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**missio5b6** · 11-05-2011, 03:03 PM

He is polite tone, looks quite sincere,mbt outlet but because each other only two children, a perfunctory means in words. Under the forest to his sister, looks innocent, but has always been very mouth Diao, sarcastically:" fortunately did not pay attention, if you pay attention to, now I'm lying wheels underneath and talk to you." The driver didn't expect them so hard, to look around the saw no adults to tell, he worried about losing the person in the vehicle ignition, press was a satirical anger, apologize again:" sorry, really sorry." Lin had seen happening here, I think the past treatment, she shook her head, looked for a moment, to see that the driver is sweating and dared not to pull two, it speaks out:" well, we go." Teach you a good, must be careful driving. Don't think the road is a bicycle and a motorcycle, you will feel great, can the rampage. Longevity that pulled the reluctant under Lin leaped aside, before leaving the glare of firm firm driver. The driver is sweating, terrified open the door, under Lin refused to go far, must have a look what is it so arrogant, see your drivers and others dispute also does not get off. The first is a long legs, wearing high heels red, yellowish pink silk stockings legs. In the autumn the Shanglin eyes, her yellowish pink silk stockings is rolling thunder. Later where people wear high heels with stockings, wearing black stockings, only more legs are slender, heart charm. Of course, there are no her, look ahead, in the eyes of the people, it is the trend of the most coquettish woman to wear flesh-colored stockings, moreover she is paired to the bright red high heels! Lin heard around the people praise the inspiratory, not by the person 's appearance and identity are curious. Drivers to hold the door open, the woman slowly appear in your eyes. Skinny black suits, white pearl necklace, <a href="http://www.mbtshoesto.com/specials.html">Discount MBT</a> a knee-length skirt success step, outlines her perfect S shape. Long hair tied up, in the back of the head plate into a smooth and clean hair. Shanglin micro sigh, beautiful though beautiful, but is a bit cold beauty. Beauty makeup delicate, just as pretty as a picture, her chin up too high, back was very too tough, at a station, the queen temperament significant legislation. Or a passionate pursuit of power, very beauty -- a glimpse of the red shoes, so that. I 've come on, surprised, he also feels that he is beautiful? Was about to speak, but the driver did not have closed, but also put the door, waiting for. The original car and one. He looked down on, stand to the side for his beauty, back to the forest, just tell him about and long age, suit and shoes, figure beautiful. Some people, and some wear a suit like monkeys fall under the forest, she is sad ... ... I made a painstaking training you, why you didn't give me a tiny bit to raise the temperament? I'm not asking you to raise the qualities of the talents, but you did give me see Confucianism elegant temperament or -- every day to practice calligraphy, drills the dog stomach go? As for Li Changsheng ... ... This guy not angry not speech. Fortunately, the anger is a bandit." ... ... Born Lord image ... ... Her sad sad, the other driver has closed the door, sending two boss in hotel. Lin and I stood in their the only way which must be passed, beauty come near, inadvertently swept away, hey sound stop. She stopped, was following behind her children naturally stopped. Beauty petite, and Walter height difference is very big, although be looked up and talk to him, but seems to look down from a height. " Hua Zi, are you in Shanghai?" Lin from falling back in sadness, surprise, understand? Look to see, but I respectfully bows, cooperate with each other:" height, mbt sport lady. I am here with something." Beauty smiles:" I used to call you my miss xu." Hua Zi did not speak, still bent over, very respectfully. Beauty behind the boys to a step, revealing stories, surprised at Hua Zi : "are you in?" Is a voice changer, sounds like Drake called ... ... To hear him talk heart flashed on smile, laugh at him and longevity as Drake throat. Smile arrives at the face, suddenly think of a person, condensation. Yin night! Although it is not the same, but different dress, but the other side looks vaguely discernible, it is in the ovary at two Yin night. He is the next night. Yin, the beauty ... ... On a step, want to call him, I seem to be entirely absorbed, with her next action, gently pull her gaze, she, in his eyes do not agree. Look at Yin night away, he just stared at Columbia talk, did not look to yourself -- however, a living man in front of us, how could you not to pay attention to? Even a honey in the initial surprise after noticing her, asked:" who's the little girl, long delicate." I humbly replied:" my relatives to come to Shanghai to play, have to go today, going to the train station." A honey looked at her eyes, also just. Just say:" since you are in Shanghai, another quickie." I respect should be under the. A honey said:" let's go." Head first into the lobby, someone to help her open the door say. Yin night. At her back, and turned to stare at Shanglin, two eyes, he remained