Lesson 1 The Purpose of Networks
Lesson 2 Common Network Components
- Legacy Network Components
- Network Media
Lesson 3 Categorizing Networks
Protocol Reference Models Introduction

Lesson 1 The Purpose of Networks

Networks are about making connections
Used to File Share, Print, Web Surfing, and Database Access

Lesson 2 Common Network Components

Routers
- Layer 3 device
  - Makes forwarding decisions on logical information
  - Gives up ability to scale and extra flexibility
Switches - Layer 2 device - Makes forwarding decisions based on what it learns
Clients - End users
Server - What end users are trying to access - Makes files/applications available to clients
Classifications
- LAN
  - WAN

Legacy Network Components

Hubs
- Interconnects clients, servers, and other devices
  - Does not make forwarding decisions
  - Also known as a bit spitter
  - One collision domain
MAU - Media Access Unit
- Interconnects clients, servers, and other network devices
  - Does not make forwarding decisions
  - Used in Token Ring networks
  - Collision domains don’t apply here
    - When you receive the token it is your turn to transmit data
  - One broadcast domain
Bridge
- Seperates networks into collision domains
  - Makes forwarding decisions based on MAC addresses
  - Predecessor to the Ethernet switch
  - One broadcast domain
  - As main dollision domains as there are ports

Network Media

Coaxial Cable
- Used in 10BASE2 and 10BASE5 Ethernet networks
  - 50 Ohms of impedance
Twisted Pair
- The twists in the wire protects the inner conductors from EMI
  - Shielded and Unshieled Options
  - Most common media type found in modern LANs
  - TIA/EIA-568 Standard - 1991
    - TIA/EIA is a Standards Body
      - Updated in 2001
  - CAT3 PBXs and 10BASE-T
  - CAT5 100BASE-TX
  - CAT5e 1000BASE-T
  - CAT6 1000BASE-T
  - CAT6a 10GBASE-T
  - Crossover Cable
    - Pins 1 & 2 connect to pins 3 & 6
      - Pins 3 & 4 connect to pins 1 & 4
      - Pins 5 & 6 connect to pins 5 & 2
      - Pins 7 & 8 connect to pins 7 & 8
  - This makes receive pair on one side go to transmit on the other side
    - MDIX can reverse a port’s transmit and receive pairs
      - Can be found on most newer Cisco switches
Fiber Optics
- Uses pulses of light to represent binary data
  - Not subject to EMI
  - Commonly used in high speed networks where the distance requirement is too great for UTP
  - Two Types:
    - MMF - Multimode Fiber
      - SMF -Single Mode Fiber
  - Multimode Delay Distortion
    - Bits get out of order, because they are represented by different paths of light
  - Dopants
    - Impurities put in the core and cladding to give the glasses different indicies of refraction
  - Angle of Incidence
    - The angle at which light intersects the core
  - Single Mode + The core has a diameter so small that light can only enter at one angle

Lesson 3 Categorizing Networks

LAN

Within a single building
Client connects to a switch
Servers also connect to switches
Routers break up and interconnect IP ranges
- Switches connect to router
LANs are typically high speed

WAN

Interconnects geographic locations that are dispersed
Speeds are slower than LAN by quite a bit
Within WANs we can have 1 or multiple LANs

MAN

Interconnects office spaces in a city
Connects at speeds much faster than WANs but still a tad slower than LANs
Different wave lengths of light, Dense Wavelength Division Multiplexing (DWDM) is used to seperate clients data
Lambda represents a wavelength
It is also redundant

PAN

Personal Area Networks interconnects personal devices
Bluetooth is most popular
Infra Red
Interconnects 2 devices
Over limited distance with limited throughput

CAN

Campus Area Network
Interconnects different buildings on a campus
Buildings usual point to one central hub (building)
Normally have buildings pointing to one another form a mesh topology
Usually uses fiber optic (multimode)

Ring Topology

Interconnects devices in a circular fashion
Supported speeds of 4 Mbps or 16 Mbps
Fiber Distributed Data Interface (FDDI)
Logical Topology describers flow of a network
Each computer gets a chance to add something to the token if it is empty
Physical Tolpolgy describes how Network Devices are physically connected
MAU Media access unit used in Token Ring Networks to Physically Interconnect Networked Devices
Star Topology - Every devices points to the MAU but there is still a ring in the MAU
Not used in modern day networks

Bus Topology

Commonly used in early Ethernet Networks
50 Ohms coaxial cable
Thinnet (10BASE2)
- Distance Limitation 185 Meters
  - Throughtput: 10 Mbps
Thicknet (10Base5)
- Distance Limitation of 500 Meters
  - Throughput: 10Mbps
One main line that each computer taps into
One challenge is that devices do not take turns causing a lot of collisions
Each device then waits a random amount of time to retransmit data
CSMA/CD - Carrier Sense Multiple Acces with Collision Detection

Star Topology

Devices connect back to a centralized device
Makes forwarding decisions based on MAC addresses
If one link fails, other links continue to function
Popular in modern networks

Hub and Spoke Topology

Used in WAN
Make one site HQ and have WAN links going to every other site
Remote sites connect back to a central site
Saves money
Can result in subpoptimal pathing

Full Mesh Topology

Every site is connected to all the other sites
Opposite of Hub and Spoke Topology
Optimal Pathing
Very expensive
(n(n-1))/2 = Links you need for Full Mesh Topology

Partial Mesh Topology

Not every site is connected but some are.
Hub and Spoke with a couple extra connections between sites

Client Server Architecture

Clients share resources made available by a server
NOS Network Operating System
- Specializes in serving up files
Also known as Client Server Network

