COMPUTER NETWORKBY DINESHY ADAV AHDHHDKDJD
- 1. Transport and Application Layers in Computer Networks A deep dive into the core responsibilities and functioning of the transport and application layers in computer network Presented by Rishiwar Singh Dinesh Yadav Swastik Gupta Semester VI
- 2. Transport Layer (Layer 4) Key Protocols Overview of Unit 5 Application Layer (Layer 7) User-facing protocols and interfaces Focuses on the Transport Layer (Layer 4) and Application Layer (Layer 7) Discusses reliable data transfer, congestion control, and flow control Explores transport protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) Describes real-world application protocols like DNS, SMTP, and MIME Illustrates how these layers collaborate to provide seamless user experiences over networks
- 3. The Transport Layer ā Core Role Bridge Between Layers Connects network and application layers End-to-End Communication Operates between source and destination Packet Sequencing Ensures in-sequence, error-free delivery Network Abstraction Hides unreliable network behavior Bridges the network and application layers, ensuring reliable communication between processes Operates end-to-end between the source and destination devices Ensures that packets are delivered in sequence and without errors Helps applications abstract away the challenges of unreliable network behavior Offers key services: Segmentation, Error Control, Flow Control, and Multiplexing
- 4. Transport Layer Services Connection-Oriented Connection-oriented service ensures reliable, sequenced delivery (TCP) ā¢ Guaranteed delivery ā¢ Packet sequencing ā¢ Error recovery Connectionless Connectionless service provides fast but unreliable delivery (UDP) ā¢ Speed prioritized ā¢ No delivery guarantees ā¢ Minimal overhead Additional Services Offers end-to-end communication between software processes Includes multiplexing using port numbers to identify services Implements error detection and recovery mechanisms
- 5. Importance of the Transport Layer Reliable Application Communication Applications require dependable delivery irrespective of the network Error Correction The network layer may drop or misroute packets ā transport layer corrects this Data Completeness Allows retransmission of lost packets, ensuring data completeness Network Abstraction Hides the details of the network's implementation from the applications Developer Interface Provides a uniform interface for developers despite underlying network variability
- 6. Key Characteristics Common Applications Technical Features UDP ā User Datagram Protocol
- 7. UDP Header Structure Source Port (16 bits) Destination Port (16 bits) Length (16 bits) Checksum (16 bits) Data (if any) Port Numbers Ports allow the delivery of data to the correct application process Length Field Length = Header + Data; Max segment size: 65,515 bytes Checksum Checksum ensures basic error detection but is optional Lightweight Design Lightweight protocol with no congestion or flow control mechanisms
- 8. TCP ā Transmission Control Protocol Connection Establishment Uses three-way handshake to establish connections Data Integrity Ensures data integrity, order, and completeness using sequence numbers Common Applications Commonly used in HTTP, FTP, Email, and file transfer Traffic Management Supports congestion and flow control, retransmission, and duplicate elimination Reliable, connection-oriented protocol used by most Internet applications
- 9. Header Fields Important Flags Optional Fields Data Validation Communication TCP Header Structure
- 10. TCP Connection Establishment Client sends SYN Initial connection request with sequence number Server replies with SYN-ACK Acknowledges client request and sends own sequence number Client responds with ACK Confirms receipt of server's sequence number - Establishes initial sequence numbers on both sides - Ensures both parties are ready for communication - Provides half-open connection detection - Adds security against unwanted or malicious connections
- 11. TCP Connection Termination FIN from sender Initiates connection termination ACK from receiver Acknowledges termination request FIN from receiver Receiver ready to terminate ACK from sender Final acknowledgment - Connection ends using a 4-segment FIN-ACK exchange - Ensures all remaining data is delivered before termination - Connection enters TIME_WAIT state for cleanup and reliability 1 2 3 4
- 12. TCP Congestion Control Slow Start Gradually increases window size Congestion Avoidance Linear growth after threshold Fast Recovery Maintains throughput during packet loss Fast Retransmit Quickly resends lost packets - Adjusts data rate to prevent network overload - Maintains balance between speed and reliability - Reacts to packet loss as a sign of congestion
- 13. Congestion Control in Wireless Links Wireless Challenges ā¢ Wireless links have variable capacity due to interference ā¢ Packet losses may not indicate congestion (false positive) ā¢ TCP may underperform on wireless paths Specialized Solutions ā¢ Special protocols are designed for wireless and mobile networks ā¢ Examples: TCP Westwood, Wireless TCP enhancements ā¢ Algorithms that distinguish between congestion and wireless losses
- 14. Application Layer and Network Services This presentation explores the Application Layer of computer networks, focusing on DNS, email systems, and related protocols that enable network services for end users.
- 15. Application Layer ā Overview Provides network services to end users Interfaces with transport layer to transmit application data Supports multiple protocols HTTP, FTP, SMTP, DNS, etc. Applications Web browsing, email, file sharing, chat Transport Foundation Built on top of reliable transport protocols like TCP or simple ones like UDP
- 16. Structure Records Function Transport DNS ā Domain Name System Purpose Converts domain names ā IP addresses
- 17. DNS Resolution Process Client Request Resolver sends query to local DNS server Query Processing Local server performs recursive or iterative queries Server Interaction ā¢ Root name server ā¢ TLD server (e.g., .com, .edu) ā¢ Authoritative server Caching Caching used to reduce repeated queries Resolution Final IP address returned to requesting client
- 18. DNS Zones and Resource Records Zone Structure DNS database divided into zones, managed by name servers Each zone contains resource records (RRs) with TTL values Updates are distributed and replicated across servers Ensures fault-tolerance and decentralization Resource Record Types Examples: A IPv4 address MX Mail server NS Name server AAAA IPv6 address CNAME Canonical name PTR Pointer record
- 19. Overview of Email System User Agent (UA) Interface for composing/reading Message Transfer Agent (MTA) Sends/receives emails Protocols SMTP, POP3, IMAP Mail Delivery Agent (MDA) Final delivery to inbox Supports MIME for multimedia Works via store-and-forward architecture
- 20. Protocol Characteristics SMTP Commands Function SMTP ā Simple Mail Transfer Protocol
- 21. Summary and References Key Takeaways Transport layer ensures reliable, end-to-end communication TCP = reliable, ordered; UDP = fast, unreliable DNS maps domain names to IPs via hierarchical structure SMTP & MIME enable rich email services Application layer directly supports user-level interactions References Tanenbaum, A. S. ā Computer Networks, 5th Edition Prescribed DU Lecture Notes & Slides RFCs: 768 (UDP), 793 (TCP), 1034 & 1035 (DNS), 5321 (SMTP) Research articles on TCP variants & DNS performance