S3-OSI Model Flashcards
OSI Model
“Open Systems interconnect”
- A Reference model used to categorize and troubleshoot the functions of a network.
What are the 7 layers of the OSI Model?
1- Physical
2 - Data Link
3 - Network
4 - Transport
5 - Session
6 - Presentation
7 - Application
Transition Modulation
Switching between levels/states to represent 1s and 0s
What are the two Ethernet Wiring Standards?
TIA/EIA - 568A
TIA/EIA - 568B
How does a Layer 1 Device View a network?
From a Physical Topology Perspective
How does Asynchronous communication work?
Start and Stop Bits are used to indicate when transmissions occur from sender to receiver.
How does Synchronous communication work?
A common reference clock is used to coordinate transmissions between sender and receiver.
Define Asynchronous vs Synchronous communication
transmissions happening at different times. (Async.)
vs
transmission happening at the same time or in real time. (Sync)
Broadband
Divides bandwidth into separate channels
Eg. TV, Cable
Baseband
Uses all frequencies on a medium
What is Bandwidth
Network bandwidth is the maximum possible amount of data transfer between two points of a network in a specific time.
Measured in bits per second (bps)
What is Time-Division Multiplexing (TDM)?
Each session is allocated a time slot to share a medium between users.
Define Multiplexing
Utilizing a limited resource more efficiently. Allows simultaneous transmission on a single baseband connection.
What is Statistical Time-Division Multiplexing (StatTDM)?
Time slots are dynamically allocated on an as-needed basis.
What is Frequency division multiplexing (FDM)?
A medium is divided into channels , allowing each session to be transmitted over a different channel.
What are Some Layer 1 devices/media?
Media
- Fiber optic
- Ethernet/Rj-45
- Coaxial
- Blutooth
- Wi-Fi
- Near Field Communication (NFC)
Devices
- Hubs
- Repeaters
- Media Converters
What is the Purpose/function of the Physical Layer (L1)?
Resolves the data signals transmitted through physical mediums like cables and radio signals into BITS.
What is the Purpose/function of the Data link Layer (L2)?
Governs error checking, multiplexing, flow control and physical addressing of devices on a network through sub-layers like MAC & LLC. Additionally, responsible for packing BITS into FRAMES.
MAC Address
“Media Access Control Address”
A means for identifying a device physically.
How many bits are in a Mac address and what does each half represent?
MAC Address is a 48-bit physical addressing system.
-first 24-bits is the vendor/manufacturer code
- last 24-bits is the unique device code
What is a “Logical Link Control” (LLC)
A sublayer within the data link layer responsible for basic error checking, multiplexing and flow control.
What are the 3 different schemes communication can be synchronized across Layer 2?
- Isochronous
- Synchronous
- Asynchronous
Isochronous
Communication on a network is synchronized using a common reference clock and time slots are created for transmission. provides less overhead.
Synchronous
Network Devices utilize the same clocking method and control characters to indicate the beginning and ending frames of a transmission.
Asynchronous
Network Devices reference their own internal clocks and use start and stop bits for synchronization.
What is a CAM Table?
“Content Addressable Memory”
A database on a network switch that stores the MAC Addresses of devices connected to its ports. Allows for network traffic to be forwarded directly to its intended device.
What are some Layer 2 Devices?
- Network Interface (NIC) Cards
- Bridges
- Switches
What is the purpose/function of the Network Layer(L3)?
Handles the logical addressing and path determination for data packet transmission across networks.
What are three methods of forwarding data across a Network?
- Packet Switching (Routing)
- Circuit Switching
- Message Switching
What is Packet Switching?
Data is divided into packets and then forwarded
-multi-path
what is Circuit Switching?
Dedicated communication link is established between 2 devices.
-single path
Message Switching
Data is divided into messages which may be stored and forwarded.
What are Routing protocols?
Protocols that help decide how data will flow across a network and how routers are going to communicate that information.
What do layer 3 Connection services do?
Augment layer 2 connection services to improve reliability.
- flow Control
- Packet reordering
What is ICMP?
“internet control message protocol”
- Sends error messages and operational info to an IP about transmission issues.
What does Ping do?
