9.2.2 PDP上下文激活流程

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9.2.2.1 PDP Context Activation Procedure
    The PDP Context Activation procedure is illustrated in Figure 63 and Figure 64.
    PDP上下文的激活流程请参考图例63和64。

Figure 63- PDP Context Activation Procedure for A_Gb mode

Figure 64- PDP Context Activation Procedure for Iu mode

   NOTE 1: All steps in figures 63 and 64, except steps 4 and 8, are common for architecture variants using Gn/Gp based interaction with GGSN and using S4 based interaction with S GW and P GW. For an S4-based interaction with S GW and P GW, procedure steps (A) and (B) are defined in clause 9.2.2.1A.
   If Emergency Service is required and an emergency PDP Context is not already active the MS shall request a PDP Context for emergency services via emergency indication in the Activate PDP Context Request message when initiating the PDP Context Request Procedure. An emergency attached MS shall initiate the PDP Context Request procedure directly after the Attach procedure is completed. Any additional emergency PDP Context Activation by an MS shall be rejected by the SGSN if there is already an emergency PDP context activated.
   注释1：所有在图例63和64描述的步骤，除了步骤4和8，对于使用Gn/Gp接口和GGSN交互，还是使用S4接口和SGW/PGW交互都是公共的流程。对于使用S4接口和SGW/PGW的交互，步骤A和B在9.2.2.1A中定义。

   如果需要紧急服务但又没有一个紧急的PDP上下文是active的，则MS应在发起PDP激活流程时，在Activate PDP Context Request消息中携带紧急指示来请求一个用于紧急业务的PDP上下文。一个已经紧急附着的MS应在附着流程完成之后发起PDP上下文激活流程。如果已经有一个紧急PDP上下文激活的话，则任意额外的PDP上下文激活请求都将被SGSN拒绝。

   1) The MS sends an Activate PDP Context Request (NSAPI, TI, PDP Type, PDP Address, Access Point Name, QoS Requested, Protocol Configuration Options, Request Type) message to the SGSN. In this version of the protocol, the MS shall leave PDP Address empty. The MS may use Access Point Name to select a reference point to a certain packet data network and/or to select a service. Access Point Name is a logical name referring to the packet data network and/or to a service that the subscriber wishes to connect to. QoS Requested indicates the desired QoS profile. For an E-UTRAN capable UE, the QoS requested shall include interactive or background traffic class in this message. If the UE is not E-UTRAN capable, in this release the QoS requested should include interactive or background traffic class in this message. If the request is as a result of a Network-Requested PDP context activation procedure, the MS shall not set the PDP Type to IPv4v6, but to the value received in the Request PDP Context Activation message: see clause 9.2.2.2.1.

   1）MS发送一个Activate PDP Context Request(NSAPI、TI、PDP Type、PDP Address、APN、Qos Requested、PCO、Request Type）消息给SGSN。在这个版本的协议中,MS应将PDP地址留为空。MS可以使用APN来选择到一个特定PDN网络的参考点并且/或者选择某项服务。APN是一个逻辑的名字，对应到一个PDN网络并且/或者一个签约用户期望连接的服务。"Qos Requested"指示了Qos profile。对于一个具有LTE能力的UE，则请求的QOS应指示交互式或背景类的流量类别。如果UE没有LTE的能力，在这个规范版本中，请求的Qos应指示交互式或背景类的流量类别。如果这个请求消息是作为一个"Network Requested PDP Context Activation"流程的结果，MS则不应将PDP类型设置为IPv4v6，但是应在请求的PDP上下文激活消息中设置，参考9.2.2.2.1。

   NOTE 2: In case an S4-SGSN is used in the network the QoS Requested information element shall be ignored in the network.
   Protocol Configuration Options is used to transfer the NRSU and Address Allocation Preference to the GGSN and may be used to transfer the BCM as well as optional PDP parameters and/or request to the GGSN (see TS 29.060 [26] and TS 24.229 [75]). Protocol Configuration Options is sent transparently through the SGSN. NRSU indicates MS support of the network requested bearer control. The Protocol Configuration Options may include the Address Allocation Preference indicating that the MS prefers to obtain an IPv4 address only after the PDP Context Accept by means of DHCPv4 as defined in RFC 2131 [47].
   注释2：如果场景中是一个S4-SGSN，则Qos Requested IE应被网络侧忽略。

   PCO用于传递NRSU和地址分配期望给GGSN并且可用来传递BCM以及可选的PDP参数以及/或者请求给GGSN（参考TS29.060以及TS24.229)。PCO通过SGSN进行透明的传递。NRSU指示了MS对网络侧请求的承载控制的支持能力。PCO也可以包含MS的地址分配期望来指示GGSN，MS是仅期望在PDP上下文接受后通过DHCPV4的方法来获取一个IPv4的地址。

   If the SGSN has stored a value for the Maximum APN restriction and the value indicates the most restrictive type, then the SGSN shall reject any Activate PDP Context requests to a different APN, using the PDP Context Activation Reject message including an appropriate error cause.
   If the SGSN decides to establish Direct Tunnel between RNC and GGSN, the SGSN provides to the RNC the Direct Tunnel specific parameters in step 5 "RAB Assignment Procedure" and shall initiate PDP Context Update procedure in step 8 to update IP Address and TEID for Downlink data.
   Request Type indicates "Handover" when the MS has already an activated PDN GW/HA due to mobility with non-3GPP accesses, and is only interpreted by SGSNs using S4.
   如果存储了一个最大APN限制的值并且这个值指示了限制类型，SGSN应拒绝任意到另一个不同APN的PDP上下文激活请求，使用PDP Context Activation Reject消息并包含一个合适的错误代码。

