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BIT 1102: COMMUNICATIONS TECHNOLOGY AND THE INTERNET

MAKERERE UNIVERSITY College of Computing and Information Sciences School of Computing and Informatics Technology. BIT 1102: COMMUNICATIONS TECHNOLOGY AND THE INTERNET. 7. Introduction to ISO/OSI Architecture. Introduction.

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BIT 1102: COMMUNICATIONS TECHNOLOGY AND THE INTERNET

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  1. MAKERERE UNIVERSITY College of Computing and Information Sciences School of Computing and Informatics Technology BIT 1102: COMMUNICATIONS TECHNOLOGY AND THE INTERNET 7. Introduction to ISO/OSI Architecture

  2. Introduction • Open system interconnection (OSI)model is a reference model developed by international organization for standardization(ISO) in 1984, as a conceptual framework of standards for communication in the networks across different equipment and applications by different vendors. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  3. The OSI model defines the communication process into seven layers which divides the tasks involved with moving information between networked computers into seven smaller ,more manageable task groups. A task is then assigned to each of the seven OSI layers. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  4. Each layer is responsibly self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  5. Networking Architecture Architecture is essentially a set of rules that describes the function of some portion of the hardware and software that constitute a stack of layers. A networking architecture is designed to implement the functions associated with a particular contiguous set of layers of the OSI Reference Model, either formally or informally. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  6. Networking Layers • A layer is a collection of related functions that provides services to the layer above it and receives services from the layer below it. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  7. The OSI Model Layers • The seven layers of the OSI reference model can be divided into two categories: a) Lower layers The lowerlayers of the OSI model handle data transport issues. • Also called Media layers BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  8. The OSI Model Layers b) Upper layers The upper layers of the OSI model deal with application issues and generally are implemented only in software. The highest layer, the application layer, is closest to the end user. • Both users and application layer processes interact with software applications that contain a communications component. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

