What is the fourth layer exchange

What is the fourth layer exchange

Although it is still weighing what it means to the third layer switching, the fourth layer exchange has already sounded the latest in networking notes. The third layer switching is routing, then what is the fourth layer of the exchange?

The fourth layer of OSI model is the transport layer. Transport layer is responsible for end to end communication, that is the source and target systems in the network communication between the co-ordination. In the IP protocol stack is TCP (a transport protocol) and UDP (user datagram protocol) protocol layer is located.

In the fourth layer, TCP and UDP header contains the port number (portnumber), they can be uniquely identified what each packet contains the application protocol (eg HTTP, FTP, etc.). Endpoint system uses this information to distinguish between packets of data, particularly the port number to a receiver computer system before it can determine the IP packet type, and gave it to the appropriate high-level software. IP address port number and device combination often called "jack (socket)".

1 and the port number 255 is reserved, they called the "well known" ports, that is, in all host TCP / IP protocol stack implementation, the port number is the same. In addition to "known" ports, the standard UNIX distribution service port in the 256-1024 range, custom application normally assigned port numbers above 1024. TCP / UDP port number to provide the additional information can be exploited for network switches, which is the basis for the exchange of the fourth floor.

Exchange of the fourth layer and the second layer, the difference between the third layer switching

Second, third and the fourth floors of the exchange in the campus network can have a good application. The second layer switching and network connected users, the guidelines in the subnet traffic, the third layer or the router to packet switching from one subnet to another subnet, the fourth layer of the package reached the terminal server exchange. The fourth tier is the network infrastructure in the exchange of important factors, it makes the server capacity increases with the network bandwidth.

From the operational point of view, the fourth layer exchange is strong, as it ended to package control in places from the source side of the interval. On the other hand, router, or third exchange, only for a single packet for processing, do not know where he comes from a bag, do not know the situation of the next packet. They are just testing the TCP packet header port number, depending on the application to establish priority queue. Routers and network is available under the link packet routing decision nodes. The fourth tier is the performance of the available server and on the basis of first identifying the interval.

The main function of the fourth layer is to increase the exchange of individual servers and groups server reliability and scalability.

If the server could not keep pace, even with the most rapid exchange of the network can not fully ensure that the end of the performance. One can imagine such a high priority of the business QoS-enabled network server in a low priority because of the queue and obstruction of business. In the worse case, the server will even lose the ability to handle business cycle.

Design of the fourth layer on the server that is extended past the purpose of the exchange server and application in the second and third floor exchange performance and business flow management.

Advantage of the fourth layer switching

Exchange of the fourth layer a third layer and fourth layer of information in the packet header information, identifying service flow according to the interval, the business section of the entire range of flow assigned to the appropriate application server for processing.

Each open interval associated with a particular server, for tracking server, the fourth layer switching allows multiple servers to support specific applications, increases linearly with the server's overall performance enhancement. Meanwhile, the fourth layer exchange by reducing the dependence on any particular server, while improving application reliability.

The fourth tier exchange also requires end to end QoS, the second and third tiers to improve the exchange of a QoS packet then a packet transmission capabilities. For example, users from high-level business or important applications to network traffic, can be assigned to the fastest I / O system and CPU, while the ordinary business allocated to the poor performance of the machine.

Brief exchange of the fourth layer

Switching function is like the fourth level virtual IP, point to the physical server. It transfers a wide range of business subject to the agreement, there are HTTP, FTP, NFS, Telnet or other agreement. These business based on the physical server, require complex load balancing algorithm. In the IP world, business type from the TCP or UDP port address of the terminal to determine, in the fourth floor of the exchange zone by the source and the terminal IP address, TCP and UDP port joint decision.

Exchange in the fourth layer for each server group for setting up the search using virtual IP address (VIP), each server supports a specific application. In the domain name server (DNS) for each application server to store address is VIP, but not the real server address.

When a user for application, a group of VIP with the target server connection requests (such as a TCPSYN package) distributed server switch. Server switches in the group select the best server, the terminal address in the VIP IP replaced with the actual server, the server will pass the connection request. In this way, the same interval all packets by the server switches to map between the user and the same server for transmission.







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Shun and up to appeal to the State should be introduced as soon as possible "exception handling comp

There is no doubt that the financial system, the enterprise is very important for high accuracy, does not allow the slightest error, naturally, in the information age, every business relies on the financial software, especially, required software function designed for enterprise development, can increase on demand. Domestic management software market, domestic and foreign firms according to the needs of enterprise customers design and develop a variety of targeted products, especially for more complex needs of SMEs, in order to smooth and up to launch represented by software vendors such as teller systems, warehousing Wang , Wang and other business software, at all levels, especially financial power count highlights the "simple and practical" features.

