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1 Chapter Five Making Connections Efficient: Multiplexing and Compression.

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1 1 Chapter Five Making Connections Efficient: Multiplexing and Compression

2 Objective สามารถอธิบายการมัลติเพล็กซ์แบบแบ่งความถี่ และระบุแอปพลิเคชั่นที่ใช้ รวมถึงข้อดี ข้อเสียที่ เกิดขึ้นได้ สามารถอธิบายการมัลติเพล็กซ์แบบแบ่งเวลาใน รูปแบบซิงโครไนซ์ และระบุแอปพลิเคชั่นที่ใช้ รวมถึงข้อดี ข้อเสียที่เกิดขึ้นได้ สามารถระบุคุณสมบัติพื้นฐานการมัลติเพล็กของ T-1, ISDN และระบบโทรศัพท์ SONET/SDH 2

3 Objective สามารถอธิบายการมัลติเพล็กซ์แบบแบ่งเวลาใน รูปแบบสถิติ และระบุแอปพลิเคชั่นที่ใช้ รวมถึง ข้อดี ข้อเสียที่เกิดขึ้นได้ สามารถบอกคุณสมบัติของการมัลติเพล็กซ์แบบ แบ่งตามความยาวคลื่น รวมถึงข้อดี ข้อเสียที่ เกิดขึ้นได้ สามารถอธิบายคุณลักษณะพื้นฐานของ เทคโนโลยี Discrete Multitone (DMT) สามารถบอกคุณสมบัติหลักของการมัลติเพล็กซ์ แบบแบ่งตามรหัส และข้อดี ข้อเสียที่เกิดขึ้นได้ 3

4 Objective สามารถบอกความแตกต่างระหว่างการบีบอัด ข้อมูลแบบสูญเสียข้อมูล และไม่มีการสูญเสีย ข้อมูลได้ สามารถระบุการทำงานพื้นฐานของการบีบอัด ข้อมูลแบบ run-length, JPEG และ MP3 สามารถประยุกต์ใช้เทคนิคมัลติเพล็กซิ่ง กับ สถานการณ์ทางธุรกิจทั่วๆไปได้ 4

5 5 Introduction Under the simplest conditions, a medium can carry only one signal at any moment in time For multiple signals to share a medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth The current techniques include frequency division multiplexing, time division multiplexing, and code division multiplexing Chapter Five - Making Connections Efficient: Multiplexing and Compression

6 6 Frequency Division Multiplexing Assignment of non-overlapping frequency ranges to each “user” or signal on a medium. Thus, all signals are transmitted at the same time, each using different frequencies A multiplexor accepts inputs and assigns frequencies to each device Chapter Five - Making Connections Efficient: Multiplexing and Compression

7 7 Frequency Division Multiplexing The multiplexor is attached to a high-speed communications line A corresponding multiplexor, or demultiplexor, is on the end of the high-speed line and separates the multiplexed signals Chapter Five - Making Connections Efficient: Multiplexing and Compression

8 8 Chapter Five - Making Connections Efficient: Multiplexing and Compression

9 9 Frequency Division Multiplexing Analog signaling is used to transmit the data Broadcast radio and television, cable television, and cellular telephone systems use frequency division multiplexing This technique is the oldest multiplexing technique Since it involves analog signaling, it is more susceptible to noise Chapter Five - Making Connections Efficient: Multiplexing and Compression

10 10 Time Division Multiplexing Sharing of the signal is accomplished by dividing available transmission time on a medium among users Digital signaling is used exclusively Time division multiplexing comes in two basic forms: –Synchronous time division multiplexing –Statistical time division multiplexing Chapter Five - Making Connections Efficient: Multiplexing and Compression

11 11 Synchronous Time Division Multiplexing The original time division multiplexing The multiplexor accepts input from attached devices in a round-robin fashion and transmits the data in a never ending pattern T-1 and ISDN telephone lines are common examples of synchronous time division multiplexing Chapter Five - Making Connections Efficient: Multiplexing and Compression

12 12 Chapter Five - Making Connections Efficient: Multiplexing and Compression

13 13 Synchronous Time Division Multiplexing If one device generates data at a faster rate than other devices, then the multiplexor must either sample the incoming data stream from that device more often than it samples the other devices, or buffer the faster incoming stream If a device has nothing to transmit, the multiplexor must still insert something into the multiplexed stream Chapter Five - Making Connections Efficient: Multiplexing and Compression

