|  | 9.1 | OSI Model
| 9.1.5 | Transport layer

The Transport Layer is responsible for end-to-end delivery of information, including error recovery and flow control. Transport Layer protocols may be reliable or unreliable. Unreliable protocols may have little or no responsibility for establishing connections, acknowledgements, sequencing and flow control. It is possible that unreliable Transport Layer protocols will leave this responsibility to another layer's protocol. The reliable Transport Layer protocols may include responsibility for: Establishing connections and closing connections, i.e. the Three-way Handshake Transferring Data Acknowledging of what has been received or not received Making sure packets arriving out of sequence can be sequenced in their proper order Maintaining flow control, i.e. window sizes TCP/IP reliable Transport Layer protocol: TCP (Transmission Control Protocol) Protocols that use TCP may include FTP, Telnet and HTTP. TCP/IP unreliable Transport Layer protocol: UDP (User Datagram Protocol) Protocols that use UDP may include TFTP, SNMP, Network File System (NFS), Domain Name System (DNS), and the routing protocol RIP. Transport Layer Protocols include: TCP/IP: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) Novell: SPX (Sequenced Packet Exchange)
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