ICMP utility that sends out a packet to a destination and reports how long it took.
What does Traceroute do?
ICMP utility that Traces the route of a packet through the network.
What are some layer 3 devices?
- Routers
- Multi-Layer switches
What are Protocols found at Layer 3?
- ICMP
- IPv4
- IPv6
What is the Function/purpose of the Transport layer (L4)?
Ensures that data reaches its destination accurately and completely.
What are the 2 Layer 4 Protocols?
- Transmission Control Protocol (TCP)
- User Datagram Protocol (UDP)
What is TCP?
Provides reliable, connection-oriented communication with features like flow control and error detection, and 3-way Handshake.
- Segments
What is UDP?
Offers unreliable, connectionless communication, prioritizing speed over guaranteed delivery.
- Datagrams
Three - Way- Handshake
Back and forth communication between 2 devices that ensure a transmission was successfully sent and received. Used by TCP.
Define Windowing
Optimizes the throughput and bandwidth of a transmission by adjusting the amount of data in each segment during transmission. Functions by opening or closing the window dynamically according to incoming data flow.
What is Buffering?
Devices allocating memory to store segments if bandwidth is not readily available.
What are some Layer 4 devices?
- WAN accelerators
- Load Balancers
- Firewalls
What is the purpose/function of the Session Layer (L5)?
responsible for establishing, managing, and terminating communication sessions between devices
What are some Layer 5 devices/protocols?
- H.323
- NetBIOs
H.323
Used to setup, maintain and tear down voice and video connection.
What is RTP?
“Real-time transport protocol”
- streaming audio/video
what is NetBIOS?
A standard used by computers to share files over a network.
What is the purpose/function of the Presentation Layer (L6)?
Formats and translates the data to be exchanged and secures it with proper encryption.
Data Formatting
Ensures data is presented in a standardized format that the receiving application can understand.
whats is ASCII?
“American Standard Code for Information Interchange”
It’s a character encoding standard that assigns a unique number to each letter, digit, and symbol.
What is Encryption?
Method of securing data by scrambling it using mathematical algorithms that can only be decrypted with the proper key.
what is TLS?
“Transport Layer Security”
A commonly used cryptographic protocol that protects data from being intercepted by hackers while it travels online.
What are some Layer 6 components?
Scripting Languages
- Html
- Xml
- Java Script
Standard Text
- ASCII
- Unicode
- ECDBIC
Picture & Video Formats
- Jpeg
- PNG
- GIF
- MPEG
- MP4
Encryption Algorithms
- TLS
- SSL
What is the purpose/function of the Application Layer (L7)?
Handles the communication between applications on different devices across a network, making network services accessible to users.
Application Services
Unites communicating components from more than one network application
Service Advertisement
Applications can announce the services they offer to other devices on the network.
What are some Layer 7 Services?
Email Protocols
- POP3
- IMAP
- SMTP
Web Browsing
- Https
- Http
File Transfer Protocols
- FTP
- FTPS
- SFTP
Remote Access
- Telnet
- SSH
- SNMP
Domain Name Service (DNS)
What is a PDU?
“Protocol Data Unit”
- A single unit of data transmitted in a computer network.
What are the six TCP header flags and their meaning?
SYN - (Synchronization) Synchronize a connection during a 3-way handshake
ACK - (Acknowledgement) Acknowledges successful receipt of packets
FIN - (Finish) Terminates the virtual connection created by the 3-way handshake
RST - (Reset) used when a client/server receives an unexpected packet
PSH - (Push) ensures that data is given priority
URG - (Urgent) identifies incoming data as urgent
what is EtherType?
The protocol encapsulated in the payload of a frame.
Eg. IPv4, Ipv6 etc.
What is the minimum size payload that can be sent over ethernet with and w/o VLANs?
42 bytes w/ VLANs
46 bytes w/o VLANs
What is the maximum size (MTU) payload that can be sent over ethernet?
1500 MTU
What is a Jumbo Frame?
A frame configured to be larger than 1500 bytes.
When is Data encapsulated?
when moving from Layer 7 - Layer 1
When is Data decapsulated?
when moving from layer 1 - Layer 7
