一叶落知天下秋

解释：从一片树叶的凋落，知道秋天的到来。比喻通过个别的细微的迹象，可以看到整个形势的发展趋向与结果。

出处：《淮南子·说山训》：“见一叶落而知岁之将暮。”宋·唐庚《文录》引唐人诗：“山僧不解数甲子，一叶落知天下秋。”

苹果树 英文要怎么写呀

apple tree

苹果用英语怎么写

苹果 [píng guǒ]

apple

关联词条:

biffin pippin spitzenburg queening Malus domestica paradise

以下摘自有道词典

apple

英 ['æp(ə)l] 美 ['æpl]

n 苹果，苹果树，苹果似的东西；[美俚]炸弹，手榴弹，（棒球的）球；[美俚]人，家伙。

网络释义专业释义英英释义

苹果

这个屏幕为7英寸的装置并非索尼对阵苹果(Apple)即将面世的平板电脑的产品。首先它必须插入电源插座。

基于4662个网页-相关网页

苹果公司

[园艺] 苹果汁

苹果树

短语

Apple puter 苹果电脑 ; 苹果电脑公司 ; 苹果计算机 ; 苹果公司

Big Apple 大苹果 ; 纽约 ; 纽约的别称 ; 大苹果城

Apple Inc 苹果公司 ; 苹果 ; 苹果电脑公司 ; 果公司

更多网络短语

21世纪大英汉词典 柯林斯英汉双解大词典

apple ['æpl]

n

植物苹果

苹果属植物的果实(如野生酸苹果、沙果)

植物苹果属(Malus)植物,苹果树(Malus pumila或Pyrus malus)

苹果状果实

植物结苹果状果实的树，苹果状产物(如番茄、番荔枝、栎五倍子、盾叶鬼臼等)

苹果树木材

(尤指使用非法功率进行通讯、播音的)民用电台(非法)使用者

[the Apple][美国口语]“大苹果”城(指纽约市)[亦作Big Apple]

更多结果

以上来源于：《21世纪大英汉词典》

词组短语同近义词

an apple 一个苹果

apple tree 苹果树

apple juice 苹果汁

apple pie 苹果派；苹果馅饼

big apple n [俚]美国纽约城

更多词组短语

双语例句原声例句权威例句

I twisted an apple off the tree

我从树上摘下来一个苹果。

《21世纪大英汉词典》

He hemisected an apple and gave it to me

他把一个苹果切成了两半，把一半给了我。

《21世纪大英汉词典》

Just give her some apple and she blisses out

只要给她一苹果，她就很开心。

《21世纪大英汉词典》

更多双语例句

百科

APPLE

“APPLE”是个多义词，它可以指APPLE（美国IT科技企业）, APPLE（英语单词）, APPLE（美国apple服饰集团）。

详细内容

更多与"APPLE"相关的百科词条 »

苹果公司

苹果公司（Apple Inc）是美国的一家高科技公司，2007年由苹果电脑公司（Apple puter, Inc）更名而来，核心业务为电子科技产品，总部位于加利福尼亚州的库比蒂诺。苹果公司由史蒂夫·乔布斯、斯蒂夫·沃兹尼亚克和罗纳德·韦恩在1976年4月1日创立，在高科技企业中以创新而闻名，知名的产品有Apple II、Macintosh电脑、Macbook笔记本电脑、iPod音乐播放器、iTunes商店、iMac一体机、iPhone手机和iPad平板电脑等。2013年9月21日凌晨，苹果公司正式发布了新一代的iPhone手机，这一代分为iPhone 5s和iPhone 5c两个版本，在中国定价分别为5288元和4488元起。2013年世界>>

苹果树的英文怎么说

Apple tree

一些苹果树 用英语怎么说

some apple trees

apple tree 苹果树，只在后面的tree 家复数

　作为一名骇客和作家，Joshua Klein对乌鸦们的智慧感到神奇(你可曾注意过它们那小小的黑眼睛中蕴藏的智慧光芒)。他在很长一段的业余时间里对乌鸦群的行为进行观察后，想出了一个堪称优雅的机器，这或许将在人类与动物间构建一种新的关系。下面是我为大家收集关于TED英语演讲：为什么说乌鸦的智商高到可怕，欢迎借鉴参考。

