4-Transport Layer

The Transport Layer is the fourth layer in the OSI Model of computer networking.

It is responsible for providing reliable data transfer services between end systems, ensuring that data is delivered accurately and in the correct order.

The Transport Layer manages end-to-end communication, including error detection and correction, flow control, and congestion control.

It uses protocols such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) to facilitate data transfer between applications running on different devices.

The Transport Layer works closely with the Network Layer to provide end-to-end data delivery across multiple networks.

TCP vs. UDP

UDP (User Datagram Protocol): - Connectionless protocol. Fire-and-forget. No handshake, no confirmation. - Fast, low overhead, no guarantees. - Use cases: Streaming, gaming, VoIP, DNS queries. For when delivering fast is more important than delivering reliably.

TCP (Transmission Control Protocol): - Connection-oriented protocol. 3-Way Handshake (syn, syn-ack, ack) to establish a connection. - SYN: Client sends a SYN packet to the server to initiate a connection. - SYN-ACK: Server responds with a SYN-ACK packet to acknowledge the receipt of the SYN and to indicate its willingness to establish a connection. - ACK: Client sends an ACK packet back to the server to acknowledge the receipt of the SYN-ACK, completing the handshake. - Guarnteed delivery, in-order delivery, flow control, congestion control. - Use cases: Web browsing (HTTP/HTTPS), email (SMTP, IMAP), file transfer (FTP). For when reliable delivery is more important than fast delivery.

Possible attacks: - TCP SYN Flood: An attacker sends a large number of SYN requests to a target server, but never finishes the handshake by sending the final ACK. This leaves the server with many half-open connections, consuming resources and potentially leading to a denial of service (DoS) for legitimate users.