1 / 36

Computer (Transport) Layer

Computer (Transport) Layer. Manages communication between two computers Platform independence: one computer does not know even what platform the other is (mainframe, PC, etc.) TCP/IP’s most popular transport standard is TCP. Terminal-Host Platform. Processing done at a central host computer

netis
Download Presentation

Computer (Transport) Layer

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Computer (Transport) Layer • Manages communication between two computers • Platform independence: one computer does not know even what platform the other is (mainframe, PC, etc.) • TCP/IP’s most popular transport standard is TCP

  2. Terminal-Host Platform • Processing done at a central host computer • Mainframe (very large) • Minicomputer (mid-size) Programs Execute on the Host Host

  3. PC Network • Client PC sits on desks of ordinary users • Receives services from servers • Stand-alone PC with hardware, software added Client PC Client PC

  4. PC Network • Servers • Provide services to client PCs • Usually PCs but not always Server Service Service Service Server Server

  5. PC Network • Servers are Specialized • Optimized for their services for cost, performance, and reliability File Server File Service Database Server Internet Access Gateway Server

  6. File Server Program Access • Programs executed on the client PC • Program and data files downloaded over the network Program Executed On Client PC Downloaded Over Network Client PC Network Server

  7. Client Workstation • Workstations are more powerful than PCs • Come in client and server versions 21” display Powerful RISC microprocessor Large, fast RAM, hard disk Usually UNIX OS, can be Windows NT Client Workstation

  8. Networked PC • The Dominant Computer Platform Today is the Networked PC • High penetration of PCs on desktops • Most are already networked • “Legacy” Systems Must be Maintained • Mainframe terminal-host systems • Minicomputer terminal-host systems • Many are being “downsized” to PC networking

  9. Managed PCs • Designed to be Managed Remotely • Slashes maintenance costs • Slashes software upgrade costs • Users have less control over their machines • Company can search for illegal games • Management standards are still immature • Eventually, all networked PCs will be managed

  10. NetPC • Standard Pushed by Microsoft, Intel • Closed box with limited upgradability • Should ease maintenance by reducing incompatibilities and add-in problems • Will users be content? • Remote management built in

  11. Network Computers (NCs) • Designed for Use on the Internet (Java) • Little or no local disk drive storage • Programs downloaded over Internet when needed (or from corporate servers using Internet standards) • User always gets the latest version of the software • Downloading can take time; small applications would load faster but might lack functionality • When the network is down, so are you The Internet

  12. Low-Cost PCs for the Home • WebTV (Microsoft) • Uses TV for its display • User only needs $500 box • Problem: TV display resolution is far lower than that of a TV screen; webpages look bad • Problem: Need special Internet service provider who cannot work with your regular PC • Problem: No printing • Problem: Limited to WWW and email • Sub $1,000 PCs

  13. Networks Mix Traffic of Multiple Platforms Network (LAN, WAN, internet) PC network traffic Terminal-host traffic

  14. F2-7: Program Interactions on a Stand-Alone PC Application Program Request Response Operating System Commands related to files Files or error messages Hardware

  15. Client/Server Processing Client Program Server Program Platform independent TWO programs on TWO machines Client Machine (PC) Server Machine (UNIX Minicomputer)

  16. Client/Server Processing • Application Layer Protocols • Control the requests and responses • Application independence: any browser can work with any webserver program • Transport Layer Protocols • Allow two computers with different architectures to work together • Brings platform independence

  17. Internet Access To connect to the Internet, you must have an ISP Webserver Internet Service Provider (ISP) The Internet Backbone Internet Service Provider (ISP) PC with browser

  18. Internet Service Provider (ISP) • Basic Service: Links You to the Internet • Provides a connection • Pays for your use. (The Internet is NOT Free.) • Most Provide Additional Services • E-mail • World Wide Web Homepage Hosting • Premium Providers have Specialized Services(America Online, CompuServ, MSN)

  19. Internet Access with PPP ISP Modem, TCP/IP software PPP software PPP link over telephone line

  20. Internet Access with PPP: routers Router Router Router The Internet: 1. a network of routers connected by transmission lines ISP Router 2. Subnets connected by routers ISP