　A thought experiment on the intelligence of crows

　演讲者：Joshua Klein

　/ 中英对照演讲稿 /

　How many of you have seen the Alfred Hitchcock film "The Birds" Any of you get really freaked out by that You might want to leave nowSo this is a vending machine for crowsOver the past few days, many of you have been asking, "How did you come tothis How did you get started doing this" It started, as with many great ideas, or many ideas you can't get rid of, anyway, at a cocktail party

　这里有多少人看过希区柯克的**《鸟》是不是认为那片子太过离奇了要是那样的话，你现在可以走了。(笑声) 大家看到的是一台专门为乌鸦设计的自动售货机。 过去几天，人们都在问我同样的问题： “你怎么开始搞这玩意的有什么吸引你的地方吗” 说实话，这玩意就像很多伟大的想法， 或者一些你无法在脑中驱散的想法一样， 是从一次鸡尾酒派对产生的。

　About 10 years ago, I was at a cocktail party with a friend of mine We were sitting there, and he was complaining about the crows that were all over his yard and making a big mess And he was telling me we ought to eradicate these things,kill them, because they're making a mess I said that was stupid, maybe we should just train them to do something useful And he said that was impossible

　大概十年前，我与一个朋友在一个鸡尾酒派对上， 我们坐在那，他一直在抱怨乌鸦 乌鸦们把他的院子搞得一团糟。 他那时很认真的跟我说，我们得想办法消灭这些鬼东西， 否则我们就不会有好日子过。 我跟他说，那才是坏主意呢， 咱们为何不训练它们，让乌鸦帮我们人类做一点有意义的事情 他丢给我一句“那不可能”。

　And I'm sure I'm in good company in finding that tremendously annoying, when someone tells you it's impossible So I spent the next 10 years reading about crows in my spare time

　我相信绝对不只我一人觉得这极度恼人——当有人告诉你“那不可能”时。于是决定用10年的时间在我的业余时间专门研究乌鸦。

　And after 10 years of this, my wife said,"You've got to do this thing you've been talking about, and build the vending machine" So I did But part of the reason I found this interesting is, I started noticing that we're very aware of all the species that are going extinct on the planet as a result of human habitation expansion,and no one seems to be paying attention to all the species that are actually living;they're surviving And I'm talking specifically about synanthropic species,which have adapted specifically for human ecologies, species like rats and cockroaches and crows

　现在10年过去了，我妻子说， “好吧，你也该把它做出来了， 你不是一直说要给乌鸦们做一个自动售货机么” 于是我就把它做出来了。 但我对这个项目感兴趣还有部分原因是因为 我开始注意到我们人类已经意识到 有很多物种因为人类无止尽的扩张 将会在地球上灭绝。 但貌似没人对那些 还生存在世上的物种有所关心——它们都还真正地活着。 这里我指的是那些长期与人共处， 并适应了人类生态系统的动物。 这样的动物包括老鼠、蟑螂、乌鸦。

　And as I started looking at them, I was finding that they had hyper-adapted They'd become extremely adept at living with us And in return, we just tried to kill them all the timeAnd in doing so, we were breeding them for parasitism We were giving them all sorts of reasons to adapt new ways So, for example, rats are incredibly responsive breeders And cockroaches, as anyone who's tried to get rid of them knows, have become really immune to the poisons that we're using

　而假如你仔细观察的话，你会发现所有的这类动物都已经对人类社会产生了高度的适应性，并且随着继续与人生活在一起，它们的适应性还加变得更强。但反观人类呢，我们只是一直在不断屠杀它们而已。为了做到这点，人类用喂养的方式来让它们寄生于我们我们给了动物们适应新环境的各种理由。比如：老鼠的生育能力变得超强。而蟑螂，逮过蟑螂的人都知道，它们已经不在乎我们的“诱饵”了。

　So I thought, let's build something that's mutually beneficial; something that we can both benefit from, and find some way to make a new relationship with these species So I built the vending machine

　于是我想，为何不制造出一些能让我们人类和这些“寄生虫”共同受益的东西呢以此和这些动物建立一种新型的关系，一种互利的关系。从而让人类找到一条与其共处的新路子。这就是我制作动物专用自动售货机的理由。

　But the story of the vending machine is a little more interesting if you know more about crows It turns out, crows aren't just surviving with human beings; they're actually thriving They're found everywhere on the planet except for the Arctic and the southern tip of South America And in all that area, they're only rarely found breeding more than five kilometers away from human beings So we may not think about them,but they're always around

　不过如果你多了解一下乌鸦，这个自动售货机的故事会更有趣。乌鸦们不仅仅是在人类环境中‘生存’得不错——事实上，他们活得还很精彩。你在地球上任何一处角落——除了两极和南美至南端——都可以见得到乌鸦。通常它们的栖息地离人类居所不出5公里。虽然你也许不会想到这一点，可是它们确确实实一直都这么活在我们身边。

　And not surprisingly, given the human population growth, more than half of the human population is living in cities now And out of those, nine-tenths of the human growth population is occurring in citiesWe're seeing a population boom with crows So bird counts are indicating thatwe might be seeing up to exponential growth in their numbers So that's no great surprise

　这也不奇怪，我们的地球上人口暴涨，其中有半数以上居住在城市。除此之外，90%的人口增长就都发生在城市里——乌鸦这个种群也在经历同样的发展。所以鸟类的数量在我们看来将会有一个爆炸型的增长，这并没有什么奇怪的。

　But what was really interesting to me was to find out that the birds were adapting in a pretty unusual way And I'll give you an example of that This is Betty She's a New Caledonian crow And these crows use sticks in the wild to get insects and what not out of pieces of woodHere, she's trying to get a piece of meat out of a tube But the researchers had a problem They messed up and left just a stick of wire in there And she hadn't had the opportunity to do this before You see, it wasn't working verywell So she adapted

　但令我感到吃惊的是这些鸟儿竟然学会了通过一些奇特的方式在我们的社会里求得生存。大家看看下面的例子：它的名字是Betty，它是一只New Caledonia(北美地名)的乌鸦。在森林里，它们会用树枝从林木里挑出虫子和其他食物。此时它正尝试用铁线取出瓶子里的那块肉。但是研究者们遇到了一个问题。他们把试验搞砸了，因为只留下了一根线在那里。而Betty以前可没尝试过这样的挑战。你可以看到，它进行得并不顺利。于是它想出了一个新法子。

　Now, this is completely unprompted; she had never seen this done before No one taught her to bend this into a hook or had shown her how it could happen But she did it all on her own So keep in mind-- she's never seen this done

　要知道，它没有看到过别的乌鸦这么做。之前也没有任何人或者别的乌鸦教它如何把线弯成钩子;或者告诉过它可以通过这种方式捞肉。这完全是它自己想出来的办法。请一定记得它以前从没有学过的哦。就这样。

　Right Yeah All rightSo that's the part where the researchers freak out

　对，就这样。这才是研究人员觉得不可思议的地方。

　It turns out, we've been finding more andmore that crows are really intelligent Their brains are in the same proportionas chimpanzee brains are There's all kinds of anecdotes for the different kinds of intelligence they have For example, in Sweden, crows will wait for fishermen to drop lines through holes in the ice And when the fishermen move off, the crows fly down, reel up the lines, and eat the fish or the bait It's pretty annoying for the fishermen

　我们发现越来越多的证据表明乌鸦的确是聪明的，它们的大脑占躯体的比例和大猩猩相当。 大家也可能听过各种各样的关于乌鸦的趣闻吧。 比如，在瑞典， 那里的乌鸦会趁渔人往冰隙里放钓钩的时候守在一边， 当渔人走了， 它们就飞过去拉起钓钩，吃掉钩上的鱼或钓饵。 这可是搞得那里的渔人很烦恼。

　On an entirely different tack, at University of Washington a few years ago, they were doing an experiment where they captured some crows on campus Some students went out, netted some crows,brought them in, weighed and measured them, and let them back out again And they were entertained to discover that for the rest of the week, whenever these particular students walked around campus, these crows would caw at them and runaround, and make their life kind of miserable

　而在华盛顿大学，那里的研究员几年前做了一个截然不同的实验。他们在校园里捉来一些乌鸦，在实验室里加以标记、称量，然后把它们放走。而随后的那个星期，他们惊喜地发现，那些被放走的乌鸦在校园里一见到那些捉过它们的学生，就会冲着他们鸣叫，并在他们周围飞来飞去，给他们的生活增添一些小烦恼。

　They were significantly less entertained when this went on for the next week And the next month And after summer break Until they finally graduated and left campus, and -- glad to get away,I'm sure -- came back sometime later, and found the crows still remembered them

　但之后几个星期还是如此，他们就不再那么惊喜了。甚至到了下个月，到了夏季学期结束，到了他们毕业离校了——我相信他们是很高兴地离去的——可当他们偶尔回校来看看时，那些乌鸦还是记得他们。

　So, the moral being: don't piss off crowsSo now, students at the University of Washington that are studying these crows,do so with a giant wig and a big mask

　所以——大家看到了吧，千万别惹乌鸦。正是这样的缘故，现在华盛顿大学做乌鸦研究的学生都带上巨大的假发，还套上面具。

　It's fairly interesting

　这真是令人哑然的一件事。

　So we know these crows are really smart,but the more I dug into this, the more I found that they actually have an even more significant adaptation

　以上说的无非是要证明乌鸦是非常聪明的，但我研究得越是深入，越是觉得它们的智慧要比我们想象的高出一个层次。

　Video: Crows have become highly skilled atmaking a living in these new urban environments In this Japanese city, they have devised a way of eating a food that normally they can't manage: drop it among the traffic The problem now is collecting the bits, without getting runover Wait for the light to stop the traffic Then, collect your cracked nut insafety

　视频：在新的城市环境中，乌鸦们的谋生技能正在变得越来越娴熟。这是一座日本城市，这里的乌鸦发明了一种吃果仁的办法——把坚果丢到车道上。然后飞走， 等待汽车开过。 之后它们在马路边等待绿灯， 然后飞到马路中央安全地衔走那颗果仁

　Joshua Klein: Yeah, pretty interestingWhat's significant about this isn't that crows are using cars to crack nuts Infact, that's old hat for crows This happened about 10 years ago in a placecalled Sendai City, at a driving school in the suburbs of Tokyo And since that time, all the crows in the neighborhood are picking up this behavior Now everycrow within five kilometers is standing by a sidewalk, waiting to collect its lunch

　JoshuaKlein: 看看，这是不是挺有趣的不过，有趣的倒不是借助过往车辆压开果核的做法，事实上，乌鸦老早就学会了这门手艺了。刚才大家看到的景象发生在10年前东京市郊的一家驾驶学校附近。从那时开始， 附近的乌鸦也学会了这样的吃坚果的方式。 如今，方圆五公里内的乌鸦都在人行道旁守候着， 等待过往车辆为他们带来午餐。

　So they're learning from each other And research bears this out Parents seem to be teaching their young They learn from their peers, they learn from their enemies If I have a little extra time,I'll tell you about a case of crow infidelity that illustrates that nicely The point being, they've developed cultural adaptation And as we heard yesterday,that's the Pandora's box that's getting human beings in trouble, and we're starting to see it with them They're able to very quickly and very flexibly adapt to new challenges and new resources in their environment, which is really useful if you live in a city

　乌鸦通过互相学习，都掌握了这种技巧。乌鸦父母还教会自己的孩子这样的技巧呢。它们向同伴学习，也向它们的敌人学习。如果我还有更多演讲时间，我会告诉你们一个有关乌鸦背信的案例来更好地证明我的观点。最关键的是它们学会了适应不同的生态文化。就如昨天我们听到的那样，是潘多拉之盒将人类引入混乱，现在是开始着手解决它的时候了。他们能快速且融洽地适应新的挑战及环境中的新资源，对于城市生活来说，这可真有用。

　So we know that there's lots of crows We found out they're really smart and they can teach each other When all this became clear, I realized the only obvious thing to do is build a vending machine So that's what we did This is a vending machine for crows And it uses Skinnerian training to shape their behavior over four stages It's pretty simple

　好了，现在我们都知道城市里有大量的乌鸦，它们很聪明，还懂得相互间分享生存的秘诀。当我知道这一切以后，我决定要专门为它们做一台自动售货机。并且还做成功了。这就是乌鸦专用自动售货机：我们用斯金纳(操作性条件反射)理论，分四阶段训练法来训练乌鸦。其实也很简单。

　Basically, what happens is that we put this out in a field or someplace where there's lots of crows We put coins and peanuts all around the base ofthe machine Crows eventually come by, eat the peanuts, and get used to the machine being there Eventually, they eat all the peanuts Then they see peanuts here on the feeder tray, and hop up and help themselves Then they leave, the machine spits up more coins and peanuts, and life is dandy if you're a crow -- you can come back anytime and get yourself a peanut

　首先，我们把这样的机器放到田野 或者乌鸦经常出没的地方。 在机器的底部放上一大堆的硬币和花生。 乌鸦来了，吃掉机器上的花生， 并且也习惯了机器的存在。 吃光了地面的花生以后， 它们发现在售货机的出货口那里也有很多花生， 于是就跳到上面，也同样尽享美味。 每一天，那机器上都会放满了硬币和花生。

　So when they get really used to that, we move on to the crows coming back Now they're used to the sound of the machine;they keep coming back and digging out peanuts from the pile of coins that'sthere When they get really happy about this, we stymie them

　嘿，要是当那样的一只乌鸦也不错哟， 每天都不愁吃的。当它们都习惯这样的生活或，我们继续下一步我们等到乌鸦都习惯于机器的声音，就把花生盖在硬币底下，它们飞过来，掀开硬币，就能吃得到花生，它们也挺开心的。这时，我们决定给它们制造一些困难。

　We move to the third stage, where we only give them a coin Now, like most of us who have gotten used to a good thing,this really pisses them off So they do what they do in nature when they're looking for something: sweep things out of the way with their beak They do that here, and that knocks the coins down the slot When that happens, they get a peanut This goes on for some time The crows learn that all they have to do is show up, wait for the coin to come out, put it in the slot, then get their peanut

　我们开始了第三阶段的训练。只把一枚硬币留在机器上，此时乌鸦飞过来，看到没有食物，自然觉得很泄气——我们人也一样嘛。所以它们出于寻找食物的本能——用它的喙在机器上扫来扫去，不经意的把硬币碰到硬币口里去了，于是它获得了一颗花生。于是它们也学会了，每次都来这里， 只要把机器上的硬币丢到硬币口，就能吃得到花生。

　When they're good and comfortable with that, we move to the final stage, where they show up and nothing happens Thisis where we see the difference between crows and other animals Squirrels, for example, would show up, look for the peanut, go away Come back, look for the peanut, go away They do this maybe half a dozen times before they get bored,and then they go off and play in traffic

　当他们对此过程非常熟练及满足以后，我们进入训练的最后一个阶段，它们来到机器旁边，却发现什么也没有。注意，就是这个关键的地方可以看出乌鸦是多么聪明。要是一只松鼠，它来到机器旁，寻找花生，找不到，就走了隔天再来，又是没有，又跑回去。如此反复五六次，它们也就觉得没意思了。

　Crows, on the other hand, show up and they try and figure it out They know this machine has been messing with them through three different stages of behavior

