资源预留协议RSVP

资源预留协议RSVP   
1.   RSVP协议： 
RSVP   (Resorce   reSerVation   Protocol)   资源预留协议并不是一个路由协议，而是一种IP网络中的信令协议，它与路由协议相结合来实现对网络传输服务质量（QoS）的控制。RSVP是为支持因特网综合业务而提出的。这是解决IP通信中QoS（服务质量）问题的一种技术，用来保证点端到端的传输带宽。 

2.   RSVP协议是如何工作： 
RSVP使用控制数据报，这些数据报在向特定地址传输时包括了需要由路由器检查（有些时候需要更新）的信息,如果路由器需要决定是不是要检查数据报的内容的时候对上层数据内容进行语法分析。这种分析的代价可不小。现在的情况是，网络终端利用它向网络申请资源，在这种表明“申请”   的信号中，包含着如下的信息：业务的种类？   使用者类型？   什么时间？   需要多大带宽？   其他参考信息？   网络在接收到上类信息后，会根据实际情况为此次连接分配一个优先代码，用户利用优先代码进行信息传递时，网络不需重新对业务进行分析与判别，从另外一个角度来说，利用RSVP   能从一定程度上减少网络对信息处理的时延，提高网络节点的工作效率，改善信息传输的服务质量（QoS）。实时应用用RSVP是为了在传输路径中保持必要的资源以保证请求能确保到达。 
RSVP是IP路由器为提供更好的服务质量向前迈进的具有深刻意义的一步。传统上IP路由器只负责分组转发，通过路由协议知道邻近路由器的地址。而RSVP则类似于电路交换系统的信令协议一样，为一个数据流通知其所经过的每个节点（IP路由器），与端点协商为此数据流提供质量保证。RSVP协议一出现，立刻获得广泛的认同，基本上被任为较好地解决了资源预留的问题。 

它跟RTP协议、RTCP协议、RTSP协议都是实时媒体控制的相近的四个协议。 

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RSVP Protocol Overview 

A host uses RSVP to request a specific Quality of Service (QoS) from the network, on behalf of an application data stream. RSVP carries the request through the network, visiting each node the network uses to carry the stream. At each node, RSVP attempts to make a resource reservation for the stream.

To make a resource reservation at a node, the RSVP daemon communicates with two local decision modules, admission controland policy control. Admission control determines whether the node has sufficient available resources to supply the requested QoS. Policy control determines whether the user has administrative permission to make the reservation. If either check fails, the RSVP program returns an error notification to the application process that originated the request. If both checks succeed, the RSVP daemon sets parameters in a packet classifier and packet scheduler to obtain the desired QoS. The packet classifier determines the QoS class for each packet and the scheduler orders packet transmission to achieve the promised QoS for each stream.

A primary feature of RSVP is its scalability. RSVP scales to very large multicast groups because it uses receiver-oriented reservation requests that merge as they progress up the multicast tree. The reservation for a single receiver does not need to travel to the source of a multicast tree; rather it travels only until it reaches a reserved branch of the tree. While the RSVP protocol is designed specifically for multicast applications, it may also make unicast reservations.

RSVP is also designed to utilize the robustness of current Internet routing algorithms. RSVP does not perform its own routing; instead it uses underlying routing protocols to determine where it should carry reservation requests. As routing changes paths to adapt to topology changes, RSVP adapts its reservation to the new paths wherever reservations are in place. This modularity does not rule out RSVP from using other routing services. Current research within the RSVP project is focusing on designing RSVP to use routing services that provide alternate paths and fixed paths.

RSVP runs over IP, both IPv4 and IPv6. Among RSVP's other features, it provides opaque transport of traffic control and policy control messages, and provides transparent operation through non-supporting regions.

For more information, see the RSVP publication list.

    

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