Chapter 3 Flashcards
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
What are example of LAN technologies
Ethernet, 802.11 wireless, Token Ring
What are examples of WAN technologies
Frame relay, FDDI, ATM
What is an unshielded twisted pair
an unshielded twisted pair or (UTP) is:
The most common media type in LANs
made up of 4 pairs of copper wires each twisted together
Comes in numbered categories
What is Fiber-optic cabling
Fiber-optic cabling uses thin strands of glass to carry pulses of light long distances and at high data rates
What is Coaxial Cable
this is obsolete as a LAN medium but it is used as the network medium for internet access via cable modem
What are the two ways network technologies can use media to transmit signals
Baseband - sends digital signals in which each bit of data is represented by a pulse of electricity or light. Sent at a single fixed frequency and no other frames can be sent along with it
Broadband - uses analog techniques to encode binary 1s and 0s across a continuous range of values. Signals flow at a particular frequency and each frequency represents a channel of data
Ethernet is the ___ ___ LAN technology
Easy to install and support with a ___ ___ factor
supports a broad range of speeds: 10 ___ to 10 ___
Can operate in physical ___ or physical ___ and logical ___ or ___ ___ topology
Most NICs/hubs/switches can operate at multiple speeds: 10/100/1000
Underlying technology is the same
Ethernet is the most popular LAN technology
Easy to install and support with a low cost factor
supports a broad range of speeds: 10 mbps to 10 Gbps
Can operate in physical bus or physical star and logical bus or switched local topology
Most NICs/hubs/switches can operate at multiple speeds: 10/100/1000
Underlying technology is the same
What is Ethernet 2 frame type
frame type used by TCP/IP
TCP/IP has become the dominant network protocol in LANs so supporting multiple frame types has become unnecessary
What are ethernet frames composed of
Destination MAC, Source MAC, Type, Data, FCS
What is Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
- Carrier Sense - Listen before send - must hear silence
- Multiple Access - If two or more stations hear silence, multiple stations may transmit at the same time
- Collision Detection - If two or more stations transmit, a collision occurs and is detected by the NIC; all stations must retransmit
What is a collision domain
The extent to which signals in an ethernet bus topology network are propagated is called a collision domain
What does the term “best-effort delivery system” mean when referring to Ethernet
- Like the post-office; you hope it gets there but there is no acknowledgement either way
- Network protocols and applications ensure delivery
- Only collisions are automatically retransmitted
Ethernet detects damaged frames, how does this occur
There is an error checking code in a frame’s trailer called a Cyclic Redundancy Check (CRC)
Uses CRC to determine that data is unchanged
If a frame is detected as damaged, it is discarded with no notification
Ethernet on hubs works only in what mode
Half duplex
How are Ethernet standards expressed
- XBaseY
- X designates speed of transmission
- Y specifies type of media (T = twisted pair, FX = fiber optic)
Describe the following Ethernet Standard: 10BaseT
- uses two of the four wire pairs
- Runs over category 3 or higher UTP cabling
- Highly susceptible to collisions and is obsolete
Describe the following Ethernet Standard: 40 Gigabit and 100 Gigabit Ethernet
Very high cost is still prohibitive
Adoption has been slow
Fiber-optic cabling is primary medium
Although there are provisions to use special copper assemblies over short distances
What is 802.11 wireless networking also referred to as
can be found in most towns and in those cases it is called what?
Wireless Fidelity (Wi-Fi)
a hotspot
what are the two modes in which Wi-Fi can operate
- Infrastructure - use central access point (AP)
- Ad hoc - no central device; data travels from device to device like a bus
- sometimes called peer-to-peer mode
what is the Wi-Fi access method
sending station can’t hear if another station begins transmitting so they cannot use the CSMA/CD access method that ethernet uses
Wi-Fi devices use carrier sense multiple access with collision avoidance (CSMA/CA)
uses request-to-send/clear-to-send (RTS/CTS) packets and acknoledgements
With this extra “chatter” actual throughput is essentially cut in half
Describe the following type of signal interference: Absorption
Solid objects absorb radio signals, causing them to attenuate (weaken)
Describe the following type of signal interference: Refraction
The bending of a radio signal as it passes from a medium of one density through a medium of a different density
Describe the following type of signal interference: Diffraction
the altering of a wave as it tries to bend around an object
Describe the following type of signal interference: Reflection
Occurs when a signal hits a dense, reflective material, resulting in signal loss
Describe the following type of signal interference: Scattering
When a signal changes direction in unpredictable ways, causing a loss in signal strength
What is signal-to-noise ratio
- the amount of noise compared with the signal strength
- Noise can come from equipment, other wireless devices, and other wireless networks
What is throughput
The actual amount of data transferred - not counting erros and acknowledgements
what is goodput
Actual application-to-application data transfer speed
What is overhead
Packet frame headers, acknowledgements, and retransmissions
What are Wi-Fi encryption protocols
Wired equivalent privacy (WEP), Wi-Fi Protected Access (WPA), and WPA2
Not all devices support all three protocols
Older devices might only support WEP and/or WPA
What are the physical and logical topologies for a Token Ring network?
They have a Star Physical topology with a ring logical topology
How does a Token Ring Network operate?
- A token is passed along the network
- Only the station with the token can transmit
- Frames are acknowledged and token is released
- no collisions
- Obsolete
What is Fiber Distributed Data Interface Technology
topology, speed, cabling and so on
This uses a physical and logical ring topology
uses a token passing method with dual rings for redundancy
Transmits at 100 mbps and can include up to 500 nodes over a distance of 60 miles
uses only fiber optic cable
Obsolete on new networks
What are the 4 primary physical topologies
bus
star
ring
point-to-point
What are the 3 primary logical topologies
bus, ring, switched