14 14 Chapter Five - Making Connections Efficient: Multiplexing and Compression

15 15 Chapter Five - Making Connections Efficient: Multiplexing and Compression

16 16 Synchronous Time Division Multiplexing So that the receiver may stay synchronized with the incoming data stream, the transmitting multiplexor can insert alternating 1s and 0s into the data stream Chapter Five - Making Connections Efficient: Multiplexing and Compression

17 17 Synchronous Time Division Multiplexing The T-1 multiplexor stream is a continuous series of frames Chapter Five - Making Connections Efficient: Multiplexing and Compression

18 18 Synchronous Time Division Multiplexing The ISDN multiplexor stream is a also a continuous series of frames. Each frame contains various control and sync info Chapter Five - Making Connections Efficient: Multiplexing and Compression

19 19 Synchronous Time Division Multiplexing Likewise, SONET incorporates a continuous series of frames. Chapter Five - Making Connections Efficient: Multiplexing and Compression

20 20 Statistical Time Division Multiplexing A statistical multiplexor transmits the data from active workstations only If a workstation is not active, no space is wasted in the multiplexed stream A statistical multiplexor accepts the incoming data streams and creates a frame containing the data to be transmitted Chapter Five - Making Connections Efficient: Multiplexing and Compression

21 21 Chapter Five - Making Connections Efficient: Multiplexing and Compression

22 22 Chapter Five - Making Connections Efficient: Multiplexing and Compression To identify each piece of data, an address is included

23 23 Chapter Five - Making Connections Efficient: Multiplexing and Compression If the data is of variable size, a length is also included

24 24 More precisely, the transmitted frame contains a collection of data groups Chapter Five - Making Connections Efficient: Multiplexing and Compression

25 25 Wavelength Division Multiplexing Wavelength division multiplexing multiplexes multiple data streams onto a single fiber optic line Different wavelength lasers (called lambdas) transmit the multiple signals Chapter Five - Making Connections Efficient: Multiplexing and Compression

26 26 Wavelength Division Multiplexing Each signal carried on the fiber can be transmitted at a different rate from the other signals Dense wavelength division multiplexing combines many (30, 40, 50 or more) onto one fiber Coarse wavelength division multiplexing combines only a few lambdas Chapter Five - Making Connections Efficient: Multiplexing and Compression

27 27 Chapter Five - Making Connections Efficient: Multiplexing and Compression

28 28 Discrete Multitone (DMT) A multiplexing technique commonly found in digital subscriber line (DSL) systems DMT combines hundreds of different signals, or subchannels, into one stream Chapter Five - Making Connections Efficient: Multiplexing and Compression

29 29 Discrete Multitone (DMT) Each subchannel is quadrature amplitude modulated (recall eight phase angles, four with double amplitudes) Theoretically, 256 subchannels, each transmitting 60 kbps, yields Mbps Unfortunately, there is noise Chapter Five - Making Connections Efficient: Multiplexing and Compression

30 30 Chapter Five - Making Connections Efficient: Multiplexing and Compression

31 31 Code Division Multiplexing Also known as code division multiple access An advanced technique that allows multiple devices to transmit on the same frequencies at the same time Each mobile device is assigned a unique 64-bit code Chapter Five - Making Connections Efficient: Multiplexing and Compression

32 32 Code Division Multiplexing To send a binary 1, a mobile device transmits the unique code To send a binary 0, a mobile devices transmits the inverse of the code Chapter Five - Making Connections Efficient: Multiplexing and Compression

33 33 Code Division Multiplexing Receiver gets summed signal, multiplies it by receiver code, adds up the resulting values Interprets as a binary 1 if sum is near +64 Interprets as a binary 0 if sum is near -64 Chapter Five - Making Connections Efficient: Multiplexing and Compression

34 34 Code Division Multiplexing For simplicity, assume 8-bit code Three different mobile devices use the following codes: –Mobile A: –Mobile B: –Mobile C: Assume Mobile A sends a 1, B sends a 0, and C sends a 1 Chapter Five - Making Connections Efficient: Multiplexing and Compression

35 35 Code Division Multiplexing Signal code: 1-chip = +N volt; 0-chip = -N volt Three signals transmitted: –Mobile A sends a 1, or , or –Mobile B sends a 0, or , or –Mobile C sends a 1, or , or Summed signal received by base station: +3, - 1, -1, +1, +1, -1, -3, +3 Chapter Five - Making Connections Efficient: Multiplexing and Compression

36 36 Code Division Multiplexing Base station decode for Mobile A: Signal received: +3, -1, -1, +1, +1, -1, -3, +3 Mobile A’s code: +1, -1, +1, +1, +1, -1, -1, +1 Product result: +3, +1, -1, +1, +1, +1, +3, +3 Sum of Products: +12 Decode rule: For result near +8, data is binary 1 Chapter Five - Making Connections Efficient: Multiplexing and Compression

37 37 Code Division Multiplexing Base station decode for Mobile B: Signal received: +3, -1, -1, +1, +1, -1, -3, +3 Mobile A’s code: -1, +1, +1, -1, +1, +1, +1, -1 Product result: -3, -1, -1, -1, +1, -1, -3, -3 Sum of Products: -12 Decode rule: For result near -8, data is binary 0 Chapter Five - Making Connections Efficient: Multiplexing and Compression

38 38 Chapter Five - Making Connections Efficient: Multiplexing and Compression

39 39 Chapter Five - Making Connections Efficient: Multiplexing and Compression

40 40 Chapter Five - Making Connections Efficient: Multiplexing and Compression Compression This is another technique used to squeeze more data over a communications line If you can compress a data file down to ½ of its original size, the file will obviously transfer in less time Two basic groups of compression: Lossless – when data is uncompressed, original data returns Lossy – when data is uncompressed, you do not have the original data

41 41 Compression Compress a financial file? You want lossless. Compress a video image, movie, or audio file? Lossy is OK Examples of lossless compression include Huffman codes, run-length compression, and Lempel-Ziv compression Examples of lossy compression include MPEG, JPEG, MP3 Chapter Five - Making Connections Efficient: Multiplexing and Compression

42 42 Run-Length Compression Replace runs of 0s with a count of how many 0s … ^ (30 0s) Chapter Five - Making Connections Efficient: Multiplexing and Compression

43 43 Run-Length Compression Now replace each decimal value with a 4-bit binary value (nibble). Note: If you need to code a value larger than 15, you need to use two code two consecutive 4-bit nibbles. The first is decimal 15, or binary 1111, and the second nibble is the remainder. For example, if the decimal value is 20, you would code which is equivalent to If you want to code the value 15, you still need two nibbles: The rule is that if you ever have a nibble of 1111, you must follow it with another nibble. Chapter Five - Making Connections Efficient: Multiplexing and Compression

44 44 Relative or Differential Encoding (Lossy) Video does not compress well using run-length encoding In one color video frame, not much is alike But what about from frame to frame? Send a frame, store it in a buffer Next frame is just difference from previous frame Then store that frame in buffer, etc. Chapter Five - Making Connections Efficient: Multiplexing and Compression

45 First Frame Second Frame Difference Chapter Five - Making Connections Efficient: Multiplexing and Compression

46 46 Image Compression One image - JPEG, or continuous images such as video - MPEG A color picture can be defined by red/green/blue, or luminance / chrominance / chrominance which are based on RGB values Either way, you have 3 values, each 8 bits, or 24 bits total (2 24 colors!) Chapter Five - Making Connections Efficient: Multiplexing and Compression

47 47 Image Compression A VGA screen is 640 x 480 pixels 24 bits x 640 x 480 = 7,372,800 bits. Ouch! And video comes at you 30 images per second. Double Ouch! We need compression! Chapter Five - Making Connections Efficient: Multiplexing and Compression

48 48 JPEG Joint Photographic Experts Group Compresses still images Lossy JPEG compression consists of 3 phases: Discrete cosine transformations (DCT) Quantization Encoding Chapter Five - Making Connections Efficient: Multiplexing and Compression

49 49 JPEG Step 1 -DCT Divide image into a series of 8x8 pixel blocks If the original image was 640x480 pixels, the new picture would be 80 blocks x 60 blocks (next slide) If B&W, each pixel in 8x8 block is an 8-bit value (0-255) If color, each pixel is a 24-bit value (8 bits for red, 8 bits for blue, and 8 bits for green) Chapter Five - Making Connections Efficient: Multiplexing and Compression

50 50 80 blocks 60 blocks 640 x 480 VGA Screen Image Divided into 8 x 8 Pixel Blocks

51 51 JPEG Step 1 -DCT So what does DCT do? Takes an 8x8 array (P) and produces a new 8x8 array (T) using cosines T matrix contains a collection of values called spatial frequencies. These spatial frequencies relate directly to how much the pixel values change as a function of their positions in the block Chapter Five - Making Connections Efficient: Multiplexing and Compression

52 52 JPEG Step 1 -DCT An image with uniform color changes (little fine detail) has a P array with closely similar values and a corresponding T array with many zero values (next slide) An image with large color changes over a small area (lots of fine detail) has a P array with widely changing values, and thus a T array with many non-zero values Chapter Five - Making Connections Efficient: Multiplexing and Compression

