1. Hub:
It has basically been eliminated (replaced by a switch). The main function of the hub is to regenerate, reshape, and amplify the received signal to expand the transmission distance of the network while concentrating all nodes on the node centered on it. It works on the first layer of the OSI (Open System Interconnection Reference Model) reference model, the "physical layer".
2. Switch:
Work at the data link layer. The switch has a high-bandwidth back bus and internal switching matrix. All ports of the switch are connected to this back bus. After the control circuit receives the data packet, the processing port will look up the address comparison table in the memory to determine the destination MAC (hardware address of the network card) and the NIC (network card) connection On which port, the data packet is quickly transmitted to the destination port through the internal switching matrix. If the destination MAC does not exist, it will be broadcast to all ports. After receiving the port response, the switch will "learn" the new address and add it to the internal MAC Address table. The switch can also be used to "segment" the network. By comparing the MAC address table, the switch allows only necessary network traffic to pass through the switch. Through the filtering and forwarding of the switch, the collision domain can be effectively reduced, but it cannot divide the network layer broadcast, that is, the broadcast domain. The switch can transmit data between multiple port pairs at the same time. Each port can be regarded as an independent network segment, and the network equipment connected to it enjoys the full bandwidth independently, without competing for use with other equipment. When node A sends data to node D, node B can send data to node C at the same time, and both transmissions enjoy the full bandwidth of the network and both have their own virtual connections. If a 10Mbps Ethernet switch is used here, then the total circulation of the switch at this time is equal to 2×10Mbps=20Mbps, and when a 10Mbps shared HUB is used, the total circulation of a HUB will not exceed 10Mbps. In short, a switch is a network device based on MAC address recognition and capable of encapsulating and forwarding data packets. The switch can "learn" the MAC address and store it in the internal address table. By establishing a temporary switching path between the originator and the target receiver of the data frame, the data frame can directly reach the destination address from the source address.
The main functions of the switch include physical addressing, network topology, error checking, frame sequence and flow control. At present, the switch also has some new functions, such as support for VLAN (virtual local area network), support for link aggregation, and some even have the function of a firewall. Specifically as follows:
Learning: The Ethernet switch understands the MAC address of the device connected to each port, and maps the address to the corresponding port and stores it in the MAC address table in the switch cache.
Forwarding/Filtering: When the destination address of a data frame is mapped in the MAC address table, it is forwarded to the port connected to the destination node instead of all ports (if the data frame is a broadcast/multicast frame, it is forwarded to all ports) .
Elimination of loops: When the switch includes a redundant loop, the Ethernet switch avoids loops through the spanning tree protocol, while allowing the existence of backup paths.
In addition to being able to connect to the same type of network, the switch can also interconnect different types of networks (such as Ethernet and Fast Ethernet). Nowadays, many switches can provide high-speed connection ports that support Fast Ethernet or FDDI, etc., which are used to connect to other switches in the network or provide additional bandwidth for key servers that take up a lot of bandwidth. Generally speaking, each port of the switch is used to connect to an independent network segment, but sometimes in order to provide faster access speed, we can connect some important network computers directly to the port of the switch. In this way, key servers and important users of the network have faster access speeds and support greater information flow.
Finally, briefly summarize the basic functions of the switch:
1. Like a hub, the switch provides a large number of ports for cable connection, so you can use star topology wiring.
2. Like repeaters, hubs, and bridges, when it forwards frames, the switch regenerates an undistorted square electrical signal.
3. Like a bridge, the switch uses the same forwarding or filtering logic on each port.
4. Like a bridge, the switch divides the LAN into multiple collision domains, and each collision domain has an independent broadband, thus greatly improving the bandwidth of the LAN.
5. In addition to the functions of a bridge, hub, and repeater, the switch also provides more advanced features, such as virtual local area network (VLAN) and higher performance.
At present, Ethernet switch manufacturers have introduced three-layer or even four-layer switches according to market demand. But in any case, its core function is still Layer 2 Ethernet packet switching.
The transmission mode of the switch is full-duplex, half-duplex, and self-adaptation. The so-called half-duplex means that only one action takes place in a period of time. For a simple example, a narrow road can only be passed by one car at the same time. When there are two cars driving in opposite directions, in this case, it can only be One vehicle will pass first, and then the other vehicle will drive after the end. This example vividly illustrates the principle of half-duplex. The full duplex of the switch means that the switch can also receive data while sending data, and the two are synchronized. This is like we usually make a phone call, and we can hear the other party's voice while talking.
