what is a network topology
a description of how a network is physically laid out and how signals travel from one device to another
All network designs today are based on what 4 basic physical topologies
- bus
- star
- ring
- point-to-point
What are the two categorizations of network topologies
- Physical topology - the arrangment of cabling and how cables connect one device to another in a network
- Logical topologies - the path data travels between computers on a network
What is physical bus topology
this is a continuous length of cable connecting one computer to another in a daisy-chain fashion
This is the simplest and at one time was the most common method for connecting computers
What are the weaknesses of physical bus topology
- There’s a limit of 30 computers per cable segment
- The maximum total length of cabling is 185 meters
- Both ends of the bus must be terminated
- Any break in the bus brings down the entire network
- Adding or removing a machine brings down the entire network temporarily
- Technologies using this topology are limited to 10 Mbps half-duplex communication since they use coaxial cabling
How does data travel in a physical bus
What is the term for signal travel across the medium and from device to device
Electrical pulses (signals) travel the cables lengths in all directions
Signal propagation
How does a signal stop in a physical bus?
- the signal continues until it weakens to the point of fading out or until it is absorbed by a terminator
- a terminator is an electrical component called a resistor that absorbs the signal instead of allowing it to bounce back up the wire
What happens to a signal if it is not terminated at the end of a wire
is bounces, or is “reflected”
signal bounce is the term used when electricity bounces off the end of a cable and back in the other direction
why can a Physical Bus only allow 30 computers, or up to 185 meters?
- the signal becomes too weak and doesn’t make it to the next computer in the chain
- As an electrical signal encounters each workstation along a daisy-chain some of its strength is absorbed by both the cabling and the connectors until the signal is eventually too weak to interpret
what is a Physical Star Topology
this is a configuration that uses a central (hub or switch) to connect computers
What are the advantages of a physical star topology
- Much faster technologies than a bus
- Centralized monitoring and management of network traffic are possible
- easier network upgrades
what does using a central device such as in the physical star topology allow for
hubs and switches can include software that collects statistics about network traffic patterns and detect errors
As long as cabling and NICs support it, a star network can be easily updated by replacing the central device
If the number or workstations you need exceed the ports on the central device you can add another at any time
What is an extended Star topology
This is when several hubs or switches are connected. It’s simply an extension of a physical star.
Also sometimes referred to as a “hierarchical star”
What determines how data travels “logical topology” in a physical star
this is determined by the type of central device:
Hub = logical bus
switch = logical switching
MAU = logical ring
What is the disadvantage of a physical star
The central device represents a single point of failure. If this device fails the entire network goes down
What is a physical ring topology similar to and in what way
it’s like a bus:
Devices are daisy-chained to one another
Instead of terminating each end, the cabling is brought around from the last device back to the first device to form a ring
What is a physical ring topology most widely used for
What is the technology involved used for
to connect LANs. Uses a technology called Fiber Distributed Data Interface (FDDI)
FDDI was most often used as a “network backbone”, which is cabling used to communicate between LANs or between hubs and switches
How does data travel in Physical Ring Topology,
what happens if a station in the ring fails
Data travels unidirectionaly, if any station fails the ring ceases function and data can no longer be transferred.
How does FDDI transfer data
Fiber Distributed Data Interface
uses dual ring (data travels in both directions)
one ring failure will not break the network
Operates using fiber-optic cable at 100 Mpbs
Extended star topologies with Gigabit Ethernet has largely replaced FDDI
What is Point-to-Point topology
this is format in which data has a direct link between two devices
Mostly used in WANs
Wireless bridge
used to connect two computers
What is Point-to-Multipoint topology
also known as (PMP) this means that a central device communicates with two or more other devices
All communication goes through the central device
often used in WANs where a main office has connections to several branch offices via a router
A single connection is made from the router to a switching device that directs traffic to the correct branch office
What is Mesh Topology
this means that each device is connected to every other device in a network
the purpose of creating a mesh topology is to ensure that if one or more connections fail, there’s another path for reaching all devices on the network
Expensive due to multiple interfaces and cabling
Found in large WANs and internetworks
What are logical topologies
- These are how data travels from computer to computer
- They are sometimes the same as physical topology
- In a physical bus and physical ring, the logical topology mimics the physical arrangement of cables
- For physical star, electronics in central device determine logical topology
What are the three logical topologies and what are the network technologies and physical topologies associated with them?
- Bus
- Ethernet
- bus or star
- Wireless LANs
- star
- Ethernet
- Ring
- Token ring
- Star
- FDDI
- Ring
- Token ring
- Switched
- Ethernet
- Star
- Ethernet
