Summary
Highlights
The Transport Layer is responsible for logical communications between applications on different hosts. It primarily uses two protocols: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP is connection-oriented, reliable, and uses flow control, while UDP is connectionless, unreliable, faster, and has low flow control. TCP is typically used for communication outside the local area network (LAN), and UDP for communication inside the LAN.
TCP establishes sessions, ensures reliable delivery, provides same-order delivery, and supports flow control. Data from the application layer is broken into smaller segments, each stamped with a sequence number for ordering and port numbers for application identification. TCP uses a 'three-way handshake' to establish a connection before data transmission. It also employs a rigorous acknowledgment system and windowing for flow control, ensuring all data is received in order, though this adds overhead and delay.
UDP is connectionless and unreliable, meaning it does not establish a session or guarantee delivery. It breaks data into segments (datagrams), labels them with port numbers, and transmits them without waiting for acknowledgments or controlling flow. UDP is faster due to less overhead and is preferred for applications like Voice over IP (VoIP) and video streaming, where speed is critical and some data loss is acceptable. Protocols like RTP and RTCP are often used with UDP to add some reliability for real-time applications.
Port numbers identify specific applications in a segment. Each segment has a source port and a destination port. A 'socket' is defined as an IP address combined with a port number. There are three types of port numbers: well-known (0-1023) for common services, registered (1024-49151) for proprietary applications, and private/dynamic (49152-65535) for client-side ephemeral ports. Netstat command can be used to view active sockets.
Both TCP and UDP pass their segments to the IP protocol in the network layer for encapsulation into packets. Understanding the differences between TCP and UDP is crucial for network communication. The video concludes by instructing viewers to take notes and submit them as homework, preparing for the next module.