Open Systems Interconnection (OSI) Reference Model for Networking COSC 513 Operating Systems Instructor : Dr. Mort Anvari Presented by Cheng Chiang Goh
Objective The aim of this topic is to understand theoretical models for what networks are and how they work. The Open Systems Interconnection (OSI) reference model for networking, which explains how networks behave within an orderly seven-layered model for networked communications.
Introduction The concept of networking is so essential in this fast-moving world nowadays, for the purpose of sharing information and resources. Open Systems Interconnection (OSI) reference model proposed by the International Standards Organization (ISO) has been so successful to create an intellectual framework within which to clarify network concepts and activities. Today, OSI reference model has become a key part of networking. The IEEE 802 is an enhancement to the OSI model. With OSI model, networking can be broken into seven layers. Therefore, the complexity of networked communications, from application to hardware is broken into a series of interconnected tasks and activities. It creates a method to solve big problem by deconstructing them into a series of smaller problems, that can then be solved individually.
Topics • Open Systems Interconnection (OSI) Model • IEEE 802 Model • OSI Reference Model Structure • Network Communications and Protocols in OSI model • Protocols in Layered Architecture • TCP/IP Protocol • Devices at each OSI model
OSIModel • Layer 7 Application • Layer 6 Presentation • Layer 5 Session • Layer 4 Transport • Layer 3 Network • Layer 2 Data Link • Layer 1 Physical Programmers Do Not Throw Sausage Pizza Away
Layer 7 Application • Top layer of OSI model • provides interfaces for application to obtain access to networked services • Services like file transfer, message handling, database query processing • Also handle general network access: movement of data (flow control), error recovery • Transfer information from program to program
Layer 6 Presentation • Handles data format for networked communications ( outgoing and incoming messages) • protocol conversion, data encryption and decryption as well as graphics commands • compress data for transmission to reduce the volume of data ( then decompression) • Redirector (software facility)
Layer 5 Session • Permits two parties to hold ongoing communication across a network • handles session setup, data or message exchanges and tear-down when session ends • permit only authorized parties to establish session (security)
Layer 4 Transport • Manages the conveyance of data from sender to receiver across a network • segment long data into chunks that match the maximum packet size for networking medium • acknowledges successful transmission and request retransmission when packets do not arrive • it make sure that long data payloads make their destination across the network
Layer 3 Network • Handles addressing messages for delivery • translates logical network addresses and names into their physical counterparts • decides how to route transmissions from sender to receiver • also handles packet-switching, routing and congestion control • Fragmentation and Reassemble ( from dissimilar media - downsizes packets
Layer 2 Data Link • Sends data frames from Network layer to Physical Layer [data frame consists of destination ID, sender ID, control, data and CRC(cyclical redundancy check-mathematical function based on bit patterns)] • adds error-checking information and formats data for physical transmission
Layer 1 Physical • Its jobs is to convert bits into signals for outgoing messages and via versa • manage hardware connection • cable, transmitter, receiver, repeater operate at this layer.
IEEE 802 extensions to the OSI reference model • Layer 7 Application • Layer 6 Presentation • Layer 5 Session • Layer 4 Transport • Layer 3 Network • Layer 2 Data Link -----Logical link control -----Media access control • Layer 1 Physical IEEE 802 standard breaks the Data Link layer into two sublayer
Logical Link Control (LLC) • Also known as IEEE 802.2 • for error control correction and flow control
Media Access Control (MAC) • for access control • direct access with NIC and ensure error-free data transmission • 802.3 CSMA/CD • 802.4 Token Bus • 802.5 Token Ring • 802.12 Demand Priority
Network Communications and Protocols in OSI model • Protocols are rules and procedures for communications • many protocols used today TCP/IP, NetBIOS/, IPX/SPX, AppleTalk, • the higher the protocols in the OSI model or layer, the more sophisticated the protocol is • protocol stack TCP/IP, the Internet protocol suite, IPX/SPX for Novell NetWare
Connectionless fast but not reliable (don’t waste time to establish, manage and tearing down connections) Connection-Oriented slower but reliable Two methods of delivering data in a network
Routable Network Layer (4) protocols like TCP/IP, IPX/SPX; suitable for large network Nonroutable NetBEUI; for small network Network layer of the OSI model is responsible for moving data across multiple network
Protocols in a Layered Architecture • Layer 7 Application • Layer 6 Presentation Application • Layer 5 Session Protocol • Layer 4 Transport Transport Protocol • Layer 3 Network • Layer 2 Data Link Network • Layer 1 Physical Protocol
Network Protocols • Provide addressing and routing information, error checking, retransmission requests and rules for communicating in a particular networking environment Protocols likes • IP (Internet Protocol) • IPX (Internetwork Packet eXchange and NWLink • NetBEUI • DDP (Delivery Datagram Protocol) • DLC (Data Link Control)
