Layer 4 Protocols

Transport Layer (Layer 4)

OSI layer responsible for delivering data efficiently, reliably, and accurately between devices

Main Transport Layer Role

Decides how packets are delivered, focusing on reliability, speed, and flow control

Segmentation

Breaking data into smaller segments for transmission and rebuilding them at the destination

Flow Control

Coordinating how fast data is sent so the receiver is not overwhelmed

Error Checking

Tracking sent packets and requesting retransmission if packets or bytes are missing

Connection Management

Organizing how devices connect and disconnect during a transmission

Port Numbers

Numbers used to direct network traffic to the correct application on a device

Protocol

A set of rules that governs how data is transmitted across a network

TCP/IP Suite

Large collection of over 100 protocols that define how data is exchanged on networks

TCP (Transmission Control Protocol)

Connection-oriented protocol that ensures reliable data delivery

UDP (User Datagram Protocol)

Connectionless protocol that prioritizes speed over reliability

Connection-Oriented Communication

Communication that establishes a connection and ensures data delivery (TCP)

Connectionless Communication

Communication that sends data without verifying delivery (UDP)

TCP Reliability

Achieved through acknowledgments, error checking, and retransmission

UDP Reliability

Not guaranteed; packets may be lost without notification

TCP 3-Way Handshake

Process used by TCP to establish a connection between two devices

SYN

First handshake packet that initiates a TCP connection

SYN/ACK

Second handshake packet that acknowledges and agrees to connect

ACK

Third handshake packet that completes the TCP connection

FIN Packet

TCP packet used to signal the end of a connection

Why Use UDP

Used when speed and efficiency matter more than reliability

UDP Examples

Video streaming, online gaming, and DHCP

Wireshark

Free packet sniffer and protocol analyzer used to capture and inspect network traffic

Packet Sniffer

Tool that captures packets traveling through a network

Packet List

Wireshark section showing a summary of captured packets

Packet Details

Wireshark section displaying detailed packet information like addresses and ports

Packet Bytes

Wireshark section showing raw packet data in hexadecimal and ASCII