OSI Model Transport Layer Protocols

This post summarizes transport layer protocols.

List of Transport Layer Protocols

Transport Layer Protocols:

TCP and UDP are the main transport protocols of the TCP/IP framework.

You can find a list of popular TCP and UDP ports on this post.

Transmission Control Protocol (TCP) is a full-duplex connection-oriented protocol.

TCP uses a port for each connection. As port numbers are 16-digit binary numbers, there are 2^16 = 65,536 ports available, from 0 to 65,535.

A socket is the combination of an IP and a port.

Ports are classified as follows:

TCP uses communication flags. They can be reviewed on this post.

A TCP connection is established through the three-way handshake process:

The client sends a SYN (synchronize) flagged packet to the server
The server responds with a SYN/ACK (synchronize and acknowledge) flagged packet back to the client.
The client responds with an ACK (acknowledge) flagged packet back to the server

Disconnection is done using either the FIN (finish) or RST (reset) flags.

User datagram protocol (UDP) is a connectionless protocol.

As it is unreliable, it is mostly used on video or audio streaming.

iSCSI is mainly a transport protocol. It is used on an Storage Area Network (SAN).

You can read this post about iSCSI.

Resource Reservation Protocol (RVSP) is used to provide Quality of Service (QoS).

You can read this post about RVSP.

M. Chapple et al, “CISSP Official Study Guide, Ninth Edition”, section “Transport Layer Protocols”, pp. 508-509; Wiley, 2021