Data transmission and packets
| English | Chinese | Pinyin |
|---|---|---|
| data transmission | 数据传输 | shù jù chuán shū |
| packets | 数据包 | shù jù bāo |
| serial | 串行 | chuàn xíng |
| parallel | 并行 | bìng xíng |
| packet switching | 数据包交换 | shù jù bāo jiāo huàn |
| header | 报头 | bào tóu |
| payload | 有效载荷 | yǒu xiào zài hè |
| routers | 路由器 | lù yóu qì |
| simplex | 单工 | dān gōng |
| half-duplex | 半双工 | bàn shuāng gōng |
| full-duplex | 全双工 | quán shuāng gōng |
Sending data around
- Data transmission 数据传输 moves data from one place to another.
- The data is broken into small equal pieces called packets 数据包.
- We also choose how it travels: serial 串行/parallel 并行 and the direction.
Packets and packet switching 数据包交换
- A packet has three parts: a header 报头 (sender + receiver IP addresses, packet number), the payload 有效载荷 (the data), and a trailer (end marker + error check).
- Benefits of packets: only a lost packet is resent (not the whole file); packets can take different routes; many users share the connection.
- In packet switching, routers 路由器 read each header and pick a route; packets may arrive out of order and are reordered by packet number.
A packet has a header, a payload (the data) and a trailer; the header carries the addresses and packet number.
Routers forward packets, and different packets can take different routes to the same receiver.
How data travels in packets
Step through packet switching. Splitting a file into addressed packets is why one lost packet only needs resending, and why many users can share the same line.
A packet header contains:
The header carries control info (addresses + packet number); the payload is the data; the trailer marks the end + error check.
Match each part of a packet to what it carries.
A packet = header (control info) + payload (data) + trailer (end + error check); splitting up means only lost packets are resent.
Serial vs parallel
- Serial sends one bit at a time down one wire — cheaper, and good over long distances (bits stay in order).
- Parallel sends several bits at once down several wires — faster but only over short distances (bits can arrive at slightly different times).
An Ethernet cable with an RJ45 plug, often used to carry data on a wired network
Serial transmission:
Serial = one bit at a time (cheaper, long-distance reliable); parallel = many bits at once (fast, short-distance).
Direction, and USB
- Simplex 单工 — one direction only (computer → printer).
- Half-duplex 半双工 — both directions, one at a time (walkie-talkie).
- Full-duplex 全双工 — both directions at once (phone call).
- USB: one standard connector, auto-detects the device and loads the driver, carries power, and only fits one way.
A fibre-optic cable carries data as pulses of light along thin glass fibres
Simplex sends data one way only, half-duplex sends both ways but one at a time, and full-duplex sends both ways at the same time (like a phone call).
The three modes differ by direction and timing: simplex (one way), half-duplex (take turns), full-duplex (both at once).
A benefit of USB is that:
USB uses one standard connector, auto-detects devices, carries power, and only fits one way.
You've got it
- a packet = header (addresses + number) + payload + trailer; only lost packets are resent
- packet switching: routers route each packet; reordered by packet number
- serial = one bit/one wire (long distance); parallel = many bits/many wires (short)
- simplex / half-duplex / full-duplex = one way / one-at-a-time / both-at-once