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DICT 301: Computer Networks Engr. Md. Nazim Uddin B.Sc. Engg., M.Sc. Eng., Ph.D. (on going) Open Systems Interconnection(OSI)

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Presentation on theme: "DICT 301: Computer Networks Engr. Md. Nazim Uddin B.Sc. Engg., M.Sc. Eng., Ph.D. (on going) Open Systems Interconnection(OSI)"— Presentation transcript:

1 DICT 301: Computer Networks Engr. Md. Nazim Uddin B.Sc. Engg., M.Sc. Eng., Ph.D. (on going) Open Systems Interconnection(OSI) Reference Model

2 Content TCP/IP Protocol Model OSI Reference Model Data Encapsulation and Decapsulation Communication over the Network Binary Number System and Conversion Hands on

3 1-3 Protocol Layers (TCP/IP Model)

4 Network Protocols Pre-determined rules that govern communications A group of inter-related protocols that are necessary to perform a communication function is called a protocol suite

5 Role of Protocols The format or structure of the message, such as how much data to put into each segment The process by which intermediary devices share information about the path to the destination The method to handle error and system messages between intermediary devices The process to setup and terminate communications or data transfers between hosts

6 Layered Task We use the concept of layers in our daily life. Networks are complex! Many pieces/ devices/ parts: hosts routers links of various media applications protocols hardware, software

7 1-7 Organization of air travel a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

8 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below

9 Why a layered model? Easier to teach communication process. Speeds development, changes in one layer does not affect how the other levels works. Standardization across manufactures. Allows different hardware and software to work together. Reduces complexity

10 1-10 Internet protocol stack (TCP/IP model) application: supporting network applications FTP, SMTP, HTTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits on the wire application transport network link physical

11 TCP/IP Reference Model Application Transport Internet Network Access (Host-to-network) Layer HTTP TELNET FTP SMTP SNMP Protocols TCP UDP IP ICMP ETHERNET PACKET RADIO

12 1-12 message segment datagram frame source application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn HlHl M router switch Encapsulation

13 Protocols at the application layer HTTP: browser and web server communication FTP : file transfer protocol TELNET: remote login protocol POP3: Retrieve email POP3 is designed to delete mail on the server as soon as the user has downloaded it IMAP (Internet Message Access Protocol ) Retrieve emails, retaining e-mail on the server and for organizing it in folders on the serve

14 Protocols at the transport layer Transmission control protocol (TCP), Connection oriented Connection established before sending data Reliable user datagram protocol (UDP) Connectionless Sending data without establishing connection Fast but unreliable

15 Protocol at the network layer IP Path selection, routing and addressing ICMP (Internet Control Message Protocol ) sends error messages relying on IP a requested service is not available a host or router could not be reached Protocols at the link layer Ethernet Uses CSMA/CD Token Ring

16 Data Formats Application data data TCP header data TCP header data TCP header data TCP header IP header data TCP header IP header Ethernet header Ethernet trailer application layer transport layer network layer data link layer message segment packet frame

17 Packet Encapsulation (TCP/IP) The data is sent down the protocol stack Each layer adds to the data by pretending headers 22Bytes20Bytes 4Bytes 64 to 1500 Bytes

18 Encapsulation Data usually transferred in blocks Protocol data units (PDUs) Each PDU contains data and control information Some PDUs only control Three categories of control Address Of sender and/or receiver Error-detecting code e.g. frame check sequence Protocol control Additional information to implement protocol functions Addition of control information to data is encapsulation Data accepted or generated by entity and encapsulated into PDU Containing data plus control information e.g. TFTP, HDLC, frame relay, ATM, AAL5, LLC, IEEE 802.3, IEEE 802.11 [Advance]

19 Assists in protocol design protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below Fosters competition products from different vendors can work together Prevents technology or capabilities changes in one layer from affecting other layer above and below Provides a common language to describe networking functions and capabilities Benefits of a Layered Model [Advance]

20 OSI Reference Model

21 2 types of networking models A protocol model provides a model that closely matches the structure of a particular protocol suite Transmission Control Protocol/Internet Protocol (TCP/IP) A reference model provides a common reference for maintaining consistency within all types of network protocols and services it is not intended to be an implementation specification or to provide a sufficient level of detail to define precisely the services of the network architecture the primary purpose is to aid in clearer understanding of the functions and processes involved Open Systems Interconnection (OSI) model Protocol and Reference Models

22 The OSI Reference Model The OSI reference model is the primary model for network communications. Allows you to view the network functions that occur at each layer. It is a framework that you can use to understand how information travels throughout a network 7 layers -- each of which illustrates a particular network function.

