Pages 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 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 17149 result(s) returned

2.4 Examples of layer functions

There are several functions that can be performed at one or more of the OSI layers. Some of the more common ones are discussed below.

Connection control

For connection-oriented services, a connection must be established between peer entities. A connection has three phases: connection set-up, data transfer and connection clear. If the peer protocol supports connections, each protocol data unit type corresponds to a primitive type; for instance, a connection request primiti
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.2 Vertical communication

Figure 6 shows the OSI view of adjacent layers. The interface between two layers in the same system is called a service access point (SAP). One of the features of a service access point is that it has an identifier, or an address, which allows each communication between adjacent layers to be uniquely identified. The processes that communicate across the interface are called entities. These are typically software routines, but may also be hardware components. The notation in Figu
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

Learning outcomes

After studying this course, you should be able to:

  • evaluate technical descriptions of communication protocols and demonstrate an understanding of their operation

  • describe the characteristics of circuit-switched and packet-switched networks, and of connectionless and connection-oriented modes in packet-switched networks

  • describe the role played by primitives in the OSI reference model

  • explain how ‘vertical’ and ‘horizontal’ com
    Author(s): The Open University

    License information
    Related content

    Copyright © 2016 The Open University

5.5.5 Summary

In this section I've briefly considered the very contentious question of what digital representations mean, but this debate must be left to another course. I have also described some of the devices that take digital information back into the analogue world of sight and sound, presenting it in a form that is meaningful to human eyes and ears.


Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

16.2.2 Storing and retrieving data

As each item is scanned, the checkout computer looks up its price. The running total for each customer's purchases is stored temporarily in the checkout terminal. Other data may also be stored, such as the amount of money that has been taken at that checkout during the day.


Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

16.2 Processes at the checkout

From the point of view of the customer and the checkout operator, a supermarket's ICT system is like the stand-alone computer you saw in Figure 10 in Section 9. The system map in Author(s): The Open University

12.1 Introduction

Data must be stored somewhere when it is not being manipulated. Modern ICT systems require increasingly large amounts of data to be stored for later use, and it is important that the data can be accessed quickly. Data may be stored on the stand-alone computer's hard disk in the form of files.

You may want to move files from one stand-alone computer to another. In addition, you may want to move files from a device, such as a digital camera, to a computer. These activities require some fo
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.2 Evaluating the quality of information on the Web

The quality of the information you will find on the Web varies enormously as there is no editorial control. Anybody can establish a website, claiming to be whoever they want to be. As Mark Twain put it:

A lie can travel half way around the world while the truth is putting on its shoes.

So how can you judge the reliability and quality of the information you find on the Web? If you think in t
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

3.1 Searching for your ancestors

In this section we consider searching for information about your ancestors. We cannot hope to cover all the techniques and information required to research genealogy, family history and local history; there is only time in this course to scratch the surface. Some of the activities here are open-ended; please do not spend too long on them. If the subject interests you, you can revisit it after the course finishes, making use of the genealogical resources in the Appendix.


Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.7 How to reference sources

You have seen how easy it is to find what what you want on the Web. When you quote any information or use any images that you have not written or created yourself it is important to ensure that you reference the source of the quote or image. This is to show that you are not trying to pass off someone else's work as your own, and to enable your reader, should they wish, to access the source of that quote.

Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.5 Bookmarking websites

Most browsers allow you to keep a record of links to websites that you have found useful. These are called 'Bookmarks' in Firefox and 'Favorites' in Internet Explorer, and may have other names, such as a 'Hot List', in other browsers. For convenience I've chosen to call them bookmarks. Browsers usually offer the facility for organising the bookmarks into folders and sub-folders so that you can keep track of them as your collection grows.

You may well have a collection of bookmarks alrea
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.1 Introduction

In this section we will cover the following topics:

  • browsing for information on the Web;

  • searching for information on the Web;

  • using search engines;

  • bookmarking websites;

  • finding images on the Web;

  • how to reference sources.

Some of the material in this section has been drawn from Safari, an interactive website provided by the Open University Library. Safari cover
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

Acknowledgements

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence

Figure 1 ENIAC Computer. Photo © Science Photo Library

Rozin, D. ‘Wooden Mirror’,
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

Keep on learning

Study another free course

There are more than 800 courses on OpenLearn for you to
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

7.3 Using flowcharts to describe a task

Application programs are designed to perform specific tasks. These tasks range from the relatively simple to the extremely complex. In this section you will look at what is involved in planning a program to perform some simple tasks.

In order to write a program, the task the program will perform has to be first written as a list of actions. The actions have to be given in an order that will ensure the task is carried out successfully.

Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.2 Electronic kitchen scales

A set of electronic kitchen scales is shown in Figure 7. Their basic operation is relatively simple. When they are switched on and, for example, a 500-gram object is placed in the scalepan, the display shows the digits 500 and the letter g.

Conclusion

This free course provided an introduction to studying Computing and ICT. It took you through a series of exercises designed to develop your approach to study and learning at a distance and helped to improve your confidence as an independent learner. 


Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.4 The message passing idea

Figure 1 shows the central idea behind the message passing paradigm. It involves an architecture in which clients and servers communicate using communication lines. In this model, in contrast with the others that are to be presented in this course, the underlying structure of the network is visible via the communication media used to connect servers and clients and devices such as sockets, ports and server sockets which are involved in the transfer of a message from one computer to another.
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.2 Fixed and adaptive protocols

The protocol described above for a simple naming service is an example of a fixed protocol. This is a protocol whose vocabulary is fixed: it is embedded in the client and server's code and data and does not change. An adaptive protocol is one where the protocol changes. A fixed protocol could change over a period of time because the functionality provided by a server changes. However, this change will be over months or years rather than over seconds.

There are some instances wher
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2.1 Protocols

Message passing is the simplest form of development paradigm. For example, the way that a client running a browser communicates with a web server is via message passing.

Message passing is based on the idea of a protocol: a language which embodies the functions required by one entity in a distributed system (usually a client) which another entity provides (usually a server). As an example of a protocol consider Table 1. It shows the protocol associated with a naming servic
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

Pages 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 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858