NIC of all network devices are attached to a single backbone cable.
Bus topology
hen any computer sends out message in the network, it is broadcasted in the entire network but only intended computer accepts the message and process it. hen the backbone cable get damaged, it will shunt down the entire network, and no computer will run on the network, and no network can be made between computers until the backbone is replaced. he file server, workstations, and peripherals are
Bus topology
he easiest topology to install oes not require a lot of cables thernet cables are used in this type of topology
Bus topology
isadvantages
ntire network shuts down if there is a break in the backbone cable ifficult to identify the problem if the entire network shuts down dvantages
Ring topology • A ring network is much like a bus network, except the length of wire, cable, or optical fiber connects to form a loop • Local computer processors are tied together sequentially in a ring; with each device being connected to two other devices. • Computers and other networking devices are attached to each other in such a way that they form a ring shape, i.e all messages(data) will travel either clockwise or counter-clockwise.
Ring topology • • • • • • • •
Disadvantages: Relatively expensive and difficult to install Adding/or removing computer disturbs the networks Failure of one computer on the ring affect the whole network Advantages: Ring networks do not require a central computer to control activity nor does it need a file server. Each computer can communicate directly with the other computers in the network Offers high bandwidth and can span larger distance.
Mesh topology • In mesh topology , computers are connected to each other by point-to-point circuits. • It uses router to choose the shortest distance for the destination. • In star, bus, ring: the message is broadcasted to the entire network and only intended computer accepts the message, but in mesh, the message is only sent to the destination computer after finding its route it self with the help of the router.
Mesh topology • In mesh topology one or more computers usually become switching centers, interlinking computers with each other. • Advantage: • The damage of on or several cables or computers may not affect the entire network. • Disadvantage • Very expensive
Hybrid/ Hierarchical topology • In hybrid/ hierarchical topology, computers are arranged in hierarchy where the host computer at the top is mainframe computers. Low levels in the hierarch could consist of minicomputers and microcomputers. • This system combine star, bus and ring network. • This topology is most effective in a centralized corporation like banking companies .
Tree network topology • A tree topology combines many star topology by using bus topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.
Tree network topology
Advantages of a Tree Topology • Point-to-point wiring for individual segments. • Supported by several hardware and software venders • Very simple to design if you have better understanding of star and bus topologies.
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
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.
LAN ARCHITECTURES • Networks are all about sharing resources of computers, servers, scanners, etc to each other. • This type of LAN architecture depend on the requirement of the network and needs before you choose any type. • There are types of networks in LAN architecture:
client/server
peer to peer
Client/Server • Has one or more dedicated computers called server(s) • All computers connected to other connecting devices is connected to the server. • The server is responsible to perform according to the request sent to it by clients, eg. Server can act a print server, if the client request a print of document, the server will send print command to print and it will be printed. The same way to all files that are stored on the server and not on the client server, the same client can retrieve data on other computer on the same network. And this concept is called centralization
Client/Server
• Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers . 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
Client/Server
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
Peer-to-Peer(p2p) • Is the most commonly used computer networks • Is very coast effective • 10-15 computers can be connected each other using p2p networking model without problem • All computers possesses the same status within the network and no computer controls any other computer but itself. • This network does not have a server to control and monitor
Peer-to-Peer(p2p)
• The security level is not high and each computer is itself responsible for security. • File can be shared among computers, files like videos,audios,pictures,spreadsheet can be sent and received within the network. • Printers, scanners and can be shared within all computers.
Peer-to-Peer(p2p) • 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. 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(p2p)
Advantages of a peer-to-peer network: • Less initial expense - No need for a dedicated server. • Setup - An operating system (such as Windows XP) 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
LAN TECHNOLOGIES • ETHERNET • LOCAL TALK • FDDI • TOKEN RING
•
The 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 wireless access points, twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps up to 1000 Mbps.
LocalTalk •
LocalTalk 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.
Token Ring •
• •
•
The 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.
FDDI •
Fiber 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.
