Types & Methods Of Data Transmission

Data Packets

• **Packets** are small 'chunks' of data that make up a larger piece of data broken down by **TCP** (Transmission Control Protocol).
• Small packets are easier and quicker to route over the internet than large chunks.
• Each packet contains a **header** (source IP, destination IP, packet number), a **payload** (actual data), and optionally a **trailer** (security info, end-of-packet notification).
• **Error checks** (e.g., parity bits) are added to detect corruption — data being changed, lost, or extra data added.
• If a packet is corrupted or lost, the receiver can request a resend of only that packet, not the whole file.

Packet Switching

• **Packet switching** is a method of sending packets across a network using routers.
• Data is broken into packets, each assigned a header with source/destination IP and packet number.
• **Routers** use routing tables to send each packet along the most optimal path, avoiding traffic.
• Packets may take different routes and arrive out of order; they are reassembled using packet numbers.
• Advantages: minimal interference/corruption (individual packets can be resent), quicker than sending one large packet, harder to hack as each packet contains minimal data.

Serial & Parallel Transmission

• **Serial transmission**: bits sent one at a time along a single wire. Example: **USB**.
• **Parallel transmission**: multiple bits sent simultaneously on separate wires. Example: traditional printer cable.
• Serial advantages: reliable over longer distances, cheaper, low interference. Disadvantage: slower.
• Parallel advantages: very fast. Disadvantages: only used over short distances, prone to interference and **skew** (timing differences).

Simplex, Half-Duplex & Full-Duplex

• **Simplex**: data travels in one direction only (e.g., computer to monitor).
• **Half-duplex**: data travels both ways but only one direction at a time (e.g., printer cable sending data then receiving 'low ink' message).
• **Full-duplex**: data travels both ways simultaneously (e.g., network cables in LAN/WAN).
• Full-duplex is fastest but most expensive; half-duplex is cheaper than full-duplex for two-way communication; simplex is simplest and cheapest.

Combinations of Transmission Methods

• Wires can combine serial/parallel with simplex/half-duplex/full-duplex (e.g., **Serial-Simplex**, **Serial-Half-duplex**, **Serial-Full-duplex**, **Parallel-Simplex**, **Parallel-Half-duplex**, **Parallel-Full-duplex**).
• Serial-Simplex: one bit at a time, one direction, single wire.
• Serial-Half-duplex: one bit at a time, both directions but not simultaneously, typically one shared wire.
• Serial-Full-duplex: one bit at a time, both directions simultaneously, requires two wires.
• Parallel-Simplex: multiple bits simultaneously, one direction, multiple wires.
• Parallel-Half-duplex: multiple bits simultaneously, both directions but one at a time, multiple wires.
• Parallel-Full-duplex: multiple bits simultaneously, both directions at once, multiple wires.

Universal Serial Bus (USB)

• **USB** is a widely used standard for serial, asynchronous data transmission between devices.
• Common devices: keyboards, mice, printers, disk drives, network adapters, mobile phones.
• Connector types: **USB-A** (flash drives, mice), **USB-B** (printers, scanners), **USB-C** (latest, small, high speed, carries power).
• Speed generations: USB 1.1 (12 Mbps), USB 2.0 (480 Mbps), USB 3.x (5–20 Gbps), USB4 (up to 80 Gbps).
• When connected, the computer automatically detects the device and loads the appropriate driver; if not found, the user must install it manually.
• Advantages: automatic detection, keyed connectors (fit one way), standardised support, backwards compatible, various speeds.
• Disadvantages: maximum cable length ~5 metres, older versions have limited speeds, very old standards may become unsupported.

Simple serial transmission: data flows one bit at a time along a single wire from sender to receiver.

Parallel transmission: multiple bits sent simultaneously on separate wires.