Functions and Protocols in the OSI Model

 Application Layer

The protocols at the application layer handle file transfer, virtual terminals, network management, and fulfilling networking requests of applications. A few of the protocols
that work at this layer include:
• File Transfer Protocol (FTP)
• Trivial File Transfer Protocol (TFTP)
• Simple Network Management Protocol (SNMP)
• Simple Mail Transfer Protocol (SMTP)
• Telnet
• Hypertext Transfer Protocol (HTTP)

Presentation
The services of the presentation layer handle translation into standard formats, data compression and decompression, and data encryption and decryption. No protocols work at this layer, just services. The following lists some of the presentation layer standards:
• American Standard Code for Information Interchange (ASCII)
• Extended Binary-Coded Decimal Interchange Mode (EBCDIC)
• Tagged Image File Format (TIFF)
• Joint Photographic Experts Group (JPEG)
• Motion Picture Experts Group (MPEG)
• Musical Instrument Digital Interface (MIDI)

Session
The session layer protocols set up connections between applications, maintain dialog control, and negotiate, establish, maintain, and tear down the communication channel.
Some of the protocols that work at this layer include:
• Network File System (NFS)
• NetBIOS
• Structured Query Language (SQL)
• Remote procedure call (RPC)

Transport
The protocols at the transport layer handle end-to-end transmission and segmentation into a data stream. The following protocols work at this layer:
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
• Secure Sockets Layer (SSL)/Transport Layer Security (TLS)
• Sequenced Packet Exchange (SPX)

Network
The responsibilities of the network layer protocols include internetworking service, addressing, and routing. The following lists some of the protocols that work at this layer:
• Internet Protocol (IP)
• Internet Control Message Protocol (ICMP)
• Internet Group Management Protocol (IGMP)
• Routing Information Protocol (RIP)
• Open Shortest Path First (OSPF)
• Novel Internetwork Packet Exchange (IPX)

Data Link
The protocols at the data link layer convert data into LAN or WAN frames for transmission, convert messages into bits, and define how a computer accesses a network. This layer is divided into the Logical Link Control (LLC) and the Media Access Control (MAC) sublayers. Some protocols that work at this layer include the following:
• Address Resolution Protocol (ARP)
• Reverse Address Resolution Protocol (RARP)
• Point-to-Point Protocol (PPP)
• Serial Line Internet Protocol (SLIP)

Physical
Network interface cards and drivers convert bits into electrical signals and control the physical aspects of data transmission, including optical, electrical, and mechanical requirements.
The following are some of the standard interfaces at this layer:
• High-Speed Serial Interface (HSSI)
• X.21
• EIA/TIA-232 and EIA/TIA-449