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CSIT127: Networks and Communications > part 2 > Flashcards

part 2 Flashcards

1
Q

circuit-switched network

A

Sub-network in which a dedicated circuit is established between sender and receiver and all data passes over this circuit

Example: telephone system

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2
Q

packet-switched network

A

A network in which all data messages are transmitted using fixed-size packages, called packets

Example: datagram

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3
Q

Differences Between Circuit and Packet-Switched Networks

A

Circuit:

  • physical path between source and destination
  • all packets use the same path
  • reserve entire bandwith in advance
  • bandwith wastage
  • no store and forward transmission

Packet:

  • no physical path
  • packets travel independently
  • no bandwith wastage
  • uses store and forward transmission
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4
Q

connection-oriented application

A

Requires both sender and receiver to create a connection together before any data is transferred

Examples: large file transfers, banking

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5
Q

connectionless application

A

Does not create a connection first, simply sends the data

Example: email

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6
Q

Differences Between Connection-Oriented and Connectionless Applications

A

Connection:

  • prior connection setup needed
  • guarantees reliability
  • transfer is slower due to initial setup
  • suitable for long, sustained connection

Connectionless:

  • no prior setup needed
  • not always reliable
  • fast transfer because no initial setup
  • suitable for bursty connection
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7
Q

protocol

A

A set of rules for communication between devices (what/how/when)

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8
Q

syntax

A

Structure or format of the data, meaning the order in which they are presented

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9
Q

semantics

A

Meaning of each section of bits

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10
Q

timing

A

When data should be sent and how fast they can be sent

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11
Q

OSI (Open Systems Interconnection Reference Model)

A 
Layer 7: Application
Layer 6: Presentation
Layer 5: Session
Layer 4: Transport
Layer 3: Network
Layer 2: Data link
Layer 1: Physical

** refer to diagram in notes **

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12
Q

OSI Application Layer

A

Semantics

  • Initiates or accepts a request
  • Provides applications to user
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13
Q

OSI Presentation Layer

A

Data Representations
- Adds formatting, display and encryption information to the packet

  • Syntax and semantics of the information exchanged between two systems
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14
Q

OSI Session Layer

A

Dialog Coordination

  • Adds traffic flow information to determine when the packet is sent
  • Responsible for dialog control and synchronization
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15
Q

OSI Transport Layer

A

Reliable Transfer of Data

  • Adds error-HANDLING information to ensure the reliable transfer of data
  • Process-to-process delivery of the entire message
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16
Q

OSI Network Layer

A

Routing and Relaying

  • Sequencing and address info is added to the packet
  • Responsible for the delivery of individual packets from the source to the destination
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17
Q

OSI Data Link Layer

A

Node-to-Node Data Transfer

  • Adds error-CHECKING information
  • Encapsulating data in a way that is suitable for transmission to the physical layer
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18
Q

OSI Physical Layer

A

Physical Parameters

  • The packet is sent as a bit stream
  • Responsible for movements of individual bits from one hop (node) to the next
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19
Q

The TCP/IP Protocol Suite

A

Communication protocols used to interconnect devices on the internet

  • Application Services: equivalent to OSI application + presentation layers
  • Transport: equivalent to OSI transport layer
  • Internet: equivalent to OSI network layer
  • Network access/Interface: OSI data link + physical layers
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20
Q

white noise

A
  • Relatively constant, can be reduced
  • If white noise gets too strong, can completely disrupt signal

Prevention:

  • Special filters for analog signals
  • Signal regeneration for digital

(Analog = filters, Digital = signal REGENERATION)

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21
Q

impulse noise

A
  • Random spikes of power that can destroy one or more bits of information
  • Difficult to remove from an analog signal because it may be hard to distinguish from the original signal
  • Can damage more bits if they are closer together

Prevention:
- Install special filters for analog; implement digital signal processing

(Analog = filters, Digital = signal PROCESSING)

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22
Q

crosstalk

A
  • Unwanted coupling between 2 different signal paths (e.g. hearing another conversation while talking on the phone)
  • Relatively constant, can be reduced

Prevention:
- Install proper shielding on cables

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23
Q

echo

A
  • Reflective feedback of a transmitted signal as the signal moves through a medium
  • Most often occurs on a coaxial cable
  • If echo is bad enough, can interfere with the original signal
  • Relatively constant, can be significantly reduced