　而乌鸦则不一样，它们要寻找出一个究竟。通过前面三个阶段，并且这样的玩笑越开越大。

　They figure there must be more to it So they poke at it and peck at it And eventually some crow gets a bright idea:"Hey, there's lots of coins lying around from the first stage, hops down,picks it up, drops it in the slot, and we're off to the races That crow enjoys a temporary monopoly on peanuts, until his friends figure out how to do it, and then there we go

　它们觉得肯定还有更多方式获得花生。它们又是用头撞，又是用嘴咬。偶尔间有一些乌鸦想到了一个绝妙的主意：“嘿，大家还记得地面上放的那一大堆硬币么。或许有用呢”——于是它们飞过来，衔起硬币，扔进投币孔。它们发现了怎么吃得上花生了!这样的技巧先是为第一批到来的乌鸦所垄断，可慢慢的别的乌鸦也学会了……故事到此为止。

　So, what's significant about this to me isn't that we can train crows to pick up peanuts Mind you, there's 216 milliondollars' worth of change lost every year, but I'm not sure I can depend on that ROI from crows

　从这个故事我们得出结论：我们可以训练乌鸦，让它们通过售货机吃上花生。你知不知道，每一年都有价值216亿的硬币丢在大街上。

　Instead, I think we should look a little bit larger I think crows can be trained to do other things For example, why not train them to pick up garbage after stadium events Or find expensive components from discarded electronics Or maybe do search and rescue The main point of all this for me is, we can find mutually beneficial systems for these species We can find ways to interact with these other species that doesn't involve exterminating them, but involves finding an equilibrium with them that's a useful balance

　嘿，当然，我不是想靠乌鸦来赚钱。我们的眼光可以放远一点：我觉得我们可以训练乌鸦来做其他事。比如，为何不可以通过训练，让乌鸦给体育馆捡垃圾或者让它们帮助我们从大堆的废弃电子元件里头挑出有用的部件又或者让它们参与搜救工作我这个演讲的主要的一个观点是我们可以寻找到一种与此类动物共存的途径，我们能找到与其他族群共处的方式而不仅仅是灭绝它们，我们可以和它们实现共赢。

　Thanks very much(Applause)

交换机内的生成树算法（STA）使你可以创建一条备用链路（当网络中存在多台交换机时）。在主链路正常工作时，备用链路处于空闲状态（不工作）；只有在主链路出现问题时，备用链路才不需要任何人工干预自动地接替主链路。这种自动重构的功能，使得网络上的用户能够最大限度地与网络保持正常的连接。生成树算法较复杂，所以，建议最好在充分研究理解其之后，再更改其一些设置。请仔细阅读并理解下述内容之后，再去更改交换机上的生成树的默认设置。

　　网络环路的侦测和预防（Network loop detection and prevention）：任何两个局域网之间应该只有一条路径，否则，网络中将出现环路。如果存在着多于一条的路径，那么生成树算法将会侦测到环路的发生，并自动选择开销值（c ost）最低的那条路径作为可使用的路径（主链路），而阻断其它路径，将它们作为备用路径（备用链路）。

　　自动拓扑重构（Automatic topology re-configuration）：当主链路出现故障时，生成树算法将自动启用备用链路，重构网络结构。

　　生成树的级别（STA Operation Levels）

　　生成树有两种工作级别：桥级别（bridge level）和端口级别（port level）。在桥一级上，生成树算法为每台交换机计算桥的标志级数（Bridge Identifier），然后设定根桥（Root Bridge）和指定桥（Designated Bridges）。而在端口一级上，生成树算法设定根端口（Root Port）和指定端口（Designated Ports）。详述如下：

　　在桥一级上（On the Bridge Level）：

　　根桥（Root Bridge）：具有最小桥标志级数的（lowest Bridge Identifier）交换机是根桥（Root Bridge）。当然，你希望根桥是环路中所有交换机当中最好的一台（交换机），以保证能够提供最好的网络性能和可靠性。

