Presentation is loading. Please wait.

Presentation is loading. Please wait.

TELE3118 extras For week 2. Slide from Ch. 3 of W. Stallings: Data and Computer Communications.

Similar presentations


Presentation on theme: "TELE3118 extras For week 2. Slide from Ch. 3 of W. Stallings: Data and Computer Communications."— Presentation transcript:

1 TELE3118 extras For week 2

2 Slide from Ch. 3 of W. Stallings: Data and Computer Communications

3 3 modem Image from 290/ _5afd150ed1 _o.jpg

4 Error checks

5 Decimal CRC ) * Add = 974 Send

6 CRC example G= What values for check bits? Verifying message with check bits Red ≠ previously

7 Detect an error in the data Detect a burst error

8 8 Hamming codes n-k check bits protect 2 n-k -(n-k)-1 payload bits, e.g. 4 protect 11 2 All bits whose offset is a power of 2 (e.g. bit 1, 2, 4…) are check bits The value of check bit 2 b-1 is chosen to ensure even parity over all bits whose position has a 1 in bit b, e.g. bit 1 (2 0 ) covers odd bits If parity checks fail, and there is only one error, the number (“syndrome”) formed using digits reflecting parity outcome (0=OK, 1=fail) indicates the location of the error, e.g.: e.g. payload of Bit #s and coverage of parity √× ×√ 0101 => error is in bit 5 Parity status Parity status in binary Hamming codes are used in IEEE Wireless networks c7d9e2ec


Download ppt "TELE3118 extras For week 2. Slide from Ch. 3 of W. Stallings: Data and Computer Communications."

Similar presentations


Ads by Google