Data transmission and packets
Introduced| English | Meaning |
|---|---|
| data transmission/ˈdeɪtə trænˈsmɪʃn/ | Moving data between devices or components through a communication channel. |
| packets/ˈpækɪts/ | Units of data sent through a network, containing payload and control information such as addressing details. |
| serial/ˈsɪərɪəl/ | Sending bits one after another over a channel rather than sending a group of bits simultaneously on separate lines. |
| parallel/ˈpærəlel/ | Describing operations that take place concurrently rather than one after another. |
| packet switching/ˈpækɪt ˈswɪtʃɪŋ/ | Routers route each packet. |
| header/ˈhedə/ | header |
| payload/ˈpeɪləʊd/ | payload |
| routers/ˈruːtəz/ | Network devices that forward packets between networks using destination addresses and routing information. |
| simplex/ˈsɪmpleks/ | simplex |
| half-duplex/hɑːf ˈdjuːpleks/ | half-duplex |
| full-duplex/fʊl ˈdjuːpleks/ | Allowing communication in both directions at the same time. |
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:
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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.
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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:
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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
Half-duplex sends data both ways at the same time, like a phone call, while full-duplex sends both ways but only one at a time.
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False. They are swapped: half-duplex sends both ways but one direction at a time (like a walkie-talkie), while full-duplex sends both ways at once (like a phone call). Simplex is one way only.
A benefit of USB is that:
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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