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  Layer 4 Transport Layer


TCP; UDP; Transporation

The tasks of the transport layer (also end-to-end control, transport control) include the segmentation of the data stream and in relieving congestion.

A data segment is a Service Data Unit, which is used for encapsulation on the fourth layer (transport layer). It consists of protocol elements that contain Layer 4 information control. When addressing the data segment assigned a Layer 4 address, so a port. The data segment is encapsulated in the layer 3 in a data packet.

The transport layer provides the application-oriented layers 5 to 7 standardized access so that they do not need to consider the characteristics of the communications network.

Five different service classes of different grades are defined in layer 4 and may be used by the upper layers, from the simplest to the most comfortable service with multiplex mechanisms, error protection and troubleshooting procedures..

OSI Layer 4 - Transport Layer

In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet Protocol Suite and the Open Systems Interconnection (OSI). The protocols of the layer provide host-to-host communication services for applications.[1] It provides services such as connection-oriented data stream support, reliability, flow control, and multiplexing.

The details of implementation and semantics of the Transport Layer of the TCP/IP model (RFC 1122), which is the foundation of the Internet, and the Open Systems Interconnection (OSI) model of general networking, are different. In the OSI model the transport layer is most often referred to as Layer 4 or L4, while numbered layers are not used in TCP/IP.

The best-known transport protocol of TCP/IP is the Transmission Control Protocol (TCP), and lent its name to the title of the entire suite. It is used for connection-oriented transmissions, whereas the connectionless User Datagram Protocol (UDP) is used for simpler messaging transmissions. TCP is the more complex protocol, due to its stateful design incorporating reliable transmission and data stream services. Other prominent protocols in this group are the Datagram Congestion Control Protocol (DCCP) and the Stream Control Transmission Protocol (SCTP).



  • Connection-oriented communication
  • Same order delivery
  • Reliability
  • Flow control
  • Congestion avoidance
  • Port Multiplexing

Popular Transport Layer Protocols

ATPAppleTalk Transaction Protocol
DCCPDatagram Congestion Control Protocol
FCPDatagram Congestion Control Protocol
ILFibre Channel Protocol
MPTCPIL Protocol
RDPMultipath TCP
RUDPReliable User Datagram Protocol
SCTPStream Control Transmission Protocol
SPXSequenced Packet Exchange
SSTStructured Stream Transport
TCPTransmission Control Protocol
UDPUser Datagram Protocol
UDP-LiteUser Datagram Protocol
µTPMicro Transport Protocol