impassive, and not to utter a single word, just look in her. Shanglin determine that he has recognized her, is to show laugh greet, I hold her hand forced a tight. Lin think, my heart as tight. A honey note Yin night. Did not catch up with, do not look back, the speaker:" come on, to the appointed time." Yin." Night lip, Lin noticed, he corners slightly fine lines, was often her lip angry people fine lines, it appears that this action was not to do less. Once again looking at her eyes, as if to give the person looking to mind, not to utter a single word, and she wiped a shoulder but lead. Lin suddenly feel the impermanence of life, or the life like play, no, a little bit of life ... ... Like the old friends meet cannot recognize scenes, what happened to him? She and Yin night. How understanding, just like heaven and earth will not tolerate? In four years no see, how to change a person?Work to the ovary Town, he would come to see the autumn forest vegetable greenhouse. Lin was frightened jump, thought Gu Cheng to the Autumn Village, east of scoop to find, Gu Zhi explains that Gu Cheng didn't come autumn village, go to other place. Town officials say greenhouse was founding stage, now also do not see any results, rather than wait until winter again. She would sigh. With Gu Zhi Yuan again look at two studio. Under the forest does not see him, and my sister say hello, pulling the autumn mbt <a href="http://www.mbtshoesto.com/mbt-kimondo-c-116.html">MBT Kimondo</a> katika brown river and longevity to go elsewhere to play. In two, a dish, another flower. In summer, the technicians to teach a farmer to shed on the plastic cloth is rolled up, so that the ventilation, Rao is so in Judah, temperature two or three degrees higher than outside, and stay for a while the sweat dripping. They look at the studio mainly planted some pepper, also known as pepper. Pepper nutrition value is high, yield, and in summer vegetable difficult time, although only a pilot plant, but also can pick many, pull into town vegetable wholesale market, were soon encroach upon a light. Shanglin hope can grow in the future be riotous with colour pepper, but according to Zhang said that currently there are not domestic this breed, and asked for details. She is not agricultural origin, only bought ate, where they deal with professional advice, had to excuse to say foreign friends mentioned, that fool the past. But also provided them with a direction, Zhang became sufficient energy to a red pepper. Corner is not empty, a few ridge tomatoes, tomato under the frame of the catch good season, she can only hope helplessly, persimmon, went to see the flower shelf, due to a limited area, just raise lush evergreen, and good support smile, but no blossom. Drill shed, wiping the sweat, thinking of two big canopy size is too small, not only vegetables, flowers, is subject to much breed varieties of several large. See covers an area of small, practical only a few simple kind, she came to hold when picking summer fruit mood, but now deflated, the basket will only put up some pepper and tomato, unavoidable. Might as well go to the mountains to find fruit harvest rich! Gu Zhi is a wink, reaching a point, asked:" what is that?" They are the front line, standing in a shelf, green vine stems, the green fat hung some long melon, epidermal Gegedada, <a href="http://www.mbtshoesto.com/mbt-sawa-c-196.html">MBT Sawa</a> looks very beautiful. Lin happy:" bitter gourd!" Summer, my impetuous, she seemed to see green balsam pear with ice cubes served in a transparent container. Rushed to pick up a maximum torque, Zhang Horror: don't stop", that is the stallion, old not delicious, you pick up small until tender!" Shanglin back spit tongue, not willing to give up the goal. East ramble ramble on the west a,, soon basket filled with assorted vegetables. Oneself to do not have, but I also came to the Autumn Village", there are so many relatives and neighbors, this to the vegetables, the root celery, Gu Zhi and holding a golden pumpkin. Lin thought, well, I see my feelings not shed and, like to plunder the villagers! In fact, she also knows, that of fruits and vegetables in farmer eye is really nothing. Their garden very much, eat also eat, sell not sell price, a lot of white water. She and Gu Cheng had discussed the plan is being carried out, the town found a place, are now trying to cover the wholesale vegetable market vegetables greenhouse -- the formation of scale, vegetable yield increase, cannot oneself eat all that? She would like to have good market. Along with the enhancement of the quality of life, and soon all city should advocate food basket project, ovary town vegetables more than to sell to the province, perhaps also to support! Work to early, late someone else will do. Don't look at her as if nothing is actually mbt jawabu sandals a pipe, a quick ear, early in the morning rush the town and the city signed an agreement, through Gu Cheng's relationship gets provincial Party committee support, vigorously develop the ovary town farming industry, not only is the ovary, the town. The town to ovary base, if you do well, and gradually spread to the experience, both benefit. Time also skillfully, look around to find her fall under the forest, when several of them