53 53 JPEG Step 2 -Quantization The human eye can’t see small differences in color So take T matrix and divide all values by 10. This will give us more zero entries. More 0s means more compression! But this is too lossy. And dividing all values by 10 doesn’t take into account that upper left of matrix has more action (the less subtle features of the image, or low spatial frequencies) Chapter Five - Making Connections Efficient: Multiplexing and Compression

54 U matrix Q[i][j] = Round(T[i][j] / U[i][j]), for i = 0, 1, 2, …7 and j = 0, 1, 2, …7

55 55 JPEG Step 3 -Encoding Now take the quantized matrix Q and perform run-length encoding on it But don’t just go across the rows. Longer runs of zeros if you perform the run-length encoding in a diagonal fashion Chapter Five - Making Connections Efficient: Multiplexing and Compression

56 56 Chapter Five - Making Connections Efficient: Multiplexing and Compression

57 57 JPEG How do you get the image back? Undo run-length encoding Multiply matrix Q by matrix U yielding matrix T Apply similar cosine calculations to get original P matrix back Chapter Five - Making Connections Efficient: Multiplexing and Compression

58 58 Business Multiplexing In Action XYZ Corporation has two buildings separated by a distance of 300 meters. A 3-inch diameter tunnel extends underground between the two buildings. Building A has a mainframe computer and Building B has 66 terminals. List some efficient techniques to link the two buildings. Chapter Five - Making Connections Efficient: Multiplexing and Compression

59 59 Chapter Five - Making Connections Efficient: Multiplexing and Compression

60 60 Possible Solutions Connect each terminal to the mainframe computer using separate point-to-point lines. Connect all the terminals to the mainframe computer using one multipoint line. Connect all the terminal outputs and use microwave transmissions to send the data to the mainframe. Collect all the terminal outputs using multiplexing and send the data to the mainframe computer using a conducted line. Chapter Five - Making Connections Efficient: Multiplexing and Compression

61 แบ่งกลุ่มเพื่อวิเคราะห์ บริษัทแห่งหนึ่ง มีอาคาร 2 อาคารที่ห่าง กัน 50 เมตร และมีอุโมงค์ขนาดใหญ่เชื่อม กันอยู่ระหว่าง 2 อาคาร – อาคารแรกมีเครื่องคอมพิวเตอร์ 30 เครื่อง – อาคารที่สองมีเครื่องเมนเฟรมอยู่ 1 เครื่อง จงบอกวิธีการเชื่อมต่อและวิธีการ มัลติเพล็กซ์ ระหว่างคอมพิวเตอร์ และ เครื่องเมนเฟรมที่ดีที่สุด พร้อมทั้งอธิบาย เหตุผล และความเป็นไปได้ที่นักศึกษาได้ เลือก 61

62 Workshop จงบอกความแตกต่างระหว่าง Synchronous TDM และ Statistical TDM จงบอกประเภทของตัวกลางที่ใช้กับการ มัลติเพล็กซ์แบบแบ่งตามความยาวคลื่น จงอธิบายว่า discrete multitone กับ เทคนิคการมัลติเพล็กซ์แบบอื่นๆ ว่ามีความ เหมือนและแตกต่างกันอย่างไร ให้นักศึกษาระบุข้อดีและข้อเสียอย่างละ 2 ข้อ สำหรับเทคนิคการมัลติเพล็กซ์ในแต่ละ ชนิด ดังต่อไปนี้ FDM, Synchronous TDM, Statistical TDM และ WDM 62

63 Workshop 63 อุปกรณ์เคลื่อนที่ของนาย A มีการใช้การ มัลติเพล็กซ์แบบแบ่งตามรหัส (CDM) และ มีการกำหนดเลขฐานสอง คือ อุปกรณ์เคลื่อนที่ของนาย B มีการใช้การ มัลติเพล็กซ์แบบแบ่งตามรหัส (CDM) และ มีการกำหนดเลขฐานสอง คือ อุปกรณ์เคลื่อนที่ของนาย A มีการส่งแบบ a1 ขณะที่อุปกรณ์เคลื่อนที่ของนาย B มี การส่งแบบ a0 จงแสดงวิธีการคำนวณและ ผลลัพธ์จากการเข้ารหัสโดยละเอียด การบีบอัดข้อมูลแบบใด เหมาะสมกับ ประเภทของข้อมูลคล้ายๆกัน และมีจำนวน มากจึงมีประสิทธิภาพมากที่สุด


ดาวน์โหลด ppt 1 Chapter Five Making Connections Efficient: Multiplexing and Compression.

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