ITT300 - CHAPTER 2 NETWORK MODELS.pdf

ITT300 INTRODUCTION TO DATA COMMUNICATION AND NETWORKING CHAPTER 2 NETWORK MODELS ADAPTED FROM: Behrouz A. Forouzan Lesson Outcomes At the end of this lesson, the students should be able to: Discuss the main function of each layer in O...

ITT300 INTRODUCTION TO DATA COMMUNICATION AND NETWORKING CHAPTER 2 NETWORK MODELS ADAPTED FROM: Behrouz A. Forouzan Lesson Outcomes At the end of this lesson, the students should be able to: Discuss the main function of each layer in OSI model. Explain the specific responsibilities of each layer in OSI model. Differentiate between layers in OSI model and TCP/IP model. Give types of addressing. MOHD HAFIZAN MUSA- UiTMCJ Layered Tasks Image source: Data Communications Figure 2.1 Sending a letter And Networking, Forouzan OSI Model Figure 2.2 Seven layers of the OSI model An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. An open system is a set of protocols that allows any two different systems to communicate regardless of their underlying architecture. Layered Architecture Figure 2.3 shows the layers involved when a message is sent from device A to device B. As the message travels from A to B, it may pass through many intermediate nodes. This intermediate nodes usually involve only the first three layers of the OSI model. Within the single machine, each layer calls upon the services of the layer just below it. Eg: layer 3 uses services provided by layer 2 and provides services for layer 4 Figure 2.3 The interaction between layers in the OSI model Layered Architecture Between machines, layer x on one machine communicates with layer x on another machine. This communication is governed by an agreed-upon series of rules and conventions called protocols. The processes on each machine that communicate at a given layer are called peer-to-peer processes - using the protocols appropriate to a given layer. Peer-to-peer Process At the physical layer, communication is direct: In Figure 2.3, device A sends a stream of bits to device B. At the higher layers, however, communication must move down through the layers on device A, over to device B, and then back up through the layers. At layer 1 the entire package is converted to a form that can be transmitted to the receiving device. Organization of the Layers Network support layers Layer 1 (physical), 2 (data link) and 3 (network) deals with the physical aspects of moving data from one device to another. Transport layer Layer 4 (transport layer) ensures that what the lower layers have transmitted is in form that the upper layers can use. User support layers Layer 5 (session), 6 (presentation) and 7 (application) allow interoperability among unrelated software systems. Organization of the Layers Figure 2.4, shows an overall view of the OSI layers. The process starts at layer 7 (the application layer), then moves from layer to layer in descending, sequential order. At each layer, a header, or trailer, can be added to the data unit. Commonly, the trailer is added only at layer 2. When the formatted data unit passes through the physical layer (layer 1), it is changed into an electromagnetic signal and transported along physical link. Figure 2.4 An exchange using the OSI model Organization of the Layers Upon reaching its destination, the signal passes into layer 1 and is transformed back into digital form. The data units then move back up through the OSI layers. When the block of data reaches the next higher layer, the headers and trailers are removed, and actions appropriate to that layer are taken. By the time it reaches layer 7, the message is again in a form appropriate to the application and is Figure 2.4 An exchange using the made available to the recipient. OSI model Physical Layer Responsible for transmitting individual bits from one node to the next It coordinate the functions required to transmit a bit stream over a physical medium Deals with mechanical and electrical specifications of the interface and transmission media (LAN / Wifi) Also defines the procedures and functions that physical devices and interfaces have to perform for Figure 2.5 Physical layer transmission to occur Other responsibilities Physical characteristics of interfaces and media Defines the characteristic of the interface between devices and the types of transmission medium and ports Representation of bits Define the type of encoding (how 0s and 1s are changed to signals). Signal to be transmitted must be encoded into signal – electrical or optical Data rate – transmission rate The number of bits to be sent each second – defines the duration of a bit, which is how long it lasts (The larger the size of packet, the longer time it take for the transmission to complete) Synchronization of bits Sender and receiver clocks must be synchronized (this topic will be discussed in further chapter) Other responsibilities Physical topology Defines how devices are connected to make a network: mesh, star, ring or hybrid topology Transmission mode Defines the direction of transmission between 2 devices: simplex, half-duplex or full-duplex Data Link Layer It responsible for delivering data units (frame) from one station to the next without errors (node-to- node delivery) It accepts a data unit from the third layer and adds meaningful bits to the beginning (header) and end (trailer) that contain addresses and other control information Figure 2.6 Data link layer Other responsibilities Framing Divides stream of bits received into manageable data units called frames Physical addressing Adds header to define sender and receiver of the frame Flow control Data absorbed by receiver less than rate produced in the sender, data link imposed flow control Error control Add mechanism to detect and retransmit damaged or loss frames Access control Two or more device connected to same link, data link determine which device has control over the link  Data Link Layer Image source: Data Communications And Networking, Forouzan