physical layer
- The physical layer defines the electrical, timing, and other interfaces related to when bits are sent over a channel as a signal. The physical layer is the foundation for building a network.
- Theoretical foundations of data communication: A method of changing a certain physical property such as voltage or current can be used to transmit information on a wire. If the value of the voltage or current is represented by a single-valued function f(t) with time t as an independent variable, The behavior of the signal can then be modeled and analyzed mathematically.
- Fourier analysis, bandwidth limited signals, channel minimum transmission rate (Shannon: minimum bit rate = )
- Wired transmission medium: twisted pair, coaxial cable, power line, optical fiber
- Wireless transmission: digital modulation (baseband modulation, passband modulation) multiplexing (frequency division multiplexing, time division multiplexing, code division multiplexing)
data link layer
- The data link layer uses the services provided by the physical layer to send and receive bits on the communication channel. Its functions are:
(1) Provide a well-defined service interface to the network layer
(2) Handling transmission errors (detecting errors, correcting errors)
(3) Regulate the data flow to ensure that slow receivers are not overwhelmed by fast receivers.
- Transmission unit: frame (frame header, payload, frame trailer)
- The data link layer provides three possible services:
(1) Connectionless service without confirmation ----> When the error rate is low, real-time communication
(2) Confirmed connectionless service
(3) There is a confirmed connection service
Media Access Control Sublayer (MAC) ? ? ?