Peer to Peer Achitecture

Clients share their rerouses with one another
In clients you can make things (printer and files) a shared resource
Different from Client Server since no machine is handling all the serving
Not as robust as using a NOS

** End of Module One **

Protocol Reference Models Introduction

OSI Model

A 7 layer reference model
Open System Interconnect Model
ISO OSI Model
Bottom of OSI Model is layer 1
- Physical Layer
  - Responsible for bits on the network
Layer 2
- Switches, makes forwarding decisions based on physical properties (MAU)
Layer 3
- Logical addressing (IP addressing)
Layer 4
- Primary protocols
  - TCP and UDP
Layer 5, 6, 7
- Session, Presentation, and Application
  - Does not need to populate all 7 layers
Presentation layer is responsible for how data is presented
- Might encode text with ASCII
  - Encryption is also at this layer
Application Layer
- Services
  - Microsoft Active Directory
All People Seem To Need Data Processing
- Starts at top
Please Do Not Throw Sausage Pizza Away
- Starts at bottom
Best metaphor
- Think of the OSI Model as a bookshelf

Layer 1

PDUs Protocol Data Units
Physical -> Bits
Data Link -> Frames, Packets
Network -> Packets, Datagrams
Transport -> Packets, Segments
Some People Fear Birthdays (Memory aid)
Physical Layer
- How bits are represents on the medium
- Current State Modulation + Binary valeus are determined by the presense or absence of electricity
  - Alternate Mark Inversion (AVI) alternates volatage polarities in an attempt to have an avg of 0 volts on the wire
    - State Transition Modulation binary values are based on a change in voltage
    - Wiring standards for connectors and jacks
    - TIA/EIA-568-B Standard
      - Descibes wiring of an RJ-45 connector
    - Physcial Topologies - Star, Bus, Ring
    - Syncronizing bits
      - Asynchronous - Sender sends Start and Stop bits
        
        Synchronous - Both sender and receiver use internal clocks
    - Bandwidth Usage
      - Broadband - different communication flows use different frequency
      - Baseband - all frequencies on a channel are used for one conversation
    - Multiplexing Strategy
      - Time Division Multiplexxing - Channel 1 gets a set amount of time and the Channel 2 and so on
        
        Statistical TDM
        
        Time slots are dynamically assigned based on need
        
        Frequency Division Multiplexxing (FDM)
        
        Range of frequencies used for download and some for upload

Data Link Layer

Has two sub layers
- Mac and LLC
MAC
- Physcial addressing
  - 48-bit addressed burned into the network burned into NIC cards
  - Each device is completely unique
  - Hex digits
  - Logical Topology + How traffic flows + MAUs physically connect has a star but logically it works as a ring
    - Method of transmitting
      - token in token ring
        
        CSMA/CD Carrier Sense Multiple Access with Collision Detection
LLC
- Flow Control - If sender is sending to quickly the receiver can tell sender to slow down
  - Error Control - Data expected to receive was not received
  - Synchronization of transmission
  - Isochronous
    - Look to common device for clocking, creates fixed timeslots
      - Low overhead
  - Asynchronous
    - Devices reference internal clock. Sender sends stop and start bit
      - Parity bits used for errors
        
        Even and odd parity
  - Synchronous
    - Share clocking over separte com channels
      - Uses CRC for error checking
        
        Cyclic Redundancy Check
- Switch is most common layer 2 device
  - As switch sees traffic it builds a MAC table or Content Addressable Memory Table
Example MAC/CAM Table Port | MAC ———- 1 |AAAA 2 |BBBB 3 |CCCC
```
  - What if one of the ports is another switch?
      + New switch learns about devices connected to it
          + Table will look like

  Port | MAC
  -----------
  1    | AAAA
  2    | DDDD
  2    | EEEE
  3    | CCCC
```

The Network Layer

Logical Addressing
- IPv4 IPv6 IPX AppleTalk
Switching - how to send packets to other devices - Packet Switching + Data is divided into packets + Has heaser with source and destination address
- Router makes packet forwarding decsions based on logical addressing
  - Circuit Switching
    - Temp connection
      - Brought up as needed
      - Think of Phone Line
  - Message Switching
    - Data stream is broken into messages
      - Similair to email
      - Not delivered immediately
  - Route discovery and selection
  - Directly connected, statically configured, Dynamically learned
  - Example of Protocols
    - RIP
      - IS-IS
      - BGP
  - Flow Control
  - Packet Reordering
Router is most common layer 3 device

The Transport Layer

Protocols
Windowing
Buffering
TCP/IP
- Transmission Controlled Protocol
  - User Datagram Protocol
  - TCP is connectionful
  - UDP is connectionless
    - Faster than TCP lower overhead
  - RTP + Is encapuslated in a UDP in voice communication
Windowing
- Sliding Window - Allows TCP window size to grow based on network reliability
  - 2 Billion bytes per window on a solid connection
Buffering
- Queue + Router stores up packets until bandwidth becomes available

The Upper Layers

No longer have PDUs at this level
Protocol was not developed for just IP
Every layer does not need to be used, OSI is a reference
Session
- Setting up a session
- Maintaining a session
  - Tearing down a session
Presentation
- Data formatting
  - ASCII
    - EBCDIC
- Encryption
Application
- Application services + Email service lives at this level + File sharing service
  - Service advertisement + Shared printer

TCP/IP Model

Network Interface in OSI it is Physical and Data
- Also know as Network Access Layer
Internet Layer
- Maps to network layer of OSI Model
Transport Layer
- Maps to same name in OSI model + TCP and UDP again
  - TCP Slow Start TCP reduces its window size if a segment gets dropped
Application Layer
- Maps to Applicatino, presentation, and session layers