Knowledge expansion*: the difference between Layer 2 switches, Layer 3 switches and Layer 4 switches
1. Layer 2 switching
The development of the two-layer switching technology is relatively mature. The two-layer switch is a data link layer device. It can identify the MAC address information in the data packet, forward it according to the MAC address, and record these MAC addresses and corresponding ports in one of its own internal Address table.
The specific workflow is as follows:
1) When the switch receives a data packet from a certain port, it first reads the source MAC address in the packet header, so that it knows which port the machine with the source MAC address is connected to
2) Read the destination MAC address in the header, and look up the corresponding port in the address table
3) If there is a port corresponding to the destination MAC address in the table, copy the data packet directly to this port
4) If the corresponding port is not found in the table, the data packet will be broadcast to all ports. When the destination machine responds to the source machine, the switch can record which port the destination MAC address corresponds to, and it will be used when the data is transmitted next time. It is no longer necessary to broadcast to all ports. This process is repeated continuously, and the MAC address information of the entire network can be learned. This is how the Layer 2 switch establishes and maintains its own address table.
From the working principle of the Layer 2 switch, the following three points can be inferred:
1) Since the switch exchanges data on most ports at the same time, it requires a wide switching bus bandwidth. If the two-layer switch has N ports, the bandwidth of each port is M, and the switch bus bandwidth exceeds N×M, then This switch can realize wire-speed switching
2) Learn the MAC address of the machine connected to the port, write it into the address table, and the size of the address table (generally in two ways: one is BEFFER RAM, the other is the value of the MAC table entry), the size of the address table affects the access capacity of the switch
3) Another is that Layer 2 switches generally contain ASIC (Application Specific Integrated Circuit) chips specially used to process data packet forwarding, so the forwarding speed can be very fast. As each manufacturer uses different ASICs, it directly affects product performance.
The above three points are also the main technical parameters for judging the performance of Layer 2 and Layer 3 switches. Please pay attention to comparison when considering equipment selection.
2. Three-layer exchange
Let's first take a look at the working process of the three-layer switch through a simple network.
IP-based equipment A------------------------Layer 3 switch------------------ ------ Device B using IP For example, A wants to send data to B, and the destination IP is known, then A uses the subnet mask to obtain the network address to determine whether the destination IP is in the same network segment as itself. If you are on the same network segment, but don’t know the MAC address required to forward the data, A sends an ARP request, B returns its MAC address, A uses this MAC to encapsulate the data packet and sends it to the switch, and the switch uses the Layer 2 switching module to find MAC address table, forward the data packet to the corresponding port.
If the destination IP address is not in the same network segment, then A needs to communicate with B. If there is no corresponding MAC address entry in the flow cache entry, the first normal data packet will be sent to a default gateway, this default gateway Generally, it has been set in the operating system. The IP of this default gateway corresponds to the third layer routing module. Therefore, for data that is not in the same subnet, the MAC address of the default gateway is first placed in the MAC table (by the source host). A completes); Then the three-layer module receives the data packet, and queries the routing table to determine the route to B. A new frame header will be constructed, where the MAC address of the default gateway is the source MAC address, and the host B is The MAC address is the destination MAC address. Through a certain recognition trigger mechanism, establish the corresponding relationship between the MAC addresses and forwarding ports of host A and B, and record it into the flow cache entry table, and the subsequent data from A to B (the layer three switch must confirm that it is from A to B instead of For the data to C, the IP address in the frame must be read.), it is directly handed over to the Layer 2 switching module for completion. This is usually referred to as one route and multiple forwarding. The above is a brief summary of the working process of the three-layer switch, you can see the characteristics of the three-layer switch:
1) High-speed data forwarding is realized by the combination of hardware. This is not a simple superposition of Layer 2 switches and routers. Layer 3 routing modules are directly superimposed on the high-speed backplane bus of Layer 2 switching, breaking through the interface rate limit of traditional routers, and the rate can reach dozens of Gbit/s. Counting the backplane bandwidth, these are two important parameters for the performance of the Layer 3 switch.
2) The concise routing software simplifies the routing process. Most of the data forwarding, except for the necessary routing, is handled by the routing software, and it is forwarded by the Layer 2 module at a high speed. Most of the routing software is processed and optimized software, not simply copying the software in the router.
Choice of Layer 2 and Layer 3 Switches
Layer 2 switches are used in small local area networks. Needless to say, in a small local area network, broadcast packets have little effect. The fast switching function, multiple access ports and low cost of the two-layer switch provide a very complete solution for small network users.
The advantage of the three-layer switch lies in the rich interface types, the supported three-layer functions, and the powerful routing ability. It is suitable for routing between large-scale networks. Its advantage lies in the selection of the best route, load sharing, link backup and other networks. Perform routing information exchange and other functions that routers have.
