Sem 2 Networking Week 10-2 UDP

UDP Header Fields

• Source Port: 16-bit field identifying the source application via port number.
• Destination Port: 16-bit field identifying the destination application via port number.
• Length: 16-bit field indicating the total length of the UDP datagram (header + data).
• Checksum: 16-bit field for error-checking of the UDP header and data.

Applications that Use UDP

• Live Video and Multimedia: Require low latency and can tolerate some data loss (e.g., VoIP, live streaming).
• Simple Request and Reply: Handle simple transactions with minimal overhead (e.g., DNS, DHCP).
• Reliability Managed by Applications: Unidirectional communication where the application handles reliability (e.g., SNMP, TFTP).

Port Numbers and Socket Pairs

• Socket: Combination of an IP address and port number used for identifying specific processes or services.
• Source and Destination Ports: Included in segments for routing and managing data between applications.
• Encapsulation: Segments containing port numbers are encapsulated within IP packets for transmission.

Purpose of Sockets

• Distinguish multiple processes on clients and differentiate multiple connections to servers.

Port Number Groups

• Well-known Ports (0 to 1,023): Reserved for common services (e.g., HTTP, FTP, SMTP) for easy identification by clients.
• Registered Ports (1,024 to 49,151): Assigned by IANA for specific processes requested by entities (e.g., Cisco's RADIUS server on port 1812).

Active Connections

• Monitoring active connections helps identify services communicating with the machine, e.g., TCP connections with various local and foreign addresses.

TCP Connection Establishment

• Port Number Assignment: Each server application uses a specific port number to identify incoming network traffic.
• Unique Port Assignment: No two services can listen on the same port within the same transport layer.
• Open Ports: Indicates that a server application is ready to accept incoming data.
• Handling Incoming Requests: Client requests directed to a socket (IP address + port number).

Session Termination Steps

• Client initiates termination with a FIN segment when no more data is to be sent.
• Server acknowledges the FIN with an ACK segment confirming receipt.
• Server initiates its termination by sending its own FIN segment.
• Client acknowledges the server's FIN with an ACK segment, ensuring an orderly shutdown.

TCP Three-Way Handshake

• Establish Device Presence: Client sends a SYN packet to initiate the connection.
• Verify Service Availability: Server responds with a SYN-ACK packet confirming it’s listening on the specified port.
• Inform of Connection Intent: Client sends an ACK packet to confirm readiness for data transmission.

Connection Termination Process

• Utilizes a four-step process (FIN and ACK) ensuring both parties agree to close the session without data loss.

Reliability Function

• TCP ensures synchronization and agreement on connection parameters through the handshake, contributing to reliable data transfer.

Control Bit Flags in TCP Header

• URG: Indicates urgent data needing immediate processing.
• ACK: Acknowledges receipt of data; set in all segments post-initial SYN.
• PSH: Instructs immediate processing of received data without delay.

Maximum Segment Size (MSS)

• Default Ethernet MTU is 1500 bytes; TCP and IP headers consume 40 bytes, leading to an MSS of 1460 bytes.
• MSS ensures efficient data transmission by setting a limit to avoid fragmentation.
• MSS negotiation occurs during the three-way handshake, with the lower of two preferred values used.

TCP Flow Control and Congestion Avoidance

• Slow Start: Initiates with a small congestion window, increasing exponentially until a threshold is reached or packet loss occurs.
• Congestion Avoidance: After threshold, congestion window increases linearly to avoid overload.
• Fast Retransmit and Recovery: Quickly retransmits lost packets upon duplicate ACKs, adjusting congestion window as needed.
• Congestion Control Algorithms: Variants like TCP Tahoe and TCP Reno optimize data flow based on network conditions.

This quiz focuses on the various fields in the UDP header, including source and destination ports, UDP length, and checksum. Each field's function and importance in networking are highlighted to enhance your understanding of UDP protocols.