TMF1254 Communication and Computer Network (CCN) Network Models OSI Model TCP/IP © 2004 Ken Baldauf, All rights reserved. Objectives • Explains how standards ensure greater compatibility and interoperability between various types of network technologies • OSI reference model networking scheme • The basic functions of the OSI model © 2004 Ken Baldauf, All rights reserved. General model of communication • Using layers to analyze problems in a flow of materials • Source, destination, and data packets • Media • Protocol • The evolution of ISO networking standards © 2004 Ken Baldauf, All rights reserved. We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office Topics discussed in this section: Sender, Receiver, and Carrier Hierarchy © 2004 Ken Baldauf, All rights reserved. Figure 2.1 Tasks involved in sending a letter © 2004 Ken Baldauf, All rights reserved. Protocol “layers” and reference models • Networks are complex, with many “pieces”: • hosts • routers • links of various media • applications • protocols • hardware, software Question: is there any hope of organizing structure of network? • and/or our discussion of networks? © 2004 Ken Baldauf, All rights reserved. Example: organization of air travel end-to-end transfer of person plus baggage ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing How would you define/discuss the system of airline travel? • a series of steps, involving many services © 2004 Ken Baldauf, All rights reserved. Example: organization of air travel ticket (purchase) ticketing service ticket (complain) baggage (check) gates (load) baggage service baggage (claim) gate service gates (unload) runway takeoff runway service runway landing airplane routing routing service airplane routing airplane routing layers: each layer implements a service • via its own internal-layer actions • relying on services provided by layer below © 2004 Ken Baldauf, All rights reserved. Why layering? Approach to designing/discussing complex systems: • explicit structure allows identification, relationship of system’s pieces • layered reference model for discussion • modularization eases maintenance, updating of system • change in layer's service implementation: transparent to rest of system • e.g., change in gate procedure doesn’t affect rest of system © 2004 Ken Baldauf, All rights reserved. OSI Model © 2004 Ken Baldauf, All rights reserved. THE OSI MODEL • Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. 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. © 2004 Ken Baldauf, All rights reserved. What you need to know? • • • • • The purpose of the OSI reference model The seven layers of the OSI reference model The functions of each layer Encapsulation Names for data at each layer of the OSI model © 2004 Ken Baldauf, All rights reserved. Introduction • OSI stands for Open System Interconnection • developed by the International Standards Organization (ISO) • The model is NOT a standard, but rather is a representation that is useful in understanding how data communications happens • In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. This separation of networking functions is called layering. © 2004 Ken Baldauf, All rights reserved. Fundamentals of the OSI model • Layered Architecture • Peer-to-Peer Processes • Encapsulation © 2004 Ken Baldauf, All rights reserved. Layered Architecture • OSI model composed of seven layers © 2004 Ken Baldauf, All rights reserved. Peer-to-Peer Processes • The processes on each machine that communicate at given layer of the OSI model at the source must communicate with its peer layer at the destination • Each layer's protocol exchanges information, called protocol data units (PDUs), between peer layers © 2004 Ken Baldauf, All rights reserved. Message structure of OSI model MESSAGE MESSAGE MESSAGE Segments PACKETS FRAMES BITS © 2004 Ken Baldauf, All rights reserved. Peer to Peer Communications © 2004 Ken Baldauf, All rights reserved. Encapsulation • Encapsulation wraps data with the necessary protocol information before network transit • At each layer, a header (h) or possibly a trailer (t), can be added to the data unit. © 2004 Ken Baldauf, All rights reserved. An exchange using the OSI model © 2004 Ken Baldauf, All rights reserved. © 2004 Ken Baldauf, All rights reserved. © 2004 Ken Baldauf, All rights reserved. A conceptual view of data encapsulation © 2004 Ken Baldauf, All rights reserved. What are the seven layers? Alligator Pet Steve’s Touch Not Do Please © 2004 Ken Baldauf, All rights reserved. Why a Layered Network Model? • Reduce complexity • Standardizes interfaces • Facilitates modular engineering • Ensures interoperable technology • Accelerates evolution • Simplifies teaching and learning © 2004 Ken Baldauf, All rights reserved. Organization of the layers • 1, 2, and 3 (physical, data link, network) classified as the network support layers. They deal with the physical aspects of pushing the data; physical addressing, actual electrical connections, etc. • 4 (transport) It has the job of insuring that what was transmitted across the network is in a form that the upper layers can use. • 5, 6, and 7 (session, presentation, and application) can be considered the user support layers they allow inter operability among unrelated software packages or systems. © 2004 Ken Baldauf, All rights reserved. OSI Model in Details © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • Network Processes to Applications – Provides network services to application processes (such as electronic mail, files transfer, and terminal emulation) © 2004 Ken Baldauf, All rights reserved. Application Layer • Refers to application interfaces. Example MHS (Message handling Service) is an interface that enable a variety of email programs can be used on a intranet. • Is closest to the user • Provides network services to applications • Does not provide services to any other OSI