wet your hand back, one asked, the original river fish to go. The boy 's bad luck, fish did not touch, but rather a canned shrimp, restless in the water swing. Gu Zhi is going to spend a few days in Autumn House, have parental permission. Lin was worried nobody help she taught under the forest and the longevity of the homework, I E, longed for him to stay in town. Gu Zhi Yuan every year is a "three good" student, one result of top-notch. The present regardless of under the forest to not willing, to take them to a small wine dinner. Gu Zhi tanshou:" eat mouth, sweating, must first wash." Lin think:" right, then go home, let you try my skill!" Gu Zhi pursed lip and smiled. Under the forest eye-rolling, whisper.:" toy boy bad. The big man, and even the point of sweat can not, bah!" Looking at some of them go far of figure, fall river is holding the Shanglin sent several of his pepper hee giggle. Aunt granny flat toothless mouth:" who is that a baby, how can enter in trouble?" Autumn three granny replied:" my second home in autumn, founding his daughter, ability to gel!" Micro not heard say, founding two more the more big hair, said to be built a new factory, bear ... ... Autumn 's aunt his mouth:" freak is a demon, the girl is not normal wow ... ..." Autumn river itself, is not normal, first enter a key middle school ... ... Autumn forest sitting opposite Gu Zhi Yuan under the sofa, stare at each other. His eyes got round to slip, expression of Gu TOWIN not welcome. Gu Zhi Yuan dog in the manger, not self-conscious and uncomfortable, bath, changed his immortal clothes, comfortable against the back cushion through newly Amoy to the ancient forest. He is the first to fall home, but from the heart feel warm. Two people in a letter discussing the interior decoration, precious ancient books, others when waste sold her the censer, labored to bronze Paperweight, and even furniture, shoe slippers in the several floor, as if in the dream appeared, than in their relax. Don't blame the Shanglin mother-in-law mouth say anything, it is two people communication frequency is too frequent. He is ancient furnishings, and family and zero zero pieces, in the face of the letter, in the face of the mind of Gu Zhi Yuan, Lin has a kind of speechless relax and trust. He is self-discipline, precocious, sensible, anything abnormal in harmony, mbt staka beluga like the friends of many years, each other as long as one eyes, known each other in what to think, what to say. This with her and longevity of forest be together morning and night train tacit understanding is not the same. It is from the bottom of my heart,. Sometimes the autumn forest like, maybe two people all are the same person, can know each other deeply. Brother and sister are more thorough than the parent parents. Back downstairs, take a shower to change clothes, suddenly heard the autumn forest lying on the balcony calling his name, busy out onto the balcony, looked up at. Shanglin stepping stool lie on the terrace, and waved his hand:" longevity longevity, the crystal dish up, oh, the refrigerator shrimp also out, on, bring me some ice, and the watermelon?" He think:"." " Cut half a watermelon, weather hot do not let people live!" Gu Zhi in the living room to look, also went to the balcony, face down, very fun. " I go get it, life can not take so many things." Li Changsheng light glanced at him. Gu Zhi swear, he looked at Li <a href="http://inbookmark.com/mybookmark.php">MBT Ema</a> Changsheng 's eyes kernel. Logically, no one will get Jen scared, but just his eyes, let him feel, as if into the icehouse to freezing, what hot irritability was gone, only was shivering cold. Again, the other side has the recovery of gaze. Shook his head, laughing himself silly. The roots have them go down to help, on a throat, fall under the forest bounced from plastic woven basket, lightweight generous. The weavers have clever hands and good sense, with different color plastic node in the basket is draw a fresh pink rose, while a few green leaves, like a basket, but placed in the senior stores sell arts and crafts. Gu Zhi Yuan at the basket look foolish eye, when he came back to feed one's sight on, feel more. A rope hanging basket, forest and forest, slowly put down, Li Changsheng took her to the East, one one rows of, say, two people together and put the basket back up. Basket full of things, some weight, two people with great care, effort to make an, wobbly, a little to put up the basket. When the basket up, Gu Zhi probe to see. Drink -- crystal plate is obliquely inserted, by watermelon firmly crowded living not tilt; covered with cling film half a watermelon red green, out of the fridge up a thin layer of cream; bagged shrimp is watermelon packed in a corner, hold the powerless popsicle. As the acme of perfection. Autumn forest seeing hundreds of times, he know this three people is a two drill.

**rogeguednen** · 11-05-2011, 03:04 PM

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**a2bzyoc3** · 11-05-2011, 10:10 PM

Switch Ethernet Switch (English: Switch, meaning It can access any two network nodes switch the electrical signal to provide exclusive access. The most common switch is the Ethernet switch. There are other common telephone voice switches, fiber optic switches.
