First, the concept of the physical layer, the role of
The physical layer is considered how to connect the various computers on the transmission medium, transmission bit stream , rather than a specific transmission medium; main task is to determine the number and the interface characteristics of the transmission : the interface shape and size, a predetermined voltage range.
Role of the physical layer is possible masked differences in the transmission media and communications means , above the physical layer is the data link layer do not feel the difference, so that only the data link layer protocol he need only consider the layer can be present ;
Second, the repeater
The relay operates in the OSI physical layer, all the center nodes on the LAN. Its role is amplified signal, the compensation signal attenuation, support communication distance. Repeater only functions as distance transmission of higher layer protocols is transparent. Connected via a network repeater corresponds to a larger network composed of the same wire. Two repeaters may be connected to the LAN cable.
Third, the hub (HUB)
Set primary function is to thread the received signal reproduced shaping amplified to expand the transmission distance of the network, while all nodes focused on the center to its nodes. Hub and card , cable and other transmission media as part of a local area network in the infrastructure, the use of the CSMA / the CD (i.e., with Collision Detection Carrier Sense Multiple Access Technology) medium access control mechanism. Simple hub interface transceiver bits each, received a forwarded 1, forwards received 0 0, collision detection is not performed.