Transcript File
Guide to Networking Essentials Fifth Edition Chapter 2 Network Design Essentials Objectives • Explain the basics of a network layout • Describe the standard networking topologies • Explain the variations on standard networking topologies • Describe the role of hubs and switches in a network topology • Construct a basic network layout Guide to Networking Essentials, Fifth Edition 2 Examining the Basics of a Network Layout • To implement a network, you must first decide how to best situate the components in a topology • Topology refers to the physical layout of its computers, cables, and other resources, and also to how those components communicate with each other • The arrangement of cabling is the physical topology • The path that data travels between computers on a network is the logical topology • Topology has a significant effect on the network’s performance and growth, and equipment decisions Guide to Networking Essentials, Fifth Edition 3 Understanding Standard Topologies Networks are based on three physical topologies A bus consists of a series of computers connected along a single cable segment Computers connected via a central concentration point (hub) are arranged in a star topology Computers connected to form a loop create a ring Physical topologies describe cable arrangement How the data travels along those cables might represent a different logical topology The logical topologies that dominate LANs include bus, ring, and switching, all of which are usually implemented as a physical star Guide to Networking Essentials, Fifth Edition 4 Bus Bus topology This type of network was widely used in the 1980’s In this configuration every computer (node) shares the networks total bus capacities. In this configuration adding more computers will reduce the access speed on the network. Each computer communicates to other computers on the network independently this is referred to as PEER-TO-PEER networking How a Bus Peer to Peer Network Works • All computers on a network have a distinct address just like your house does • a message would be send from one computer with the address of another computer attached to the message • The message is broadcasted to all the computers on the network until the addressed PC accepts the message How it worked The type of wires used for Bus Networks in the 80’s were called Thicknet and Thinnet A Thicknet cable (very large about 1 inch in diameter usually yellow was hung around a room) Thinnet cables were connected to the PC’s NIC and a Transceiver. The Transceiver was tapped into the Thicknet cable To stop the message from bouncing back and forward down the wire (known as signal bounce) both ends of the network are terminated with 50Ω resistors Problems • One of the main problems with this type of network is that it is not very fault tolerant, a break or defect in the bus would affect the whole network Ring Topology • In Ring topology each node is connected to the two nearest nodes so the entire network forms a circle • Data only travels in one direction on a Ring network How this Topology works a node has information to send to another computer on the network so it sends the information out on the network to the PC it is connected to, if the information is for this PC (the recipients NIC address is attached to the message, which is like putting an address on an envelope) then the PC accepts the data otherwise it passes the information on to the next PC by repeating the data back out on the line This method of repeating the data helps keep the integrity of the data readable by other computers How it Works • As it is better to have computers take turns using the connecting Data cable, Ring topologies incorporated a system called Token passing • In this topology, to transmit on the wire your computer must have control of the token or wait for the token to be free • Larger Token Ring networks use multiple tokens Problems and Solutions The drawback to this type of topology is that a single malfunctioning workstation can disable the whole network To make sure all the information is sent the receiving PC sends the token back to the sending PC after it has received all the data If the sending PC is finished sending it passes the token to the next PC This type of network was also widely used in the 1980’s This type of network used Thinnet cable joining nodes. In the mid 1980’s Thinnet cable was replaced by Category 3 Ethernet cable capable of handling up to 10Mbps Star Topology Guide to Networking Essentials, Fifth Edition 14 Star topology HUB • In a Star topology every node is connected through a central device such as a Hub, Switch or Router • Compared to a Ring or Bus topology a Star topology requires that more thought be put into its setup The Good and Bad of a Star Network • The upside of a star network is that if any one cable fails then only the node connected on that cable would be affected • Another positive point to this type of network is that it is very simple to join two star networks together by connecting their central devices to each other The Good and Bad of a Star Network • As each computer is connected to a central device (Hub) the location of the Hub must be made as central as possible, so as to reduce cable lengths • The drawback to this type of topology is if a central device was to fail then all computers connected to that device would not be able to see the network Wireless Topologies • Wireless networking has a logical and physical topology • Ad hoc topology: two computers can communicate directly with one another; sometimes called a peer-to-peer topology • Infrastructure mode: Use a central device, called an access point (AP), to control communications • Star physical topology because all the signals travel through one central device Guide to Networking Essentials, Fifth Edition 18 Examining Variations of Physical Topologies • The major physical topologies have three typical variations or combinations • Extended star • Mesh • Combination star and bus • These combinations can be used to get the most from any network Guide to Networking Essentials, Fifth Edition 19 Extended Star Topology Guide to Networking Essentials, Fifth Edition 20 Mesh Topology Guide to Networking Essentials, Fifth Edition 21 Full Mesh Topology • Every node has a circuit connecting it to every other node in the network • Yields greatest redundancy, so if one node fails, network traffic can be redirected to any of the other nodes • Usually reserved for backbone networks since it is very expensive Combination Star Bus Topology Guide to Networking Essentials, Fifth Edition 23 Hubs Most common type of hub today Regenerate, or repeat, the signals Require electrical power to run Generally, have many ports—eight or more Also called multiport repeaters or repeating hubs 1. 2. 3. 4. Takes a signal coming in on one port Cleans the signal (e.g., by filtering out noise) Strengthens the signal Sends the regenerated signal out to all other ports Drawback: require sharing the hub bandwidth among all connected stations Guide to Networking Essentials, Fifth Edition 24 Switches • Central connecting point in a star topology network • Does more than simply regenerate signals • Looks just like a hub, with several ports for connecting workstations in a star topology • Determines to which port the destination device is connected and forwards the message to that port • This capability allows a switch to handle several conversations at one time, thereby providing the full network bandwidth to each device rather than requiring bandwidth sharing Guide to Networking Essentials, Fifth Edition 25 Router • A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP.s network. Routers use headers and forwarding tables to determine the best path for forwarding the packets, Guide to Networking Essentials, Fifth Edition 26 Constructing a Network Layout • The first step in any network design is to evaluate the underlying requirements • First determine how the network will be used, which often decides the topology you use • Decide the types of devices for interconnecting computers and sites • Finally, the type and usage level of network resources dictates how many servers you need and where to place servers Guide to Networking Essentials, Fifth Edition 27 Creating the Layout Network must be documented Useful questions before drawing the diagram How many client computers will be attached? How many servers will be attached? Will there be a connection to the Internet? How will the building’s physical architecture influence decisions, such as whether to use a wired or wireless topology, or both? Which topology or topologies will you use? Network diagram must be kept up to date Guide to Networking Essentials, Fifth Edition 28 Creating the Layout (continued) Guide to Networking Essentials, Fifth Edition 29 Summary • Basic physical topologies: bus, star, or ring • Physical bus: easy to install but outdated • The logical bus topology is still used, but is almost always implemented as a physical star • Physical ring: connects devices in such a way that the cabling starts and ends with the same computer • Rarely used (except in FDDI) • Logical ring topology typically uses token passing to send data around ring; normally implemented as a star • Physical star: centralized management and higher degree of fault tolerance • Topology of choice in today’s networks Guide to Networking Essentials, Fifth Edition 30 Summary (continued) • For wireless networks: ad hoc or infrastructure mode • Variations on major topologies • Extended star (most widely used) • Mesh (most fault tolerant) • Combination star and bus • Hub: central point of concentration for a star network • Can be active (if it regenerates the signals) or passive • Switch: provides better performance than a hub • Device of choice in corporate star topology networks • Network layout should be consistent and maintained accurately as the network changes Guide to Networking Essentials, Fifth Edition 31