CCNA Cisco Netacad Introduction to Networks: Module 14 - Transport Layer

Overview

• Focus on transport layer within network communication.
• Compare operations of transport layer protocols: TCP, UDP.
• Key topics: Data transportation, TCP/UDP overview, port numbers, TCP communication process, reliability, flow control, UDP communication process.

Transportation of Data

Role of the Transport Layer

• Responsible for logical communication between applications on different hosts.
• Provides end-to-end communication host-to-host.
• Integral in both OSI (between session and network layers) and TCP/IP models (between application and internet layers).

Transport Layer Responsibilities

• Tracking Conversations: Manage multiple communication sessions.
• Segmenting and Reassembly: Splits data into segments; reassembles on arrival.
• Header Information: Adds header data for tracking and managing sessions.
• Reliability: Manages delivery reliability and flow.

Transport Layer Protocols

Transmission Control Protocol (TCP)

• Provides reliability through acknowledgments, sequence data, and retransmission.
• Manages flow control to prevent overload.
• Key features: connection-oriented, reliable delivery, same-order delivery, flow control.
• TCP Header Fields: Include source port, destination port, sequence number, acknowledgment number, window size, and checksum.
• Applications using TCP: FTP, SMTP, SSH, HTTP.

User Datagram Protocol (UDP)

• Connectionless protocol with minimal overhead.
• Suitable for applications where speed is critical over reliability (e.g., VoIP, DNS).
• UDP Header Fields: Source port, destination port, length, and checksum.
• Applications using UDP: DNS, DHCP, SNMP, live video.

Port Numbers

• Well-known ports: 0-1023 (e.g., HTTP, HTTPS).
• Registered ports: 1024-49151 for specific applications.
• Dynamic/private ports: 49152-65535 assigned dynamically.

Importance of Port Numbers

• Manage multiple conversations simultaneously.
• Socket concept: Combination of source/destination IP and port.

TCP Communication Process

Connection Establishment

• 3-way Handshake: Sync, Sync/ACK, ACK to establish connection.
• Important for ensuring devices are ready for communication.

Session Termination

• FIN/ACK Process: Used to close communication sessions.

Reliability and Flow Control

• Mechanisms to ensure all data is received accurately and in order.
• Uses sequence numbers and acknowledgments.
• Congestion avoidance mechanisms included.

UDP Communication Process

• Low overhead with no connection establishment, making it faster but less reliable.
• Reassembles data in received order without tracking sequence numbers.

Summary

• Transport layer links application layer to network transmission responsibilities.
• TCP and UDP have distinct functionalities tailored to different application needs.
• Understanding port numbers and managing multiple connections is key.
• TCP offers reliability and order; UDP offers speed and simplicity.

Additional Notes

• Netstat Command: Useful for verifying established TCP connections on a device.
• Selective Acknowledgment (SAC): Modern feature for acknowledging segments in TCP.

Next Steps

• Engage with packet tracer labs via Cisco Netacad for practical understanding.
• Familiarize with well-known port numbers for exams/quizzes.