1 Protocol Interaction (ISO’s Open Systems Interconnection (OSI model)) the 7 layers

2 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 affecting functions at other layers – encapsulation of implementation details 3

3 + 4 division The top three layers know nothing about the network The bottom four layers handles about network communications. 4

The Top Three 5

The Bottom Four 6

7 Data Encapsulation

8 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 s. 9

10 The Presentation Layer The presentation layer uses the following translation process: 1. The sender translates its abstract syntax to transfer syntax, such as encrypted data. 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

11 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

12 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

13 Connection-Oriented and Connectionless Protocols Connection-Oriented (CO) Protocols Connectionless (CL) Protocols Require a handshakeDo not require a handshake Have larger headers and more overhead Have smaller headers and less overhead Provide packet acknowledgments, data segmentation, flow control, and error detection and correction Do not provide additional services Acknowledge transmitted packets, so they are considered reliable Do not acknowledge transmitted packets, so they are considered unreliable Example: TCPExample: UDP

14 The Network Layer (level 3) 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 15

Routing Example (figure 2.8) 16

17 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

18 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

19 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

Encapsulation 20

Encapsulation – steps 21

22 Summary: The OSI Reference Model OSI Model Layer Function PhysicalDefines the hardware elements and structure of the network installation Data-linkProvides addressing, data encapsulation, and media access control NetworkProvides end-to-end routing and addressing TransportProvides packet acknowledgment, flow control, and error detection SessionProvides dialog control and dialog separation PresentationTranslates syntaxes between different systems ApplicationProvides an interface to applications running on the computer