Error detection
Why errors happen, and checksums, echo checks and ARQ.
Transcript
When data is transmitted, it can be corrupted, lost, or even gained.
Causes include interference, problems during packet switching, and skewing of data.
A checksum is calculated from a block of data, and sent at the end. The receiver recalculates it, and compares.
With an echo check, the data is sent back to the sender, who compares the two copies.
With A R Q, the receiver sends an acknowledgement when the data arrives correctly, and then the sender sends the next block.
If no acknowledgement arrives before the timeout, or a negative acknowledgement arrives, the block is sent again.
Checksums, echo checks, and A R Q. Different ways to catch errors, and fix them.
More in this series
1:32Data packets and packet switching
Packet structure, routing, out-of-order arrival and reassembly.
1:19Simplex, half-duplex and full-duplex
Which way the data flows, and when.
1:43Serial and parallel transmission
Bits one by one or all at once, skew, crosstalk and USB.
1:13Parity checks
Parity bits and parity blocks, including finding and fixing a flipped bit.
1:32Check digits
The multiply, add, divide-by-10 method with a worked example and a practice question.
1:28Encryption
Eavesdroppers, symmetric keys and the public and private key pair.
5:08Unit 2 quiz
Ten questions with a think-time countdown and explained answers.