Prevention:
- Install proper termination of cables

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24
Q

jitter

A
  • Small timing irregularities during the transmission of digital signals
  • Occurs when a digital signal is repeated over and over
  • If serious enough, jitter forces systems to slow down their transmission

Prevention:
- Use better quality electronic circuitry, use fewer repeaters, slow the transmission speed

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25
Q

attenuation

A
  • Part of the energy gets lost in transmission–converted into heat and lost
    • loss of signal strength as it travels through a medium

Prevention:
- Install device that amplifies analog signals; implement digital signal regeneration

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26
Q

delay distortion

A
  • Happens when all signals do not arrive at the same time

- Occurs because of the velocity of propagation of a signal through a medium varies with the frequency of the signal

27
Q

Error Detection Methods

A
  1. Parity Checks (Simple and Longitudinal)
  2. Arithmetic Checksum
  3. Cyclic Redundancy Checksum (CRC) **best
  4. Error Control
  5. Correcting the Error

** check notes for implementation of 1-3 **

28
Q

“do nothing” error control

A
  • Toss the frame or packet

- A higher protocol will detect the tossed frame and ask for retransmission

29
Q

“return a message” error control

A
  • Once an error is detected, an error message is returned to the transmitter
30
Q

2 Types of Message Return Error Controls

A

Stop-and-Wait Error Control:

  • Transmitter sends a frame then waits for an acknowledgment (ACK)
  • If +ACK received = next frame is sent
  • If -ACK received = same frame retransmitted

Sliding Window Error Control:

  • Assumes that multiple frames are in transmission at the same time
  • Allows the transmitter to send a number of data packets at one time before receiving any acknowledgments
  • When a receiver acknowledges receipt, the returned ACK contains the number of the frame expected next
  • ACK is not always sent after each frame is received; more efficient to wait for a few received frames before returning an ACK
  • If packet is lost, the following frame will be “out of sequence”. The receiver will hold the “out of sequence” bytes in a buffer and request to retransmit the missing frame
  • When an ACK is lost, the sender will wait for the ACK to arrive and eventually time out. When timeout occurs, the sender will resend the last frame
31
Q

Basic Rules Concerning ACKs Using TCP/IP

A
  1. Receiver just received data and wants to send own data -> piggyback an ACK along with that data
  2. Receiver has no data to return + has just ACKed last packet -> receiver waits 500ms in which if a packet is received, an ACK is sent, otherwise an ACK is sent for no packet
32
Q

“correct the error” error control

A
  • For receiver to correct the error with no further help from the transmitter, requires a large amount of redundant information to accompany the original data
  • Redundant info allows the receiver to determine the error and make corrections
  • This form of error control involves Hamming codes which add additional check bits to a character. These check bits perform parity checks on various bits

Used in: transmission of radio signals, applications that send data over long distances

33
Q

Advantages of LAN

A
  1. Allows resources to be shared, i.e. software and hardware resources
  2. Component + system evolution possible
  3. Private ownership
  4. Secure transfers at high speeds with low error rates
34
Q

Disadvantages of LAN

A
  1. Equipment and support can be costly
  2. Some types of hardware may not interoperate
  3. LAN is only as strong as its weakest link, and there are many links
35
Q

star-wired bus

A
  • Logically operates like a bus but physically looks like a star
  • All workstations are attached to a hub
  • All traffic goes to hub
  • UTP usually used to connect workstations to hub
  • Hubs can be interconnected with cables to extend the size of the network
36
Q

Advantages of The Star-Wired Bus

A
  1. Cheap
  2. High volume
  3. Easy to set up
37
Q

Disadvantages of The Star-Wired Bus

A
  1. Single point of failure
  2. Traffic
  3. When one station talks, everyone hears it (e.g. a shared network)
38
Q

contention-based protocols

A
  • First come, first served
  • If no one transmitting, workstation can transmit, if not, workstation “backs off” and waits
  • If 2 transmit at the same time, collision occurs -> both “back off” for a random amount of time before trying again

Example: CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

39
Q

hub

A

Networking device that allows one to connect multiple PCs to a single network, making them act as a single segment

40
Q

switch

A

Control unit that turns the flow of electricity on or off in a circuit; connects network segments

41
Q

Differences Between a Switch and a Hub

A

Switch:

  • Operates using virtual circuit model
  • Determines destination of each individual traffic element and selectively forwards data to the one computer that needs it

Hub:

  • Operates using broadcast model
  • Passes through all network traffic to each of the other computers