   如果决定在RNC和GGSN之间建立直接隧道，则SGSN在步骤5"RAB Assignment流程"中给RNC提供直接隧道相关的参数并且应在第8步发起PDP Context Update流程来更新下行数据的IP地址和TEID。

   Request Type在MS因为非3GPP接入的移动已经有一个激活的PDN GW/HA，指示为"Handover"。并仅仅由使用S4接口的SGSN来解释。

   The PDP context activation for emergency services shall be exempted from the Maximum APN restriction control. If there is already an emergency bearer activated, the SGSN shall reject any PDP context activation request for normal services if the mobility and access restrictions do not allow the MS to access normal services.
   If the message is being sent via a HNB which has a collocated L-GW, it includes the L-GW address in the Direct Transfer message to the SGSN.

   对于紧急业务的PDP上下文激活不受最大APN限制的控制。如果已经有紧急承载激活了，并且移动和接入限制不允许MS来接入正常业务的话，则SGSN应拒绝任何正常业务的PDP上下文激活请求。

   如果消息是通过带有捆绑LGW的HNB（家庭基站）发送，它将在直传消息中包含L-GW地址给SGSN。

   2) In A/Gb mode, security functions may be executed. These procedures are defined in clause "Security Function".
   3) In A/Gb mode and if BSS trace is activated, the SGSN shall send an Invoke Trace (Trace Reference, Trace Type, Trigger Id, OMC Identity) message to the BSS. Trace Reference, and Trace Type are copied from the trace information received from the HLR or OMC.
   4) The SGSN validates the Activate PDP Context Request using PDP Type (optional), PDP Address (optional), and Access Point Name (optional) provided by the MS and the PDP context subscription records. The SGSN shall use the CSG Subscription Data to authorize the LIPA connection to the APN provided by the MS. A PDP Address may only be sent by an MS implemented according to an earlier protocol release. The validation criteria, the APN selection criteria, and the mapping from APN to a GGSN are described in annex A.
   2）对A/Gb模式，可以执行安全功能。这些流程请参考章节“安全功能”。

   3）对于A/Gb模式并且BSS的trace功能激活了，SGSN应发送Invoke Trace(Trace Reference, Trace Type, Trigger Id,OMC Identity)消息给BSS。Trace Reference，以及Trace Type是从HLR或OMC收到的trace信息中复制过来的。

   4）SGSN使用PDP上下文的签约数据来对MS的Activate PDP Context Request消息中的PDP Type（可选），PDP地址（可选）以及APN（可选）来进行验证。SGSN应使用CSG签约信息来为提供了APN的MS的LIPA连接进行授权。PDP地址仅可以是由一个早期协议版本实现MS发送。验证的原则，APN选择的原则，APN和GGSN的映射请参考附录A。

   For an emergency PDP Context Activation the SGSN applies the parameters from SGSN Emergency Configuration Data for the emergency bearer establishment performed in this step and any potentially stored IMSI related subscription data are ignored by the SGSN.
   If no GGSN address can be derived or if the SGSN has determined that the Activate PDP Context Request is not valid according to the rules described in annex A, the SGSN rejects the PDP context activation request.

   If a GGSN address can be derived, the SGSN creates a TEID for the requested PDP context. If the MS requests a dynamic address, the SGSN lets a GGSN allocate the dynamic address. The SGSN may restrict the requested QoS attributes given its capabilities and the current load, and it shall restrict the requested QoS attributes according to the subscribed QoS profile.
   对于一个紧急的PDP上下文激活，SGSN将应用SGSN中关于紧急配置数据中的参数来建立紧急承载，其他的可能存储的和IMSI相关的签约数据在SGSN中将被忽略。

   如果获取不到GGSN的地址，或者如果SGSN认为这个请求的Activate PDP Context Request消息经过对照附录A的规则进行检查发现是invalid,则SGSN拒绝这个PDP上下文的激活请求。

   如果可以获取到GGSN的地址，则SGSN为请求的PDP上下文创建一个TEID。如果MS请求一个动态地址，SGSN将让GGSN来分配动态地址。SGSN可以根据它的能力以及当前的负荷状况来限制MS请求的Qos，并且也应根据用户签约的Qos profile里的数据来限制用户请求的Qos属性。