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  11. Layer 1 – The Physical Layer • Provides the physical interconnections through the network hardware. • This layer deals with the physical plugs, sockets and electrical specification of signals. This is the medium over which the digital signals are to be transmitted. • Provides low level services involving the transmission of raw bits BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  12. Layer 1 – The Physical Layer cont’d • Involves twisted pair, coaxial cable, optical fiber, wireless, Network adapters, transmitters, repeaters or other media. • Physical layer specifications define. characteristics such as voltage levels, timing of voltage changes, physical data rates, Maximum transmission distances, and physical connectors. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  13. Main Functions of the physical Layer • Establishing and terminating the physical connections to the network. • Converting “raw bits”, (Zeros and ones) into the respective communication channel energy such as Light, electrical signals (Known as data encoding) • Guides transmission and reception of data. • Perform services requested by the Data Link Layer BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  14. Layer 2 – The Data-Link Layer • Physical addressing (as opposed to network addressing) defines how devices are addressed at the data link layer- MAC address. • Packages raw bits from the Physical layer into frames BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  15. Layer 2: Data Link Layer • Mainly concerned with reliabletransmission of data including detecting and correctingerrors that may have occurred at thephysical layer • This Layer provides lowlevelservices involving the transmission of rawbits BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  16. Main Functions of the Data Link Layer • Provides low level error detection and control using Techniques like CRC – Discussed in details at an advanced level. • Media Access control sub-layer controls access to the shared medium to avoid conflict (for example what does the Ethernet protocol use to control Media access?) BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  17. Main Functions of the Data Link Layer cont’d • The Data Link Layer responds to service requests from the Network layer and sends requests to the physical layer. • Responsible for “Framing of data” i.e. conversion of data into information understandable by different protocols. • Basic Addressing using MAC address(hardware address) enables frames to be forwarded to the destination. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  18. Main Functions of the Data Link Layer cont’d • Defines how devices are to be physically connected, such as in a bus or a ring topology. • Error notification: Alerts upper-layer protocols that a transmission error has occurred, • Eg if a frame fails to get to its destination e.g. when a wrong destination address is given. • Tasks of the s/w at layer 2 are; • Flow control, • Error notification, • Generating frames BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  19. Main Functions of the Data Link Layer cont’d • Finally, flow control moderates the transmission of data so that the receiving device is not overwhelmed with more traffic than it can handle at one time. • Two most common network devices exist at the second layer of the OSI model: Bridges and switches. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  20. Common data Link Layer H/w and protocols • Ethernet • ATM (This Uses fixed packets in the transmission) • FDDI MoreHardware includes: • Switch, intelligent Hub, • NIC (more advanced NICs handle both physical and DLL functions) BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  21. Layer 3 – The Network Layer • This layer responds to service requests from the transport layer and issues service requests to the data link layer • The network layer defines the network address(IP address), which differs from the MAC address. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  22. Layer 3 – The Network Layer cont’d • IP addresses are written as four dot-separated decimal numbers between 0 and 255, e.g., 192.168.2.1. (Assigned by either a DHCP or Manually configured.) • Handles the addressing and delivery of data- This aids routers in finding the destination. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  23. Functions of the Network Layer • While the functions of the Physical and Data Link Layer are local (they are concerned with the devices that are connected to each other), the Network layer defines functions that involve the complete transmission of data across inter connected networks. • The Primary function of the Network layer is the delivery of the data from the source to the destination. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  24. Functions of the Network Layer • Logical address also known as layer 3 address for example on the internet, an IP address is implemented at the network layer. • Ensures that the data packets are transmitted to the destination over the best possible route by the process known as routing. Also involved in breaking and re-assembling data packets. • Attaches network headers , which contain information about the destination address, to the data frames to make them “datagrams” or data packets that can be delivered across networks. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  25. Common Network Layer Protocols The most well-known examples of layer-3 protocols are: • Internet Protocol (IP), • Internet Control Message Protocol (ICMP), • Internetwork Packet Exchange, X.25 (IPX), • Asynchronous Transfer Mode(ATM). • Data gram Delivery Protocol. Network Layer hardware include: • Router (Recall router definition) • Brouter, • ATM Switch (Used to handle ATM Protocol) BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  26. Layer 4 – The Transport Layer • The major responsibility of this layer is dataintegrity- ensures that data transmitted between hosts is reliable and timely. • Note: The sent data is expected not to be altered before the destination. • Act as an Intermediary or a go-between layers 1-3 and the 5-7 to ensure delivery of data to the right application. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  27. Functions of the Transport layer • Generally ensures reliable end-to-end data delivery. • Completes the Network Layer services, which only cater for “best effort” communication by enhancing quality of service. (QoS) and ensuring accurate data delivery (as in the case of TCP). • However, some layer 4 protocols like User Data Protocol (UDP) don't ensure reliable transmission. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  28. Layer 4 – The Transport Layer cont’d • ProvidesconnectionServicesie “connectionoriented” and “connection-less” where the former requires a logical link to be established before transmission occurs and terminated after. Functions of the Transport layer • Connection Control -The layer can offer connectionless or connection oriented services. With connectionless transmission, the layer treats each Segment as an independent packet and delivers it to the transport layer at the destination. • With connection oriented transport layer makes a connection with the transport layer at the destination machine first before delivering the packets. After all the data has been transmitted the connection is terminated. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  29. Functions of the Transport layer • Flow control. • Error Control • Segmentation and reassembly - A message is divided into transmittable segments with each segment containing a sequence number. • These numbers enable the transport layer to reassemble the message correctly upon arriving at the destination and to identify and replace packets that were lost during transmission. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  30. Transport layer looks to “see” if data is coming from more than one application and integrates each application's data into a single stream for the physical network Main Transport layer protocols: TCP, UDP, TLS User Datagram Protocol (UDP) a connectionless protocol that, like TCP, runsontop of IP networks. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  31. Unlike TCP/IP- UDP/IP provides very few error recovery services, offering instead a direct way to send and receive datagram over an IP network. • Transmission Control Protocol (TCP) TCP keeps track of the packet delivery order and the packets that must be resent (guaranteeddelivery- i.e. we have to ensure data has no errors) BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  32. Layer 5 – The Session Layer • The primaryfunction of the session layer is to establish,manage and terminate a “session”. • A session generally refers to a logicallink between softwareapplications. • Layer 5 provides for Duplex communication that can be either simplex, half duplex or full Duplex. • Session Layer Protocols include • NETBIOS , ASP (Apple Talk Session Protocol), SCP (Session Control Protocol), ZIP (Zone Information Protocol), etc. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  33. Layer 5 – The Session Layer • Establishes, maintains and ends / terminates communication with the receiving device. • Provides the mechanism for managing the dialogue between end-user application processes. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  34. Layer 6 – The Presentation Layer • The Presentation Layer is primarily concerned with translating data with different formats for “presentation” to the application layer. • For example the network may have computers running UNX, Windows, MAC OS or data encoded in ASCII Or EBCDIC etc like GIF,JPEG, etc . The presentation layer caters for differences in these formats. • Note: In practice, the application layer maybe able to handle these differences. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  35. Layer 6 – The Presentation Layer • Takes the data provided by the Application layer and converts it into a standard format that the other layers can understand (On sending). • Its responsible for defining the syntax (language rules) BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  36. Encryption and compression- this allows applications to agree on standardized representations for data, like American Standard Code for Information Interchange- ASCII; codes that represent text in computers, communications equipment, and other devices that work with text BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  37. Layer 7 – The Application Layer • Directly interfaces with the Application or service that is using the network. • Examples include Email software, or requesting an Ms power point (.ppt) file that is stored on a server across a Network. Common Application Layer Protocols include, • FTP • TELNET • DNS (Discussed in details under the Internet) BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  38. Layer 7 – The Application Layer • This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network-related activities • Responsible for providing end-user services, such as file transfers, electronic messaging, e-mail, virtual terminal access, and network management. Note: • This is the layer with which the user interacts. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  39. Makes sure that the other party is identified and can be reached. If appropriate, authenticates either the message sender or receiver or both Ensures agreement at both ends about error recovery procedures, data integrity, and privacy Determines protocol and data syntax rules at the application level. Protocols that are commonly used and exist at layer 7 of the OSI model are HTTP (Web requests), FTP (File Transfer Protocol), BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

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  41. What goes on when data passes from Host A to Host B • The application ,presentation and session layer take user input and converts it into data. • The transport layer adds a segment header converting the data into segments. • The network layer adds a network header and converts the segments into packets /datagram BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  42. 4.The data link layer adds a frame header converting the packets /datagrams into frames 5. The MAC sub layer converts the frames into bits which the physical layer can put on the wire. The above steps are known as the 5 steps of data encapsulation. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  43. When the bit stream arrives at the destination ,the physical layer takes it off the wire and converts it into frames ,each layer will remove their corresponding header while the data flows up the OSI model until it is converted back to data and presented to the user. This is also known as decapsulation. BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

  44. Note: A handy way to remember the seven layers is the sentence "All people seem to need data processing." The beginning letter of each word corresponds to a layer. All-----------------Application layer People-----------Presentation layer Seem -----------Session layer To-----------------Transport layer Need-------------Network layer Data--------------Data link layer Processing-----Physical layer READ MORE ON THE ENCAPSULATION AND DECAPSULATION CONCEPTS BIT 1102: COMMUNICATION TECHNOLOGY AND THE INTERNET

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