layer • Think of browsers © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • Data Representation – Insure data is readable by receiving system – Format of data – Data structure – Negotiates data transfer syntax for application layer © 2004 Ken Baldauf, All rights reserved. Presentation Layer • Ensures that the information that the application layer of one system sends out is readable by the application layer of another system – Translation • ensuring interoperability between different encoding • Changes information from sender-dependant format into common format and to receiver-dependant format – Encryption (sender)/ Decryption (receiver) – Compression • To reduces the number of bits contained in the information • Text, audio, and video • Think of a common data format © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • Inter-host communication – Establishes, manages and terminates sessions between applications © 2004 Ken Baldauf, All rights reserved. Session Layer • Synchronizes dialogue between the two hosts' presentation layers and manages their data exchange • Offers provisions for efficient data transfer, class of service, and exception reporting • Think of dialogues and conversations or transaction © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • End to end connections – Concerned with transportation issues between hosts / process – Data transport reliability – Establish, maintain, terminate virtual circuits – Fault detection and recovery – Information flow control © 2004 Ken Baldauf, All rights reserved. Transport Layer • Segments the data into acceptable packet size • Responsible for data integrity of packet segments • Provide a data transport service that shields the upper layers from transport implementation details • Levels of service are segmenting, reassembly, error recovery, flow control • Think of quality of service, and reliability © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • Address and Best Path – Provides connectivity and path selection between end systems – Domain of routing © 2004 Ken Baldauf, All rights reserved. Network Layer • Think of path selection, routing, and addressing. • Sometime called Internet layer. • The header includes the source and destination addresses, the sequence order, and other data necessary for correct routing and rebuilding at the destination. © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • Access to Media – Provides reliable transfer of data across media – Physical addressing, network topology, error notification, flow control © 2004 Ken Baldauf, All rights reserved. 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 • Think of frames and media access control © 2004 Ken Baldauf, All rights reserved. The 7 Layers of the OSI Model • Binary Transmission – Wires, connectors, voltages, data rates © 2004 Ken Baldauf, All rights reserved. Physical Layer • Defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems – Voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other • Think of signals and media © 2004 Ken Baldauf, All rights reserved. OSI Service Types Connection oriented service Connectionless © 2004 Ken Baldauf, All rights reserved. Connection oriented service • A physical link is established between the sending and receiving nodes • This link remains in effect for the duration of the session • After the session is completed, the link is removed. • Wasted bandwidth, link remain even during idle periods of a transmission • Exp: telephone system © 2004 Ken Baldauf, All rights reserved. Connectionless service • No physical link is established • A message is partitioned into packets and routed through the network • Each packet is independent of the other packets • Packets can arrive out of order • Example: post office (once mailed, the mail / parcel do not necessarily follow exactly the same delivery route) • It is reliable or unreliable (regular letter versus register letter) © 2004 Ken Baldauf, All rights reserved. OSI Model Functional Drawing © 2004 Ken Baldauf, All rights reserved. Summary of OSI layers © 2004 Ken Baldauf, All rights reserved. TCP header © 2004 Ken Baldauf, All rights reserved. Model of TCP/IP © 2004 Ken Baldauf, All rights reserved. History of Internet • Under the project or ARPA (advanced Research Projects Agency) within the Department of Defense (DoD) • Early interenetwork called ARPANET • Access restricted to the military, defense contractors and university personnel involved in defense research. © 2004 Ken Baldauf, All rights reserved. Father of Internet © 2004 Ken Baldauf, All rights reserved. TCP/IP • TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world • It is the protocol that defines how transmissions are exchanged across the Internet • U.S. Department of Defense (DoD) © 2004 Ken Baldauf, All rights reserved. TCP/IP protocol suite The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. © 2004 Ken Baldauf, All rights reserved. Comparison of the OSI Model and the TCP/IP Model • • • • The TCP/IP reference model The layers of the TCP/IP reference model TCP/IP protocol graph Comparison of the OSI model and the TCP/IP model © 2004 Ken Baldauf, All rights reserved. Comparison of the OSI and TCP/IP Layers TCP/IP’s application layer corresponds to OSI’s application, presentation, and session layer TCP/IP’s host-to-host transport layer corresponds to OSI’s transport layer TCP/IP’s Internet layer corresponds to OSI’s network layer TCP/IP’s network interface layer corresponds to OSI’s data link and physical layer © 2004 Ken Baldauf, All rights reserved. Application Layer • Higher level protocols should include the session and presentation layer details • Handles high-level protocols, issues of representation, encoding, and dialog control • Serve as the communication interface for users by providing specific application services to the user such as remote terminal login, file