Learning computer network (1) physical layer

A unit of data transmitted on the physical layer: the bit.
Second, the function: the role of the physical layer to achieve transparent transfer between the computer nodes adjacent bit stream, the specific transmission medium masked differences and physical devices as possible. The above data link layer so that the specific transmission medium regardless of what network Yes. "Transparent transmission bit stream" indicates the bit stream transmitted by the actual circuit has not changed, the bit stream is transmitted, if this circuit is invisible.
Third, the physical characteristics of the interface layer
(1) Mechanical characteristics: shape and dimensions of the interface connector used for specified number and arrangement of the lead, and fixing the locking device and the like.
(2) Electrical characteristic: the specified voltage range appearing in respective lines of the interface cable.
(3) features: a specified voltage level indicates a strip line appears what is intended.
(4) the procedural characteristics: specify the order of appearance for the various functions of possible events.
Fourth, the physical layer device:
(1) the card
　　1, data encapsulation and decapsulation of
　　the upper layer to the transmission data plus header and trailer, the Ethernet frame to be transmitted when. Upon receiving the Ethernet frame header and trailer stripped, and then sent to a layer
　　2 link management
　　mainly through the CSMA / CD (Collision Detection band carrier Sense Multiple Access) protocol
　　3, and the target data encoding code
　　4, serial / parallel conversion
　　with a processor and memory (including RAM and ROM) card above. Communication between the card and the LAN is transmitted in a serial manner via a cable or twisted pair. And the communication between the card and the computer is O bus in a parallel transmission via a computer motherboard I /.
(2) an optical fiber
(3) CAT-5 cable
(4) RJ-45 connector
RJ45 socket is a wiring system information (i.e. communication pigtail) a connector, the connector plug (connector, RJ) and the socket (modules), the plug has eight grooves and eight contacts.
(5) a hub: pure hardware equipment, the whole wave is mainly used to connect computers and other network terminals.
(6) repeaters (Repeater): to strengthen the signal, and regeneration of the network signal retiming the bit level, so that they can be transmitted over a longer distance network.
(7) serial, parallel