The most important function of the three-layer switch is to speed up the fast forwarding of data within a large local area network. The addition of the routing function also serves this purpose. If a large-scale network is divided into small LANs according to departments, regions and other factors, this will lead to a large number of inter-internet visits, and the simple use of Layer 2 switches cannot achieve inter-internet visits; such as the simple use of routers, due to the limited number of interfaces and The routing and forwarding speed is slow, which will limit the network speed and network scale. The use of a fast forwarding three-layer switch with routing function becomes the first choice.
Generally speaking, in a network with large intranet data traffic and fast forwarding and response, if all the three-layer switches do this work, the three-layer switches will be overloaded, the response speed will be affected, and the routing between the networks will be overwhelmed. It is a good networking strategy to make full use of the advantages of different devices by routers. Of course, the premise is that the customer's pockets are very strong, otherwise, the second step is to let the three-layer switch also serve as the Internet interconnection.
3. Four-layer exchange
A simple definition of Layer 4 switching is: it is a function that determines transmission not only based on MAC address (Layer 2 bridge) or source/destination IP address (Layer 3 routing), but also based on TCP/UDP ( Fourth layer) Application port number. The fourth layer switching function is like a virtual IP, pointing to a physical server. It transmits services subject to various protocols, including HTTP, FTP, NFS, Telnet or other protocols. These services require complex load balancing algorithms based on physical servers.
In the IP world, the service type is determined by the terminal TCP or UDP port address, and the application interval in the fourth layer exchange is determined by the source and terminal IP addresses, TCP and UDP ports. In the fourth layer of exchange, a virtual IP address (VIP) is set up for each server group for searching, and each group of servers supports a certain application. Each application server address stored in the domain name server (DNS) is a VIP, not a real server address. When a user applies for an application, a VIP connection request (such as a TCP SYN packet) with a target server group is sent to the server switch. The server switch selects the best server in the group, replaces the VIP in the terminal address with the IP of the actual server, and transmits the connection request to the server. In this way, all packets in the same section are mapped by the server switch and transmitted between the user and the same server.
The principle of the fourth layer of exchange
The fourth layer of the OSI model is the transport layer. The transport layer is responsible for end-to-end communication, that is, coordinated communication between network source and target systems. In the IP protocol stack, this is the protocol layer where TCP (a transmission protocol) and UDP (user data packet protocol) are located. In the fourth layer, TCP and UDP headers contain port numbers, which can uniquely distinguish which application protocols (such as HTTP, FTP, etc.) each data packet contains. The endpoint system uses this information to distinguish the data in the packet, especially the port number so that a receiving end computer system can determine the type of IP packet it receives and hand it over to the appropriate high-level software. The combination of port number and device IP address is usually called "socket". Port numbers between 1 and 255 are reserved, and they are called "familiar" ports, that is to say, these port numbers are the same in all host TCP/IP protocol stack implementations. In addition to "familiar" ports, standard UNIX services are allocated in the range of 256 to 1024 ports, and custom applications generally allocate port numbers above 1024. The most recent list of assigned port numbers can be found in RFC1700 "Asfound on "signed Numbers".
The additional information provided by the TCP/UDP port number can be used by the network switch, which is the basis of the fourth layer of exchange. The switch with the fourth layer function can play the role of the "virtual IP" (VIP) front end connected to the server. Each server and server group supporting a single or general application is configured with a VIP address. This VIP address is sent out and registered on the domain name system. When sending a service request, the fourth layer switch recognizes the beginning of a session by determining the start of TCP. It then uses complex algorithms to determine the best server to handle this request. Once this decision is made, the switch associates the session with a specific IP address and replaces the VIP address on the server with the real IP address of the server.
Each Layer 4 switch keeps a connection table associated with the source IP address and source TCP port of the selected server. Then the fourth layer switch forwards the connection request to this server. All subsequent packets are re-mapped and forwarded between the client and the server until the switch discovers the conversation. In the case of using the fourth layer of switching, access can be connected with real servers to meet user-defined rules, such as having an equal number of accesses on each server or allocating transmission streams according to the capacity of different servers.
Currently, in the Internet, nearly 80% of routers come from Cisco. Cisco's switch products are under the trademark "Catalyst". Contains more than ten series such as 1900, 2800...6000, 8500, etc. In general, these switches can be divided into two categories:
One type is fixed configuration switches, including most models of 3500 and below, except for limited software upgrades, these switches cannot be expanded; the other type is modular switches, mainly referring to models of 4000 and above. Network designers can According to network requirements, choose different numbers and models of interface boards, power modules, and corresponding software.
