ics 216 computer network principles€¦ · networking topologies topology: commonly used to...
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Network Topologies
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Networking Topologies
Topology: Commonly used to discuss the properties of various types of networks.
Topology is the branch of mathematics that examines the characteristics of geometric shapes.
Networks have shapes, and the shape of a network determines the way it functions.
Different types of topologies are used because each topology has strength and weaknesses.
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Types of topology
Physical topology: The layout or actual appearance of the cabling scheme used on a network If you can see it and touch it, it is physical.
Logical topology: How the data flows through the physical topology. If you cannot see it or touch it, it is logical.
The logical topology is closely related to the mechanisms used to manage the way stations access the network (medium access).
Similar-looking networks can have quite different logical topologies
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Factors affecting the choice of
topology used
Impact of cable breaks on a network.
Impact of adding or removing nodes.
Flow of messages and which nodes see the messages.
Ability to use nodes as repeaters.
Maximum physical size of the network.
Amount of cable used.
The final choice of topology could be either one or more likely a combination of topologies that depend upon, need, cost, speed, and reliability.
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Physical Topologies
All physical topologies are variations of two
fundamental methods of connecting devices:
Point-to-point.
Multipoint.
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Point-to-point Topologies
Point-to-point (PTP) topology connects two nodes directly together.
Examples of point-to-point links: Two computers communicating via modems.
A mainframe terminal communicating with a front-end processor.
A workstation communicating along a parallel cable to a printer.
Two devices monopolize a communication medium.
The medium is not shared, hence no need for addressing.
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Point-to-point Topologies
Point-to-point links can be
Simplex
Half-duplex
Full duplex
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Multipoint Topology
Multipoint topologies link three or more devices together through a single communication medium.
Each device needs a way to identify itself and the device to which it wants to send information (Addressing).
Multipoint Physical Topologies
Star
Bus
Ring
Hybrid
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Star Topology
Has its roots in the mainframe world.
Each device connects to a central point via a point-to-point link.
Depending on the logical architecture used, several names are used for the central point including the following:
Hub
Multipoint Repeater
Concentrator
Multi-Access Unit (MAU)
Switch
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Star Topology
In its most basic configuration, cables radiate
from a hub or switch as shown.
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Star Topology
It can also be designed using the following configurations
Distributed star: This is a modification of the basic star topology in which the
stations are not connected
IBM Compatible
Hub
Workstation Workstation
Workstation
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Star Topology
Clustered star: It is similar to the tree topology but there are clusters of
devices at the end of each branch.
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Star Topology
Hierarchical star: It is an extension of the star topology.
The devices are connected to a hub or switch as in a star topology.
These hubs or switches are connected to each other via a central hub.
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Ring Topology
It is a physical, closed loop consisting of point-to-point links.
Ring topology
Each node is connected to the two nearest nodes so the entire network forms a circle
One method for passing data on ring networks is token passing
Active topology
Each workstation transmits data
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Bus Topology
The bus is considered a multipoint system because all
devices tap into the same backbone cable.
A Bus topology consists of a single cable called a bus
connecting all nodes on a network without intervening
connectivity devices
In bus topologies, all data signals are broadcast
throughout the bus structure.
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Bus Topologies
There are two variations of the bus topology.
One uses a T-connector to connect the cable to the
workstation adapter card.
A terminator is connected to the last T-connector
at each end of the network.
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Bus Topologies
Another type uses drop cables to connect each
workstation to the main “backbone”.
Examples of Bus topology
ARCnet, (Token bus)
Ethernet, (10Base2)
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Hybrid Physical Topologies
Hybrid topology
Complex combination of the simple physical topologies
Star-wired ring
Star-wired topologies use physical layout of a star in conjunction with token ring-passing data transmission method
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Hybrid Physical Topologies
Star-wired bus
In a star-wired bus topology, groups of workstations
are star-connected to hubs and then networked via
a single bus
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Hybrid Physical Topologies
Daisy-Chained
A Daisy chain is linked series of devices
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Hybrid Physical Topologies
Hierarchical hybrid topology
Uses layers to separate devices by priority or
function
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Enterprise-Wide Topologies
Enterprise
An entire organization
Backbone networks
Serial backbone
Distributed backbone
Collapsed backbone
Parallel backbone
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Enterprise-Wide Topologies
Serial backbone
Two or more hubs connected to each other by a single cable
Distributed backbone
Hubs connected to a series of central hubs or routers in a hierarchy
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Enterprise-Wide Topologies
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A distributed backbone connecting multiple LANs
Enterprise-Wide Topologies
Collapsed backbone
Uses a router or switch as the single central
connection point for multiple subnetworks
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Enterprise-Wide Topologies
Parallel Backbone
Collapsed backbone arrangement that consists of
more than one connection from central router or
switch to each network segment
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Enterprise-Wide Topologies
Mesh networks
Routers are interconnected with other routers, with
at least two pathways connecting each router
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Wide Area Network (WAN) Topologies
Peer-to-peer topology
WAN with single interconnection points for each location
Dedicated circuits
Continuous physical or logical connections between two
access points that are leased from a communication provider
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Wide Area Network (WAN) Topologies
Ring WAN topology
Each site is connected to two other sites so that
entire WAN forms a ring pattern
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Wide Area Network (WAN) Topologies
Star WAN topology
Single site acts as the central connection point for
several other points
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Wide Area Network (WAN) Topologies
Mesh WAN topology
Many directly interconnected locations forming a
complex mesh
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Wide Area Network (WAN) Topologies
Tiered WAN topology
Sites connected in star or ring formations are
interconnected at different levels, with
interconnection points organized into layers
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Logical Topologies
Refers to the way in which data are transmitted
between nodes
Describes the way:
Data are packaged in frames
Electrical pulses are sent over network’s physical media
Logical topology may also be called network transport
system
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Comparison of Topologies –
StarConfiguration Strength Weaknesses
Star Network control is centralized at one point
Network intelligence is limited to the central workstation
Radiating workstations can use the CPU processing of the central workstation
Congestion at the central workstation can slow transmissions
Failure of the central workstation renders the network useless.
Workstations can only communicate with each other by going through the central workstation.
All workstations have their own communication media, which can become expensive
The central workstation has a physical limitation for the number of workstations that can be connected
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Comparison of Topologies –
Bus Configuration Strength Weaknesses
Bus Workstations can communicate directly with each other.
A single shared medium is inexpensive
The loss of one workstation does not affect the functionality of the network
High transmission speed is possible.
Adding another station amounts to making another connection to the bus
The approach is appropriate to a limited geographical area.
The causes of faults and failures are difficult to determine.
Failure of the backbone renders the network useless.
Network intelligence may have to be distributed to all workstations.
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Comparison of Topologies – Ring
and HybridConfiguration Strength Weaknesses
Ring All workstations share the same communication medium.
The loss of one workstation does not affect the functionality of the network.
The cost of a single shared medium is low.
Adding another station amounts to making a connection to the single communication medium.
Each workstation must pass on unintended messages.
Response speed degrades as the network size increases.
Network intelligence must be distributed.
Hybrid Benefits of several topologies can be combined.
Workgroup efficiency and traffic can be customized.
Devices on one topology can not be placed onto another topology without hardware changes.
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Comparison of Topologies –
Mesh Configuration Strength Weaknesses
Mesh Fast response time.
Single workstation failure does not affect network.
Connections determined by movement of data
Network intelligence must be distributed.
Adding a new station can be expensive.
Making connections between many stations is expensive.
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