But with the rapid development of the whole market forward, companies will inevitably be some urgent and exceptional situation, the need for computerization of financial exception handling, but because the relevant departments of the enterprise inventory valuation has made changes to provisions related to: valuation methods have been determined shall not be changed. And volatile in price, the FIFO method will be a "Stock Unit" is zero or negative. Therefore, in actual practice, many users often do not know how to Tiaozhang strain and for exception handling, the inconvenience to the normal development of enterprises.

I learned from the smooth and up to now only a smooth and up and their users to understand, change the pricing method must first apply for the tax department, but specifically how to provide for, is not clear. Then the author has interviewed a number of other vendors and enterprise users, it is learned, they are also faced with the problem. Therefore, the center has always been user-Shun and up, For the removal of this provision is not clear to business users in distress, and has urged the countries to the early introduction of the computerization of financial exception handling on the specific requirements to further protect the corporate finance Computing efficient and perfect, so as to promote overall development.

At the same time, as a provider of software products, the manufacturers should also increase demand for our business development process research and infiltration, to develop more practical products. In particular, to estimate the various business development company, to set aside enough room for expansion to accommodate the business of high-level, diversified development. Taking into account the financial system is the business end-users, frontline operational staff, so special emphasis on simple, user-specific operations should be as simple as possible to learn. In the current business computer applications, management level is not very high case, the "user-oriented" of the highest priority.

This, along and up to chairman Cai Zhongliang said that the software is designed according to business needs, is one of the core, smooth, and up to full line of products currently under research the latest market demands and a brand new smart Gaizao, for users, more peace of mind and convenient. If the authorities can introduce anomalies in financial accounting has become more clear and specific provisions, then the ICC will all aspects of the financial processing are convenient, practical help enterprise development.

In this, I also hope that the relevant state regulations promulgated as soon as possible, improve the computerization of financial development in China, thus clearing the way for the enterprise information, gain the upper hand!







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To license 3G operators should have been five major power

Telecommunications Research Institute of Ministry of Information Industry recently said Chen Yuping, director of communication, if the 3G started building, then there should be three-year transitional period or period of development, so 2G to 3G transition gradually, after two years of gradual expansion in order to start profitable side side of the practice of construction operations should be more reasonable.

Chen Yuping that the operator wants to get any 3G licenses, should have five strengths:

First, the network strength. Have large-scale network operations, currently have this capability is only four, namely China Telecom, China Netcom's PHS system, to the current nearly 60 million users, PHS moved to 3G, has a mature network or more large-scale network operations, to obtain a license for his conduct after the construction of 3G is a good strong point. China Mobile, China Unicom as such, existing network is the mobile network, as long as its upgrades.

Second, the strength needed funds. On the one hand the strength of their investment carriers, on the other hand need financing, how to finance is a problem. The 3G one go to vote, millions of users of the network should be in the tens of billion yuan.

Third, technical strength. In addition to the four major carriers have more operators, maintenance and operation of large capacity, China Satcom, CRC is relatively weak. China Telecom, China Netcom PHS strongly pushed, mainly to the accumulation of experience, accumulated a group of users and network operators, a number of aspects of human resources, to prepare for future transition.

Fourth, business strength. Four operating companies ability to innovate with new business, when to get a license to build 3G network quickly and business.

Fifth, the user strength, mainly refers to the operator and the number of potential users. Four companies have tens of millions or billions of users, the strength of its great potential for development and guarantee.

Chen Yuping said, 3G existing problems: 3G standard version too much, too frequent updates. The final version has been changed, the three standard version of the ITU in a version to out and out a few version of the first half, second half of the several versions out there are frequent, reason is not yet begun operations or small-scale operators found many problems, 3G technology is so far still can not say mature, there are many need to update, modify, technical.

3G technology is not yet mature, 3G terminal development lags behind, 2G terminal thousands, but only a few dozen types of 3G terminal, the terminal's development lagged far behind development of the system; 3G market immaturity, lack of Feicibuke critical applications, on killer app still not a definite view, because 3G is too small scales, which apply yes 3G market, the application of essential and which applications can Jinxingtuiguang 3G on, expand, many people believe that a mature 3G 甯傚満 not market development for 3G How, how to pull, is still under discussion; 3G license and spectrum auction at high prices to operators and users overwhelmed. The pressure on the operators is very large, users find all kinds of fees are too high, the current national 3G commercial issues remain.







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