   The SGSN sends a Create PDP Context Request (PDP Type, PDP Address, Access Point Name, QoS Negotiated, Negotiated Evolved ARP, TEID, NSAPI, MSISDN, Selection Mode, Charging Characteristics, Trace Reference, Trace Type, Trigger Id, OMC Identity, Protocol Configuration Options, serving network identity, Maximum APN Restriction IMEISV, CGI/SAI, User CSG Information, RAT type, S-CDR CAMEL information, MS Info Change Reporting support indication, NRSN, Dual Address Bearer Flag, APN-AMBR) message to the affected GGSN. The Negotiated Evolved ARP IE shall contain the Subscribed Evolved ARP value. If the SGSN did not receive a Subscribed Evolved ARP value in subscription data from the HLR the SGSN shall derive this value from the Allocation/Retention Priority of the QoS profile negotiated according to Annex E in TS 23.401 [89]. The inclusion of the Negotiated Evolved ARP IE indicates that the SGSN supports the Evolved ARP feature. The SGSN shall send the serving network identity to the GGSN. Access Point Name shall be the APN Network Identifier of the APN selected according to the procedure described in Annex A. PDP Address shall be empty if a dynamic address is requested. The GGSN may use Access Point Name to find a packet data network and optionally to activate a service for this APN. Selection Mode indicates whether a subscribed APN was selected, or whether a non-subscribed APN sent by an MS or a non-subscribed APN chosen by the SGSN was selected. Selection Mode is set according to Annex A. The GGSN may use Selection Mode when deciding whether to accept or reject the PDP context activation. For example, if an APN requires subscription, the GGSN is configured to accept only the PDP context activation that requests a subscribed APN as indicated by the SGSN with Selection Mode. Charging Characteristics indicates which kind of charging the PDP context is liable for. The charging characteristics on the subscription and individually subscribed APNs as well as the way the SGSN handles Charging Characteristics and chooses to send them or not to the GGSN is defined in TS 32.251 [70]. The SGSN shall include Trace Reference, Trace Type, Trigger Id, and OMC Identity if GGSN trace is activated. The SGSN shall copy Trace Reference, Trace Type, and OMC Identity from the trace information received from the HLR or OMC. The Maximum APN Restriction denotes the most stringent restriction as required by any already active PDP contexts. If there are no already active PDP contexts, this value is set to the least restrictive type (see clause 15.4). If the GGSN receives the Maximum APN Restriction, then the GGSN shall check if the Maximum APN Restriction value does not conflict with the APN Restriction value associated with this PDP context request. If there is no conflict the request shall be allowed, otherwise the request shall be rejected with the SGSN sending a PDP Context Activation Reject Message to the MS including an appropriate error cause. NRSN indicates SGSN support of the network requested bearer control. The Dual Address Bearer Flag shall be set when the MS requests PDN type IPv4v6 and all SGSNs, which the MS may be handed over to, are Release 8 or above supporting dual addressing, which is determined based on node pre configuration by the operator.

   SGSN发送一个Create PDP Context Request(PDP Type, PDP Address, Access Point Name, QoS Negotiated, Negotiated Evolved ARP, TEID, NSAPI, MSISDN, Selection Mode, Charging Characteristics, Trace Reference, Trace Type, Trigger Id, OMC Identity, Protocol Configuration Options, serving network identity, Maximum APN Restriction IMEISV, CGI/SAI, User CSG Information, RAT type, S-CDR CAMEL information, MS Info Change Reporting support indication, NRSN, Dual Address Bearer Flag, APN-AMBR)消息给相应的GGSN。协商的演进ARP IE应包含签约的演进ARP的值。如果SGSN没有从HLR的签约数据中获取这个值，那SGSN应按照TS23.401附录E的规则，从协商的Qos profile里面的ARP值来获取对应的演进ARP。协商的演进ARP IE指示了SGSN是否支持这个特性。SGSN应发送服务网络ID给GGSN。APN应该是根据附录A的规则选择的APN的Network ID部分。如果请求的是动态地址，则PDP地址 IE应留为空。GGSN可以使用APN来找到对应的PDN网络以及可选的来为这个APN激活某项业务。选择模式指示了是否选择的是一个签约的APN，或者是由MS发送的未签约的APN，或者是由SGSN选择未签约的APN。选择模式根据附录A进行设置。GGSN可以使用选择模式来决定是接受还是拒绝这个PDP上下文的就好哦。例如：如果是一个请求签约的APN，GGSN上配置了可以接受由SGSN通过选择模式指示请求一个签约APN。计费特征CC指示了PDP上下文适用于什么类型的计费。签约数据中的CC以及个别签约的APN以及SGSN处理CC的方法以及选择它们来发送或不发送给GGSN，在TS32.251中定义。如果GGSN trace激活了，SGSN则应在消息中包含Trace Reference, Trace Type, Trigger Id, 和OMC Identity。上述这些和trace有关的信息是从HLR或OMC中收到，并复制过来的。最大APN限制指示了针对任意已经激活的PDP上下文的最严厉的限制。如果没有已经激活的PDP上下文，这个值将设置为最少限制类型（参考章节15.4）。如果GGSN收到了这个最大APN限制，那么GGSN应检查最大APN限制的值和这个PDP上下文请求关联的APN限制的值不冲突。如果没有冲突，则请求被允许，否则请求应被拒绝，并带上合适的原因代码。NRSN指示了SGSN是否支持网络侧请求的承载控制。Dual Address Bearer Flag是在MS请求PDN类型为IPv4v6的时候设置。

