Welcome to blogger Apeiron's blog, I wish you a pleasant journey! When it is time to stop, it will stop; when it is time to go, it will go. Movement and stillness do not lose their time, and the way is bright.
Table of contents
1. Basic concepts of physical layer
2. The main tasks of the physical layer protocol
1. Basic concepts of physical layer
In computer networks, there are many types of transmission media used to connect various network devices. It can be roughly divided into two categories, one is guided transmission media , and the other is unguided transmission media .
guided transmission media
① Twisted pair
② Coaxial cable
③ Optical fiber
unguided transmission media
① Microwave communication (2~40 GHz)
② WiFi in 2.4 GHz and 5.8 GHz frequency bands
The physical layer in the computer network architecture is to solve the problem of transmitting bits 0 and 1 on various transmission media , and then provide the data link layer with a transparent transmission bit stream service. The so-called "transparent" means that the data link layer is invisible, and there is no need to see what method the physical layer uses to transmit bits 0 and 1. It just needs to enjoy the bit stream transmission service provided by the physical layer.
2. The main tasks of the physical layer protocol
In order to solve the problem of transmitting bits 0 and 1 on various transmission media, the physical layer mainly has the following four tasks.
① Mechanical properties
Specify the shape and size of the connector used for the interface , the number and arrangement of pins , and the securing and locking devices.
② Electrical characteristics
Indicates the range of voltages that appear on each line of the interface cable .
③ Functional characteristics
Indicates what a certain level of voltage appearing on a certain line means .
④ Process characteristics
Specify the order of occurrence of various possible events for different functions .
There are many types of transmission media , such as twisted pairs, optical fibers, etc. There are also many physical connection methods , such as point-to-point links, broadcast connections, etc. Therefore, there are many types of physical layer protocols . Each physical layer protocol contains the specific content of the above four tasks. Therefore, when learning the physical layer, we should focus on mastering basic concepts rather than a specific physical layer protocol.
3. Physical layer tasks
① How can the physical layer transmit data bit streams on transmission media connecting various computers.
② The physical layer shields the data link layer from the differences in various transmission media, so that the data link layer only needs to consider how to complete the protocols and services of this layer without having to consider the specific transmission media of the network.
4. Summary
This is the summary of this issue’s sharing. If you have any questions, let’s discuss them in the comment area~~~. The author will definitely reply. See you in the next issue! ! !
It is inevitable that there will be omissions and errors in the blog, which are all due to the limited skill of the author. We sincerely ask readers to correct me!
<Computer Network> The column series is continuously updated, welcome to subscribe and follow!