The OSI (Open System Interconnection) Reference Model Not UPS, but APS transport network data physically.
The OSI Reference Model • Created by the International Organization for standardization in the 70’s • Accepted world wide as standard for data network communications • An example of layered approach • This allow changes at one layer not affect functions at other layers – encapsulation of implementation details
3 + 4 division • The top three layers know nothing about the network • The bottom four layers handles about network communications.
The Application Layer • Includes the following protocols: • File Transfer Protocol (FTP) • Hypertext Transfer Protocol (HTTP) • Simple Mail Transfer Protocol (SMTP) • Post Office Protocol, Version 3 (POP3) • Internet Mail Access Protocol (IMAP) • Simple Network Management Protocol (SNMP) • Domain Name System (DNS) • Dynamic Host Configuration Protocol (DHCP)
The Application Layer • IE, an application, interacts with this layer to carry out FTP related operations • I can write an app using C#, IIS and Visual Studio 2012 that sends emials using SMTP library. If the SMTP service is available, the app can actually send the emails.
The Presentation Layer • The presentation layer uses the following translation process: 1. The sender translates its abstract syntax to transfer syntax. 2. The sender transmits data to the receiver. 3. The receiver translates transfer syntax to it in abstract syntax. Example, PC and Apple data formats conversion Other examples are Unicode, compression, encryption/decryption, and multimedia data
The Session Layer • The two most important functions at this layer are • Dialog control • Two way alternate TWA • Two way simultaneous TWS • Dialog separation • For example, you have two browser sessions connected to your bank account, this layer makes sure messages in this two sessions are not mixed up
The Transport Layer • Includes the following protocols: • Transmission Control Protocol (TCP) • User Datagram Protocol (UDP) • IPX • NetWare Core Protocol (NCP) • Sequenced Packet Exchange (SPX) • Performs the following functions: • Packet acknowledgment • Data segmentation – different from Fragmenting • Flow control (Figure 2.5 and 2.6) • Error detection
The Network Layer • Includes the following protocols: • Internet Protocol (IP and IP v6) • Internetwork Packet Exchange (IPX) • NetBIOS Extended User Interface (NetBEUI) • Performs the following functions: • IP level Addressing • Fragmenting (message size) • Routing • Protocol identification
Routing • Two types of packets: data and route-update • It uses the routing table to determine where to send • One protocol per routing table (IP and IP v6 use different tables) • It drops the packet if it cannot determine where to send • It does not forward broadcast messages , which can be used to build up the routing table
The Data-Link Layer • Includes the following protocols: • Ethernet (10Base2, 10Base5, 10BaseT, 100BaseT, etc) • Token Ring • Fiber Distributed Data Interface (FDDI) • Serial Line Internet Protocol (SLIP) • Point-to-Point Protocol (PPP) • The selection of data-link layer protocols defines NIC and driver, cable, and hubs/switch • Mostly LAN level communications or between routers
The Data-Link Layer (Cont.) • Includes the following protocol components: • Frame format • Media Access Control (MAC) mechanism • Physical layer specifications (Coaxial cable or UTP) • Performs the following functions: • Hardware addressing (MAC address, 48 bits) • Error detection • Protocol identification
The Physical Layer • Defines the hardware elements of the network, including • The network medium • How the network is installed • The type of signaling • Includes the following elements: • Cables (UTP – EIA/TIA 568A (Electronics/Telecommunications Industry Association)) • Network interface adapters (also called network interface cards, or NICs) • Hubs