McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Lapisan Data Link BAGIAN III.

Presentasi berjudul: "McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Lapisan Data Link BAGIAN III."— Transcript presentasi:

1 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Lapisan Data Link BAGIAN III

2 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Position lapisan data-link

3 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Tugas-tugas Lapisan Data Link

4 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Sub lapisan LLC dan MAC

5 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Standar-standar IEEE untuk LAN

6 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Bab-Bab Bab 10 Error Detection and Correction Bab 11 Data Link Control and Protocols Bab 12 Point-To-Point Access Bab 13Multiple Access Bab 14Local Area Networks Bab 15 Wireless LANs Bab 16 Connecting LANs Bab 17 Cellular Telephone and Satellite Networks Bab 18 Virtual Circuit Switching

7 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Bab 10 Deteksi galat dan koreksi (Error Detection and Correction)

8 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Data dapat terkorupsi selama transmisi, reliable communication, error harus dapat dideteksi dan dikoreksi. Catatan: Catatan:

9 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.1 Tipe-tipe Error Error bit-tunggal (Single-Bit Error) Error deburan (Burst Error)

10 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Dalam error bit tunggal (single-bit error), berarti hanya ada satu bit yang berubah dalam data unit. Catatan:

11 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Gambar 10.1 Error bit-tunggal

12 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Error deburan (burst error) jika terdapat lebih dari 2 bit yang berubah pada data unit. Catatan:

13 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Gambar 10.2 Burst error of length 5

14 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.2 Deteksi Error Redundancy Parity Check Cyclic Redundancy Check (CRC) Checksum

15 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Deteksi error menggunakan konsep menambahkan bit-bit (redundancy), berarti menambahkan bit ekstra untuk mendeteksi error pada tujuan (penerima). Catatan:

16 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Gambar 10.3 Redundancy

17 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Gambar 10.4 Metode deteksi

18 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.5 Konsep paritas genap (even-parity)

19 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Pada parity check, suatu bit paritas ditambahkan pada setian satuan (unit) data sehingga jumlah bitnya ditambah 1, dapat diterapkan dua jenis paritas yaitu paritas ganjil (even- parity atau odd parity). Catatan:

20 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Catatan 1 Suppose the sender wants to send the word world. In ASCII the five characters are coded as 1110111 1101111 1110010 1101100 1100100 The following shows the actual bits sent 11101110 11011110 11100100 11011000 11001001

21 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 2 Now suppose the word world in Contoh 1 is received by the receiver without being corrupted in transmission. 11101110 11011110 11100100 11011000 11001001 The receiver counts the 1s in each character and comes up with even numbers (6, 6, 4, 4, 4). The data are accepted.

22 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 3 Now suppose the word world in Contoh 1 is corrupted during transmission. 11111110 11011110 11101100 11011000 11001001 The receiver counts the 1s in each character and comes up with even and odd numbers (7, 6, 5, 4, 4). The receiver knows that the data are corrupted, discards them, and asks for retransmission.

23 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Simple parity check can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd. Catatan:

24 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Gambar 10.6 Sistem paritas dua-dimensi

25 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 4 Suppose the following block is sent: 10101001 00111001 11011101 11100111 10101010 However, it is hit by a burst noise of length 8, and some bits are corrupted. 10100011 10001001 11011101 11100111 10101010 When the receiver checks the parity bits, some of the bits do not follow the even-parity rule and the whole block is discarded. 10100011 10001001 11011101 11100111 10101010

26 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 In two-dimensional parity check, a block of bits is divided into rows and a redundant row of bits is added to the whole block. Catatan:

27 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.7 CRC generator and checker

28 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.8 Binary division in a CRC generator

29 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.9 Pembagian biner pada metode CRC

30 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.10 Polinomial

31 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.11 Polinomial sebagai bilangan pembagi

32 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Tabel 10.1 Polinomial Standar NamePolynomialApplication CRC-8x 8 + x 2 + x + 1ATM header CRC-10x 10 + x 9 + x 5 + x 4 + x 2 + 1ATM AAL ITU-16x 16 + x 12 + x 5 + 1HDLC ITU-32 x 32 + x 26 + x 23 + x 22 + x 16 + x 12 + x 11 + x 10 + x 8 + x 7 + x 5 + x 4 + x 2 + x + 1 LANs

33 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 5 It is obvious that we cannot choose x (binary 10) or x 2 + x (binary 110) as the polynomial because both are divisible by x. However, we can choose x + 1 (binary 11) because it is not divisible by x, but is divisible by x + 1. We can also choose x 2 + 1 (binary 101) because it is divisible by x + 1 (binary division).

34 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 6 The CRC-12 x 12 + x 11 + x 3 + x + 1 which has a degree of 12, will detect all burst errors affecting an odd number of bits, will detect all burst errors with a length less than or equal to 12, and will detect, 99.97 percent of the time, burst errors with a length of 12 or more.

35 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.12 Checksum

36 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.13 Data unit and checksum

37 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 The sender follows these steps: The unit is divided into k sections, each of n bits.The unit is divided into k sections, each of n bits. All sections are added using one’s complement to get the sum.All sections are added using one’s complement to get the sum. The sum is complemented and becomes the checksum.The sum is complemented and becomes the checksum. The checksum is sent with the data.The checksum is sent with the data. Catatan:

38 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 The receiver follows these steps: The unit is divided into k sections, each of n bits.The unit is divided into k sections, each of n bits. All sections are added using one’s complement to get the sum.All sections are added using one’s complement to get the sum. The sum is complemented.The sum is complemented. If the result is zero, the data are accepted: otherwise, rejected.If the result is zero, the data are accepted: otherwise, rejected. Catatan:

39 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 7 Anggap pada block berikut yang terdiri atas 16 bit, dikirimkan menggunakan suatu checksum 8 bit. 10101001 00111001 Kedua bilangan dijumlahkan menggunakan penjumlahan one’s complement 10101001 00111001 ------------ Sum 11100010 Checksum 00011101 Pola bit yang dikirimkan 10101001 00111001 00011101

40 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 8 Sekarang anggap suatu penerima menerima pola bit yang dikirim oleh pengirim seperti Contoh 7 dan anggap tanpa error pada transmisi. 10101001 00111001 00011101 Jika ketiga bilangan tersebut dijumlahkan,maka akan diperoleh bilangan yang bernilai 1 semuanya, jika dilakukan operasi komplemen (complementing), menghasilkan bilangan yang bit- bitnya bernilai 0 semua, hal ini menunjukan tidak terjadi error. 10101001 00111001 00011101 Sum11111111 Complement 00000000 berarti polanya benar.

41 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Contoh 9 Anggap pada transmisi terjadi suatu error deburan (burst error) yang panjangnya 5 bir dan ber pengaruh pada 4 bit. 10101111 11111001 00011101 Jika pada penerima ketiga bilangan tersebut dijumlahkan, akan diperoleh 10101111 11111001 00011101 Partial Sum 1 11000101 Carry 1 Sum11000110 Complement 00111001 Terjadi korupsi pada pola bit yang diterima.

42 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.3 Koreksi Retransmission Forward Error Correction Burst Error Correction

43 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Table 10.2 Data and redundancy bits Number of data bits m Number of redundancy bits r Total bits m + r 1 23 2 35 3 36 4 37 5 49 6 410 7 411

44 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.14 Positions of redundancy bits in Hamming code

45 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.15 Redundancy bits calculation

46 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.16 Contoh kalkulasi bit redundancy

47 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.17 Error detection using Hamming code

48 McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 10.18 Contoh koreksi error deburan (burst error)