NETWORK TOPOLOGIES There are three basic configurations used to connect computers they are the  Bus  Ring  Star

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

Bus (continued)

How it worked  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 (cont,,)  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

Advantages of Bus Topology  Works well for small networks  Relatively inexpensive to implement  Easy to add to it

Disadvantages of Bus Topology  Management costs can be high  Potential for congestion with network traffic  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

Ring

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

Advantages of Ring Topology  Easier to manage; easier to locate a defective node or cable problem  Well-suited for transmitting signals over long distances on a LAN  Handles high-volume network traffic  Enables reliable communication

Disadvantages of Ring Topology  Expensive  Requires more cable and network equipment at the start  Not used as widely as bus topology –Fewer equipment options –Fewer options for expansion to high-speed communication

Star topology –Every node on the network is connected through a central device

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

Advantages of Star Topology  Good option for modern networks  Low startup costs  Easy to manage  reduce cable lengths  If one cable fails then only the node connected on that cable would be affected

Disadvantages of Star Topology  if a central device was to fail then all computers connected to that device would not be able to see the network  Requires more cable than the bus

What is a Hub?  A hub is usually a small rectangular box, often made of plastic, which receives its power from an ordinary wall outlet  A hub joins multiple computers (or other network devices) together to form a single network segment segment  On this network segment, all computers can communicate directly with each other

What is a Hub(cont,,,)  A hub includes a series of ports that each accepts a network cable ports  Small hubs can network four computers together  They contain four or sometimes five ports

What is a Hub?  Many times the fifth port is reserved for "uplink" which is the connecting of one hub to another hub or similar device (joining two segments together).  Larger hubs contain eight, 12, 16, and even 24 ports

Key Features of Hubs  Hubs classify as Layer 1 devices in the OSI model OSI modelOSI model  Hubs do not read any of the data passing through them and are not aware of their source or destination

Key Features of Hubs  Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network - including the one that originally sent the packet! packets  a packet is a formatted block of data carried by a computer network

Different Types of Hubs  Technically speaking, three different types of hubs exist PassiveActiveIntelligent

Passive hubs  Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network Active hubs  amplify the electrical signal of incoming packets back to their original level before broadcasting them back out on the network

Intelligent hubs  add extra features to an active hub that are of particular importance to businesses  An intelligent hub is typically stackable (built in such a way that multiple units can be placed one on top of the other to conserve space).

What is a Network Switch?  A network switch is a small hardware device that joins multiple computers together within one local area network (LAN) local area network (LAN)local area network (LAN)  Technically, network switches operate at layer two (Data Link Layer) of the OSI model OSI modelOSI model

Network Switch  Network switches appear nearly identical to network hubs, but a switch generally contains more "intelligence" (and a slightly higher price tag) than a hub network hubs network hubs  Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately packets

Network Switch  By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub network bandwidthnetwork bandwidth

What is a Router?  Routers are physical devices that join multiple wired or wireless networks together  Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless router connects networks together gateway  A Gateway is a device that acts like a security guard and only allows data in or out if it has the right network headers headers