Network Topologies

By:Nawaraj Kumar Mahato&Bayo Ken Munduni

Network Topologies Network topology is the arrangement of the various elements

(links, nodes, etc.) of a computer network. Essentially, it is the topological structure of a network, and may be depicted physically or logically.

Physical topology refers to the placement of the network's various components, including device location and cable installation.

Logical topology shows how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical.

Physical topology

Logical topology

Basic Network Topologies

• Point-to-point• Bus• Star• Mesh• Tree• Hybrid• Daisy chain

Point-to-point The simplest topology is a permanent link between two endpoints.

Switched point-to-point topologies are the basic model of conventional telephony. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, and has been expressed as Metcalfe's Law. It may be permanent or switched.

Bus Each node is connected to a single cable. Each computer or server is connected

to the single bus cable. A signal from the source travels in both directions to all machines connected on

the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted.

Advantages Easy to setup Small amount of wire

Disadvantages Slow Easy to crash

Star Each network host is connected to a central hub with a point-to-point

connection. In Star topology every node (computer workstation or any other peripheral) is connected to central node called hub or switch.

The switch is the server and the peripherals are the clients. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater.

Advantages Easy to setup One cable can not crash network

Disadvantages One hub crashing downs entire

network Uses lots of cables

Mesh– All computers connected together– Internet is a mesh networkAdvantage

Data will always be deliveredDisadvantages

Lots of cable Hard to setup

Tree Tree topology is a combination of Bus and Star topology. The type of network topology in which a central 'root' node (the top level of

the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node.

Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree.

Hybrid

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network.

Daisy chain Except for star-based networks, the easiest way to add more computers into a

network is by daisy-chaining, or connecting each computer in series to the next. If a message is intended for a computer partway down the line, each system

bounces it along in sequence until it reaches the destination. A daisy-chained network can take two basic forms: linear and ring.

Linear A linear topology puts a two-way link between one computer and the

next. However, this was expensive in the early days of computing, since each

computer (except for the ones at each end) required two receivers and two transmitters.

Ring • By connecting the computers at each end of a linear topology, a ring

topology can be formed. An advantage of the ring is that the number of transmitters and receivers can be cut in half, since a message will eventually loop all of the way around.

Network Hardware• Network interface cards(NIC)

– Network adapter– Connects node to the media– Unique Machine Access Code (MAC)

Network linking devices

– Connect nodes in the network– Cable runs from node to device– Crossover cable connects two computers

Hubs

– Center of a star network– All nodes receive transmitted packets– Slow and insecure

Switches

– Replacement for hubs– Only intended node receives transmission– Fast and secure

Bridge

– Connects two or more LANs together– Packets sent to remote LAN cross

• Other packets do not cross

– Segments the network on MAC addresses

Router

– Connects two or more LANs together– Packets sent to remote LAN cross– Network is segmented by IP address– Connect internal networks to the Internet– Need configured before installation

Gateway

– Connects two dissimilar networks– Connects coax to twisted pair– Most gateways contained in other

devices

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