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History of the concept of the origin principle of technological development of artificial exchange circuit PBX classification function Ethernet switches optical switching of several switching exchange 1. Port switch 2. Frame exchange 3. Cell switching different layers of development prospects of three-layer exchange exchange exchange How to choose the right four fourth floor of the exchange management through the serial management network management software through the Web management by main purpose of purchasing standard brand management model introduced Huawei switches Cisco switch MAC table flooding, forward the concept of exchange (switching) at both ends of transmission of information in accordance with the needs of communication, an artificial method or device automatically, the information to be transferred to meet the requirements of the appropriate term for the technology route. Generalized switch (switch) in the communication system is a complete exchange of information enabled devices. Computer networks [1] system, the exchange concept proposed to improve the sharing mode. We previously introduced the hub is a shared device HUB, HUB itself can not identify the destination address, and when the same LAN A host to host transmission of data B, the data packets in the HUB for the structure of the network in broadcast mode transmitted by each terminal through the authentication header for address information to determine whether the receiver. That is, in this manner, the same time the network can only transmit a data frame of the communication, if the collision had to try again. This approach is the sharing of network bandwidth. Principle switch has a high bandwidth bus and the internal switch fabric back. All switch ports are attached to the back of this bus, the control circuit receives the packet after processing will find the memory port address table to determine the purpose of MAC (network card's hardware address) of the NIC (network card) articulated in which port, through the internal switch fabric to quickly transfer data packets to the destination port, the destination MAC if there is broadcast to all ports, the port response from the receiving switch will table. Switches can also use the network Filtering and forwarding through the switch, you can effectively isolate the broadcast storm, reducing packet error and packet error occurs, avoid sharing violation. Switches at the same time can be between multiple ports on the data transfer. Each port can be regarded as a separate segment, connected to the network device on which to enjoy all of the bandwidth alone, without competing with other devices use. When a node A sends data to the node D, node B can simultaneously send data to node C, and that the two transfers are entitled to the full bandwidth of the network, has its own virtual connection. If used here is the 10Mbps Ethernet switch, then the total flux when the switch is equivalent to 2 × 10Mbps = 20Mbps, 10Mbps of shared use of HUB, a HUB will not exceed the total circulation of 10Mbps. In short, the switch is based on MAC address recognition, to complete the package forwarding packets function network devices. The switch can Origin History of technology Switch . In fact, the switching technology is a simplified, low-cost, high performance and features high port density switching products, reflects the complexity of bridging technology exchange in the second layer of OSI reference model operation. with the same bridge, switches, per MAC address of a packet of information transmitted is relatively simple decision-making. and this generally does not consider packet forwarding decisions hidden deeper in the additional information. and the bridge device is a switch different forwarding delay is very small, operating close to the performance of a single local area network , far more than the ordinary bridge between the Internet forwarding performance. switching technology allows the sharing of type and segment-specific type of LAN bandwidth is adjusted to reduce the flow of information between local area network bottlenecks occur. now have Ethernet, Fast Ethernet, FDDI and ATM switching technology products. similar to the traditional bridge, the switch provides many networking functions. switch to the economy to the conflict in the network into smaller domains, in order to provide higher bandwidth for each workstation . the agreement makes clear simple switch in the software configuration installed directly in the case of multi-protocol networks; switch using existing cable, repeaters, hubs and workstations, network cards, do not make high-level hardware upgrades; switches workstation is transparent, so that low administrative overhead and simplifies network nodes increases, the operation of mobile and network changes. using specially designed integrated circuit can switch to the port line rate on all forwarding information in parallel, providing a bridge than the traditional much higher performance device operation. If in theory a single Ethernet port on an octal number containing 64 packets, providing 14880bps transfer rate. This means that one has 12 ports, support for six parallel data streams lower than the conventional bridge. the history of artificial exchange of signals exchanged phone there should be traced back to the beginning. When the telephone was invented, it only need a wire long enough, with the end of the two phones, you can make apart far two people to voice chat. call more later, that every person has a phone can communicate with each other, we can not have one way or another each one between two telephone lines. So people set up a telephone office, Each phone users are connected a line to the telephone office, a large circuit board. When the A and B want to call to request the operator telephone office connected to B's phone. operator with a wire, a pick inserted in A to the circuit board holes, the other end into the hole B, which is the removed, this is the easier to understand terms. Circuit PBX artificial exchange efficiency too low to meet the needs of large-scale deployment of phones. With the development of semiconductor technology and switching circuit technology matures, it was discovered that electronic technology can be used to replace the manual exchange. phone end-users as long as the signal to the electronic device to send a bunch of electronic equipment to pre-set according to the procedure, the requesting party and the requested party circuit connected, and exclusive to this circuit, not shared with third parties (of course, result of defective design's sake, people may appear to share the case of the circuit,cheap Nike air max shoes, which is commonly known as the developed countries, the exchange of technology has long been monopolized by expensive equipment, China's telephone penetration rate has been low. As the year Huawei, ZTE and other companies are using self-developed program-controlled switchboards, telephones have rapidly spread