　　桥标志级数（Bridge Identifier）：桥标志级数是桥的优先级（Bridge Priority）和交换机的MAC地址的综合数值，其中桥的优先级（Bridge Priority）是一个你可以设定的参数。例如，“4 00 80 C8 00 01 00”中的“4”是桥的优先级，“00 80 C8 00 01 00”是交换机的MAC地址。交换机的桥标志级数越低，则交换机的优先级越高，这样可以增加其成为根桥的可能性。

　　指定桥（Designated Bridge）：在每个网段中，到根桥（Root Bridge）的路径开销最低的（lowest Root Path Cost）桥将成为指定桥（Designated Bridge），数据包将通过它转发到网段。一旦所有的交换机具有相同的根路径开销（Root Path Cost），那么具有最低的桥标志级数的（lowest Bridge Identifier）交换机才会被定为指定桥（De signated Bridge）。

　　根路径开销（Root Path Cost）：一台交换机的根路径开销（Root Path Cost）是根端口（Root Port）的路径开销（Path Cost）与数据包经过的所有交换机的根路径开销（Root Path Cost）之和。根桥（Root Bridge）的根路径开销（Root Path Cost）是零。

　　桥的优先级（Bridge Priority）：是一个用户可以设定的参数。设定的值越小，优先级越高。交换机具有越高的优先级，才越有可能成为根桥。

　　在端口一级上（On the Port Level）：

　　根端口（Root Port）：每台交换机都有一个根端口（Root Port），这个端口到根桥的路径开销最低。一旦多个端口具有相同的到根桥的路径开销时，那么具有最低的端口标志级别的才会成为根端口。

　　指定端口（Designated Port）：指定端口就是指定桥（Designated Bridge）上的端口。

　　端口优先级（Port Priority）：数值越小，端口的优先级就越高。具有越高端口优先级，才越有可能成为根端口。

　　路径开销（Path Cost）：这是一个可变的参数，它将随着生成树中的设定值的变化而变化。依据STA的默认参数值，每个1000Mbps网段有一个指定的路径开销值为4 ，100Mbps网段的路径开销值19，10Mbps网段的路径开销值100

　　生成树参数（STA Parameters）

　　生成树的参数用户可以根据自己的需要进行修改，但是建议最好使用出厂时的默认设置。除非确实需要对出厂设置值进行变动时，再去改动默认值。用户可以改动的生成树参数有如下几个：

　　桥优先级（Bridge Priority）：数值范围从0到65535“0”的优先级最高。

　　呼叫时间（Bridge Hello Time）：数值范围从1秒到10秒。是指根桥向其它所有交换机发出BPDU数据包的时间间隔，以告知其它所有交换机它是根桥。如果你的交换机还未是根桥时为其设置了呼叫时间，那么，一旦你的交换机成为根桥，该呼叫时间就会派上用处。

　　注意：呼叫时间不能大于桥的最大老化时间（Max Age），否则，将出现错误信息。

　　最大的桥老化时间（Bridge Max Age）：数值范围从6秒到40秒。如果在超出最大老化时间之后，还没有收到根桥发出的BPDU数据包，那么，在允许的条件下你的交换机将充当根桥向其它所有的交换机发出B PDU数据包。如果交换机确实具有最小的桥标志级数，那么，它将随之成为根桥。

　　桥转发时延（Bridge Forward Delay）：数值范围从4秒到30秒。是指交换机的端口从阻塞状态转为转发状态所用的监听时间。

　　当你欲变动生成树参数时，请一定记住下述公式：

　　最大的桥老化时间≤ 2 x（桥转发时延 – 1秒）

　　即：Max Age ≤ 2 x （Forward Delay - 1 second）

　　最大的桥老化时间≥ 2 x（呼叫时间 + 1秒）

　　即：Max Age ≥ 2 x （Hello Time + 1 second）

　　端口优先级（Port Priority）：数值范围从0到255数值越小，那么该端口越可能成为根端口。