Transport Protocols • Ensure reliable data delivery between computers Protocols likes • TCP (Transmission Control Protocol) • SPX (Sequenced Packet eXchange) and NWLink • NetBEUI/NetBIOS • ATP (AppleTalk Transaction Protocol) and NBP (Name Binding Protocol)
Application Protocols • Provide application-to-application services Protocols likes • SMTP (Simple Mail Transport Protocol) • FTP (File Transfer Protocol) • SNMP (Simple Network Management Protocol) • NCP (NetWare Core Protocol) • AFP (AppleTalk File Protocol)
OSI Model TCP/IP Protocol Stack Telnet FTP SMTP • Layer 7 Application • Layer 6 Presentation • Layer 5 Session • Layer 4 Transport • Layer 3 Network • Layer 2 Data Link • Layer 1 Physical TCP DNS UDP IP ICMP ARP OSPF RIP ODI or NDIS NIC Driver Physical Connection
TCP/IP Allows for easy cross-platform communications and is the basic for Internet • ICMP (Internet Control Message Protocol) --- network layer; used to send control messages • ARP (Address Resolution Protocol) --- network layer; used to associate a logical IP address to a physical MAC address • TCP (Transmission Control Protocol) --- transport layer; connection-oriented; transport protocol • UDP (User Datagram Protocol) --- transport layer; connectionless; faster than TCP • DNS (Domain Name System) --- transport layer; name-to-address resolution protocol (for example www.Microsoft.com to 126.96.36.199)
FTP ( File Transfer Protocol) --- session, presentation and application layer; provides services for file transfer as well as directory and file-manipulation services • Telnet --- remote terminal emulation protocol; used to provide connectivity between dissimilar system • SMTP (Simple Mail Transport Protocol) --- used for messaging services and is the basic for e-mail across Internet • (RIP) Routing Information Protocol --- a distance-vector protocol used for route discovery • OSPF (Open Shortest Path First) --- a link-state routing protocol; used to determine the best path through a network • IP (Internet Protocol) --- network layer; responsible for addressing and routing; (32 bits, e.g. 188.8.131.52);
Advantages Suitable for WAN Direct Access to the Internet Supported by most of the computer and operating system support routing support SNMP, DHCP (dynamically assign client IP addresses), support Internet Protocols like POP(Post Office Protocol), HTTP. Centralized TCP/IP domain assignment to allow internetworking between organizations IP address Disadvantages Difficult to administer global expansions of Internet has limited the availability of unique domain numbers difficult to set up high overhead slower than IPX and NetBEUI Advantages and Disadvantages of TCP/IP
Devices Devices that allow expansion of network locally or across the world and layer of the OSI model they operate. Repeater • operate at Physical layer • has no concern for the type of data being transmitted, packet address and the protocol being used • cannot perform filtering or translation of the data and does not help to ease network congestion • cannot connect different network architectures • allows easy expansion of the network over larger distance and connection between different media
Bridge • Operates at the Data Link Layer of the OSI model or Media Access Control sublayer of the Data Link layer (has access to this address information) • can filter to ease network congestion • can connect different media and network architectures • slower than repeater
Router • Operate at the Network layer • can connect different media and network architectures • choose the best path for packet through an internetwork • reduce network traffic by not forwarding broadcasts or corrupt packets • more expansive and complex than repeater and bridge • only work with routable protocol (like TCP/IP, IPX/SPX, AppleTalk and etc) • dynamic routing updates create network traffic • slower than bridge because need to perform more calculation on the packet
Brouter • Combination of bridge and router • good at hybrid network using mixture of routable and nonroutable protocols • routable packet -- function as router (choosing the best path to forward packet) • nonroutable packet --- function as bridge (forwarding packet based on hardware address
Gateway • work at the Application layer of OSI model • can translate information between two different network architectures or data formats ( for example, allows network communication between a TCP/IP LAN and IBM mainframe system using SNA and also can convert Microsoft Mail to SMTP for transmission over Internet • hard to install and configure; slower and more expensive
Summary OSI reference model plays a vital role in networking. OSI model. Networking can be broken into seven layers with OSI model. Therefore, the complexity of networked communications, from application to hardware is broken into a series of interconnected tasks and activities. It creates a method to solve big problem by deconstructing them into a series of smaller problems, that can then be solved individually.
References & Related Websites • Matthew Strebe, Charles Perkins and James Chellis. “MCSE: NT Server 4 Study Guide” Second Edition. SYBEX Inc 1998. • Joe Casad. “MCSE: Windows NT Server & Workstation 4”. New Riders Publishing 1996. • TCP/IP Networking : Architecture, Administration and Programming,James Martin, Joe Leben / Prentice Hall / August 1994 • MCSE:Networking Essentials (2nd Edition),James Chellis. Sybex / June 1998 • http://www.cit.ac.nz/smac/winnt/pt1_9.htm#Start • http://www.vcs-s.com/network_topology.htm • http://dir.yahoo.com/Computers_and_Internet/Communications_and_Networking/ • http://www.mcpmag.com/