NETWORK TOPOLOGIESNETWORK TOPOLOGIESPrf.Madhuri Nitin Badgujar(M.Sc.IT,MCA)Birla College of Arts, Commerce and science, Kalyan(w)

NETWORK TOPOLOGIESNETWORK TOPOLOGIESThere are three basic configurations used to connect computers they are the Bus Ring Star

Bus topologyBus 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 How a Bus Peer to Peer Network WorksNetwork WorksAll 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 workedHow it workedThe 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

ProblemsProblemsOne 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

Advantages▸ It is easy to set up, handle, and implement. ▸ It is best-suited for small networks.▸ It costs very less.

Disadvantages▸ The cable length is limited. This limits the number of network nodes that can be connected.▸ This network topology can perform well only for a limited number of nodes. When the number of devices connected to the bus increases, the efficiency decreases.▸ It is suitable for networks with low traffic. High traffic increases load on the bus, and the network efficiency drops.▸ It is heavily dependent on the central bus. A fault in the bus leads to network failure.▸ It is not easy to isolate faults in the network nodes.▸ Each device on the network "sees" all the data being transmitted, thus posing a security risk.

Ring TopologyRing 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 worksHow 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 WorksHow it WorksAs 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 SolutionsProblems and SolutionsThe 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▸ The data being transmitted between two nodes passes through all the intermediate nodes. A central server is not required for the management of this topology.▸ The traffic is unidirectional and the data transmission is high-speed.▸ In comparison to a bus, a ring is better at handling load.▸ The adding or removing of network nodes is easy, as the process requires changing only two connections.▸ The configuration makes it easy to identify faults in network nodes.▸ In this topology, each node has the opportunity to transmit data. Thus, it is a very organized network topology.▸ It is less costly than a star topology.

Disadvantages▸ The failure of a single node in the network can cause the entire network to fail.▸ The movement or changes made to network nodes affect the entire network's performance.▸ Data sent from one node to another has to pass through all the intermediate nodes. This makes the transmission slower in comparison to that in a star topology. The transmission speed drops with an increase in the number of nodes.▸ There is heavy dependency on the wire connecting the network nodes in the ring.

Star topologyStar topology

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

HUB

The Good and Bad of a The Good and Bad of a Star NetworkStar NetworkThe 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 The Good and Bad of a Star NetworkStar NetworkAs 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

What is a Hub?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

On this network segment, all computers can communicate directly with each other

What is a Hub?What is a Hub?Ethernet hubs are by far the most

common type, but hubs for other types of networks such as USB also exist

A hub includes a series of ports that each accepts a network cable

Small hubs can network four computers together

They contain four or sometimes five ports

What is a Hub?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 HubsKey Features of Hubs

Hubs classify as Layer 1 devices in the OSI model

OSI stands for :The Open Systems Interconnection Basic

Reference Model At the physical layer, hubs can support

little in the way of sophisticated networking

Hubs do not read any of the data passing through them and are not aware of their source or destination

Key Features of HubsKey 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!

a packet is a formatted block of data carried by a computer network

Different Types of HubsDifferent Types of HubsTechnically speaking, three

different types of hubs exist PassivePassiveActiveActive

IntelligentIntelligent

Passive hubsPassive hubsPassive hubs do not amplify the electrical

signal of incoming packets before broadcasting them out to the network

Active hubsActive hubs

amplify the electrical signal of incoming packets back to their original level before broadcasting them back out on the network

Intelligent hubsIntelligent 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).

Intelligent hubsIntelligent hubs It also typically includes remote

management capabilities via SNMP and virtual LAN (VLAN) support (You can configure or check it from a computer that is connected to it).

SNMP-Simple Network Management Protocol

Advantages▸ Due to its centralized nature, the topology offers simplicity of operation. ▸ It also achieves isolation of each device in the network.▸ Adding or removing network nodes is easy, and can be done without affecting the entire network.▸ Due to the centralized nature, it is easy to detect faults in the network devices.▸ As the analysis of traffic is easy, the topology poses lesser security risk.▸ Data packets do not have to pass through many nodes, like in the case of a ring network. Thus, with the use of a high-capacity central hub, traffic load can be handled at fairly decent speeds.

Disadvantages▸ Network operation depends on the functioning of the central hub. Hence, central hub failure leads to failure of the entire network.▸ Also, the number of nodes that can be added, depends on the capacity of the central hub.▸ The setup cost is quite high.

What is a Network Switch?What is a Network Switch?A network switch is a small

hardware device that joins multiple computers together within one local area network (LAN)

Technically, network switches operate at layer two (Data Link Layer) of the OSI model

Network SwitchNetwork 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

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

Network SwitchNetwork SwitchBy 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

Mesh topologyMesh topology A mesh network is a network topology in which each node (called

a mesh node) relays data for the network. All nodes cooperate in the distribution of data in the network.

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination.

Some WANs , most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is

called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

Mesh technology comes into two flavors: Full Mesh: All hosts have a point-to-point connection to every

other host in the network. Thus for every new host n(n-1)/2 cables (connection) are required. It provides the most reliable network structure among all network topologies.

Partially Mesh: Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some host whereas others are not as such necessary.

Advantages▸ The arrangement of the network nodes is such that it is possible to transmit data from one node to many other nodes at the same time.▸ The failure of a single node does not cause the entire network to fail as there are alternate paths for data transmission.▸ It can handle heavy traffic, as there are dedicated paths between any two network nodes.▸ Point-to-point contact between every pair of nodes, makes it easy to identify faults.

Disadvantages▸ The arrangement wherein every network node is connected to every other node of the network, many connections serve no major purpose. This leads to redundancy of many network connections.▸ A lot of cabling is required. Thus, the costs incurred in setup and maintenance are high.▸ Owing to its complexity, the administration of a mesh network is difficult.

What is a Router?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

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

RoutersRoutersHome “networkers” often use an

Internet Protocol (IP) wired or wireless router

IP is the most common OSI network layer protocol

Protocols are the rules governing the transfer of data information, it can also be compared to how humans use languages (to get your point across you must talk in the same language as the person you are speaking to).

RoutersRoutersAn IP router such as a DSL or

cable modem are broadband routers and joins the home's local area network (LAN) to the wide-area network (WAN) of the Internet

A Broadband Router is a device that allows multiple PC’s to access the Internet using only one address.