Network+ #2 -- OSI Model

OSI model was developed in _____

1977 by the International Organization of Standarization

OSI model is not a _____

applied model, just a reference one

OSI model is useful for _____

categorizing networking funtions and troubleshooting

Under which model networks operate as of today

TCP/IP Model

List OSI layers

Physical, Data Link, Network, Transport, Session, Presentation, Application

Name data representation at each layer

Physical: Bits
Data Link: Frames
Network: Packets
Transport: Segments
Session, Presentation and Application: Data

State the 7 layer mnemonic

Please Do Not Throw Sausage Pizza Away

State data traversal mnenonic

Do Some People Fear Birthdays

Data type at the Physical Layer

Binary bits

which characteristics does the physical layer has

physical and electrical network characteristics

Transition Modulation

Switching between levels to represent 1 or 0

Transition Modulation on Copper cable

voltage at 0V for 0, and + or -5V for 1

Transition Modulation on fiber optioc

Light: On for 1 and Off for 0

Cables are part of the ____ layer

physical

RJ-45, or _____ which is used for ___

Registered Jack, Ethernet

TIA/EIA-568B on both ends is the standard for

Straight-Through Cables

TIA/EIA-568A on one end and TIA/EIA-568B on the other is the standard for

Crossover Cables

how do Physical layer devices view networks from a phyisical topology perspective

based on how cables are connected

Asynchronous Communication

Two parties exchange information without requiring them to be activeliy on sync at the same time

Async Communication functioning

Start and Stop bits to indicate when transmission occur from sender to the receiver

Async comms examples

voice mail, messaging

Synchronous Communication

Real-Time communication using a common time source

Sync Comms functioning

Reference clock to coordinate transmission by both sender/receiver

Sync Comms examples

Call

Bandwidth Utilization

percentaje of available network capacity that is actually being used over a period of time

Broadband bandwitdh utilization

Dividides bandwitdh into separate channels

Broadband examples

Tv service: single cable with multiple channels

Baseband bandwidth utilization

Uses all frequency of the cable

Baseband examples

telephone, one call at a time

Baseband reference clock

clock signal used by sender/receiver as the timing reference for baseband functions

Multiplexing

process of combining multiple singals/steams into one shared transmission channel and separating them again at the receiver

Multiplexing benefits

Increased efficiency (one cable/freq/link), low cost, low complexity, concurrency

Time-Division Multiplexing

dedicated time-slots, each session takes a turn on the slot to share medium between all users

TDM analogy

Shared singular tv on a household, each person gets asigned a turn (timeslot) to use and watch said tv

Statistical Time-Division Multiplexing

Dynamically allocates timeslots on as-needed basis

Stat TDM analogy

follows household tv example, as long as nobody is using the TV (slot) anyone can use it

Frequency-Division Multiplexing

Divides medium into channels based on frequencies and each session is transmitted over a different channel

Multiplexing Main objective

optimizing a limited amount on resources for more efficient utilization

Multiplexing Golden Exam Rule

Multiplexing enables simultaneous usage of a baseband connection by multiple users

Physical layer media —> Cables

Fiber Optic, Ethernet, Coaxial

Physical Layer media —> Wireless

BT, WiFi, Near Field Communication

Physical layer devices

Hubs, Access Points, Media Converters

Physical Layer devices main purpose

to simply pass along whatever is received

Data link Layer purpose

to package data into frames and transmit them on the network

Media Access Control

physical hexadecimal addressing system of a device which operates on a logical topology

MAC Address bit count

48bits

MAC Address first 24 bits —>

Manufacturer identifier

MAC Address last 24 bits —>

Device identifier

MAC Address importance

crucial for physical topology and device id on the network (such as NICs)

Logical Link Control

provices connection services and allows acknowledgement of receipt of messages

LLC Example

Hand raise System of elect whom may speak on a classroom setting

LLC is the basic form of ____

flow control

flow control

limit on data sent to prevent the receiver to be overwhelmed

LLC basic error control functions

receivers may notify if the received data frames are corrupted or correctly received utilizing a checksum

LLC Checksum

small value added to the data frame so the receiver can check wheter the data was corrupted/changed while traversing the network

Isonchronous method at Data link layer

devices use a common reference clock and create time slots for transmission

synchronous method at Data link layer

device use same clock with beggining/ending frames and control characters

Asynchronous method at Data link layer

devices reference internal clock and use start/stop bits for sync with no strict control over comm timing

Data Link devices

NICs, Bridges, Switches

Network layer

all about routing and forwarding traffic using logical addresses

Logical Addressing — IPv4

dotted octet notation composed of four sets of numbers separated by dots

since Routing is a Network layer term, what its another equivalent

Switching

Packet switching

data divided in packages and then forwarded based on its IP address

What other protocols has IP replaced

AppleTalk and IPX

Circuit Switching

Dedicated and constant comm link established between two devices maintained for the duration of the conversation

Message switching

Data is divided into messages which may be stored and then forwarded

Most common type of switching

Packet switching

Switching

moving data from an input to the correct output

Route discovery and selection

manually configured as a static route or dynamically through a routing protocol

Routing protocols purpose

to help us decide how data is going to flow across the network and how routers communicate it

Connection services at network layer

augment layer 2 connection services to improve reliability

Packet reordering at connection services in network layer

ensures data packets arrive and are reassembled in the correct order

Internet Control Message Protocol

sends error messages and operational information to an IP destination

ICMP Ping protocol

used to troubleshoot network issues by testing connectivity and response times

ICMP Traceroute protocol

traces the route of a package through the network (list router addresses)

Network Layer devices

Routers and multilayer s