Software development speed learning area Network: Physical Layer

Preface, because the physical layer tend to hardware, software, I do, so do not write the whole, only need to know the meaning of existence of the physical layer, as well as some simple understanding. To learn all depends on this, Han Ligang teacher's class, absolutely interesting , and this is my reference Mu class network: network programming necessary foundation in the articles, all the software, not very wide, but to engage in software, I think enough , please indicate wrong.

1. Role

• Connect different physical devices. Such as cable, optical cats.
• Transmission bit stream.
  

2. physical media (Learn)

The main ones are: twisted pair, coaxial cable, fiber optic, infrared, radio, activation and the like.

• Twisted Pair: such as network cable.
  

• Coaxial cable: Learn
  

• Fiber: using optical characteristics.
  

Basic concepts channel

Channel is a media transmitting information in one direction.

A communication circuit comprising a receive channel and a transmit channel.

Here's a question: Send a receiving circuit and will not conflict? Answer: because of this reason, the communication circuit provided us with the following channels:

• Simplex communication channel : a communication can only be in one direction, there is no feedback channel in the opposite direction. Such as cable television, wireless radio.
• Half-duplex communication channel : both parties can send and receive information, but not both simultaneously transmit nor receive simultaneously. So this channel is now relatively backward.
• Full-duplex communication channel : both parties can send and receive information. Now we used channels, such as cable, Internet and other transmission media.

4. demultiplexing - Multiplexing

Necessary connection between many computers, there will be many transmission channel and a reception channel, but many times these channels are always in a dormant state, the result of channel utilization is not high, so it is proposed demultiplexing - multiplexing .

Just you need to know in the channel watched by multiplexing technology and the causes of the line.

Multiplexing, comprising: frequency division multiplexing, time division multiplexing, wavelength division multiplexing, code division multiplexing.

5. Summary

1. Role of the physical layer.
2. The basic concept of the channel and three kinds of channels.
3. Demultiplexing - generation and multiplexing effect.

6. Extras

Reprint: NIC, switches, bridges, routers, gateways work in which layer of the OSI model it?

A device in which a layer of work, you need to look at its main use is to realize the function which layer protocol header information.

Bridge: working the data link layer, or between the different types of the same LAN and stored in forwarding data frames, the protocol conversion necessary on the link layer. It connects two or more networks, in which the transport packet.

Switch: working data link layer, equivalent to the principle of multi-port bridge. Role is to connect segments of the same number of different hosts, to reduce the conflicts within the network, isolating collision domains. Using the stored forwarding and filtering techniques to separate from the physical network segment.

Router: work in the network layer between different networks store and forward packets. May be dissimilar networks (i.e., different types of LAN interconnection, a local area network and a wide area network, a wide area network and a wide area network) and data transmission path selection, specialized software protocol partitioning of the whole network logically.

Gateway: The higher-level protocols (including transport layer and the higher level) for converting gateways. Allows the use of incompatible protocols, such as system and network interconnection SPX / IPX and TCP / IP's. Because the protocol conversion is the most important function of a gateway, so the answer is to work in the transport layer and above level.

NIC: Function After the card at the physical layer is mainly connected to the physical interfaces is completed, the transmission of electrical signals and the data into appropriately sized packets sent over the network to a data link layer comprising a link setup and teardown functions, the frame synchronization sequence delimited these error control. Most believe that the main work in the physical layer.

Of course, many devices become increasingly blurred in the concept. Bridging router is a combination of bridges and routers allow multiple connections, has a dedicated routing method of a protocol, other protocols act only as a bridge effect.

Bridges, routers, switches and gateways can be installed in the same building or campus area, you can also use the remote connection.