Common LAN topology and network system applications (1)

I. Common LAN Topologies 　

Computers and other devices in the network need to be connected in a certain structure. This connection method is called "topological structure ", in general, how are these network devices connected together. Currently, the following network topologies are common:

1) Star Structure

2) Ring Structure

3) bus structure

4) Star-and total-line Compound Structure

Next we will give a one-to-one introduction to these network topologies.

1. Star Structure 　

This structure is currently the most widely used in LAN, and is widely used in enterprise networks. A star network is almost a dedicated Ethernet network. It is because the devices on each workstation node in the network are connected by a centralized network device, such as a hub or a switch, each node is named after star distribution. Currently, the most widely used transmission medium for such networks is twisted pair wires, such as common cat5e wires and cat5e twisted pair wires.

The basic features of such a topological network are as follows:

1) easy to implement: the transmission medium it uses is generally the use of generic twisted pair wires, this transmission medium is relatively cheap, such as the current genuine cat5e twisted pair wires per meter is only about 1.5 yuan, the cheapest coaxial cable is about 2.00 yuan a meter, not to mention the cable. This topology is mainly used in IEEE 802.2 and IEEE 802.3 standard Ethernet LAN;

2) node expansion and mobility convenience: you only need to pull a line from the hub or switch and other centralized devices to expand the node, to move a node, you only need to move the device of the corresponding node to the new node, instead of "taking the global lead" like a ring network ";

3) Easy maintenance; failure of one node does not affect the connection of other nodes, and the faulty node can be removed at will;

4) broadcast information transmission: Any node that sends information can be received by all nodes in the network. This poses a certain risk in the network, but this has little impact on LAN usage;

5) fast network data transmission: this can be seen from the latest Mbps to 10G Ethernet access speed.

In fact, its main features are far more than that, but we will also talk about various types of network access devices later, and the characteristics of the network are mainly restricted by the characteristics of these devices, so we will add some other features when talking about the corresponding network devices later.

2. Ring Structure　

This network structure is mainly used in the token network. In this network structure, each device is directly connected through a cable, and finally forms a closed loop, the information sent by the entire network is transmitted in this ring. This type of network is often referred to as the "Ring-based network ".

In fact, in most cases, the network in this topology is not physically connected to all computers. Generally, the two ends of the ring are closed by an impedance pair, because it is inconvenient to physically connect the two ends of the ring due to geographical location restrictions in the actual networking process.

The network with this topology has the following features:

1) This network structure is generally only applicable to the Token network Token ring network of IEEE 802.5. In this network, the "Token" is transmitted in turn in a ring connection. The transmission medium used is generally a coaxial cable.

2) This network implementation is also very simple and the investment is minimal. It can be seen from the network structure that the workstation is the transmission medium-coaxial cable, and some connection equipment, without expensive node centralized equipment, such as hubs and switches. However, because of this, the network can achieve the most simple functions, and can only be used as a general file service model;

3) fast transmission speed: 16 Mbps transmission speed is allowed in the token network, which is much faster than normal 10 Mbps Ethernet. Of course, with the wide application of Ethernet and the Development of Ethernet technology, the speed of Ethernet has also been greatly improved. At present, it is generally possible to provide a Mbps network speed, far higher than 16 Mbps.

4) difficult maintenance: from the network structure, we can see that the nodes in the entire network are directly connected in series. If any node fails, the entire network may be interrupted or paralyzed, it is inconvenient to maintain. On the other hand, the coaxial cable uses the contact method of the plug-in, so it is very easy to cause poor contact, network interruption, and it is very difficult to find out, I believe that people who have maintained this network will have a deep understanding of this.

5) poor scalability: because of its ring structure, it determines that its scalability is far better than that of the star structure. If you want to add or move a new node, the entire network must be interrupted, make a connector at both ends of the ring to connect.

3. Bus Structure 　

In this network topology, all devices are directly connected to the bus, and the media used is usually coaxial cables including coarse and fine cables ), however, optical fiber cables are also used as bus transmission media. For example, the networks used by the ATM network and Cable Modem that we will talk about later are bus-type network structures.

This structure has the following features:

1) Low Cost of networking: From the Perspective of such a structure, there is no need for another interconnected device. Instead, it is directly connected through a bus, so the cost of networking is low;

2) because each node in this network shares the bus bandwidth, the transmission speed will decrease as the number of users accessing the network increases;

3) Flexible expansion of network users: you only need to add a receiver when you need expansion, but the number of users that can be connected is limited;

4) Easy Maintenance: failure of a single node does not affect the normal communication of the entire network. However, if the bus is disconnected, the entire network or the corresponding backbone network segment will be disconnected.

5) the disadvantage of this network topology is that only one end user can send data at a time, and other end users must wait for the sending permission.

4. Hybrid Topology 　

This kind of network topology is a network structure that combines the star structure and the total line structure mentioned above. This kind of topology structure can meet the needs of larger network expansion, the limitations of the star network on the transmission distance and the limit on the number of connected users of the bus network are also solved. This network topology combines the advantages of a star network and a bus network, and makes up for its shortcomings.