in China. At present, voice PBX commonly used communication protocol VII signaling (Signalling System No.7) Ethernet switch with the computer and Internet technology (also often called the highest penetration rate of short-range two-story computer network. The Ethernet is a core component of the Ethernet switch. whether it is manual or program-controlled exchange of exchange, are designed to transmit voice signals, is the need exclusive line of Ethernet is a computer network, you need to transfer the data, uses a Ethernet equipment, switches and hubs is that essential difference: When A sent information to B, if through the hub, the hub access to all network nodes will receive this information (also is sent to radio), but the hardware level card will not filter out the information sent to the machine; and if by the switch unless the switch A notice broadcast, or information sent to B, C will not receive (for the switch control except in cases where permission to monitor). Currently, the Ethernet switch vendor according to market demand, the introduction of the three or four switches. But in any case, the core functionality is still the second floor of the Ethernet packet switching,air max sale, but with IP layer of a certain treatment or even the ability of high-level packet. optical switching optical switching is that people are developing the next generation of switching technology. At present all of the switching technology is based on electrical signals, and even the current fiber-optic switch is also the first optical signals into electrical signals, through the exchange of treatment, and then back to optical signals sent to the other fibers. As low photoelectric conversion rate, while the processing speed of the circuit there is a bottleneck in physics, so people want to design a without going through the photoelectric conversion of the full duplex / half duplex adaptive full-duplex switch is the switch to send data to receive data at the same time, both simultaneously, as we usually call it, like, talk at the same time be able to hear each other's voices. The current switches support full duplex. Quanshuang Gong is to delay the benefits of small, fast. that full-duplex, one has to mention the closely corresponds to another concept, that is, refers to a period of time only one action occurs, give a simple example, a narrow road, while only a car passed, when there are two cars off the amount, in which case only one first had to , until after the boss to open another one, this example to illustrate the image of the principle of half-duplex. early radio, and early implementation of half-duplex hubs and other equipment are all the products. As technology continues to progress, semi-double unions gradually from the historical stage. Broadly speaking, the network switch into two types: the LAN switch and WAN switches. WAN switches are mainly used in the field of telecommunications, providing the basic platform for communication. The local area network LAN switches are used for connected devices such as PC, and network printers. from the transmission medium and transmission speed can be divided into Ethernet switches, Fast Ethernet switches, Gigabit Ethernet switches, FDDI switches, ATM switches, and Token Ring Switches and so on. from the application of scale can be divided into enterprise-class switches, departmental and workgroup switches, switches and so on. yardstick by various manufacturers are not entirely consistent, in general, enterprise-class switches are rack, departmental switches can be rack-mounted (slot a few less), it can be fixed profile, the working group level for the fixed configuration switch type (simple function). On the other hand, the scale from the application point of view, when the switch as the backbone to support more than 500 information points for the large-scale enterprise applications enterprise-class switches switch to support 300 below the medium-sized switch information for the departmental switches, and support 100 information points within the switch for the working group level switches. described in this article switch refers to the LAN switch. The main function of the switch functions, including physical addressing, network topology, error checking, frame sequence and flow control. At present the switch also has some new features, such as VLAN (virtual LAN) support, link aggregation support, and even some also have firewall capabilities. learning: understanding each port Ethernet switch connected to the device MAC address and the address together with the corresponding port mapping cache stored in the switch MAC address table. forwarding / filtering: When the destination address of a data frame in the MAC address table with mapping, it is forwarded to the destination node port connected,Nike air max shoes, but not all ports (such as the data frame for broadcast / multicast frames are forwarded to all ports). to eliminate loop: When the switch includes a redundant circuit, the Ethernet switch to avoid the loop through the generation of spanning tree protocol, while allowing the existence of backup paths. switches in addition to the same type of network connection, you can also different types of networks (such as Ethernet and Fast Ethernet) interconnection between the role play. Today many switches are able to provide support such as Fast Ethernet or FDDI high-speed ports for connecting to other network volume switch or the key for the server bandwidth to provide additional bandwidth. In general, the switches are used to connect each port a separate network segment, but sometimes in order to provide faster access speeds, we can bring some important network computer directly connected to the switch port. Thus, the key network servers and key users with faster access speeds to support greater information flow. Finally, the switch briefly summarize the basic functions: 1. like a hub devices like switches provide a large number of ports available for connecting the cable, so you can use a star topology wiring. 2. as repeaters, hubs and bridges, as when it forwards the frame, the switch will re-generate an distortion of the square signal. 3. like a bridge, as in every port on the switch using the same forward or filter logic. 4. like a bridge, as the switch to the LAN into multiple collision domains,air max shoes on sale, each collision domain is there is a separate broadband, thus greatly improving the local area network bandwidth. 