Data packets and packet switching
Packet structure, routing, out-of-order arrival and reassembly.
Transcript
Data sent over a long distance is broken into data packets, sometimes called datagrams.
Each packet has three parts: a header, the payload, and a trailer.
The header holds the I P address of the sender, the I P address of the receiver, the sequence number, and the packet size.
In packet switching, each packet travels independently, and routers decide its route.
A router picks the shortest available path, avoiding routes that are broken or busy.
Packets can arrive out of order, so the receiver puts them back together using the sequence numbers.
The benefit is that there are alternative routes if one is broken or overloaded. The drawback is that the data must be reassembled.
Split into packets, routed independently, and reassembled at the destination.
More in this series
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.
1:21Error detection
Why errors happen, and checksums, echo checks and ARQ.
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.
1:32Crosstalk in transmission
How a signal leaks into a neighbouring wire, corrupts data, and how twisted pairs and shielding fix it.
1:48When to use serial or parallel
Choosing between serial and parallel: inside a computer, computer to printer, USB, Ethernet and a distance rule of thumb.