transfer, email. • Application protocols include Telnet, FTP, and SMTP © 2004 Ken Baldauf, All rights reserved. Transport Layer • Also called, host-to host transport layer • Deals with the quality-of-service issues of reliability, flow control, and error correction • End-to end data delivery • Two protocols – Transmission control protocol (TCP) – User datagram protocol (UDP) – Stream Control Transmission protocol (SCTP) © 2004 Ken Baldauf, All rights reserved. Internet layer • Also called network layer • Transfers user messages from a source host to a destination host • Internet / Internetworking protocol (IP) • Best path determination and packet switching • Example: Postal system © 2004 Ken Baldauf, All rights reserved. Network Access Layer • Host-to-network layer • Making a connection to the physical medium. • Includes the LAN and WAN technology details, and all the details in the OSI physical and data link layers © 2004 Ken Baldauf, All rights reserved. Protocol Graph: TCP/IP © 2004 Ken Baldauf, All rights reserved. Applications • • • • • FTP - File Transfer Protocol HTTP - Hypertext Transfer Protocol SMTP - Simple Mail Transfer protocol DNS - Domain Name System TFTP - Trivial File Transfer Protocol © 2004 Ken Baldauf, All rights reserved. • The transport layer involves two protocols transmission control protocol (TCP) and user datagram protocol (UDP) • There is only one network protocol – internet / internetworking protocol, or IP • The network access layer, refers to the particular LAN or WAN technology that is being used © 2004 Ken Baldauf, All rights reserved. © 2004 Ken Baldauf, All rights reserved. OSI Model and TCP/IP Model © 2004 Ken Baldauf, All rights reserved. © 2004 Ken Baldauf, All rights reserved. Similarities • 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 © 2004 Ken Baldauf, All rights reserved. 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, so the TCP/IP model gains credibility just because of its protocols. In contrast, typically networks aren't built on the OSI protocol, even though the OSI model is used as a guide © 2004 Ken Baldauf, All rights reserved. Summary of TCP/IP • Internet Layer – Heart and soul is Internet / Internetworking Protocol (IP) – the IP of TCP/IP – Transfer user massages from source host to destination host – Is a connectionless datagram service – Route selection is based on some metric – Users Internet or IP addresses as road map to locate a host within the Internet – Relies on routers or switches (dedicated notes that connect two or more dissimilar network) – Integral part is Internet Control Message Protocol (ICMP), which uses an IP datagram to carry messages about state of communications environment © 2004 Ken Baldauf, All rights reserved. Summary of TCP/IP • Connects a host to the local network hardware • Makes a connection to the physical medium • Uses a specific protocol to accessing the medium • Places data into frames • Effectively performs all functions of the first two layers of the OSI model © 2004 Ken Baldauf, All rights reserved. Summary of TCP/IP • Transport layer – Defined by two protocol • User Datagram Protocol (UDP) – – – – – Is a connectionless protocol Provides unreliable datagram service(no end-to end detection or correction). Does not retransmit any unreceived data Requires little overhead Application protocols include Trival File Transfer Protocol (TFTP), NFS, Simple Network Management Protocol (SNMP), Bootstrap Protocol (BOOTP), and Domain Name Service (DNS) • Transmission Control Protocol (TCP) – This is the TCP of TCP/IP – Is a connection oriented protocol – Provides reliable data transmission via end – to end error detection and correction – Guarantees data are transferred across a network accurately and in proper order – Retransmits any data not received by destination node. – Guarantees against data duplication between sending and receiving nodes – Application protocols include Telnet, FTP, SMTP, and POP © 2004 Ken Baldauf, All rights reserved. Summary of TCP/IP • Application layer – Similar to OSI application layer – Serves as communication interface by providing specific application services – Examples include e-mail, virtual terminal, file transfer, WWW © 2004 Ken Baldauf, All rights reserved. Addressing Physical addresses, logical (IP) addresses, port addresses, specific addresses © 2004 Ken Baldauf, All rights reserved. Type of addresses © 2004 Ken Baldauf, All rights reserved. Relationship of layers and addresses in TCP/IP © 2004 Ken Baldauf, All rights reserved. Physical address • Known as link address • It included in the frame used by the data link layer. • Lowest level address • Most LAN use a 48 bit (6 byte) physical address written as 12 hex digits • 07:01:02:01:2C:4B © 2004 Ken Baldauf, All rights reserved. Logical address • Uniquely define a host connected to the Internet • A logical address in the Internet is currently 32 bit address • It remains the same address from the source to destination • 192.168.2.1 © 2004 Ken Baldauf, All rights reserved. Port address • Used to label the different processes • For example, computer A can communicate with computer B by using TELNET. • 16 bit in length in TCP/IP © 2004 Ken Baldauf, All rights reserved. © 2004 Ken Baldauf, All rights reserved. Specific Addresses • User friendly address – example: email address (ali@hotmail.com) – URL (universal Resource Locator) (www.yahoo.com) © 2004 Ken Baldauf, All rights reserved. Summary • • • • • • OSI reference model TCP/IP Seven numbered layers Encapsulation Peer-to-Peer Communications Addressing © 2004 Ken Baldauf, All rights reserved. References • Data Communications and Networking 5th edition Behrouz A. Forouzan, McGraw-Hill Education, 2013 • Computer Networking: A Top-Down Approach 8th edition Jim Kurose, Keith Ross Pearson, 2020 © 2004 Ken Baldauf, All rights reserved. Thank you © 2004 Ken Baldauf, All rights reserved.