  21. Layered Interactions in Internet Access User PC Router Webserver Browser Webserver Software TCP Software TCP Software Subnet Layer (PPP) IP Software IP Software IP Software CSLIP/PPP Software PPP Software Subnet Point-to-Point Connection

  22. Point-to-Point Connection • Physical Layer • Serial Port • Modem • Telephone Transmission • Data Link Layer • Packaging of data for delivery over line • Error detection and correction • CSLIP or PPP standard

  23. Layered Interactions in Internet Access User PC Routers Webserver Browser Webserver Software Internet Layer Governs Routing Across Multiple Routers On the Internet TCP Software TCP Software IP IP IP Software IP Software IP Software PPP Software Subnet Software Subnet

  24. Routing Across the Internet • Routing • Message (packet) must travel over a network of routers • The user PC tells the first router the destination address of the webserver (e.g., voyager.cba.hawaii.edu) • Working together, routers route the packet to its destination host

  25. Layered Interactions in Internet Access User PC Routers Webserver Browser Webserver Software Transport Layer (TCP) TCP Software TCP Software IP Software IP Software IP Software PPP Software Subnet Software Subnet

  26. Transport Layer • Connects the Two Computers • Establishes a temporary connection • Breaks connection when transmission ends • Asks for the retransmission of damaged packets • Asks for the retransmission of lost packets • Flow control: tell the other computer to pause • Platform independence: connects computers from different vendors

  27. Layered Interactions in Internet Access User PC Routers Webserver Browser Webserver Software Application Layer (HTTP, HTML) TCP Software TCP Software IP Software IP Software IP Software PPP Software Subnet Subnet

  28. Protocol Data Units (PDUs) • At each layer, messages are strings of 1s and 0s • These messages are organized • Called protocol data units (PDUs) • Each layer (except Physical) has a PDU • E.g., Application PDU or APDU • E.g., Computer (Transport) PDU or CPDU PDU

  29. Organization of PDU • Header (delivery information) • Trailer (sometimes present for error handling) • Data Field • Often PDU of next higher layer PDU at Layer N+1 PDU at Layer N Trailer Data Field Header

  30. PDU Transmissions from the PC User PC Application Layer Browser Application PDU APDU Computer (Transport) Layer TCP Software (CPDU) TCP PDU APDU CH Internet Layer IP Software Internet PDU (IPDU) CPDU IH Subnet Layer CSLIP/PPP Or Other Subnet Software Subnet PDU (SnPDU) CSLIP or PPP SnT IPDU SnH

  31. At Each Router 2. Subnet process removes IP PDU from SnPDU, delivers it to the IP process. 3. IP process considers best route Router 4. IP process delivers the IP PDU to the subnet process IP Software IP PDU IP PDU Subnet Process SnPDU for Subnet A SnPDU on Subnet B SnA SnB 1. Router subnet process accepts the SnPDU Subnet A Subnet B

  32. At the Webserver Webserver 4. TCP Software delivers APDU to Webserver Program Webserver Software APDU 3. IP Software delivers CPDU to Transport Process TCP Software CPDU 2. delivers IPDU to IP Software Process IP Software IPDU Subnet Software 1. accepts SnPDU SnPDU Subnet

  33. Intranets • Use of Internet Technology within Firms • Standards are mature • Standards for many applications • Security is good for internal use • Platform independent: No need to create separate applications for PCs, Macs, Unix • Browser runs software: no need to install software on PCs • Major concern of corporations today

  34. Intranets • Must keep out hackers • Yet users need access to Internet services outside the Internet • Solution: create a firewall to limit access from the outside Firewall OK Intranet No Hacker

  35. Internal Extranets • Give Buyers or Suppliers Access • Limited to certain resources, such as inventory and pricing databases • Uses the Internet for transmission Extranet Resource OK Customer No Any Other Resource

  36. Extranets • Tunneling • Extranet transmission uses the unsecure Internet • Add secure transmission through the Internet by means of encryption, other measures • Creates a secure “tunnel” through the Internet Tunnel

More Related