Basic network knowledge

I. Lan features:

LAN has the following features:
1. high transmission rate: generally 1 Mbps-20 Mbps, optical fiber high-speed network can reach 100 Mbps, 1000 Mbps
2. multiple types of transmission media are supported.
3. Generally, the network adapter completes communication processing.
4. Good transmission quality and low error rate.
5. A rule-based topology.

Ii. Lan composition:

Generally, a LAN consists of four parts: Server, user workstation, transmission media, and networked devices.

1. Server:
Running the network for 0 s, providing services such as hard disk, file data, and printer sharing, is the core of network control.
For applications, more than 486 of compatible general machines with higher configurations can be used for file servers. However, to improve the overall performance of the network, especially for the stability of the network system, we recommend that you use a dedicated server.
Currently, common Nos types include NetWare, UNIX, and Windows NT.
Netware:
Popular versions: v3.12, v4.11, and V5.0 have low hardware requirements. The application environment is similar to dos. They are well-developed and reliable. They support multiple workstations and protocols and are suitable for LAN Operating Systems and serve as file servers, the printing server has good performance.
UNIX: a typical 32-bit multi-user Nos. It is mainly used on super minicomputers and mainframes. Currently, common versions include UNIX sur4.0. It supports Network File System services and provides data and other applications. It is powerful, difficult to master, and has complicated commands. It was launched by at&t and SCO.
Windows NT Server 4.0:
Distributed Graphics applicationsProgramIs similar to Win95, which is easy to install and manage. It integrates Internet network management tools and has broad prospects.
Servers are divided into file servers, print servers, database servers, on the Internet, as well as web, FTP, e-mail and other servers.
The Network 0 s is evolving towards supporting multiple communication protocols, multiple NICs, and workstations.

2. Workstation: it can work independently for 0 s. By running workstation network software, it can access server shared resources. Common examples include DOS Workstation and Windows95 workstation.

3. NIC: connects a workstation server to the network for resource sharing and communication, data conversion, and electrical signal matching.
Nic (NTC) classification:
(1) Speed: 10 Mbps, 100 Mbps
(2) Bus Type: ISA/PCI
(3) transmission media interface:
Single Port: BNC (thin cable) or RJ 45 (twisted pair)

4. Transmission Media: Common transmission media include twisted pair wires, coaxial cables, and optical fiber cables.
(1) twisted pair wires (TP ):
More than one pair of twisted wires are encapsulated in an insulated jacket. To reduce interference, each pair is twisted around each other. It can be divided into unshielded twisted pair wires (UTP) and shielded twisted pair wires (STP). In Lan, UTP can be divided into three categories, 4 categories, 5 categories, and 5 categories.
Take company amp as an example:
Category 3: 10 Mbps, thin skin, note "cat3' on the skin, note" 3 categories "on the box, 305 meters/box, 400 yuan/box
Category 4: not used in Networks
Category 5: (over 5 categories) 100 Mbps, 10 Mbps, thick skin, turns, "cat5" on the skin, 5 categories on the box, 305 meters/box, 100-500 RMB/box (meters per segment, connected with 4 relay devices, up to meters)

Wiring sequence: Normal: White orange white green blue white blue green white Brown
1 2 3 4 5 6 7 8
Consortium: white green white orange brown white brown orange white blue
1 2 3 4 5 6 7 8
STP: similar to UTP, external aluminum foil, apple, and IBM network products require STP twisted pair wires for high speed and high price.
(2) coaxial cable:
It is composed of a hollow outer cylindrical conductor and an inner wire located on the central axis. The two conductors are separated by insulating material.
The cables are divided into coarse and fine cables by diameter.
Rough cable: long transmission distance, high performance but high cost. It is used for large LAN trunk lines. The two ends must be connected by a final adapter.
A. The thick cable is connected to the external transceiver.
B. Connect the transceiver to the NIC using the AuI cable.
C. The NIC must have an AuI interface: 500 m for each segment, 100 users, 4 relay connections up to 2500 m, a minimum of 2.5 m between transceiver and a maximum of 50 m of transceiver cable.
Thin cable: Short Transmission Distance, relatively cheap, with a T-head, connected to the BNC Nic, the two ends of the terminal resistance of 50 euro.
Each segment is 185 meters, 4 reconnections, a maximum of 925 meters, 30 users per segment, and a minimum of 0.5 meters between T-headers.
The bandwidth is divided into baseband and broadband transmission.
Baseband: a digital signal that occupies the entire channel and can transmit a signal at the same time.
Broadband: transmits signals of different frequencies.
(3) optical fiber:
The Optical Principle is used to generate a beam from the optical transmitter, convert an electrical signal into an optical signal, then import the optical signal into an optical fiber, and then the optical receiver receives the optical signal uploaded from the optical fiber at the other end and converts it into an electrical signal, decoded before processing. It can be divided into single-mode optical fiber and multi-mode optical fiber. Insulation and confidentiality are good.
Single-Mode Optical Fiber: laser light source, only one optical channel, long transmission distance, more than 2 kilometers.
Multimode Optical Fiber: light emitting by diode, low speed short distance, less than 2 kilometers.

Iii. Computer Network Software System:

4. LAN working modes:

1. dedicated server structure: (server-baseb)
It is also known as the "workstation/File Server" structure. It is composed of several computer workstations and one or more file servers connected through communication lines to form a workstation to access server files and share storage devices.
The file server naturally aims to share disk files.
Generally, data transmission is sufficient. However, when the database system and other complex application systems used by more and more users arrive, the server can no longer undertake such tasks, as the number of users increases, the number of programs serving each user increases, and each program is a large file that runs independently, causing users to feel extremely slow, resulting in a Client/Server mode.

2. Client/Server mode: (Client/Server)
One or several large computers collectively manage and access shared databases, which are called servers. Other applications and processing work are distributed to other computers in the network, to form a distributed processing system, the server's ability to control and manage data has increased from file management to database management. Therefore, the C/S server is also called a database server, focuses on data definition and access security backup and restoration, concurrency control and transaction management, and implements database management functions such as selection retrieval and index sorting, it has enough ability to transmit the part of data that the user needs after processing, rather than the entire file, to the client through the network, reducing the network transmission load. The C/S structure is the result of combining the development and universal application of database technology with the development of LAN technology.

3. Peer-to-Peer)
The topology is the same as the dedicated server and C/S. In a peering network structure, there is no dedicated server
Each workstation can act as both a client and a server.