Router:
Router (Router) is the main node equipment of the Internet. The router determines the forwarding of data through routing. The forwarding strategy is called routing, which is also the origin of the router name (router, forwarder). As a hub for interconnecting different networks, the router system constitutes the main context of the Internet based on TCP/IP. It can also be said that routers constitute the backbone of the Internet. Its processing speed is one of the main bottlenecks of network communication, and its reliability directly affects the quality of network interconnection. Therefore, in campus networks, regional networks, and even the entire Internet research field, router technology has always been at the core, and its development process and direction have become a microcosm of the entire Internet research.
Router (Router) is used to connect multiple logically separated networks. The so-called logical network represents a single network or a subnet. When data is transmitted from one subnet to another, it can be done through a router. Therefore, the router has the function of judging the network address and selecting the path. It can establish flexible connections in a multi-network interconnection environment. It can connect various subnets with completely different data packets and media access methods. The router only accepts the source station or other The information of the router is a kind of interconnection equipment at the network layer.
Examples of working principles
(1) Workstation A sends the address 12.0.0.5 of workstation B along with data information to router 1 in the form of data frames.
(2) After router 1 receives the data frame of workstation A, it first takes out the address 12.0.0.5 from the header, and calculates the best path to workstation B according to the path table: R1->R2->R5->B; and Send the data packet to router 2.
(3) Router 2 repeats the work of Router 1 and forwards the data packet to Router 5.
(4) Router 5 also takes out the destination address and finds that 12.0.0.5 is on the network segment connected to the router, so the data packet is directly delivered to workstation B.
(5) Workstation B receives the data frame from Workstation A, and the communication process ends.
In fact, in addition to the above-mentioned main function of routing, the router also has a network flow control function. Some routers only support a single protocol, but most routers can support the transmission of multiple protocols, that is, multi-protocol routers. Since each protocol has its own rules, it is bound to reduce the performance of the router to complete the algorithms of multiple protocols in a router. Therefore, we believe that the performance of routers that support multiple protocols is relatively low.
One function of the router is to connect different networks, and the other function is to select the route of information transmission. Choosing an unobstructed and quick shortcut can greatly increase the communication speed, reduce the communication load of the network system, save network system resources, and increase the unblocking rate of the network system, so that the network system can exert greater benefits.
From the perspective of filtering network traffic, the role of routers is very similar to that of switches and bridges. But unlike switches that work at the physical layer of the network and physically divide network segments, routers use special software protocols to logically divide the entire network. For example, a router that supports the IP protocol can divide the network into multiple subnet segments, and only network traffic directed to a special IP address can pass through the router. For each received data packet, the router will recalculate its check value and write a new physical address. Therefore, the speed of using a router to forward and filter data is often slower than that of a switch that only looks at the physical address of the data packet. However, for those complex networks, the use of routers can improve the overall efficiency of the network. Another obvious advantage of routers is that they can automatically filter network broadcasts.
The main job of the router is to find an optimal transmission path for each data frame passing through the router, and to effectively transmit the data to the destination site. It can be seen that the strategy of selecting the best path, that is, the routing algorithm, is the key to the router. In order to complete this work, the relevant data of various transmission paths—Routing Table—is stored in the router for use in routing selection. The path table stores the subnet identification information, the number of routers on the Internet, and the name of the next router. The path table can be fixedly set by the system administrator, can also be dynamically modified by the system, can be automatically adjusted by the router, or controlled by the host.
1. Static path table
The fixed path table set up by the system administrator in advance is called a static path table, which is generally pre-set according to the network configuration when the system is installed, and it will not change with future network structure changes.
2. Dynamic path table
The dynamic (Dynamic) path table is a path table automatically adjusted by the router according to the operating conditions of the network system. According to the functions provided by the Routing Protocol, the router automatically learns and memorizes the operation of the network, and automatically calculates the best path for data transmission when needed.
Routers can be seen everywhere in various levels of the Internet. The access network allows homes and small businesses to connect to an Internet service provider; the router in the corporate network connects thousands of computers in a campus or enterprise; the router terminal system on the backbone network is usually not directly accessible, they Connect the ISP and enterprise network on the long-distance backbone network.
Broadband router
Broadband router is an emerging network product in recent years, which came into being with the popularization of broadband. Broadband routers integrate functions such as routers, firewalls, bandwidth control and management in a compact box, with fast forwarding capabilities, flexible network management, and rich network status. Most broadband routers are optimized for China's broadband applications, can meet different network traffic environments, and have good grid adaptability and network compatibility. Most broadband routers adopt a highly integrated design, integrated 10/100Mbps broadband Ethernet WAN interface, and built-in multi-port 10/100Mbps adaptive switch, which is convenient for multiple machines to connect to the internal network and the Internet. It can be widely used in homes, schools, offices, and Internet cafes. , Community access, government, enterprise and other occasions.
