|  | 3.3 | Basics of Data Flow Through LANs
| 3.3.2 | Packet flow through Layer 1 devices
The Figure illustrates that certain devices operate at Layer 1, only. The packet flow through Layer 1 devices is simple. Physical media are considered Layer 1 components. All they attend to are bits (e.g. voltage or light pulses). If the Layer 1 devices are passive (e.g. plugs, connectors, jacks, patch panels, physical media), then the bits simply travel through the passive devices, hopefully with a minimum of distortion. If the Layer 1 devices are active (e.g. repeaters or hubs ), then the bits are actually regenerated and retimed. Transceivers, also active devices, act as adapters (AUI port to RJ-45), or as media converters (RJ-45 electrical to ST Optical). In all cases the transceivers act as a Layer 1 devices. No Layer 1 device examines any of the headers or data of an encapsulated packet. All they work with are bits.
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| Encapsulation
| Packets
| Data Encapsulation
| Encapsulation Slide
| Encapsulation of PDUs