5. In addition to bridges, hubs and repeater functions, the switch also offers more advanced features, such as virtual LAN (VLAN) and higher performance. exchange [2] switches exchange the following three ways: 1) straight-through: pass-through mode can be understood as Ethernet switch ports in the vertical and horizontal cross-line Matrix is the telephone exchange. It detected at the input port to a data packet, examine the packet header, the destination address for the package to start the internal dynamic lookup table into the corresponding output port, connected to the intersection of input and output, the data packets to the appropriate ports through to achieve exchange. because no storage, delay is very small, very fast exchange, which is its advantages. The disadvantage is that, because the packet contents have not been preserved Ethernet switch, so can not check whether the packet transmitted error, can not provide error detection capabilities. because there is no cache, you can not have different rates of input / output port directly connected to, and easy to packet loss. 2) store and forward: store and forward approach is the field of computer networks, the most widely used way. It is the first input port of data packets stored, then CRC (cyclic redundancy check) check after the removal of the error packet processing packet destination address, through a lookup table to convert the output port sends packets. Because So, store and forward mode when the delay in data processing large, which is its lack of, but it can switch the data packets into the error detection, effectively improve the network performance. is particularly important is that it can support different speeds between ports conversion, to maintain high-speed ports and low-speed ports to work together. 3) fragment isolation: This is a range between the first two solutions. It checks whether enough of the packet length 64 bytes, if less than 64 bytes, that is a ######## bag, discard the packet; if greater than 64 bytes, the packet. This approach does not provide data validation. its data processing speed faster than the store and forward mode, but lower than through type slow. Several switching 1. port switch port switching technology first appeared in the slot of the hub, the hub of such a number of the Ethernet backplane is usually divided into segments (each segment as a broadcast domain), no bridge or routing connection network between the mutually unintelligible. After the big main module into the backplane is usually assigned to a network segment, the port switching module for the port will be too Back allocated between the various segments and balance. According to the level of support, port switch can be broken down into:? module exchange: the migration of the entire module segment.? port group exchange: on the module port is usually divided into several groups,air max 2011, each port allows for segment migration.? port class switching: support for each port transfer between different network segments. This exchange technology is based on the completion of the first layer of OSI, flexibility and load balancing and so on. If configured properly, it can also be tolerant to a certain extent, but did not change the characteristics of shared transmission medium, since the exchange could not call it real. 2. frame switching frame exchange is the most widely LAN switching, it adopted the traditional transmission media for micro-segments, providing parallel transmission mechanism to reduce the collision domains, access to high bandwidth. In general, each company's products are there differences in implementation technology, but handling of network frames generally have the following: Direct Exchange: provides wire-speed processing power, network switches, read out the first 14 bytes of the frame, put the network frames transmitted to the appropriate port. Store and Forward: On the Web the wrong reading frame to carry out inspection and control. The former method of exchange is very fast, but the lack of more advanced network control frames, the lack of intelligence and security, but also can not support the port has a different exchange rate. Therefore, after the manufacturers have a technology focus. Some manufacturers even decomposition of the network frame, the frame is broken down into fixed-size cell, the cell processing easily implemented in hardware, processing speed, while able to complete high control functions (such as LET U.S. MADGE's hub) such as priority control. 3. ATM cell switching technology uses 53 byte fixed length cell switching. as a fixed length, and thus easy to implement in hardware. ATM using a dedicated non-differential connections, parallel operation, a switch can create multiple nodes simultaneously, but does not affect the communications between each node. ATM also allows the source node and destination node to create multiple virtual links in order to protect sufficient bandwidth and fault tolerance. ATM circuits using a statistical time-division multiplexing, which can greatly increase the channel utilization. ATM bandwidth can reach 25M, 155M, 622M, or even the transmission capacity of Gb. but with Gigabit Ethernet The emergence of network, network and communication technologies used to represent the future direction of the development of ATM technology, began to gradually lose the meaning of existence. development prospects as the main local area network connected devices, Ethernet switches became popular application on one of the fastest network equipment. With the exchange of technology continues to evolve, a sharp decline in the price of Ethernet switches, switching to the desktop is the general trend. If your Ethernet network with a large number of users, a busy server applications and a wide range, and you network structure did not make any adjustments, then the overall network performance may be very low. One solution is to add a 10/100Mbps Ethernet switch, it can not only handle the regular 10Mbps Ethernet data stream, and also can support 100Mbps Fast Ethernet connection. If the network utilization over 40%, and the collision rate is greater than 10%, the switch can help you solve a problem. with a 100Mbps Fast Ethernet and 10Mbps Ethernet port The switch can run full-duplex mode, you can set up a dedicated 20Mbps to 200Mbps connections. not only to switch different network environment, the action was not the same, in the same network environment to add new switches and switch ports to increase the existing network switches effects are not the same. fully understand and master the network flow model is able to switch role to play a very important factor. Because the purpose is to use the switch as much as possible to reduce and filter network traffic, so if the network As the installation of a switch position is set properly, almost need to forward all packets received, then the switch will not be able to play its role in optimizing network performance, but reduces the data transmission rate, increased network latency. In addition to the installation location outside If the load in those smaller, less information is also blind to add a network switch, the same may also be a negative impact. by the packet processing time, the switch buffer size and the need to generate new data packets and other factors effects, in this case using a simple switch more desirable than HUB. Therefore, we can not Yigai that the switch has an advantage than the HUB, especially when the user's network is not crowded, there is considerable space available , the use of HUB better able to take full advantage of existing resources. layers