MODEM
Modem, that is, modem: a general term for modulator and demodulator. A conversion interface that enables digital data to be transmitted on the analog signal transmission line. The so-called modulation is to convert a digital signal into an analog signal transmitted on a telephone line; demodulation is to convert an analog signal into a digital signal. Collectively referred to as a modem.
Common modems now include ordinary dial-up modems, baseband modems and optical fiber modems.
Extended knowledge*:
"Baseband Modem", also known as short-range modem, is a device that connects computers, network bridges, routers and other digital communication equipment within a relatively short distance, such as buildings, campuses, or cities. Baseband transmission is an important data transmission method. The role of baseband MODEM is to form appropriate waveforms so that when data signals pass through a transmission medium with limited bandwidth, there will be no inter-symbol interference due to overlapping waveforms. It is opposite to the frequency band modem. The frequency band modem uses the frequency band in a given line (such as the frequency band occupied by one or more phones) for data transmission. Its application range is much wider than the baseband, and the transmission distance is also longer than the baseband. . The 56K Modem that our family uses every day is the frequency band Modem.
The more accurate name of the baseband modem is CSU/DSU (chanel service unit/date service unit). It has two ports. The analog port is connected to a high-quality twisted pair cable. The two csu/dsu are connected, and the other digital port and two Digital interface connection at the end. It is used to connect to the DDN dedicated line. The compatibility of baseband modems is poor, so it is best to use equipment from the same manufacturer. The baseband cat is used in the digital circuit, our ordinary modem is analog-to-digital conversion, and the baseband cat is the digital-to-digital conversion. So the baseband cat is not a real MODEM.
NAT
NAT, or Network Address Translation, belongs to the access wide area network (WAN) technology. It is a translation technology that converts private (reserved) addresses into legal IP addresses. It is widely used in various types of Internet access. Ways and various types of networks. The reason is simple. NAT not only perfectly solves the problem of insufficient IP addresses, but also effectively avoids attacks from outside the network, hiding and protecting computers inside the network.
Related case: Using address translation to achieve load balancing
Case description: With the increase in access volume, when one server is difficult to perform, load balancing technology must be adopted to reasonably distribute a large number of accesses to multiple servers. Of course, there are many ways to achieve load balancing, such as server cluster load balancing, switch load balancing, DNS resolution load balancing, and so on.
In fact, in addition to this, it is also possible to implement server load balancing through address translation. In fact, most of these load balancing implementations are implemented by polling, so that each server has an equal opportunity to be accessed
Network environment: The local area network is pulled into the Internet with a 2Mb/s DDN dedicated line, and the router uses the Cisco 2611 with the WAN module installed. The IP address range used by the internal network is 10.1.1.1~10.1.3.254, the IP address of the LAN port Ethernet 0 is 10.1.1.1, and the subnet mask is 255.255.252.0. The legal IP address range allocated by the network is 202.110.198.80~202.110.198.87, the IP address of the port Ethernet 1 connected to the ISP is 202.110.198.81, and the subnet mask is 255.255.255.248. It is required that all computers inside the network can access the Internet, and load balancing is achieved on 3 Web servers and 2 FTP servers.
Case study: Since all computers in the network are required to be able to access the Internet, and there are only 5 legal IP addresses available, of course, the port multiplexing address conversion method can be used. Originally, the server can be given a legal IP address by using static address translation. However, due to the high amount of server visits (or poor server performance), multiple servers have to be used for load balancing. Therefore, a legal IP address must be converted into a multi-phase internal IP address, which is reduced by polling. The access pressure of each server.
Configuration file:
interface fastethernet0/1
ip adderss 10.1.1.1 255.255.252.0 //Define the IP address of the LAN port
duplex auto
speed auto
ip nat inside //defined as a local port
The difference between Ethernet and ATM network
1. Ethernet
Ethernet is the most common communication protocol standard adopted by existing local area networks today, and was established in the early 1970s. Ethernet is a common local area network (LAN) standard with a transmission rate of 10 Mbps. In Ethernet, all computers are connected to a coaxial cable, and the carrier-sensing multiple access (CSMA/CD) method with collision detection is adopted, and the competition mechanism and bus topology are adopted. Basically, Ethernet consists of a shared transmission medium, such as twisted-pair cable or coaxial cable and multi-port hubs, bridges or Switch composition. In a star or bus configuration, the hub/switch/bridge connects computers, printers, and workstations to each other through cables.
