CHAPTER 2 THE OSI MODEL

2.1 General Model of Communication CHAPTER 2 2.1 General Model of Communication

2.1.1 Using layers to analyze problems in a flow of materials Analyzing Network in Layers What is flowing? What different forms flow? What rules govern flow Where does the flow occur?

2.1.1 Using layers to analyze problems in a flow of materials

2.1.2 Source, Destination, and Data Packets PC PLATFORM SOURCE MACINTOSH PLATFORM DESTINATION Data Packet A data packet is a logically grouped unit of information that moves between computer systems. It includes the source information along with other elements that are necessary in order to make communication possible and reliable with the destination device. The source address in a packet specifies the identity of the computer that sends the packet. The destination address specifies the identity of the computer that finally receives the packet.

2.1.3 MEDIA The plural form of medium is media. In networking, a medium is a material through which data packets travel. It could be any of the following materials: Telephone wires Category 5 UTP (used for 10BASE-T Ethernet) Coaxial cables (used for cable TV) Optical fibers (thin glass fibers that carry light)

2.1.3 MEDIA

2.1.3 MEDIA

2.1.3 MEDIA

2.1.3 MEDIA

2.1.3 MEDIA Communication without some type of wires or cables is called wireless or free-space communication. This is possible using electromagnetic (EM) waves.

2.1.4 PROTOCOL A Protocol is a set of rules that make communication on a network more efficient. Protocol is a set of rules, or an agreement, that determines the format and transmission of data.

2.1.5 The Evolution of ISO Networking Standards The early 1980's saw tremendous increases in the numbers and sizes of networks. By the mid-1980's, these companies began to experience growing pains from all the expansions they had made. It became harder for networks that used different specifications and implementations to communicate with each other. They realized that they needed to move away from proprietary networking systems.

2.1.5 The Evolution of ISO Networking Standards Proprietary systems are privately developed, owned, and controlled. In the computer industry, proprietary is the opposite of open. Proprietary means that one or a small group of companies controls all usage of the technology. Open means that free usage of the technology is available to the public.

2.1.5 The Evolution of ISO Networking Standards To address the problem of networks being incompatible and unable to communicate with each other, the International Organization for Standardization (ISO) researched network schemes As a result of this research, the ISO created a network model that would help vendors create networks that would be compatible with, and operate with, other networks.

2.1.5 The Evolution of ISO Networking Standards The OSI reference model released in 1984, was the descriptive scheme they created. It provided vendors with a set of standards that ensured greater compatibility and interoperability between the various types of network technologies that were produced by the many companies around the world.

2.1.5 The Evolution of ISO Networking Standards The OSI model is like a blue print for the building of a car: it specifies the functions of each layer

2.2 The OSI REFERENCE MODEL CHAPTER 2 2.2 The OSI REFERENCE MODEL

2.2.1 The purpose of the OSI reference Model This separation of networking functions is called layering.

2.2.2 The seven layers of the OSI reference model Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Host layers: Provide accurate data delivery between computers Media layers: Control Physical delivery of messages over the network

2.2.2 The seven layers of the OSI reference model All Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 People Seem To Need Data Processing

2.2.2 The seven layers of the OSI reference model Networks processes to applications Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Data representation Interhost communication End-to-end connections Addresses and best path Access to media Binary Transmission

2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 7: The Application Layer     The application layer is the OSI layer that is closest to the user; it provides network services to the user's applications. It differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. BROWSER

2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 6: The Presentation Layer The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system. Responsible for compression and encryption DATA FORMAT

2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 5: The Session Layer the session layer establishes, manages, and terminates sessions between two communicating hosts. DIALOGUES

2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 4: The Transport Layer The transport layer segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system. QUALITY OF SERVICE RELIABILITY

2 2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 3: The Network Layer The network layer is a complex layer that provides connectivity and path selection between two host systems that may be located on geographically separated networks. ADDRESSING PATH SELECTION

2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 2: The Data Link Layer The data link layer provides reliable transit of data across a physical link. In so doing, the data link layer is concerned with physical (as opposed to logical) addressing, network topology, network access, error notification, ordered delivery of frames, and flow control. FRAMES MEDIA ACCESS CONTROL

2 2.2.3 The functions of each layer Application Presentation Session Transport Network Data Link Physical 7 6 5 4 3 2 1 Layer 1: The Physical Layer The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. SIGNALS MEDIA

Analogy 2.2.4 Encapsulation 1 2 3 4 5 Encapsulation wraps data with the necessary protocol information before network transit. Analogy 1 2 3 4 5

2.2.4 Encapsulation Header – Control Information placed before the data. It tells the network where to send the data packet. Trailer – Control Information added after the data when encapsulation data for network transmission

Five Conversion Steps: Build the data Package the data for end-to-end transport Add the network address to the header Add the local address to the data link header Convert to bits for transmission

2.2.4 Names for data at each layer of the OSI model In order for data packets to travel from the source to the destination, each layer of the OSI model at the source must communicate with its peer layer at the destination. This form of communication is referred to as Peer-to-Peer Communications.

2.2.4 Names for data at each layer of the OSI model Protocol data unit. In the OSI model, the generic name for the structure of data (messages) sent between peer layers of communicating network devices.

2.3 Comparison of the OSI Model and the TCP/IP Model CHAPTER 2 2.3 Comparison of the OSI Model and the TCP/IP Model

2.3.1 The TCP/IP reference model Transmission Control Protocol/Internet Protocol (TCP/IP). The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light.

2.3.2 The Layers of the TCP/IP reference model The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions, even a nuclear war. The TCP/IP Model Application Transport Internet Network Access

2.3.2 The Layers of the TCP/IP reference model The TCP/IP Model Application Layer The designers of TCP/IP felt that the higher level protocols should include the session and presentation layer details. They simply created an application layer that handles high-level protocols, issues of representation, encoding, and dialog control. The TCP/IP combines all application-related issues into one layer, and assures this data is properly packaged for the next layer. This is also referred to as the process layer. Application Transport Internet Network Access

2.3.2 The Layers of the TCP/IP reference model The TCP/IP Model Application Transport Layer The transport layer deals with the quality-of-service issues of reliability, flow control, and error correction. Transport Internet TCP Network Access

2.3.2 The Layers of the TCP/IP reference model The TCP/IP Model Application Internet Layer The purpose of the Internet layer is to send source packets from any network on the internetwork and have them arrive at the destination independent of the path and networks they took to get there. Transport Internet Network Access IP

2.3.2 The Layers of the TCP/IP reference model The TCP/IP Model Application Network Access Layer It is also called the host-to-network layer. It is the layer that is concerned with all of the issues that an IP packet requires to actually make a physical link, and then to make another physical link. It includes the LAN and WAN technology details, and all the details in the OSI physical and data link layers. Transport Internet Network Access

2.3.3 TCP/IP Protocol Graph

2.3.4 Comparison of the OSI model and the TCP/IP model

2.3.4 Comparison of the OSI model and the TCP/IP model SIMILIRATIES both have layers both have application layers, though they include very different services both have comparable transport and network layers packet-switched (not circuit-switched) technology is assumed networking professionals need to know both DIFFERENCES TCP/IP combines the presentation and session layer issues into its application layer TCP/IP combines the OSI data link and physical layers into one layer TCP/IP appears simpler because it has fewer layers TCP/IP protocols are the standards around which the Internet developed