of different layer switches, three switches and four second floor of the exchange layer the difference between the switch exchange technology is relatively mature, the second floor is a data link layer device switches , can identify the MAC address of a packet of information, according to MAC address forwarding, and these MAC addresses and records of the corresponding port within an address in their own table. a specific work process is as follows: 1) When the switch from one port receive a packet, it first reads the source MAC address in the header, so that it knows the source MAC address of the machine is connected on which port; 2) go to the purpose of reading the header in the MAC address and the address table to find the corresponding port; 3) If the table has a MAC address corresponding with the purpose of the port, the data packets directly copied to the port; 4) If can not find the appropriate port in the table put the data packet is broadcast to all port, when the purpose of the machine to respond to the source machine, the switch and can record the MAC address for this purpose and which ports correspond to when the next data transfer on all ports eliminates the need for the broadcast. continuous cycle of this process, for all MAC address information network can learn, two-story building and maintaining such a switch is its own address table. The working principle of the switch from the second floor can deduce the following three points: 1) Since the majority of ports on the switch while the data exchange This requires the exchange of a wide bus bandwidth, if the second floor of the switch has N ports, each port's bandwidth is M, the switch bus bandwidth than N × M, then this switch can achieve wire-speed switching; 2) Learning Port MAC address connected to the machine, write the address table, address table size (usually two structures: one for BEFFER RAM, a MAC table entry for the value), address table size of the access capacity of the switch; 3) there One is the story switches are generally designed to process data packets containing the forwarding ASIC (Application specific Integrated Circuit, ASIC) chip, it can be done very fast forward speed. As all the different manufacturers use ASIC a direct impact on product performance. The above three points is the second evaluation, three main technical advantages and disadvantages of switch performance parameters of this equipment, please consider the selection of the attention in comparison. three following the first exchange to the network through a simple look at the work of three switches process. using IP-layer switch equipment A ------------------------ ---------------- -------- B using IP device to send data such as A to give B, known to the purpose of IP, then the A to obtain the network address with a subnet mask to determine whether the purpose of their own in the same IP network segment. If the same network segment, but do not know the MAC address to forward the data needed, A requests to send an ARP, B returns its MAC address, A MAC with this package and send the packet switch, the switch switching modules only use the second floor, find the MAC address table, the packet is forwarded to the appropriate port. If the destination IP address appears not in the same segment, then A and B to achieve the communication, not in the flow cache entry corresponding to MAC address entry, it will be the first normal data packet Send to a default gateway, the default gateway is usually set in the operating system is good, corresponding to the third layer routing module, so not the same subnet can be seen for the data, first put in the MAC table is the default Gateway's MAC address; then receive this data from the three-module package, the query routing table to determine the route to reach B, will construct a new header, in which the default gateway MAC address as the source MAC address, MAC address to host B, for the purpose of MAC addresses. By identifying the trigger mechanism must establish the host A and B, MAC address and port forwarding correspondence and records into the flow cache entry table, after the data A to B to completed by the second floor of the exchange module directly. This is often times referred to a route forward. These are the three switches brief summary of the work process, we can see layer switching features: 1) by a combination of hardware high-speed data forward. This is not a simple superposition of the second floor switches and routers, three directly superimposed on the second floor of the routing module exchange of high-speed backplane bus, breaking the traditional router, the interface rate limiting, the rate of up to tens of Gbit / s. count backplane bandwidth, these are the three switches, two important parameters of performance. 2) simple routing software to simplify the routing process. Most of the data forwarding, except the necessary routing processing by the routing software, are the two layer module high-speed forwarding, routing software, mostly through the efficient processing optimization software, not simply copying the router's software. the second floor and second floor of the choice of three switches for small-scale local area network switch. This would not dwell on the , in a small local area network, broadcast packets has little effect on the fast switching layer switches, multiple access ports and low-modest price for small network users with a very complete solution. routers has the advantage of rich interface type, support The three powerful, powerful routing capability, suitable for large-scale routing between networks, it has the advantage of choosing the best routing, load sharing, link and network backup and the exchange of routing information and so has the function of the router . three of the most important function of the switch is to speed up large-scale local area network within the fast forwarding of data to add routing service is also for this purpose. If the large networks by sector, by geographical factors such as a small local area network, which will lead to a large number of Internet visits, simply can not be achieved using the two-story switches Internet visits; such as the use of a simple router, due to the limited number of interfaces and routing forward slowly, will limit the network speed and network size, using a routing function Fast forward three switches to become the first choice. In general, network traffic, including large, requiring rapid response network to forward, as do all of this work by the three switches, three switches will cause an excessive burden, the response speed affected by the inter-network router to complete the route, give full play to the advantages of different devices, be a good networking strategy, of course, that customer's pockets are drums, or on the next best thing, so that the three Layer switches and also to internetworking. four exchange a simple exchange of the fourth layer is defined: it is a feature, which determines the transmission is not only based on MAC address (layer bridge) or source / destination IP address ( The third layer routing), and based on TCP / UDP (fourth layer) application port number. The fourth layer switching functions like a virtual IP, point to the physical server. It transfers a variety of business subject to the agreement,air max shoes, there are HTTP, FTP , NFS, Telnet or other agreement. these businesses based on the physical server, require complex load balancing algorithm. In the IP world, business type from TCP or UDP port address of the terminal to determine, in the fourth layer is the exchange of range by the source IP address and terminal, TCP and UDP port joint decision. In the fourth layer switching for each group for the establishment of the search using the virtual server IP address (VIP), each server supports a specific application. in the domain name server ( DNS) server for each application stored in the address is the VIP, but not the real server address. When a user to application, a group of VIP with the target server connection requests (such as a TCP SYN packet) to the server switch. server switches in the group selected the best server, the terminal address in the VIP IP replaced with the actual server, and the connection request to the server. so that all packets the same interval by the server switches to map, between the user and the same server transmission. The fourth layer OSI model of the principle of exchange of the fourth layer 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 IP protocol stack is TCP (a Transfer Protocol) and UDP (User Datagram Protocol) protocol layer is located. In the fourth layer, TCP and UDP header contains the port number (port number), they can be the only distinction which 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 put it to the appropriate high-level software. port IP address number and combination of equipment, often called protocol stack implementation, the port number is the same. In addition to In RFC1700 determine the TCP layer switch by the fourth began, to identify the beginning of a session. Then it uses complex algorithms to determine the best server processing the request. Once such a decision, the switch will be a session with a specific IP address of contact together, and use the real IP address of the server instead of server VIP address. each of the fourth floor of a switch are saved match with the selected source IP address of the server and the source TCP port associated connection table. and then the fourth layer switch connected to this server to forward requests. all subsequent packets between the client and the server re-mapping and forward, until the session switch found so far. In the case of using the fourth floor of the exchange, the access server can be connected with the real together to meet the user to the rules, such as the number on each server to have equal access or on different servers to allocate the capacity of transport streams. How to choose the appropriate exchange of a fourth level) speed to be effective in the enterprise network , the fourth layer switch to provide wire-speed router with a third layer of comparable performance. In other words, the fourth level of the exchange must be in all ports operate at full media speed, even in multiple Gigabit Ethernet connections are so . gigabit Ethernet speed is equal to 1.488 million packets per second maximum speed route (assuming the worst case, that all network packets as well as the definition of the minimum size of 64 bytes long). 2) balancing algorithm based on server capacity The capacity of the desired balance of granularity, the fourth distribution layer switch will apply the algorithm to the server there are many, there is a simple connection to the recent detection of loops, testing or testing the server loop delay feedback loop itself. In all projections , the closed-loop feedback to provide the volume of business reflected in the existing server, the most accurate test. 3) Table size should be noted that the fourth layer switches need to distinguish between the exchange and storage capacity of a large number of entries sent. switches in an enterprise especially when the core network. many second / three switches tend to send the table size is proportional with the number of network devices. on the fourth floor of the switch, this must be multiplied by the number of different applications used in network protocols and the number of sessions. thus sending the size of the table with the type of endpoint devices and the growing number of applications grew rapidly. The fourth layer switch design in the form of their products need to consider this growth. large tables to support wire-speed transmission capacity on the fourth floor manufacturing flow of high-performance switch is essential. 4) The fourth level redundant internal switches feature redundant topology. In fault-tolerant network card with dual-link connection to be established from a server to the network card, link and server switches fully redundant system. management Managed switches can be managed through the following ways: through RS-232 serial port (or parallel port) management, through a web browser management and network management software. Managed Switch through the serial port management with a serial cable for the switch and management. first one end of serial cable plugged into the serial port of the switch on the back, the other end into the computer's serial port in the ordinary. and then turn the switch and the computer power supply. In Windows 98 and Windows 2000 li is offering a bandwidth occupied by the switch, so called keys to move the menu and sub menu, press the Enter key to execute the appropriate commands, or use a dedicated set of switch management commands manage the switch. a different brand of switch command set is different, even the same brand of switch, the command is also different. use menu command in the operation more convenient. through the Web Managed switches can be managed Web (Web browser) to manage, but you must specify an IP address to the switch. In addition to the IP address used for the management of the switch outside, and no other purpose . In the default state, the switch is no IP address, or other means must be specified via the serial port of a IP address, to enable the management approach. manage the switch using a web browser, the switch is equivalent to a Web server, but web pages do not stored in the hard disk inside, but inside the switch NVRAM, NVRAM through the program can be inside the Web program upgrade. When an administrator in the browser, enter the IP address of the switch, the switch as a server computer as the web passes , then you feel like visiting a Web site, as shown in Figure 2. In this way the bandwidth occupied by the switch, so called function of the corresponding page entry in the text box or drop-down list to change the parameters can switch. Web management in this way can the LAN, therefore we can realize remote management. through the network management software to network switches are