EPC网络中，网络侧发起的Qos控制和实时计费High Level场景说明。

爱卫生

本文摘自：“SAE and the Evolved Packet Core”一书的第8.2.3.3章节。下图描述了在EPC的网络中，由网络侧发起的Qos控制和实时计费的场景。

1 UE发起一个应用业务，这里的例子是一个IMS的语音呼叫，并且执行端到端的信令交互，这里的对端服务节点为IMS网络中的AF（应用功能）即P-CSCF来处理用户的IMS呼叫，使用的信令协议是SIP以及SDP协议。通过SDP协议可以来描述这个会话的相关信息（通常和SIP是一起使用的）。

2 根据包含在应用层信令中对业务的描述信息，AF通过Rx接口为PCRF提供了和业务相关的信息（PCRF可以据此来做为对Qos控制的参考依据）。AF将把SDP和应用相关的会话信息映射到Rx接口消息中的信息元素并提供给PCRF。这些信息通常就包括了Qos的信息（即对这种业务，bit rate的需求）以及流量的参数（例如IP包的五元组），这样将使得PCRF上能够将这个业务会话和IP flow对应起来。

3 PCRF可以向SPR请求用户的一些签约的业务信息。

4 PCRF根据运营商制定的业务策略、会话相关的信息、用户的签约信息以及其他数据综合考虑，来制定这个业务的策略决定（即怎样做Qos控制）。如果用公式化来表达，可以把这个策略决定叫做一个PCC规则（policy charging control)。

5 PCC规则将由PCRF发给PCEF（策略的执行者，通常是GGSN，EPC中，PCEF是PGW）。PCEF将根据接收到的PCC规则来强制执行Qos管控。所有的和这个用户相关的用户面流量和IP连接将创过PCEF。

6 如果PCC规则中设置了实时计费的规则，则PCEF将通过Gy接口向OCS去申请本次用户访问所需要的quota（即申请本次用户建立SIP会话所需要的字节数），所使用的申请方法在PCC规则中指明。

7 PCEF在本地安装好PCC规则，并且和相应的承载做一个绑定（即IP-CAN）来确保这个业务流量能获取到相应的Qos保障。这有可能需要发起建立一个新的承载（即专有承载），或对现有的承载进行Qos的修改更新。

8 现在UE开始发送上行数据（SIP消息）并且在网络中传递并送给PCEF，PCEF对这个业务流执行检测，发现这是一个SIP会话，并且在第7步中，已经和一个承载进行了绑定（对应到一种Qos待遇）。那这个IP flow就会通过对应的承载进行传送。

原文如下：

1.  The subscriber initiates a service, for example, an IMS voice call, and per-forms end-to-end application session signalling that is intercepted by the AF (P-CSCF in the IMS case). In the IMS case, the application signalling is using the Session Initiation protocol (SIP). A description of the service is provided as part of the application signalling. In IMS, the Session Description Protocol (SDP) is used to describe the sessions.

2.  Based on service description information contained in the application sig-nalling, the AF provides the PCRF with the service-related information over the Rx interface. The session information is mapped at the AF from a SDP (e.g. SIP/SDP for IMS) into information elements in the Rx messages to the PCRF. This information typically includes QoS information (type of service bit rate requirements) as well as traffic parameters (e.g. the IP 5-tuple) that allow identification of the IP flow(s) corresponding to this service session.

3. The PCRF may request subscription-related information from the SPR. (The PCRF may have requested subscription information earlier but it is shown at this step for illustrative purposes.)

4. The PCRF takes the session information, operator-defined service policies, subscription information and other data into account when building policy decisions. The policy decisions are formulated as PCC rules.

5. The PCC rules are sent by the PCRF to the PCEF. The PCEF will enforce the policy decision according to the received PCC rule. All user plane traffic for a given subscriber and IP connection pass through the network entity where the PCEF is located. For EPS, the PCEF is located in the PDN GW.

6. If the PCC rule specified that online charging shall be used for this PCC rule, the PCEF contacts the OCS via the Gy reference point to request credit according to the measurement method specified in the PCC rule.

7. The PDN GW (PCEF) installs the PCC rules and performs bearer binding to ensure that the traffic for this service receives appropriate QoS. This may result in the establishment of a new bearer, or a modification of an existing bearer. More details on bearer binding is provided further below.

8. The media for the service session is now being transported across the net-work and the PCEF performs SDF detection to detect the IP flow for this service. This IP flow is transported over the appropriate bearer. Further details on SDF detection can be found below.

zzz

爱版主能否举个数据业务的例子（如手机上某个APP应用程序触发的PCC过程）呢？

爱卫生

zzz 发表于 2013-8-12 23:01
爱版主能否举个数据业务的例子（如手机上某个APP应用程序触发的PCC过程）呢？

任何一种业务都会触发PCC啊（只要运营商部署了PCC的话），包括你的default bearer以及dedicated bearer创建可能都需要和PCC交互。