The general characteristics of Ethernet are summarized as follows:
Shared media: All network devices use the same communication media in turn.
Broadcast domain: The frame that needs to be transmitted is sent to all nodes, but only the addressed node will receive the frame.
CSMA/CD: Carrier Sense Multiple Access/Collision Detection is used in Ethernet to prevent twp or more nodes from sending at the same time.
MAC address: All Ethernet network interface cards (NICs) in the media access control layer use 48-bit network addresses. This kind of address is unique in the world.
2.ATM
ATM, namely asynchronous transfer mode, is a data transmission technology. It is suitable for local area networks and wide area networks, has high-speed data transmission rates and supports many types of communications such as voice, data, fax, real-time video, CD quality audio and image.
Through ATM technology, the local area network interconnection between the corporate headquarters and various offices and company branches can be completed, so as to realize the company's internal data transmission, corporate mail service, voice service, etc., and realize e-commerce and other applications through the Internet. At the same time, because ATM uses statistical multiplexing technology, and the access bandwidth breaks through the original 2M, reaching 2M-155M, it is suitable for applications such as high bandwidth, low latency or high data bursts.
Judging from the current situation, Gigabit Ethernet has blocked the development of ATM, and ATM technology is already in the dark. "ATM market share now only accounts for 10%, and most of them are still in the telecommunications sector."
What is broadband?
Although the term "broadband" appears frequently in major media, it has been rarely seen to define it accurately. In layman's terms, broadband is relative to traditional dial-up Internet access. Although there is currently no unified standard for how much broadband bandwidth should be reached, based on popular habits and network multimedia data traffic considerations, the network data transmission rate should be at least 256Kbps to be called. Broadband, its biggest advantage is that the bandwidth far exceeds 56Kbps dial-up Internet access.
PPPoE
PPPoE is short for point-to-point protocol over ethernet (point-to-point connection protocol), which allows an Ethernet host to connect to a remote access concentrator through a simple bridging device. Through the pppoe protocol, the remote access device can realize the control and charging of each access user.
Common network access methods today
1. Ordinary dial-up mode, dial-up Internet access is by telephone, calculated by the minute, the highest rate is 56K. Required equipment: ordinary dial-up Modem. (Almost eliminated)
2. N-ISDN, "Narrowband Integrated Services Digital Network", commonly known as "One Line". It is developed on the basis of a telephone line, and can provide comprehensive services such as voice, data, and image on an ordinary telephone line, with a maximum speed of 128K. (Basically eliminated)
3. Cable Modem HFC access scheme
Cable Modem is a device that can access high-speed data through a cable TV network, commonly known as "Radio and Diantong" or "Wired Communication". Among them, the "HFC+Cable Modem+Ethernet/ATM" approach can be used to provide Internet access services. The central office needs to be equipped with an HFC head-end device, which is interconnected with the Internet through ATM or Fast Ethernet, and completes signal modulation and mixing functions. The data signal is transmitted to the user's home through the optical fiber coaxial hybrid network (HFC), and the Cable Modem completes the signal decoding, demodulation and other functions, and transmits the digital signal to the PC through the Ethernet port. Compared with ADSL, its bandwidth is relatively high (10M).
At present, there are not many cities in China that have opened cable communication, mainly in large cities such as Shanghai and Guangzhou. Although the theoretical transmission rate is very high, a cell or a building usually only opens 10Mbps bandwidth, which is also a shared bandwidth. The biggest advantage is that there is no need to dial up, and it will always be online when it is turned on.
4. ADSL (Asymmetric Digital Subscriber Loop) broadband technology
ADSL technology is a new high-speed broadband technology that runs on the original ordinary telephone line. It uses the existing pair of telephone copper wires to provide users with asymmetrical transmission rate (bandwidth) for the uplink and downlink. The asymmetry is mainly reflected in the asymmetry between the uplink rate (up to 640Kbps) and the downlink rate (up to 8Mdps). Local telecommunications bureaus often use some nice names when promoting ADSL, such as "Super One Line" and "Internet Express". In fact, these all refer to the same broadband method.
Required equipment: To install ADSL on the existing telephone line, you only need to install an ADSL MODEM and a splitter on the user side, and the user line does not need to be modified, which is extremely convenient.
Single user connection: the telephone line is connected to the splitter, the splitter is then connected to the ADSL MODEM and the phone, and the PC is connected to the ADSL MODEM.
