The IEEE 802.5 token ring allows the user to define multiple message priorities. The priority mechanism is implemented using a reservation scheme whereby packets attempt to reserve the token. We present an analytic model that predicts mean delay for each priority level. We show that operation of the priority mechanism is not free; that is, there is a well-defined cost (measured in terms of increased average message delay) associated with its implementation, and that in general there is minimal discrimination made between the various priority levels. We also show that the cost of the priority mechanism is an easily computable function of various network parameters. One of the circumstances where the priority mechanism results in a large discrimination between priorities is when service is limited to a single packet per received token. We show that single-packet-per-token service is necessary (but not sufficient) to gain maximum benefit from priority operation. Our main conclusion is that the network user will not, in general, receive much benefit from the priority mechanism since the priority mechanism can in fact
IEEE 802.5令牌环允许用户定义多个消息优先级。使用保留方案来实现优先级机制,由此数据包尝试保留令牌。我们提出了一个分析模型,可以预测每个优先级的平均延迟。我们证明优先级机制的运作不是免费的。也就是说,有一个明确的成本(以增加的平均消息延迟来衡量)与其实施相关,并且通常在各个优先级之间的区别很小。我们还表明,优先级机制的成本是各种网络参数的易于计算的函数。优先级机制导致优先级之间有较大区别的情况之一是,服务被限制为每个接收到的令牌只有一个数据包。我们展示了单令牌单令牌服务是必要的(但不足),以便从优先级操作中获得最大的收益。我们的主要结论是,网络用户通常不会从优先级机制中获得很多收益,因为优先级机制实际上可以
Univ. of Virginia, Charlottesville;
机译:优先级在802.5令牌环中有用吗?
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机译:优先级在802.5令牌环中有用吗?