23 Summary of layers

24 The TCP/IP model describes the functions that occur at layer of protocols within the TCP/IP suite (Protocol Model) The OSI model is used for network design, operation specifications and troubleshooting (Reference Model) TCP/IP and OSI Models

25 The functions of the Application, Presentation and Session layers of the OSI model are combined into one Application layer in the TCP/IP model The Data Link and Physical layers of the OSI model combine to make the Network Access layer of the TCP/IP model The key parallel between the two models occur at layers 3 and 4 of the OSI model –TCP operates at the transport layer –IP operates at the Internet layer Comparing the OSI and TCP/IP Models

26 Communicating over the Network

27 Creation of data at the application layer of the originating source end device Segmentation and encapsulation of data as it passes down the protocol stack in the source end device Generation of the data onto the media at the network access layer of the stack Transportation of the data through the internetwork, which consists of media and any intermediary devices Reception of the data at the network access layer of the destination end device Decapsulation and reassembly of the data as it passes up the stack in the destination device Passing this data to the destination application at the application layer of the destination end device Communication Process

28 1 2 3 4 5 6 7 Source Destination Communication Process cont…

29 Communication with OSI Model Data (Port) Segment (IP) Packet (MAC) Frame

30 Device Operation Layer DevicesOperate at Layer ComputerLayer-7 (6,5,4) RouterLayer-3 SwitchLayer-2 HubLayer-1

31 The virtual interaction between layers [Advance]

32 Protocol data unit (PDU) is the generic term for data at each level Encapsulation is the process of adding control information as it passes through the layered model Protocol Data Unit and Encapsulation

33 The Application layer begins the process by delivering the data to the Transport layer The Application data is broken into TCP segments and each segment is given a label, called a header the header contains information about which process running on the destination computer should receive the message it also contains the information to enable the destination process to reassemble the segments The TCP segment is sent to the Internet layer and encapsulated within an IP packet, which adds an IP header the IP header contains the source and destination IP addresses Sending Process

34 The IP packet is sent to the Network Access layer where it is encapsulated with a frame header and trailer each frame header contains the source and destination physical addresses the trailer contains error checking information Finally the bits are encoded onto the Ethernet media by the end- device network interface card (NIC) Sending Process cont…


36 Receiving Process

37 Data Encapsulation and Decapsulation

38 An exchange using the OSI model [Advance]

39 How the OSI and TCP/IP Models Relate in a Networking Environment

40 Addressing

41 Various types of addresses are needed to successfully deliver the data from a source application running on one host to the correct destination application running on another Data Link physical addresses (MAC) Network logical addresses (IP) Transport service port numbers (Port) Addressing MAC AddressIP AddressPort Number

42 MAC Addresses (6 Byte unique) A MAC address is a unique 6-byte address that is burned into each network interface or more specifically, directly into the PROM chip on the NIC.

43 IPv4 Address Each device on a network must be uniquely defined. The packets of the communication need to be identified with the source and destination addresses of the two end systems IPv4 is 32 bits in length and difficult for human to remember. Therefore, represent IPv4 addresses using dotted decimal format. 10101100.00010000.00000100.00010100 ( IP has two portion: network and host networkhost

44 This is the physical address of the host (or end device) in a LAN using Ethernet, this address is called the Media Access Control (MAC) address Layer 2 addresses are used to communicate between devices on a single local network (packet) Layer 2 Address (MAC address)

45 Ch 2 - 45 This is the logical address Layer 3 addresses are primarily used to move data from one local network to another local network enable intermediary network devices to locate hosts on different networks (segment) Network 209.165.200 Device 230 Layer 3 Address (IP address)

46 Why MAC and IP both Address? 1.Source and destination MAC change each time to transport packet from one device to another device. 2.Source and destination IP address is fixed. [Advance]

47 Ch 2 - 47 At layer 4, the information contained in the PDU header identifies the specific process or service running on the destination host device the separately running programs are examples of individual processes Layer 4 Service Port Number

48 Bank Service Port Example Cash Pay Counter Cash Receive Counter Electric Bill Counter Remittance Service Counter Information Desk ……… Networking (PC) Email/ SMTP File Transfer/ FTP Web/ HTTP Telnet ………. Different Service, different Counter Different Service, different Port

49 Service Port List ServiceProtocolPort MailSMTP25 POP3POP, POP3110 WebHTTP80 File TransferFTP20, 21 Telnet 23 Domain Name ResolutionDNS53 Dynamic Host ConfigurationDHCP67, 68

50 Port numbers Well known ports (Numbers 0 to 1023) Registered Ports (Numbers 1024 to 49151) Dynamic or Private Ports (Numbers 49152 to 65535) The Internet Assigned Numbers Authority (IANA) assigns port numbers. netstat

