Network interconnection is to connect two or more independent autonomous, homogeneous or heterogeneous computer networks to realize data flow, expand the scope of resource sharing, or accommodate more users. Network interconnection includes LAN to LAN interconnection, LAN to wan interconnection, WAN to wan interconnection, which can expand the scope of resource sharing, so that more resources can be shared by more users.
1 Network interconnection device
In the network interconnection, the nodes can not be simply connected directly, but need to be realized through an intermediate device. According to OSI/RM layering principle, this intermediate device should realize the protocol conversion function between different networks and be classified according to the different protocol layer they work on. Network interconnection devices include repeater (to achieve the physical layer protocol conversion, To convert binary signals between cables), Bridges (to convert physical layer and data link layer protocols), routers (to convert network layer protocols to the following layers), gateways (to convert protocols from the lowest layer to the transport layer or above) and switches, etc. In practical applications, the equipment provided by various manufacturers is multi-functional combination and downward compatible. Table 1 is a summary of the above devices.
| Connected devices | Work level | The main function |
|---|---|---|
| repeater | The physical layer | The regeneration and transmission of received signals only extends the transmission distance, is transparent to high-level protocols, and can be used in a limited number (for example, only four in Ethernet). |
| A hub | The physical layer | Multi-port repeater. |
| The network card | Data link layer | That is, the Network Interface Card, NIC (Network Interface Card), NIC and driver have realized the basic functions of the Network protocol. They are responsible for sending and receiving signals and realizing the related functions at the frame level. |
| The bridge | Data link layer | Forwarding requests between networks according to the physical address of frames can reduce network traffic and improve efficiency. Only networks at the same MAC layer can be connected. |
| Layer 2 switch | Data link layer | A traditional switch, multi-port bridge. |
| The router | The network layer | Heterogeneous networks can be interconnected by forwarding information between networks using logical addresses. Only subnets that use the same network layer protocol can be connected. |
| Layer 3 switch | The network layer | Layer 2 switch with routing function. |
| The gateway | Upper floors (4th ~ 7th floors) | The most complex network interconnection device, used to connect subnets above the network layer that execute different protocols. |
| Multilayer exchange | Upper floors (4th ~ 7th floors) | Switch with protocol conversion. |
With the increasingly extensive application of wireless technology, there are many products based on wireless network in the market at present, including wireless network card, wireless AP, wireless bridge and wireless router.
2 Switching Technology
In the computer network, when there are more users and the transmission distance is far, usually do not use two fixed connection of the special line, but the use of switching technology, so that the communication transmission line for each user public, in order to improve the utilization rate of transmission equipment, reduce the system cost.
According to the actual data transmission technology, switching technology can be divided into circuit switching, message switching and packet switching. Their main characteristics are as follows:
(1) Circuit switching
A path must be set up before data can be transmitted. Until the line is released, the channel is exclusive to a pair of users.
(2) Message exchange
Packets are transmitted from the source point to the destination in store-and-forward mode, occupying only one channel at a time. In switching nodes, buffer storage is required and packets need to be queued. Therefore, message switching cannot meet the requirements of real-time communication.
(3) Packet switching
The switching mode is similar to the packet switching mode, but packets are divided into packets and the maximum packet length is specified. In datagram packet switching, the destination needs to reassemble the message; In virtual circuit packet switching, a virtual circuit must be set up through a virtual call before data is transmitted. Packet switching is the most widely used switching technology in data networks.
According to their own characteristics, different switching technology is suitable for different occasions. For example, for interactive communication, message switching is definitely not suitable; Circuit switching is most suitable for lighter and intermittent loads, so communication can be carried out by telephone dial lines; For heavy or persistent loads, the use of leased lines for circuit-switched communication is appropriate; Packet switching is used when medium data must be exchanged to a large amount of data.
3 Routing Technology
Router is an important network interconnection device working at the network layer, which constitutes the main vein of the Internet based on TCP/ IP protocol. The router working on the Internet is also called IP gateway.
The main function of a router is to select routes. When a computer in one network wants to send a packet to a computer in another network, it first sends the packet to a router in the same network for network connection. The router selects an appropriate route according to the destination address information and forwards the packet to a router in the destination network for network connection. The packet is then delivered to the destination computer through a routing protocol used internally on the destination network.
3.1 Application scope
According to the application range of routing Protocol, it can be divided into Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (Exterior Gateway Protocol). EGP and Gateway Gateway Protocol (GGP).
(1) Internal gateway protocol
An internal gateway Protocol is a Routing Protocol running in an Autonomous System (AS), including Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF) and Interior Gateway Routing Protocol (IGRP) Internal gateway routing protocol) and EIGRP (Enhanced IGRP). AS refers to the interconnection network connected to gateways of the same configuration and is usually controlled by a network management center.
(2) External gateway protocol
An external Gateway Protocol is a routing Protocol used between two ass. The latest EGP includes the Border Gateway Protocol (BGP), which controls routing policies.
(3) Core gateway protocol
There is a backbone network in the Internet. All ass are connected to the backbone network. The gateways in the backbone network are called core gateways, and GGP is used to exchange routing information between core gateways.
3.2 Algorithm Differentiation
Routing protocols can be classified into the following three categories:
(1) Distance vector protocol
The vector and distance of all links in the network are calculated, and the optimal path is determined based on this. This protocol periodically sends all or part of the routing table to neighboring routers.
(2) Link state protocol
The topology database created for each router is used to create routing tables, which are formed by calculating shortest paths. This protocol periodically sends network link status information to neighboring routers.
(3) Balanced protocol
The advantages of distance vector protocol and link state protocol are combined.
Multiplexing technology
Multiplexing technology can combine multiple signals and transmit them in a physical channel, which can greatly save the cost of cable installation and maintenance when transmitting over a long distance. Multiplexing technology can be divided into frequency division multiplexing (FrequencyDivisionMultiplexing, FDM) time division multiplex (TimeDivisionMultiplexing, TDM) two kinds.
FDM is divided into channels according to the frequency spectrum, and signals of multiple subgrade bands are modulated on different frequency spectrums. So they do not overlap in the spectrum, that is, they are orthogonal in frequency, but they overlap in time and can be transmitted simultaneously in one channel. The advantage of FDM is that the channel multiplexing rate is high, the number of multiplexing channels is allowed, and the shunt is also very convenient. Therefore, FDM has become one of the most important multiplexing methods in modern analog communication and has been widely used in analog telemetry, cable communication, microwave relay communication and satellite communication.
TDM divides a physical channel into several time slices and allocates them to multiple signals in turn. Each time slice is occupied by one signal reused, unlike FDM, which sends multiple signals at the same time. In this way, multiple digital signals can be transmitted over a physical channel, using the crossing of each signal in time. TDM is not limited to transmitting digital signals, but can also cross transmit analog signals simultaneously.
For analog signals, time division multiplexing and frequency division multiplexing can sometimes be used in combination. A transmission system can be divided into many sliver channels, and each sliver channel is subdivided by time division multiplexing. This hybrid technology can be used in broadband local area networks.
5 Transmission medium
Transmission medium refers to the carrier that transmits information in the network. The commonly used transmission medium is divided into wired transmission medium and wireless transmission medium.
Wireless transmission media refers to the technology of transmitting through space between two communication devices without using any physical connection. Wireless transmission media mainly include microwave, infrared and laser. They all have poor anti-interference; Wired transmission media refers to the physical connection between two communication devices, which can transmit signals from one party to the other. Wired transmission media mainly include twLST-pair, coaxial cable, and optical fiber.
The following are common Ethernet media types:
