Transport layer - wikipedia Transport layer This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( October 2015 ) Internet protocol suite Application layer BGP DHCP DNS FTP HTTP IMAP LDAP MGCP MQTT NNTP NTP POP ONC / RPC RTP RTSP RIP SIP SMTP SNMP SSH Telnet TLS / SSL XMPP more... Transport layer TCP UDP DCCP SCTP RSVP more... Internet layer IP IPv4 IPv6 ICMP ICMPv6 ECN IGMP IPsec more... Link layer ARP NDP OSPF Tunnels L2TP PPP MAC Ethernet DSL ISDN FDDI more... 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. 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 easily compared. 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 ). OSI model by layer 7. Application layer NNTP SIP SSI DNS FTP Gopher HTTP NFS NTP SMPP SMTP SNMP Telnet DHCP Netconf more... 6. Presentation layer MIME XDR 5. Session layer Named pipe NetBIOS SAP PPTP RTP SOCKS SPDY 4. Transport layer TCP UDP SCTP DCCP SPX 3. Network layer IP IPv4 IPv6 ICMP IPsec IGMP IPX AppleTalk X. 25 PLP 2. Data link layer ATM ARP IS - IS SDLC HDLC CSLIP SLIP GFP PLIP IEEE 802.2 LLC MAC L2TP IEEE 802.3 Frame Relay ITU - T G.hn DLL PPP X. 25 LAPB Q. 921 LAPD Q. 922 LAPF 1. Physical layer EIA / TIA - 232 EIA / TIA - 449 ITU - T V - Series I. 430 I. 431 PDH SONET / SDH PON OTN DSL IEEE 802.3 IEEE 802.11 IEEE 802.15 IEEE 802.16 IEEE 1394 ITU - T G.hn PHY USB Bluetooth RS - 232 RS - 449 Contents 1 Services 2 Analysis 3 Protocols 4 Comparison of transport layer protocols 5 Comparison of OSI transport protocols 6 References Services Transport layer services are conveyed to an application via a programming interface to the transport layer protocols. The services may include the following features : Connection - oriented communication : It is normally easier for an application to interpret a connection as a data stream rather than having to deal with the underlying connection-less models, such as the datagram model of the User Datagram Protocol ( UDP ) and of the Internet Protocol ( IP ). Same order delivery : The network layer does n't generally guarantee that packets of data will arrive in the same order that they were sent, but often this is a desirable feature. This is usually done through the use of segment numbering, with the receiver passing them to the application in order. This can cause head - of - line blocking. Reliability : Packets may be lost during transport due to network congestion and errors. By means of an error detection code, such as a checksum, the transport protocol may check that the data is not corrupted, and verify correct receipt by sending an ACK or NACK message to the sender. Automatic repeat request schemes may be used to retransmit lost or corrupted data. Flow control : The rate of data transmission between two nodes must sometimes be managed to prevent a fast sender from transmitting more data than can be supported by the receiving data buffer, causing a buffer overrun. This can also be used to improve efficiency by reducing buffer underrun. Congestion avoidance : Congestion control can control traffic entry into a telecommunications network, so as to avoid congestive collapse by attempting to avoid oversubscription of any of the processing or link capabilities of the intermediate nodes and networks and taking resource reducing steps, such as reducing the rate of sending packets. For example, automatic repeat requests may keep the network in a congested state ; this situation can be avoided by adding congestion avoidance to the flow control, including slow - start. This keeps the bandwidth consumption at a low level in the beginning of the transmission, or after packet retransmission. Multiplexing : Ports can provide multiple endpoints on a single node. For example, the name on a postal address is a kind of multiplexing, and distinguishes between different recipients of the same location. Computer applications will each listen for information on their own ports, which enables the use of more than one network service at the same time. It is part of the transport layer in the TCP / IP model, but of