Unit 4 Part 2 Flashcards
Introduction to the OSI Model
Purpose:
OSI Model helps standardize network communications.
Addresses compatibility issues between networks by using a 7-layer model.
Function:
Data is passed vertically through these layers from sender to receiver.
At each layer, data is processed, headers are added on the sending side, and removed on the receiving side.
OSI Model Layer Functions
Layer Communication:
Layers on the sender’s device correspond directly to layers on the receiver’s device.
Each layer has a specific function, defined by the OSI model.
Data Processing:
As data passes through the layers, it is broken up and manipulated for transmission.
The receiving device reassembles the data as it moves up the layers.
Layers 7, 6, and 5 (Application, Presentation, Session)
Layer 7: Application
Manages network applications like Skype.
Uses application protocols (e.g., HTTP, FTP).
Layer 6: Presentation
Converts data to binary, encrypts/decrypts, and compresses data.
Layer 5: Session
Manages communication sessions between devices.
Determines which data packets belong to which files.
Layer 4 (Transport)
Transport Layer Overview:
Receives data from the Session layer and breaks it into segments.
Adds source and destination port numbers, and sequence numbers.
Functions:
Controls data transmission speed based on device capabilities.
Performs error-checking, resending missing segments.
Protocols:
TCP: Prioritizes data quality over speed.
UDP: Prioritizes speed over data quality.
Layer 3 (Network)
Network Layer Overview:
Transmits data segments between networks as packets.
Adds source and destination IP addresses.
Routing:
Determines the best paths for data delivery.
IP addresses identify the source and destination devices.
Layer 2 (Data Link)
Data Link Layer Overview:
Receives packets from the Network layer and adds MAC addresses.
Forms a data unit called a frame.
Functions:
Controls how data is placed on and received from the media (e.g., copper wire, fiber optic).
Embedded as software in the Network Interface Card (NIC).
Layer 1 (Physical)
Physical Layer Overview:
Converts binary data into electrical, light, or radio signals.
Transmits signals over local media (e.g., cables, fiber optic).
Function:
Hardware layer that includes cables, RJ45 connectors, etc.
Translates signals back into binary for the receiving application.
OSI Model Summary
Layers 1-7 Overview:
Physical (e.g., cable, RJ45)
Data Link (e.g., MAC, switches)
Network (e.g., IP, routers)
Transport (e.g., TCP, UDP, port numbers)
Session (e.g., Syn/Ack)
Presentation (e.g., encryption, ASCII, PNG)
Application (e.g., HTTP, FTP)
Data Transmission:
Each layer adds headers to the data segment, forming a frame that is transmitted across the network.
The receiving side removes the headers as data moves up through the layers.
Overview of Packets
Packets are created at Layer 3 (Network) of the OSI model.
They enable information exchange between different LANs.
Packet Structure
Three Main Parts:
Header
Payload
Trailer
Packet Header
Packet Length: Defines the size of the packet.
Synchronization: Helps align the packet with the network.
Packet Number: Indicates the sequence in a series of packets.
Protocol: Specifies the type of data (e.g., email, video).
Destination Address: IP address of where the packet is going.
Source Address: IP address of where the packet originated.
Packet Payload
Also called the “body” or “data” of the packet.
Contains the actual data being delivered.
Packet Trailer
Signals the end of the packet.
Includes error-checking bits, like CRC (Cyclic Redundancy Check).
Ensures the packet’s integrity by comparing values with the receiving device.
Packet Transmission
Routing:
Routers use the destination IP address to forward the packet across networks.
Once the packet arrives, the receiving device strips the header and trailer, reassembling the data.
Role of Network and Data Link Layers
Network Layer:
Uses IP addresses to send data across different networks (inter-network).
Data Link Layer:
Handles data forwarding within a local network (intra-network).
Uses MAC addresses to identify devices and forward data frames.
Overview of Frames
Frames are created by Layer 2 (Data Link) by encapsulating a packet as the frame’s payload.
The Ethernet frame adds source and destination MAC addresses.
Frame Transmission Process
Switch Function:
Switches forward frames based on MAC addresses.
They check the destination MAC address against a lookup table to determine which physical port to forward the frame to.
Frame vs. Packet
Switches vs. Routers:
Switches: Inspect frame headers and trailers to transfer data within a LAN.
Routers: Remove frame data to extract the packet and transfer data to external networks (e.g., the Internet).