Multi-user connection: PC-Ethernet (HUB or Switch)-ADSL router-splitter, that is to say, an ADSL router is needed. If there are too many users, a switch is also needed.
Knowledge expansion: DSL (Digital Subscriber Line) technology is a broadband access technology based on ordinary telephone lines. DSL includes ADSL, RADSL, HDSL, VDSL and so on. VDSL (Very-high-bit-rate Digital Subscriber loop) is a high-speed digital subscriber loop. Simply put, VDSL is a fast version of ADSL.
5. Residential broadband (FTTX+LAN, that is, "fiber access + LAN")
This is currently a popular broadband access method in large and medium-sized cities. Network service providers use optical fiber to connect to the building (FTTB) or community (FTTZ), and then connect to the user’s home through a network cable to provide sharing for the entire building or community. Bandwidth (usually 10Mb/s). At present, many domestic companies provide such broadband access methods, such as Netcom, Great Wall Broadband, China Unicom, and China Telecom.
This access method has the lowest requirements for user equipment, and only needs a computer with a 10/100Mbps adaptive network card.
At present, most of the residential broadband is 10Mbps shared bandwidth, which means that if there are more users going online at the same time, the network speed will be slower. Even so, the average download speed in most cases is still much higher than the telecom ADSL, reaching several hundred KB/s, which has a greater advantage in speed.
6. Other access methods
Other access methods include: Optical Access Network (OAN), unlimited access network, high-speed Ethernet, 10Base-S solution, etc.
Fiber access mode (fiber is a fixed IP, no cat):
(1) Optical fiber —> Photoelectric converter —> Layer 3 switch (After the photoelectric is converted to RJ-45 interface, you can directly connect it to the switch, and then set the default route in the switch, you can go online.)
(2) Optical transceiver (optical modem)-----firewall-----router-----switch-----PC (10 sets).
(3) The form of the community: (optical fiber -> photoelectric converter -> proxy server) -> PC ADSL / VDSL PPPoE: run third-party dial-up software such as Enternet300 or WinXP on the computer, and fill in the dial-up program provided by the ISP Account and password, you must dial each time before going online.
Commonly used Internet access methods are 3, 4, and 5 above, the comparison in actual selection:
Generally speaking, as long as the user has a phone at home, ADSL can basically be opened (provided that the local telecommunications has provided this service), while the broadband and cable communication of the community depends on the specific area, and can be inquired in advance.
The first type of users are very concerned about the network download speed, and the community broadband or cable communication should be considered first. The download speed of ADSL is absolutely a terrible nightmare for them; the second type of users value the stability of broadband services, while the download speed is Take the second place (512Kbps ADSL speed can fully meet the bandwidth requirements of online games). In this regard, Telecom ADSL has a unique advantage, because many online game servers are provided by Telecom to ensure stability. The third type of users can comprehensively consider the price and installation convenience according to the actual local conditions. First consider installing residential broadband or cable communication, if not, you can only install ADSL. The fourth type of users need a stable public IP address, and they need to understand the actual situation of various local broadband services before installation. Generally speaking, telecommunications ADSL uses public network IP, but the PPPoE dial-up method is dynamic IP. At this time, you can consider choosing a static IP address to access the service or borrowing software to bind the IP address. Residential broadband and wired communication mostly use intranet IP, which is not suitable for this type of users (except for residential broadband in some areas, users need to learn more about the local network service provider).
Feel the broadband service in the domestic big city Shanghai: ADSL, residential broadband and cable communication three mainstream broadband access methods have been put into use in Shanghai on a large scale, and the service providers involved include Shanghai Telecom, Great Wall Broadband, Cable Communication and Netcom.
Wireless AP and wireless router
Unlimited AP: Simple AP has relatively simple functions, lacks routing function, and can only be equivalent to a wireless hub; for this type of wireless AP, no products that can be interconnected have been found! The extended AP is also a wireless router on the market. Because of its comprehensive functions, most extended APs not only have routing and switching functions, but also DHCP, network firewalls and other functions.
Wireless router: A wireless router is a combination of a simple AP and a broadband router; with the help of the router function, it can realize the Internet connection sharing in the home wireless network, and realize the wireless shared access of ADSL and residential broadband. In addition, the wireless router It is possible to assign all terminals that are connected wirelessly and wiredly to a subnet, so that it is very convenient for various devices in the subnet to exchange data.
It can be said that the wireless router is a collection of AP (Access Point, wireless access node), routing function and switch. It supports wired and wireless to form the same subnet and is directly connected to the MODEM. A wireless AP is equivalent to a wireless switch, connected to a wired switch or router, and assigns an IP from the router for the wireless network card connected to it.
