The OSI model revisited

• Physical layer: transmits data bits (0,1) over a circuit according to rules such as voltages of electricity, timing, full duplex/half duplex, connector cable standards

• Data Link Layer: manages the transmission and looks for error free circuits; solves problems caused by damaged, lost or duplicated message frames

(levels above assume error free transmission)



• sometimes divided into two sub-levels
  • Media Access Control (MAC) performs most of the Data Link Layer functions
  • Logical Link Control (LLC) is an interface between MAC and Network Layer (cf., middleware = changing MAC does not change the Network Layer; e.g., IEEE802.2

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