  For emergency attached UEs IMSI is included if available and if the IMSI cannot be authenticated the IMSI is included and marked as unauthenticated.
  The GGSN creates a new entry in its PDP context table and generates a Charging Id. The new entry allows the GGSN to route PDP PDUs between the SGSN and the packet data network, and to start charging. The way the GGSN handles Charging Characteristics that it may have received from the SGSN is defined in TS 32.251 [70]. The GGSN may restrict QoS Negotiated given its capabilities and the current load or increase the QoS Negotiated based on any external input (e.g. policy control). The GGSN then returns a Create PDP Context Response (TEID, PDP Type, PDP Address, Protocol Configuration Options, QoS Negotiated, Negotiated Evolved ARP, Charging Id, Prohibit Payload Compression, APN Restriction, Cause, MS Info Change Reporting Action, CSG Information Reporting Action, BCM, APN-AMBR) message to the SGSN. The GGSN sets the Negotiated Evolved ARP based on local policy or PCC. The Allocation/Retention Priority of the QoS Profile Negotiated is derived from the Evolved ARP according to the mapping principles of TS 23.401 [89], Annex E. The Prohibit Payload Compression indicates that the SGSN should negotiate no data compression for this PDP context. The SGSN shall apply the Negotiated Evolved ARP if received from the GGSN. If the MS has requested PDP type IPv4v6 and both IPv4 and IPv6 addressing is possible in the PDN but the Dual Address Bearer Flag is not set, or only single IP version addressing is possible in the PDN, the GGSN selects a single IP version (either IPv4 or IPv6). If the MS has requested PDP type IPv4 or IPv6, the GGSN uses the PDP type supplied by the MS in case it is supported in the PDN, otherwise an appropriate error cause will be returned. The GGSN allocates a PDP Address according to the selected PDP type. If the GGSN has selected a PDN type different from the one sent by the MS, the GGSN indicates, together with the PDP type IE, a reason cause to the MS why the PDP type has been modified as described in clause 9.2.1. PDP Address is included if the GGSN allocated a PDP address. If the GGSN has been configured by the operator to use External PDN Address Allocation for the requested APN, PDP Address shall be set to 0.0.0.0, indicating that the PDP address shall be negotiated by the MS with the external PDN after completion of the PDP Context Activation procedure. The GGSN shall relay, modify and monitor these negotiations as long as the PDP context is in ACTIVE state, and use the GGSN-Initiated PDP Context Modification procedure to transfer the currently used PDP address to the SGSN and the MS. However, the MS cannot rely on always getting a session management level update of the IP address, which it has negotiated with the external PDN. This is because the P-GW does not update the IP address within the EPS bearer modification procedure, see clause 9.2.3.2A. Protocol Configuration Options contains the BCM as well as optional PDP parameters that the GGSN may transfer to the MS. BCM shall also be sent as a separate IE to the SGSN. These optional PDP parameters may be requested by the MS in the Activate PDP Context Request message, or may be sent unsolicited by the GGSN. Protocol Configuration Options is sent transparently through the SGSN.The Create PDP Context messages are sent over the backbone network. The BCM is used by the SGSN to handle unexpected session management signalling.
  GGSN在它的PDP上下文中创建一个新的条目并且生成一个Charging Id.这个新的条目允许GGSN在SGSN和PDN网络之间为PDP PDUs进行路由，并且开始计费。GGSN上处理计费特征码的方法（可能从SGSN上获取）在TS32.251定义。GGSN可以根据它自己的能力以及当前的负荷情况对协商的Qos进行限制，或者根据任何外部输入（例如来自PCRF的策略控制）来增加协商的Qos。GGSN然后将返回一个Create PDP Context Response(TEID、PDP Type、PDP Address、PCO、Qos Negitiated、Negotiated Evolved ARP, Charging Id, Prohibit Payload Compression, APN Restriction, Cause, MS Info Change Reporting Action, CSG Information Reporting Action, BCM, APN-AMBR)消息给SGSN。GGSN根据本地策略或PCC来设置协商的演进ARP。协商的Qos Profile里的ARP是根据TS23.401的映射规则从演进的ARP里提取出来的。"禁止Payload压缩"指示了SGSN应为这个PDP上下文来协商无数据压缩。SGSN如果从GGSN收到协商的演进ARP的话，将应用这个值。如果MS请求的PDP Type IPv4v6并且IPv4和IPv6的地址在PDN网络中都可用的情况下则可为MS提供IPv4或IPv6，但是如果Dual Address Bearer Flag没有设置，或在PDN中仅支持一种单一的IP版本，GGSN将选择这个单一的IP版本（IPv4或IPv6）。如果MS请求的PDP类型是IPv4或IPv6，GGSN则使用MS提供的PDP类型---如果这在PDN网络中支持的话，否则将返回一个合适的原因代码。GGSN根据选择的PDP类型分配一个PDP地址。如果GGSN为MS选择了之前不一样的PDP类型，GGSN则和PDP类型 IE一起，给MS一个指示，告诉MS为什么PDP类型被修改，在9.2.1章节描述。如果GGSN分配了一个PDP地址则要包含这个PDP地址。如果GGSN配置了使用外部PDN地址分配机制（例如DHCP），则PDP地址应设置为0.0.0.0，指示MS应在完成PDP上下文激活流程之后和外部PDN网络协商来获取PDP地址。只要这个PDP上下文一直保持在Active状态，则GGSN应能为这种地址协商提供透传、修改和监控机制，并且能使用GGSN发起的PDP上下文修改流程来传递当前使用的PDP地址给SGSN和MS。然而，MS不能总是依赖于得到一个IP地址的会话管理级别的更新（如果这个IP地址是和外部PDN协商获取的）。这是因为P-GW不能在EPS承载修改流程中更新IP地址，参考9.2.3.2A章节。PCO包含了BCM以及可选的由GGSN传递给MS的PDP参数。BCM应该作为一个单独的IE来发给SGSN。可选的PDP参数可以由MS在Activate PDP Context Request消息中请求，或者由GGSN主动发送。PCO是由SGSN进行透明传递的。Create PDP Context消息通过骨干网络进行发送。BCM被SGSN用于处理不期望的会话管理信令。

