|  | 6.1 | LAN Standards
| 6.1.3 | Comparing the IEEE model with the OSI model
The IEEE standard appears, at first glance, to violate the OSI model in two ways. First, it defines its own layer (LLC), including its own Protocol Data Unit (PDU), interfaces, etc. Second, it appears that the MAC layer standards, 802.3 and 802.5, cross over the Layer 2/Layer 1 interface. However, 802.3 and 802.5 define the naming, framing, and Media Access Control rules around which specific technologies were built. Basically, the OSI model is an agreed-upon guideline; the IEEE came later to solve the problems that networks encountered after they had been built. The curriculum will continue to use the OSI model, but it is important to remember that LLC and MAC perform important functions in the OSI data link layer. One other difference between the OSI model and the IEEE standards is that of the NIC. The NIC is where the Layer 2 MAC address resides, but in many technologies the NIC also has the transceiver (a Layer 1 device) built into it and connects directly to the physical medium. So it would be accurate to characterize the NIC as both a Layer 1 and a Layer 2 device.