the session layer in the OSI model. Analysis The transport layer is responsible for delivering data to the appropriate application process on the host computers. This involves statistical multiplexing of data from different application processes, i.e. forming data segments, and adding source and destination port numbers in the header of each transport layer data segment. Together with the source and destination IP address, the port numbers constitutes a network socket, i.e. an identification address of the process - to - process communication. In the OSI model, this function is supported by the session layer. Some transport layer protocols, for example TCP, but not UDP, support virtual circuits, i.e. provide connection oriented communication over an underlying packet oriented datagram network. A byte - stream is delivered while hiding the packet mode communication for the application processes. This involves connection establishment, dividing of the data stream into packets called segments, segment numbering and reordering of out - of order data. Finally, some transport layer protocols, for example TCP, but not UDP, provide end - to - end reliable communication, i.e. error recovery by means of error detecting code and automatic repeat request ( ARQ ) protocol. The ARQ protocol also provides flow control, which may be combined with congestion avoidance. UDP is a very simple protocol, and does not provide virtual circuits, nor reliable communication, delegating these functions to the application program. UDP packets are called datagrams, rather than segments. TCP is used for many protocols, including HTTP web browsing and email transfer. UDP may be used for multicasting and broadcasting, since retransmissions are not possible to a large amount of hosts. UDP typically gives higher throughput and shorter latency, and is therefore often used for real - time multimedia communication where packet loss occasionally can be accepted, for example IP - TV and IP - telephony, and for online computer games. Many non-IP - based networks, such as X. 25, Frame Relay and ATM, implement the connection - oriented communication at the network or data link layer rather than the transport layer. In X. 25, in telephone network modems and in wireless communication systems, reliable node - to - node communication is implemented at lower protocol layers. The OSI connection - mode transport layer protocol specification defines five classes of transport protocols : TP0, providing the least error recovery, to TP4, which is designed for less reliable networks. Protocols This list shows some protocols that are commonly placed in the transport layers of the Internet protocol suite, the OSI protocol suite, NetWare 's IPX / SPX, AppleTalk, and Fibre Channel. ATP, AppleTalk Transaction Protocol CUDP, Cyclic UDP DCCP, Datagram Congestion Control Protocol FCP, Fibre Channel Protocol IL, IL Protocol MPTCP, Multipath TCP RDP, Reliable Data Protocol RUDP, Reliable User Datagram Protocol SCTP, Stream Control Transmission Protocol SPX, Sequenced Packet Exchange SST, Structured Stream Transport TCP, Transmission Control Protocol UDP, User Datagram Protocol UDP - Lite μTP, Micro Transport Protocol Comparison of transport layer protocols Feature Name UDP UDP - Lite TCP Multipath TCP SCTP DCCP RUDP Packet header size 8 bytes 8 bytes 20 -- 60 bytes 50 -- 90 bytes 12 bytes 12 or 16 bytes 14 + bytes Typical data packet overhead 8 bytes 8 bytes 20 bytes ? ? bytes 44 -- 48 + bytes 12 or 16 bytes 14 bytes Transport layer packet entity Datagram Datagram Segment Segment Datagram Datagram Datagram Connection oriented No No Yes Yes Yes Yes Yes Reliable transport No No Yes Yes Yes No Yes Unreliable transport Yes Yes No No Yes Yes Yes Preserve message boundary Yes Yes No No Yes Yes Yes Ordered delivery No No Yes Yes Yes No Yes Unordered delivery Yes Yes No No Yes Yes Yes Data checksum Optional Yes Yes Yes Yes Yes Optional Checksum size ( bits ) 16 16 16 16 32 16 16 Partial checksum No Yes No No No Yes No Path MTU No No Yes Yes Yes Yes