  If QoS Negotiated received from the SGSN is incompatible with the PDP context being activated, the GGSN rejects the Create PDP Context Request message. The GGSN operator configures the compatible QoS profiles.
  If an APN Restriction is received from the GGSN for this PDP Context, then the SGSN shall store this value for the PDP Context and the SGSN shall check this received value with the stored value for the Maximum APN Restriction to ensure there are no conflicts between values. If the consequence of this check results in the PDP context being rejected, the SGSN shall initiate a PDP Context Deactivation and return an appropriate error cause. If the PDP Context is accepted, it shall determine a (new) value for the Maximum APN Restriction. If there is no previously stored value for Maximum APN Restriction, then the Maximum APN Restriction shall be set to the value of the received APN Restriction.
  The emergency PDP context activation shall be exempted from the Maximum APN restriction control.
  If the MS Info Change Reporting Action and/or the CSG Information Reporting Action are received from the GGSN for this PDP context, then the SGSN shall store this for the PDP context and the SGSN shall report to that GGSN whenever a CGI/SAI/RAI or user CSG information change occurs that meets the GGSN request, as described in clause 15.1.1a.
  The GGSN derives the BCM based on NRSU, NRSN and operator policy if previously received in the Create PDP Context Request message. The derived BCM is sent to the MS indicating the Bearer Control Mode applicable to all PDP Contexts within the activated PDP Address/APN pair.
  The SGSN shall re-verify and may restrict the QoS Negotiated received in the response from the GGSN against the subscribed QoS profile and additionally restrict the QoS negotiated based on its capabilities and current load. The SGSN shall use this updated QoS Negotiated for the subsequent steps.
  The SGSN shall apply a Negotiated Evolved ARP even if it is different from the Subscribed Evolved ARP.
  The SGSN determines the UE AMBR to be used by the RAN based on the subscribed UE-AMBR and the APN AMBR for active APNs, see clause 15.2.2.

   如果从SGSN收到的"Qos Negotiated"参数和准备激活的PDP上下文不兼容，则GGSN将拒绝这个PDP激活请求。GGSN的运营商配置这个兼容的Qos profile。
  如果从GGSN收到了关于这个PDP上下文的APN Restriction,那么SGSN应为这个PDP上下文存储这个值，并且SGSN应检查收到的这个值和Maximum APN Restriction的值，来确保两者没有冲突。如果作为检查的结果导致PDP上下文被拒绝，则SGSN应发起PDP上下文去激活流程并返回一个合适的原因代码。如果PDP上下文接受了，它应决定一个新的Maximum APN Restriction的值。如果之前没有存储Maximum APN Restriction的值，那Maximum APN Restriction的值应根据收到的APN Restriction的值来进行设置。
  紧急PDP上下文激活不受Maximum APN Restriction控制的限制。
  如果从GGSN收到PDP上下文的MS Info Change Reporting Action and/or the CSG Information Reporting Action，那么SGSN应为这个PDP上下文存储这些值，并且SGSN应在用户所处的CGI/SAI/RAI或用户CSG信息在满足GGSN发生改变的情况下，向GGSN进行报告，这在15.1.1a章节描述。
  GGSN根据NRSU、NRSN以及运营商策略来获取BCM，如果前面3个值在之前的Create PDP Context Request消息中收到的话。生成的BCM将发给MS来指示"Bearer Control Mode"将应用到所有的 激活的PDP地址/APN对的所有PDP上下文中。
  SGSN应重新验证并且可以根据自己的能力和当前的实际负荷情况来限制从GGSN收到的"Qos Negotiated"。SGSN应使用这个更新后的"Qos Negotiated"用于后续的步骤中。
  SGSN应应用收到的协商的演进ARP，即使这个值和签约的演进ARP不同。
  SGSN根据签约的UE-AMBR和APN AMBR来为active的APN来决定在RAN中使用的UE AMBR。参考章节15.2.2。

5) In Iu mode, RAB setup is done by the RAB Assignment procedure, see clause "RAB Assignment Procedure".
6) In Iu mode and if BSS trace is activated, the SGSN shall send an Invoke Trace (Trace Reference, Trace Type, Trigger Id, OMC Identity) message to the RAN. Trace Reference, and Trace Type are copied from the trace information received from the HLR or OMC.
   NOTE 3: Step 6 is applied when the trace activation is triggered by means of signalling. Another alternative is the triggering of trace activation by the OMC. The details of both Trace Activation procedures are described in TS 32.422 [84].
7) In A/Gb mode, BSS packet flow context procedures may be executed. These procedures are defined in clause "BSS Context".
   5)在Iu模式，RAB的建议通过"RAB Assignment流程"完成，参考章节"RAB Assignment流程"。
   6)在Iu模式并且如果BSS的trace激活了，SGSN应发送一个Invoke Trace(Trace Reference, Trace Type, Trigger Id, OMC Identity)消息给RAN。Trace Refercen以及Trace Type是从HLR或OMC收到的trace信息中复制过来的。
   注释3：步骤6是由信令的方式来触发的trace激活。作为可选的，也可以由网管中心来激活。细节在TS32.422描述。
  7)在A/Gb模式，BSS packet flow context流程应被执行。这些流程在章节"BSS Context"中定义。

8) In case the QoS attributes, used as input to step 5 for Iu mode or step 7 for A/Gb mode, have been downgraded during those steps, the SGSN may inform the GGSN about the downgraded QoS attributes by sending an Update PDP Context Request to the affected GGSN. The GGSN shall not attempt to renegotiate the QoS attributes. The No QoS negotiation indication is set in Update PDP Context Request to indicate to the GGSN that the SGSN does not upgrade the previously negotiated QoS attributes and that the GGSN shall accept the provided QoS attributes without negotiation. The GGSN confirms the new QoS attributes by sending an Update PDP Context Response to the SGSN. If the SGSN established Direct Tunnel in step 5 it shall send Update PDP Context Request and include the RNC's Address for User Plane, TEID for downlink data, No QoS negotiation indication and the DTI. DTI is used to instruct the GGSN to apply Direct Tunnel specific error handling as described in clause 13.8. The GGSN(s) shall not include a PCO in the Update PDP Context Response if the No QoS negotiation indication is set.
  8)关于Qos属性，如果在用于Iu模式的步骤5中，或者A/Gb模式的步骤7中，被降级了，则SGSN应给受到影响的GGSN发送Update PDP Context Request消息来通知GGSN关于降级的Qos属性。在这个请求消息中将携带一个"No Qos negotiation"指示来告诉GGSN，SGSN不能升级之前协商的Qos，并且GGSN现在也不允许协商这个Qos了，而只能接受这个降级的Qos。GGSN将确认这个新的Qos属性，发送Update PDP Context Response消息给SGSN。如果SGSN在步骤5建立了Direct Tunnel，则它应发送一个Update PDP Context Request消息给GGSN，消息包含了RNC用于下行数据的用户面的地址和TEID，No Qos negotiation指示以及DTI。DTI用于指示GGSN应用直接隧道，错误处理流程在13.8中定义。GGSN发现，如果有No Qos negotiation指示，则不应在Update PDP Context Response消息中包含PCO。