Practical application:
Independent APs are often used in companies that require a large number of APs to cover a large area. All APs are connected via Ethernet and connected to an independent wireless LAN firewall.
Wireless routers are often used in private environments. In this environment, one AP is sufficient. In this case, a wireless router that integrates a broadband access router and an AP provides a single machine solution. Wireless routers generally include a network address translation (NAT) protocol to support network connection sharing among wireless LAN users-this is a very useful feature in a private environment.
AP cannot be directly connected to ADSL MODEM, so you must add a switch or hub when using it: However, most wireless routers have broadband dial-up capabilities, so they can be directly connected to ADSL MODEM for broadband sharing.
The Institute of Electrical and Electronics Engineers (IEEE) formally approved the latest Wi-Fi wireless standard 802.11n on September 14th, 2009. In theory, 802.11n can reach a transmission rate of 300Mbps, which is 6 times that of the 802.11g standard and 30 times that of the 802.11b standard.
3G wireless router: Xiaohei A8 is a MINI-type portable battery-powered WIFI product that converts 3G network signals/wired broadband signals into WIFI signals and shares them with the surrounding WIFI devices. It has excellent performance and is the best for surfing the Internet on iPad tablets. Excellent companion. Xiaohei A8 supports the IEEE 802.11b/g/n protocol, the WiFi LAN rate is up to 150Mbps, and the effective range of its WIFI signal can reach 100M, which can cover an ordinary office building. Xiaohei A10 has a built-in rechargeable battery that can work continuously for 4 hours and has a long battery life. It can support 20 Wi-Fi users online at the same time. It also has strong compatibility and has a built-in HSUPA wireless network card. You only need to purchase a SIM tariff card to go online. At the same time, A8+ also supports home ADSL wired broadband network dial-up access, and office static IP broadband access. Huawei e5: Supports up to 5 Wi-Fi users, suitable for Wi-Fi devices such as PCs, mobile phones, game consoles, and digital cameras.
ADSL virtual dial-up access
ADSL virtual dialing is dialing on the ADSL digital line, which is different from dialing with a modem on an analog telephone line. It uses a special protocol PPP over Ethernet (PPPoE) (PPPoE (Broadband Communication) client software needs to be installed). After dialing, The verification is performed directly by the verification server. The user needs to enter the user name and password. After the verification is passed, a high-speed user number is established and the corresponding dynamic IP is assigned. Virtual dial-up users need to verify their identity through a user account and password. This user account is the same as the 163 account, which is selected by the user when applying, and this account is restricted. It can only be used for ADSL virtual dial-up and cannot be used. Dial in ordinary MODEM.
The broadband access method of ADSL virtual dial-up is currently the mainstream method provided by domestic broadband operators. The ADSL virtual dial-up access that requires a broadband router is mainly an ADSL MODEM with no built-in routing function on the Ethernet interface. If you use this kind of equipment , Please set up the broadband router in the following way: log in to the router management interface, take Kingnet’s broadband router as an example, click the menu "Internet Wizard" under the interface, and then select the "ADSL virtual dial-up" item.
Network card and wireless network card
The network card, also known as the network adapter (adapter), is a network component that works at the data link layer. It is the interface between the computer and the transmission medium in the local area network. It can not only realize the physical connection and electrical signal matching with the transmission medium of the local area network. , It also involves the sending and receiving of frames, the encapsulation and unpacking of frames, media access control, data encoding and decoding, and data caching functions.
Different network interfaces are suitable for different network types. At present, the common interfaces mainly include Ethernet RJ-45 interface, thin coaxial cable BNC interface and thick coaxial electrical AUI interface, FDDI interface, ATM interface, etc. And some network cards provide two or more types of interfaces, if some network cards provide RJ-45 and BNC interfaces at the same time. The RJ-45 interface is the most common type of network card interface, mainly due to the popularity of twisted pair Ethernet.
Wireless network card: Its main working principle is microwave radio frequency technology. According to the IEEE802.11 protocol, the wireless LAN card is divided into a media access control layer and a physical layer. Between the two, a media access control-physical sublayer is also defined. USB wireless network card is currently the most common.
In fact, a wireless network card alone cannot connect to a wireless network. You must also have a wireless router or wireless AP. The wireless network card is like a receiver, and the wireless router is like a transmitter. In fact, it is necessary to connect the wired Internet line to the wireless modem, and then convert the signal into a wireless signal for transmission, which is received by the wireless network card. The general wireless router can drag 2-4 wireless network cards, the working distance is within 50 meters, the effect is better, and the communication quality is very poor if it is far away.
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