DSDV的问题（Problems of DSDV）

今天上课的时候还听见可爱的胖胖老师说，很多文章只告诉你一项技术的优点，但讲到缺点的文章就会少很多了。那么，现在就接着翻译来数落下DSDV的缺点吧！

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The main purpose of DSDV is to address the loopingproblem of the conventional distance vector routingprotocol and to make the distance vector routing moresuitable for ad hoc networks routing. However, DSDVarises route fluctuation because of its criteria of routeupdates. At the same time, DSDV does not solve thecommon problem of all distance vector routingprotocols, the unidirectional links problem.

DSDV的主要目的是消除传统的DV路由协议中出现的循环问题，从而使DV更适合应用于ad hoc网络中的路由问题。然而，因为它的路径更新的准则使DSDV增加了路径波动。同时，DSDV没能解决所有DV路由协议中一个常见的问题：单向链接问题。

阻尼振动 Damping Fluctuation

Fluctuation is a general problem arising in DSDV by thefollowing criteria of route updates:

• Routes are always preferred if the sequencenumbers are newer, routes with older sequencenumbers are discarded.
• A route with a sequence number equal to that ofan existing route is preferred if it has a bettermetric, and the existing route is discarded orstored as less preferable.

因为路径更新标准，波动问题是DSDV中一个常见的问题：

• 具有更新的序列号码的路径总是更被接受，而有老的序列号的路径将被舍弃。
• 一个具有与已存在的路径相同序列号码的路径，如果它有很小的metric值，那么已存在的路径将被舍弃或被存储为less preferable。

The broadcasts of routing information by mobile nodesare asynchronous events, though some regularity isexpected. In the case of many mobile nodesindependently transmitting update messages and havingmarkedly different transmission intervals, it may turn outthat a particular mobile node receives new updatepackets in a way that causes this mobile node toconsistently change route back and forth betweendifferent next hops, even though no network topologychange has taken place. This fluctuation happensbecause of the above two route selection criteria.Conceivably, a mobile node can always receive tworoutes with equal sequence numbers or with a newersequence number one after the other via differentneighbors to the same destination, but the mobile nodealways gets the route with the worse metric first. Thissituation leads to the fluctuation with a continuing burstof new update packets. This can happen when there aremany mobile nodes, all transmitting their updatesirregularly. Alternatively, if the mobile nodes are actingindependently and with and with markedly differentlytransmission intervals, the situation can occur with fewermobile nodes.

先出去下。。。一会补全！