9) The SGSN inserts the NSAPI along with the GGSN address in its PDP context. The PDP address received from the GGSN or from HSS subscription records is inserted in the PDP context. The SGSN selects Radio Priority and Packet Flow Id based on QoS Negotiated, and returns an Activate PDP Context Accept (PDP Type, PDP Address, TI, QoS Negotiated, Radio Priority, Packet Flow Id, Protocol Configuration Options) message to the MS. If the MS indicated in the MS Network Capability it does not support BSS packet flow procedures, then the SGSN shall not include the Packet Flow Id. In A/Gb mode, the QoS Negotiated shall take into account the Aggregate BSS QoS Profile, if any, returned from the BSS. Protocol Configuration Options are used to transfer the BCM to the UE and may be used to transfer optional PDP parameters to the UE (see TS 29.060 [26] and TS 24.229 [75]). Protocol Configuration Options is sent transparently through the SGSN. The BCM indicates the Bearer Control Mode applicable to all PDP Contexts within the activated PDP Address/APN pair. If the BCM parameter is not included in the message then the MS shall set the Bearer Control Mode to 'MS_Only' for the PDP Address/APN pair (see clause 9.2). The SGSN is now able to route PDP PDUs between the GGSN and the MS, and to start charging.
   9)SGSN在它的PDP上下文中和GGSN地址一起插入一个NSAPI。PDP地址是从GGSN或者是从HSS的签约记录中收到，也插入到PDP上下文中。SGSN根据"Qos Negotiated"来选择无线优先级和Packet Flow Id，并且给MS返回一个Activate PDP Context Accept(PDP Type, PDP Address, TI, QoS Negotiated, Radio Priority, Packet Flow Id, Protocol Configuration Options)。如果MS在它的MS Network Capability能力集中指示了它不支持BSS packet flow流程，那么SGSN则不应包含Packet Flow Id。在A/Gb模式，在Aggregate BSS Qos Profile中应考虑从BSS返回的"Qos Negotiated"。PCO用于给UE传递BCM并且可以用来传递可选的PDP参数给UE（参考TS29.060和TS24.229）。PCO由SGSN进行透明的传递。BSM指示了应用Bearer Control Mode到所有激活的PDP地址/APN对的所有PDP上下文。如果BCM参数在消息中没有包含，那MS应将Bearer Control Mode设置为'MS_Only'（章节9.2）。SGSN现在可以在GGSN和MS之间路由PDP PDUs了，并且开始计费。
   If the MS is incapable of accepting the new QoS Negotiated, the MS should initiate application level signalling to lower the QoS requirements for the concerned application(s). If this is not possible then the MS shall instead de-activate the PDP context with the PDP Context Deactivation Initiated by the MS procedure.
For each PDP Context a different quality of service (QoS) profile may be requested. For example, some PDP contexts may be associated with E mail that can tolerate lengthy response times. Other applications cannot tolerate delay and demand a very high level of throughput, interactive applications being one example. These different requirements are reflected in the QoS profile. The QoS profile is defined in clause "Quality of Service Profile". If a QoS requirement is beyond the capabilities of a PLMN, the PLMN negotiates the QoS profile as close as possible to the requested QoS profile. The MS either accepts the negotiated QoS profile, or deactivates the PDP context.
   如果MS没有能力接受新的"Qos Negotiated",MS应从应用层这个级别发起一个信令消息来为相关的应用请求降低Qos的要求。如果这也不行，那么MS应发起一个去激活流程来将PDP上下文去激活。对每个PDP上下文可以请求不同的Qos profile。例如，一些PDP上下文可以和E-mail关联，并能忍受比较长的响应时间。其他的应用则不能忍受延迟并期望一个很高的吞吐量，例如一些交互式的应用。这些不同的需求都反映到Qos profile中。
   After an SGSN has successfully updated the GGSN, the PDP contexts associated with an MS is distributed as shown in clause "Information Storage".
  If the PDP Context Activation Procedure fails or if the SGSN returns an Activate PDP Context Reject (Cause, Protocol Configuration Options) message, the MS may attempt another activation to the same APN up to a maximum number of attempts.
   If the MS requested for a dual address PDP type (IPv4v6) to a given APN and was granted a single address PDP type (IPv4 or IPv6) by the network with a reason cause 'single address bearers only', the MS should request for the activation of a parallel PDP Context to the same APN with a single address PDP type (IPv4 or IPv6) other than the one already activated.
   在SGSN和GGSN成功的更新完之后，和MS相关的PDP上下文将被分发，在“信息存储”章节描述。
   如果PDP Context Activation流程失败或者如果SGSN返回了一个Activate PDP Context Reject(Cause,PCO)消息,MS可以在一个最大次数的范围内发起到相同APN的另一次激活。
   如果MS请求APN对应的PDN网络分配一个双地址PDP类型（IPv4v6），但网络侧只分配了一个单一的地址PDP类型（IPv4或IPv6）并且原因是'single address bearers only'，MS应再发起一个并行的PDP上下文激活请求，请求分配另外一个单一的PDP类型的地址。
   If the MS requested for a PDP type IPv4v6 to a given APN and was granted PDP type IPv4 with no reason cause indicating that only the assigned PDP type is allowed, the MS should request for the activation of a parallel PDP Context to the same APN with PDP type IPv6.
   If the MS receives no reason cause in response to an IPv4v6 PDP type and it receives an IPv6 prefix and Interface Identifier apart from the IPv4 address or 0.0.0.0 in the PDP Address field, it considers that the request for a dual address PDP was successful. It can wait for the Router Advertisement from the network with the IPv6 prefix information or it may send Router Solicitation if necessary.
  如果MS请求APN对应的PDN网络分配一个双地址PDP类型（IPv4v6），但网络侧只分配了一个单一的地址PDP类型是IPv4并没有携带原因值来指示只允许使用分配的PDP类型，MS应发起到相同APN的并行的PDP激活请求来请求分配IPv6的地址类型。
  如果MS针对请求的IPv4v6 PDP类型的响应中没有原因代码，但是它收到了一个IPv6的前缀和一个在PDP地址字段中除了IPv4地址或0.0.0.0地址以外的接口ID，它将认为请求的双地址PDP类型是成功的。它将等待网络侧的一个路由通告消息，来通告一个IPv6的地址前缀信息或如果有必要的话，它将发送一个RS消息。

