英语翻译5.2.4 Distance Vector RoutingModern computer networks generally use dynamic routing algorithms rather than the static ones described above because static algorithms do not take the current network load into account.Two dynamic algorithms

英语翻译5.2.4 Distance Vector RoutingModern computer networks generally use dynamic routing algorithms rather than the static ones described above because static algorithms do not take the current network load into account.Two dynamic algorithms
英语翻译
5.2.4 Distance Vector Routing
Modern computer networks generally use dynamic routing algorithms rather than the static ones described above because static algorithms do not take the current network load into account.Two dynamic algorithms in particular,distance vector routing and link state routing,are the most popular.In this section we will look at the former algorithm.In the following section we will study the latter algorithm.
Distance vector routing algorithms operate by having each router maintain a table (i.e,a vector) giving the best known distance to each destination and which line to use to get there.These tables are updated by exchanging information with the neighbors.
The distance vector routing algorithm is sometimes called by other names,most commonly the distributed Bellman-Ford routing algorithm and the Ford-Fulkerson algorithm,after the researchers who developed it (Bellman,1957; and Ford and Fulkerson,1962).It was the original ARPANET routing algorithm and was also used in the Internet under the name RIP.
In distance vector routing,each router maintains a routing table indexed by,and containing one entry for,each router in the subnet.This entry contains two parts:the preferred outgoing line to use for that destination and an estimate of the time or distance to that destination.The metric used might be number of hops,time delay in milliseconds,total number of packets queued along the path,or something similar.
The router is assumed to know the ''distance'' to each of its neighbors.If the metric is hops,the distance is just one hop.If the metric is queue length,the router simply examines each queue.If the metric is delay,the router can measure it directly with special ECHO packets that the receiver just timestamps and sends back as fast as it can.
As an example,assume that delay is used as a metric and that the router knows the delay to each of its neighbors.Once every T msec each router sends to each neighbor a list of its estimated delays to each destination.It also receives a similar list from each neighbor.Imagine that one of these tables has just come in from neighbor X,with Xi being X's estimate of how long it takes to get to router i.If the router knows that the delay to X is m msec,it also knows that it can reach router i via X in Xi + m msec.By performing this calculation for each neighbor,a router can find out which estimate seems the best and use that estimate and the corresponding line in its new routing table.Note that the old routing table is not used in the calculation.
This updating process is illustrated in Fig.5-9.Part (a) shows a subnet.The first four columns of part (b) show the delay vectors received from the neighbors of router J.A claims to have a 12-msec delay to B,a 25-msec delay to C,a 40-msec delay to D,etc.Suppose that J has measured or estimated its delay to its neighbors,A,I,H,and K as 8,10,12,and 6 msec,respectively.

英语翻译5.2.4 Distance Vector RoutingModern computer networks generally use dynamic routing algorithms rather than the static ones described above because static algorithms do not take the current network load into account.Two dynamic algorithms
5.2.4距离矢量路由
现代计算机网络的普遍使用动态路由算法,而不是上述静态的,因为静态算法不考虑到当前的网络负载.特别是两个动态算法,距离矢量路由和链接状态路由,是最受欢迎的.在本节中,我们将看到前算法.在下面的章节中,我们会研究后者算法.
距离矢量路由算法操作由每个路由器维护一个表（即向量）给予最知名的距离,每个目标和使用的线到达那里.这些表更新与邻居交换信息.
距离矢量路由算法有时也被称为其他的名字,最常见的是分布的Bellman - Ford路由算法和Ford - Fulkerson算法,在研究人员开发的是谁（贝尔曼,1957和福特和富尔克森,1962）.它也是最早的ARPANET路由算法,也是在互联网上使用的名义RIP协议.
在距离矢量路由,每个路由器维护一个路由表索引,并载有一个条目,每个子网的路由器.这个项目包含两个部分：首选出线使用该目的地和对时间或距离估计的目的地.度量可以使用跳数,延迟时间以毫秒为单位,沿路径,或类似的排队数据包的总数.
路由器假定知道'' ''的距离,它的每一个邻国.如果度量啤酒花,这种距离只是一跳.如果度量队列长度,路由器只需检查每个队列.若度量延误,路由器可以直接测量,特别欧共体的数据包接收时间戳和刚刚发回的速度,因为它可以.
作为一个例子,假设延迟用作度量和路由器的拖延知道它的每一个邻国.一旦每T毫秒每个路由器发送到每个邻居其估计延误清单中每个目的地.这也从每个邻居类似的名单.想象一下,这些表中的一个刚刚从邻居的X与习近平是X的估计,需要多长时间到达路由器岛如果路由器知道到X延迟米毫秒,但也知道,能经西安X路由器一+米毫秒.通过执行此为每个邻居,路由器计算可以找出估计似乎是最好的,估计和利用在其新的路由表中相应的行.请注意,旧路由表中没有计算.
这个更新过程如图所示.5-9.第（一）显示子网.第一部分的四个纵队（b）显示延迟向量从路由器j.这时邻居声称已收到12毫秒延迟到B,25毫秒延迟至C,40毫秒延迟至D等.假设J有测量或延误,估计其邻国,阿,我,H和为8,10,12 K和6毫秒,分别