** Switch is effectively a higher performance alternative to a hub

42
Q

virtual LAN (VLAN)

A

Created via switches and software rather than by manually moving wiring from one network device to another

43
Q

link aggregation

A
  • Allows you to combine 2 or more links into one higher-speed link
  • Attempts to balance the flow of messages over multiple paths
  • If the flow of frames belong to a particular conversation then the frames are sent over one of the links
44
Q

spanning tree algorithm

A
  • When a large set of networks are interconnected with many switches, a loop can be created
  1. Identify a switch as a root
  2. Visit each switch and identify the one that has shortest path back to root
  3. Visit each LAN and do the same
  4. The ports remaining that don’t have either a root part or designated port can be removed (blocked ports)
45
Q

wired ethernet

A
  • Most common type of LAN used today
  • Primarily based on star-wired bus using CSMA/CD
  • Comes in many forms depending on medium
  • Has feature Power over Ethernet (PoE): power to drive ethernet NIC sent over wiring using ethernet signals
46
Q

routers

A
  • Connecting devices between LANs and WANs
  • Serves as gateways to the Internet
  • Perform more slowly than switches
47
Q

Internet Protocols

A
  1. Internet Protocol (IP)
  2. IPv4
  3. IPv6
  4. Transmission Control Protocol (TCP)
  5. Dynamic Host Configuration Protocol (DHCP)
  6. Network Address Translation (NAT)

The World Wide Web (WWW):

  1. Hypertext Transport Protocol (HTTP)
  2. Domain Name System (DNS)
48
Q

Internet Protocol (IP)

A
  • Prepares packet for transmission across internet
  • IP header is encapsulated onto transport data packet
  • IP packet/datagram gets passed to next layer where further network info is encapsulated onto it
  • Connectionless protocol
49
Q

IP Address

A

Logical address compared to NIC which has physical/permanent addresses

50
Q

subnetting

A

Allows a network to be segmented into smaller sections but all must be the same size

51
Q

IPv4

A
  • 32-bit addresses
52
Q

IPv6

A
  • 128-bit addresses
  • No fragmenting
  • Simple header
53
Q

Transmission Control Protocol (TCP)

A
  • Creates connection between sender and receiver using port numbers
  • Port number identifies a particular application on a particular device
  • Can multiplex multiple connections
  • End-to-end flow control (ensures receiver is not overrun with data) and error correction (checksum)
  • Allows for sending of high priority data
54
Q

Dynamic Host Configuration Protocol (DHCP)

A
  • IP addresses can be assigned to workstation permanently or dynamically
  • Dynamic IP addresses more efficient use of scarce IP addresses
  • When DHCP client issues IP request, DHCP server looks in its static table
  • if (!entry) -> sever selects address from available pool
  • Address assigned by DHCP is temporary (if no time is specified, default time is 1 hour)
55
Q

Network Address Translation (NAT)

A
  • Lets router represent entire LAN to Internet as a single IP address
  • All traffic leaving LAN appears as originating from global IP addresses
  • This security feature allows a LAN to hide all workstation IP addresses from the Internet
  • When user inside sends packet to outside, NAT interface changes user’s inside address to global IP address; change is stored in a cache; when response received, NAT switches addresses back from the cache
  • if (!cacheEntry) -> packet is dropped
56
Q

Static NAT

A

One-to-one; mappings from private to public addresses

57
Q

Dynamic NAT

A

One-to-many; maps private IP to public from a group of public addresses

58
Q

Address and Port Bindings (NAPT)

A

Keeps track of the port numbers in the session request

59
Q

The World Wide Web (WWW)

A

Immense collection of web pages and other resources that can be downloaded across the Internet and displayed on a workstation via a web browser

60
Q

Hypertext Transport Protocol (HTTP)

A
  • Protocol to transfer a web page

- Every document on the Internet has a Uniform Resource Locator (URL)

61
Q

Parts of a URL

A
  1. Service type
  2. Host/domain name
  3. Directory/Subdirectory Information
  4. File name
62
Q

Domain Name System (DNS)

A

Large, distributed database of URLs and IP addresses

  • Queries local database for URL/IP information
  • If local server does not recognize address, next level server queried
  • Eventually root server will be queried
63
Q

Examples of Internet Services

A
  • Email
  • File transfer protocol (FTP)
  • Remote login (Telnet)
  • VOIP
  • Audio and video streaming
  • Instant messaging, tweets, blogs

CSIT127: Networks and Communications (4 decks)

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