laomeibulao

A GPRS subscription contains the subscription of one or more PDP addresses.
帮忙解释一下gprs subscirption，是不是就是所谓的gprs 签约数据？

爱卫生

回复 laomeibulao 的帖子

  是的，这句话是TS23.060第9章的第一句话。（唉呀，我是不是太学究了，呵呵！）
  一个用户的GPRS签约数据包括很多东西，包括APN列表和PDP地址。如果是包含多个PDP地址，则可以对应到多个APN，以及不同的PDP类型（如IPV4或IPV6）。当然，HLR当中的签约数据只会是静态IP。动态IP是由GGSN或外部PDN网络来分配的。

laomeibulao

回复 爱卫生 的帖子

学究很好。能不能举个实例我学习一下。

爱卫生

回复 laomeibulao 的帖子

   可以啊。你可以参考3 用户附着成功后，SGSN删除用户数据，用户关机再附着（但仍是同一个SGSN的服务区）这篇帖子中的抓包。#11号包就是HLR给SGSN回的MS的签约数据。你点开看以后，会发现有PDP-Type、APN以及Qos信息。这些在实际现网中，都是用户到移动营业厅花不同的钱开通的服务，将这些签约信息在后台转变成配置数据，配置到HLR上再通过附着流程下载到SGSN中。就可以检查用户的一些行为（如请求的APN、Qos等）是否违背了签约数据，网络侧可以拒绝。友好一点的，给你发个短信让你去交钱，或者重定向到一个欢迎页面。
   在这个例子里签约的APN为012a，对应的字符是*号，代表一个通配符。
   但这里没有用户签约的PDP地址信息，因为采用的是动态分配的方式。静态IP可能会比较少。只适用于一些特殊用户或高级别用户。

laomeibulao

回复 爱卫生 的帖子

比如APN列表的内容，什么时候是静态ip什么时候是动态ip。应该大多数情况下是动态ip，静态ip是不是收费就比较高?另外还有个问题就是关于APN的，你在primary pdp context activation视频讲解中讲过关于APN的内容。比如说：APN FULL NAME = CMWAP.MCC460.MNC00.GPRS。如果是这样的话sgsn就可以把这个apn发送给DNS进行地址解析。SGSN通过解析得到的ip地址寻址到GGSN。然后再去访问外部网络。整个一个过程是这样的。SGSN和GGSN是一个多对多的关系。问题如下：
1、比如SGSN发送给DNS的APN地址是CMWAP.MCC460.MNC00.GPRS。dns解析出来的是一个ip地址还是多个ip地址？
A Create PDP Context Request shall be sent from a SGSN node to a GGSN node as a part of the GPRS PDP Context Activation procedure. The GGSN IP address where the SGSN sends the Create PDP Context Request is the first IP address in the list of IP addresses provided by the DNS server. （09.60--7.5.1）
如果是一个ip地址，如何解释the list of ip addresses?如果不是一个ip，如何解释一个apn能被dns解析为对应多个ip？（我理解apn类似于我们平时上网的网址，但是又感觉不是那么回事，希望楼主斧正）
2、我对手机上网不太熟悉。手机访问baidu、Google等internet的网站是否跟我们普通pc访问的是相同的。假如说我的手机想访问www.baidu.com。那么首先我必须要具有什么样的apn签约数据。手机发给SGSN的Active pdp context request的里面是否必须含有什么样的apn？手机应该是想我们平时pc上网一样会输入www.baidu.com。然后这个网址是被包含在那个数据包或者信令里面来告诉网络它要访问www.baidu.com呢？手机这个访问该网址的这个目的是首先被那个网元所了解呢，SGSN?GGSN?OR SGSNandGGSN?另外www.baidu.com也需要DNS来解析出目的ip地址，这个DNS是否和解析APN的DNS为同一个DNS?
3、apn的概念希望楼主能够再介绍一下，总是感觉理解不对。
thank you for you help！

