5.2 Explain the basics of network theory and concepts - Paiet/Tech-Journal-for-Everything GitHub Wiki

5.2 Explain the basics of network theory and concepts

Encapsulation/de-encapsulation
- Encapsulation is the process of adding wrapping data with protocol information at each layer of the OSI model
  - PDU Protocol Data Unit
    - Segments>Packets>Frames>Bits
  - Each layer communicates only with its peer layer on the receiving host
- Data needs to be sent over the network
  - Data is user information that has been converted by the upper OSI model layers for network transmission
  - Data is passed to the lower layers beginning with the Transport Layer or Layer 4
  - The Transport layer wraps the data with its header info creating a SEGMENT
    - The Transport layer also establishes a TCP connection for reliable delivery
  - SEGMENTs are passed to the Network layer where that layer's information is attached
    - Now we have a PACKET
    - Logical addressing is in the PACKET header for transmission through an internetwork
  - PACKETs are passed to the Data-Link layer and its header information is added creating a FRAME
    - FRAME headers contain MAC addressing for local data delivery
  - FRAMEs are passed to the Physical layer where they are converted into BITs
    - BITs contain digital encoding and clocking for transmission over the physical media
- Decapsulation is the process of removing protocol headers for the purpose of communicating and exchanging data between the layers of the OSI model
  - Basically the reverse of encapsulation
Modulation techniques
- Modulation is the process of varying one or more properties of a waveform, called the Carrier Signal, with a signal that typically contains information to be transmitted
- Analog and digital techniques
  - Analog modulation is used to transfer an Analog signal across a digital line
  - Digital modulation is used to transfer a Digital signal across an analog line
  - MoDem: Modulate/demodulate
- Multiplexing
  - FDM (Frequency Division Multiplexing)
    - Send multiple signals over the same physical media by dividing the data into different frequencies
- De-multiplexing
- TDM (Time Division Multiplexing)
  - A method of transmitting and receiving many independent signals over a common signal path
  - Network devices use synchronization so that the signals can be transmitted for only a fraction of time in an alternating pattern
Numbering systems
- Binary
  - Base-2 numbering system (only 2 numbers in the system)
  - 1 and 0
  - Place values
  - Bits(1bit), nibbles(4bits), and bytes(8bits aka octet)
    - Addressing typically read in bytes
- Hexadecimal
  - Base-16 numbering system (16 different characters)
  - 1 - 9 and A - F
  - Hex numbers are made up of 2 nibbles
    - 0x6A to decimal
      - 0x lets you know this is a hex number
      - 6A are the two nibbles
        
        6 = 0110
        
        A = 1010
        
        6A = 01101010 = 108
    - 10110101 to hex
      - 1011|0101
      - 11 | 05
      - B | 5 = 0xB5
- Octal
  - Base-8 numbering system (8 numbers)
  - 0 - 7
Broadband/base band
- Broadband is the ability to send multiple digital or analog (or both) signals down a single wire
  - Sending both voice(analog) and data(digital)
  - Uses Frequency Division Multiplexing
- Baseband is the ability to send a single analog or digital (not both) signal down a single wire
  - Used in LAN environments
  - All the available bandwidth is allocated for one digital signal
  - Multiple signals create collisions
    - This applies to wireless as well
    - This doesn't apply to analog signals (no collisions on a signal without packets)
Bit rates vs baud rate
- Bit rate is the measurement of the number of data bits (1s and 0s) transmitted in one second by an analog or digital signal
  - 56,000 bits per second (bps) = 56,000 1s and/or 0s can be transmitted in one second
- Baud rate
  - Named after French engineer Jean-Maurice-Emile Baudot
    - Baudot measured the speed of telegraph transmissions
  - Baud is one electronic stat change per second
    - Change from 0.2 volts to 3 volts (analog)
    - Change from 0 to 1 (digital)
  - Baud was discarded because it wasn't as accurate as bps
    - A single state change can involve more than a single bit of data
Sampling size
- Used for converting analog audio into digital signals
- Computer captures a series of analog samples in specified sizes; aka Sampling Size
- The measured amplitude level in each sample is given a corresponding digital value and then played back in the same order and rate as the original
  - This is a digital copy of the analog signal
Collision
- A collision is when two hosts attempt to simultaneously send data over a shared media forcing them to resend the data
  - This increases network latency and overall network performance suffers
  - Devices that share the same media are said to be in the same Collision Domain
    - Think network hubs
CSMA/CD and CSMA/CA
- Carrier Sense Multiple Access with Collision Detection
  - Checks the physical media to see if it is being utilized
  - If the wire is clear then the host will start to transmit
  - The transmitting host continually monitors the line to make sure no other hosts attempt to transmit
  - If another host does transmit, the original host generates a jamming signal (busy signal)
    - This informs the sending host(s) that a collision has occurred
    - Hosts will then wait a while and then attempt to retransmit
      - Backoff Algorithm or random wait
      - If the line is still being utilized then reissue backoff and increment the retransmission counter
      - If 15 retries are reached then time out and abort
- Carrier Sense Multiple Access with Collision Avoidance
  - Checks the physical media to see if it is being utilized
  - If the wire is not clear then the host will wait for a period of time and then check again
    - Repeats this process until the line is clear
  - If the wire is clear then the host will start to transmit
    - Request to Send/Clear to Send (RTS/CTS)
      - Optional
  - Has no procedure for dealing with collisions if they occur
  - Typically used in wireless networks
Wavelength
- The graphical representation of electromagnetic energy
- Crests and Troughs
- The distance between two crests is the Wavelength
  - Shorter Wavelengths have higher frequencies
  - Longer Wavelengths have lower frequencies
  - Data can be multiplexed using a combination of multiple frequencies
TCP/IP suite
- ICMP
  - Management protocol and messaging service provider for IP
  - PING
    - Uses ICMP echo request and reply messages to check physical and logical connectivity
- UDP
- TCP