Figure 2.7 Node-to-node delivery Network Layer It responsible for source to destination delivery of a individual packet across multiple network links It provide two related services Switching – temporary connections between physical link Routing – selecting the best path for sending data when more path available Figure 2.8 Network layer Other responsibilities Logical Addressing If the packet passes the network boundary, we need another addressing to distinguish the source and destination system Routing For large network or internetwork, the connecting devices route or switch the packets to their final destination Network Layer Figure 2.9 Source-to-destination delivery Image source: Data Communications And Networking, Forouzan Transport Layer Responsible for process to process delivery (end to end delivery) of the entire message Delivery not only from one computer to the next but also from a specific application on one computer to specific application on other Ensure that the whole message arrives intact and in order Create connection between the two end ports Figure 2.10 Transport layer Other responsibilities Service-point/Port addressing Get the entire message to the correct process Segmentation and reassembly Message divided into transmittable segments, each segment contain sequence number – enable to reassemble the message correctly & to identify and replace packets that were lost Connection control Flow control Error control  Session Layer Responsible for dialog control and synchronization Establishes, maintains, and synchronizes the interaction among communicating systems Figure 2.12 Session layer Other responsibilities Dialog control Allows 2 systems to enter into a dialog: either half-duplex or full-duplex mode Synchronization o Allows a process to add checkpoint, or synchronization points, to a stream of data. Presentation Layer Responsible for translation, compression, and encryption Concerned with the syntax and semantics of the information exchanged Figure 2.13 Presentation layer between two systems Other responsibilities Translation The information must be changed to bit streams before being transmitted. This layer is responsible for interoperability between these different encoding methods Encryption Encryption: the sender transforms the original information to another form & sends the resulting message out over the network Compression Reduces the number of bits contained in the information  Application Layer Enables user, whether human or software to access the network Provides user interfaces and support for services (e.g. electronic mail, file access, file transfer, shared database management and other types of information services) No header and trailers are added Figure 2.14 Application layer Other responsibilities Mail services Basis for mail forwarding and storage File transfer and access User access file in remote Remote log-in User can log into a remote computer Accessing to World Wide Web Most application today Summary of OSI Model Figure 2.15 Summary of layers Image source: Data Communications And Networking, Forouzan TCP/IP Protocol Suite TCP/IP is a 5 layers (physical, data link, network, transport, and application) hierarchical protocol suite developed before the OSI model The first 4 layers provide physical standards, network interfaces, internetworking, and transport functions that correspond to the first 4 layers in OSI model The 3 topmost layers in the OSI model, represented in TCP/IP by a single layer called the application layer  OSI TCP/IP 7 6 5 5 4 4 3 3 2 2 1 1 Figure 2.16 TCP/IP and OSI Image source: Data Communications model And Networking, Forouzan  The most dominant protocol is TCP/IP, even the Internet uses TCP/IP. The OSI model is a more generic network model issued by ISO.ISO try to push OSI family protocols (example : ipx/spx, decent ) but failed in becoming popular, because the TCP/IP protocols family that was released earlier used for the Internet and became very popular. MOHD HAFIZAN MUSA- UiTMCJ Addressing Four levels of addresses are used in an internet employing the TCP/IP protocols: physical (link) address, logical (IP) address, port address, and specific address (see Figure 2.17) Figure 2.17 Addresses in TCP/IP Addressing Each address is related to a specific layer in the TCP/IP architecture, as shown in Figure 2.18 Figure 2.18 Relationship of layers and addresses in TCP/IP Physical Addresses Also known as the link address, is the address of a node as defined by its LAN or WAN. In networking, physical address refers to a computer's MAC address, which is a unique identifier associated with a network adapter that is used for identifying a computer in a network. It is included in the frame used by the data link layer. The size and format of these addresses vary depending on the network Eg. Ethernet uses a 6-byte (48-bit) physical address, LocalTalk (Apple) has a 1-byte dynamic address that changes each time the station comes up It is attached in the network interface card (NIC) Logical Addresses Also known as IP addresses are necessary for universal communications that are independent of underlying physical network A universal addressing system is needed in which each host can be identified uniquely, regardless of underlying physical network A logical address in the Internet is currently a 32-bit address that can uniquely define a host connected to the Internet Each of the four(4) numbers can be between 0 to 255 Port Addresses Today, computers are devices that can run multiple processes at the same time The end objective of Internet communication is a process communicating with another process So, port address identifies a process on a host A port address is TCP/IP is 16-bits in length MOHD HAFIZAN MUSA- UiTMCJ Specific Addresses Some applications have user-friendly addresses that are designed for that specific address e.g. The email address (e.g [email protected]) and the Universal Resource Locator (URL) (e.g www.mhhe.com)