51 Relationship of layers and addresses in TCP/IP [Advance]

52 Getting Data to the End Device The host physical address, is contained in the header of the Layer 2 PDU, called a frame. Layer 2 is concerned with the delivery of messages on a single local network. The Layer 2 address is unique on the local network and represents the address of the end device on the physical media. In a LAN using Ethernet, this address is called the Media Access Control (MAC) address. When two end devices communicate on the local Ethernet network, the frames that are exchanged between them contain the destination and source MAC addresses. Once a frame is successfully received by the destination host, the Layer 2 address information is removed as the data is decapsulated and moved up the protocol stack to Layer 3. [Advance]

53 Getting the Data Through the Internetwork Layer 3 protocols are primarily designed to move data from one local network to another local network within an internetwork. Layer 3 addresses must include identifiers that enable intermediary network devices to locate hosts on different networks At the boundary of each local network, an intermediary network device, usually a router, decapsulates the frame to read the destination host address contained in the header of the packet, the Layer 3 PDU Routers use the network identifier portion of this address to determine which path to use to reach the destination host. [Advance]

54 Getting Data to the Right Application Think about a computer that has only one network interface on it. How to differentiate various type of data? Each application or service is represented at Layer 4 by a port number When the data is received at the host, the port number is examined to determine which application or process is the correct destination for the data Example of popular port numbers? [Advance]

55 OSI Reference Model at a Glance

56 Division of Layers Upper Layers Lower Layers Middle Layer 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical

57 OSI – The Application Layer Provides network services to the user's applications. It does not provide services to any other OSI layer ***Think of any network application you use daily

58 OSI – The Presentation Layer It ensures that the information that the application layer of one system sends out is readable by the application layer of another system. *** Think of any common file formats (JPEG, txt etc)

59 OSI – The Session Layer *** After you prepare your data, you need to establish the communication channels to send data This layer establishes, manages, and terminates sessions between two communicating hosts. It also synchronizes dialogue between the two hosts' presentation layers and manages their data exchange.

60 Application Layer Protocols Domain Name Service (DNS) used to resolve Internet names to IP addresses Hypertext Transfer Protocol (HTTP) used to transfer files that make up the web pages of the world wide web Simple Mail Transfer Protocol (SMTP) used for the transfer of mail messages and attachments Telnet (terminal emulation protocol) used to provide remote access to servers and networking devices File Transfer Protocol (FTP) used for interactive file transfers between systems

61 Application Layer Software Network-aware applications implement the application layer protocols and are able to communicate directly with the lower layers of the protocol stack e-mail clients and web browsers Application layer services are programs that interface with the network and prepare the data for transfer different types of data (text, graphics or video) require different network services to ensure that it is properly prepared for processing by the functions occurring at the lower layers of the OSI model

62 DNS Service and Protocol DNS uses TCP/UDP port 53 Domain names were created to convert the numeric IP address into a simple, recognizable name –domain names are easier to remember than actual numeric addresses –any change to the address is transparent to the user since the domain name is the same

63 DNS Directory Structure Uses a hierarchical structure to create a name database hierarchy is an inverted tree with the root at the top and branches below The different top-level domains (TLD) represent either the country origin or the type of organization After TLD are second- level domain names, and below them are other lower level domains [Advance]

64 WWW Service and Protocol The web browser establishes a connection to the web service running on the server using the Hypertext Transfer Protocol (HTTP) request a page using an URL (uniform resource locator) or web address a web browser is a client application running on a client device HTTP uses TCP port 80 An URL consists of three parts the protocol – hypertext transfer protocol (http) the server name the specific file name requested Browsers can interpret and present many data types plain text and Hypertext Markup Language (HTML) other data types require another service or program such as plug-ins or add-ons

65 WWW Service and HTTP cont… The web client makes a connection to the HTTP server and requests a page In response to the request, the HTTP server returns the code for a web page The browser interprets the HTML code and displays a web page

66 HTTP Protocol HTTP specifies a request/response protocol HTTP protocol uses three common messages – GET, POST and PUT HTTP is not a secure protocol –POST messages in plain text can be intercepted and read –HTML pages are not encrypted HTTP Secure (HTTPS) protocol can use authentication and encryption to secure the data

67 E-mail Services and SMTP/POP3 User composes an e-mail using an application called a mail user agent (MUA) or e-mail client Client sends e-mails to a server using Simple Mail Transfer Protocol (SMTP) and receives e-mails using Post Office Protocol version 3 (POP3) SMTP uses TCP port 25 POP uses UDP port 110