Unsure Flow control No No Yes Yes Yes No Yes Congestion control No No Yes Yes Yes Yes Unsure Explicit Congestion Notification No No Yes Yes Yes Yes Multiple streams No No No No Yes No No Multi-homing No No No Yes Yes No No Bundling / Nagle No No Yes Yes Yes No Unsure Jump up ^ RUDP is not officially standardized. There have been no standard - related developments since 1999. Jump up ^ Excluding data chunk headers and overhead chunks. Without embedded chunks, an SCTP packet is essentially useless. Jump up ^ Counted as follows : 12 bytes SCTP header + 16 bytes DATA chunk header or 20 bytes I - DATA chunk header + 16 + bytes SACK chunk. Additional non-data chunks ( e.g. AUTH ) and / or headers for additional data chunks, which might easily increase the overhead with 50 bytes or more, not counted. Comparison of OSI transport protocols ISO / IEC 8073 / ITU - T Recommendation X. 224, `` Information Technology - Open Systems Interconnection - Protocol for providing the connection - mode transport service '', defines five classes of connection - mode transport protocols designated class 0 ( TP0 ) to class 4 ( TP4 ). Class 0 contains no error recovery, and was designed for use on network layers that provide error - free connections. Class 4 is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. All OSI connection - mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of the classes are shown in the following table : Service TP0 TP1 TP2 TP3 TP4 Connection oriented network Yes Yes Yes Yes Yes Connectionless network No No No No Yes Concatenation and separation No Yes Yes Yes Yes Segmentation and reassembly Yes Yes Yes Yes Yes Error Recovery No Yes No Yes Yes Reinitiate connection ( if an excessive number of PDUs are unacknowledged ) No Yes No Yes No multiplexing and demultiplexing over a single virtual circuit No No Yes Yes Yes Explicit flow control No No Yes Yes Yes Retransmission on timeout No No No No Yes Reliable Transport Service No Yes No Yes Yes There is also a connectionless transport protocol, specified by ISO / IEC 8602 / ITU - T Recommendation X. 234. References Jump up ^ RFC 1122, § 1.1. 3. Jump up ^ RFC 1122, Requirements for Internet Hosts -- Communication Layers, IETF, R. Braden ( Editor ), October 1989 Jump up ^ Lou Frenzel ( 2013 - 10 - 02 ). `` What 's The Difference Between The OSI Seven - Layer Network Model And TCP / IP ? ''. Electronic Design. Retrieved 2017 - 01 - 17. Jump up ^ `` Difference between OSI Reference Model and TCP / IP Reference Model Computer Network Tutorial ''. Studytonight.com. Retrieved 2017 - 01 - 17. Jump up ^ `` Four Layers of TCP / IP model, Comparison and Difference between TCP / IP and OSI models ''. Omnisecu.com. Retrieved 2017 - 01 - 17. Jump up ^ Tetz, Edward. `` Network Basics : TCP / IP and OSI Network Model Comparisons ''. Dummies.com. Retrieved 2017 - 01 - 17. Jump up ^ `` ITU - T Recommendation X. 224 ( 11 / 1995 ) ISO / IEC 8073 ''. Itu.int. Retrieved 2017 - 01 - 17. Jump up ^ `` ITU - T Recommendation X. 234 ( 07 / 1994 ) ISO / IEC 8602 ''. Itu.int. Retrieved 2017 - 01 - 17. Wikiversity has learning resources about Transport layer Retrieved from `` https://en.wikipedia.org/w/index.php?title=Transport_layer&oldid=814851888 '' Categories : OSI model Hidden categories : Pages using RFC magic links Articles needing additional references from October 2015 All articles needing additional references Talk Contents About Wikipedia Български Català Čeština Dansk Deutsch Español Euskara فارسی Français Galego 한국어 Bahasa Indonesia Italiano עברית Қазақша Latviešu Magyar Македонски Bahasa Melayu Монгол Nederlands 日本 語 Norsk Norsk nynorsk Português Русский Slovenčina Slovenščina Српски / srpski Svenska Türkçe Українська Tiếng Việt 中文 Edit links This page was last edited on 11 December 2017, at 08 : 54. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. 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Question: what are the responsibilities of the transport layer in the osi model
Answer: provide host-to-host communication services for applications