CCNA Cisco NetAcad Introduction to Networks: Transport Layer

Overview

• Focus on Module 14: Transport Layer
• Key Topics:
  • Transport layer protocols (TCP and UDP)
  • Port numbers
  • TCP communication process
  • Reliability and flow control
  • UDP communication process

Transport Layer Responsibilities

• Logical communication between applications on different hosts
• Provides end-to-end communication between hosts
• Sandwiched between application layer and internet layer (TCP/IP model)
  • Responsible for data transmission via TCP and UDP

Transport Layer Functions

• Track conversations
• Segment and reassemble data
• Add header information
• Manage multiple conversations using segmentation and multiplexing
• Specify delivery and manage reliability requirements

TCP Protocol

• Provides reliability and flow control
• Basic Operations:
  • Number and track segments
  • Acknowledge received data
  • Retransmit unacknowledged data
  • Sequence out-of-order data
  • Efficient data rate management

TCP Features

• Connection-oriented protocol
• Ensures reliable delivery, same order delivery, and flow control
• Stateful protocol with features like source port, destination port, sequence number, and acknowledgment number
• Applications using TCP: FTP, SMTP, SSH, HTTP, HTTPS

TCP Header Fields (Important for Exams)

• Source Port: 16-bit
• Destination Port: 16-bit
• Sequence Number: 32-bit
• Acknowledgment Number: 32-bit
• Window Size: 16-bit
• Checksum: 16-bit

UDP Protocol

• Connectionless with minimal overhead
• Used for fast, low-overhead applications
• Best effort delivery, no guaranteed delivery or order
• Applications using UDP: VoIP, DNS, video streaming

UDP Header

• Simpler than TCP: Source Port, Destination Port, Length, Checksum

Port Numbers

• TCP and UDP use port numbers to manage multiple conversations
• IANA assigns port numbers
• Well-known ports: 0-1023
• Registered ports: 1024-49151
• Private/Dynamic ports: 49152-65535
• Key Port Numbers (for Exams):
  • FTP: 20/21, HTTP: 80, HTTPS: 443, SSH: 22, SMTP: 25

TCP Communications

TCP Connection Establishment

• Utilize a three-way handshake (SYN, SYN-ACK, ACK)
• Ensures destination device is present and ready

TCP Session Termination

• Uses FIN and ACK flags to close connections

TCP Reliability and Flow Control

• Sequence numbers ensure ordered data delivery
• Sliding windows and MSS manage flow control

UDP Communication

• Low overhead, fast data transport
• No sequence tracking or retransmission of lost data

Important Concepts

• Socket: Combination of source/destination IP and port
• Selective Acknowledgement (SACK) for handling segment losses

Resources

• Packet Tracer Lab: TCP and UDP Communications

Conclusion

• Understand and prepare for exams by familiarizing with TCP/UDP functions, port numbers, and connection processes.