68 Mail Transfer Agent The MTA process is used to forward e-mail the MTA receives messages from a MUA or another MTA based on the message header, it determines how a message has to be forwarded to reach its destination –if the recipient resides on the local server, the mail is passed to the mail delivery agent (MDA) –if the recipient is not on the local server, the MTA routes the e-mail to the MTA on the appropriate server

69 Mail Delivery Agent The MDA receives the inbound mail from the MTA and delivers the mail to the appropriate users mailboxes It can also resolve final delivery issues, such as virus scanning, spam filtering and return-receipt handling

70 SMTP and POP POP and POP3 are inbound mail delivery protocols MDA listens for a client connection to the server SMTP governs the transfer of outbound e-mail from the sending client to the MDA, as well as the transport of e-mail between MTA –enables e-mail to be transported across data networks between different types of server and client software [Advance]

71 File Transfer Protocol FTP uses TCP ports 20 (data) and 21 (commands and replies) An FTP client is used to push and pull files from a server running the FTP daemon (FTPd) TCP port 21 TCP port 20 Client establishes the first connection to the server on TCP port 21 –for control traffic such as client commands and server replies Client establishes the second connection to the server over TCP port 20 –for file transfer in both direction

72 Telnet Telnet uses TCP port 23 Provides a method of emulating text-based terminals over the network allows a local device to access a remote device as if the keyboard and monitor are connected to the remote device directly A connection using Telnet is called a virtual terminal (VTY) session The Telnet server runs a service called the Telnet daemon

73 OSI – The Transport Layer Data will be segmented and send to destination device. Transport layer of destination device will reassemble them. This layer handles details of reliable transfer. (ensures that the data arrive completely )

74 Basic functions of the Transport layer Segmentation and Reassembly Conversation Multiplexing Plus : Connection-oriented conversations Reliable delivery Ordered data reconstruction Flow control Protocols The two most common Transport layer protocols of TCP/IP protocol suite are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

75 User Datagram Protocol (UDP) UDP is a simple, connectionless protocol, described in RFC 768. It has the advantage of providing for low overhead data delivery. The pieces of communication in UDP are called datagrams. These datagrams are sent as "best effort" by this Transport layer protocol. 8 bytes overhead

76 User Datagram Protocol Applications that use UDP include: Domain Name System (DNS) Video Streaming Voice over IP (VoIP)

77 Transmission Control Protocol (TCP) TCP is a connection-oriented protocol, described in RFC 793. Each TCP segment has 20 bytes of overhead in the header encapsulating the Application layer data. Same order delivery Reliable delivery Flow control.

78 Transmission Control Protocol Applications that use TCP are: Web Browsers E-mail File Transfers

79 OSI – The Network Layer Many paths to the same destination. So, which path to follow? Segmented data needs address to reach the destination (network address) This layer handle 2 above stated issues.

80 Ch 5 - 80 Network Layer Processes Addressing Network layer must provide a method for addressing the end devices each device must have a unique address Encapsulation Network layer receives the Layer 4 PDU and adds a Layer 3 header the Layer 3 header contains a source address, destination address and other control information this Layer 3 PDU is known as a packet the packet is sent down to the Data Link layer Routing the Network layer must provide services to direct these packets to the destination host intermediary devices, called routers, are used to direct packets toward the destination [Advance]

81 Ch 5 - 81 Network Layer Processes cont… Decapsulation the destination host examines the destination address to verify that the packet was addressed to this device the packet is decapsulated by the Network layer and the Layer 4 PDU contained in the packet is passed up to the appropriate service at the Transport layer encapsulation decapsulation [Advance]

82 OSI – The Data Link Layer It provides means for exchanging data frames over a common media To detect and possibly correct errors that may occur in the Physical layer Physical Addressing, topologies and flow control

83 OSI – The Physical Layer It 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, similar, attributes defined by physical layer specifications.

84 Hands on

85 Binary Number System Decimal: 10 digit 0 1 2 3 4 5 6 7 8 9 Octal: 8 digit 0 1 2 3 4 5 6 7 Hexadecimal: 16 digit 0 1 2 3 4 5 6 7 8 9 A B C D E F Binary: 2 digit 0 1 Computer only understand binary Decimal: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Binary: 0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 1110 1111 {0,1} each called a bit, Binary Digit = Bit 8 bit = 1 Byte 1000 Byte (1024) = 1 Kilobyte 1000 Kilobyte (1024) = 1 Megabyte 1000 Megabyte (1024) = 1 Gigabyte 1000 Gigabyte (1024) = 1 Terabyte … MAC- Hexadecimal IP- Decimal

86 Decimal to Binary Conversion and vise versa

87 Thank you…

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