laomeibulao

上面的写的太久了，没有看到你最新的回复。解答过的问题就不用再讲了，呵呵！

爱卫生

回复 laomeibulao 的帖子

  哦，没关系的。呵呵。可能在别的帖子里有提过，但一下子我也搜索不到。但我看得出来，你能打这么多字，说明你对GPRS核心网很感兴趣啊。只要你有兴趣，我就非常乐于回答。而且我在公告区提过，其实论坛欢迎任何形式的提问，不要去管提问的技巧。只要提出来就应大声鼓励。
  你的问题，我尝试用一些简洁的语言来回答下。
1 APN列表的内容实际上就是一堆用户签约的APN的集合。例如大部分的用户的GPRS套餐都签约了cmwap、cmnet这两个APN。上述两个APN将在HLR的用户签约数据中定义，这就构成了一个APN列表（APN List）。
2 普通用户一般都是动态IP。一些有特殊需求的如高级领导要求使用固定的IP则会签约静态IP。另外还有一些行业应用例如银行的ATM取款机可能也会使用静态的IP。静态IP的收费不是特别清楚，可能会稍微高一点，但不会太高。因为不管动态还是静态，都是私有IP。对运营商来说，没有太多影响。主要是静态IP可能要求的Qos会更高一些，所以对应收费会更高。但并不一定是针对静态IP本身来说收的费。
3 SGSN通过APN的Full Name解析，从DNS得到的GGSN的地址是一堆IP地址的列表，如IP1、IP2、IP3等，分别对应GGSN1、GGSN2、GGSN3。SGSN将按照顺序依次和GGSN1/2/3进行PDP激活请求，但如果GGSN1响应了PDP激活请求，就不会和GGSN2去交互PDP激活请求了。除非GGSN1联系不上，产生了故障（这是由N3T3的Timer来控制的）。
4 APN是外部PDN网络的名字。PDN是一个通用的名字，基本上是代表数据网的一个通称。常见的PDN网络有传统的Internet、企业网还有基于WAP的网络。这3种网络是完全独立的，功能也不一样。而在这些PDN网络里可能就会有很多应用包括你说的很多网站来提供服务。例如www.baidu.com 就是cmnet这个APN（对应的是Internet这张PDN网）里的一个Web站点。
  在论坛“GPRS的故事”里，有提到，假设MS是用户，GGSN是物资局，那APN就代表不同的商家出售不同的商品，这些商家所组成的一张服务营销网可以对应成PDN的概念，每个商家的网络和商品都是独立的。GGSN即物资局和各商家进行通信，确保商品供货状态。而www.baidu.com就好象是这个商家提供的一个商品，代表的是新闻类业务，是一种商品名。
  或者就像你去医院看病一样，有各种专科医院。儿童医院、牙科医院、妇幼保健院、肿瘤医院等。这些医院类似就是APN。完全是独立的。而每个医院里又有不同的专业科室，对应的就是网站来提供各种不同的应用了。
5 如果手机是通过cmnet这个APN来上网，则流程和PC机上网是完全相同的（除了PS核心网侧的交互外）。你需要具备的签约数据就是去移动营业厅选择相应的GPRS套餐，现在所有的GPRS套餐都包含了cmnet这个APN。所以选任一种套餐都可以。手机发出来的APN一般都有默认设置，缺省可能是cmwap（取决于手机厂家的出厂设置，不需要用户人工去设，但用户可以在手机里选手机设置去改），这个APN就将包含在发给SGSN的Active pdp context request消息里。手机访问这个网址首先是发给SGSN的，然后是GGSN，HLR不参与（HLR只在附着流程时参与）。
6 www.baidu.com也需要DNS来解析出目的ip地址，这个DNS是否和解析APN的DNS为同一个DNS?
   这个问题问得很好。这两个DNS是完全不一样的。解析www.baidu.com对应的DNS是由GGSN来分配的，通常来说这个DNS和你用PC机上网用的DNS Server是一样的。而SGSN解析APN用到的DNS是属于运营商的专用DNS，对手机用户来说是不可知的。

爱卫生

  The Secondary PDP Context Activation procedure may be used to activate a PDP context while reusing the PDP address and other PDP context information from an already active PDP context, but with a different QoS profile. Procedures for APN selection and PDP address negotiation are not executed. A unique TI and a unique NSAPI shall identify each PDP context sharing the same PDP address and APN.
   PDP上下文二次激活流程可以用于激活一个PDP上下文，但仍复用一个已经激活的PDP上下文的PDP地址和其他PDP上下文信息，但是一定具有不同的Qos profile。APN的选择流程和PDP地址的协商将不被执行。每个共享了相同PDP地址和APN的PDP上下文都将有唯一的TI和一个唯一的NSAPI用来标识自己。
  The Secondary PDP Context Activation procedure may be executed without providing a Traffic Flow Template (TFT) to the newly activated PDP context if all other active PDP contexts for this PDP address and APN already have an associated TFT. Otherwise a TFT shall be provided. The TFT contains attributes that specify an IP header filter that is used to direct data packets received from the interconnected packet data network to the newly activated PDP context.
  如果所有其他具有相同PDP地址和APN的active的PDP上下文已经有一个关联的TFT，则PDP上下文二次激活流程可以不提供TFT来执行。否则，需要提供一个TFT。TFT包含的属性指明了一个IP包头过滤器，用于将从互联网络收到的数据包引导到新激活的PDP上下文。
  The Secondary PDP Context Activation procedure may only be initiated after a PDP context is already activated for the same PDP address and APN. The procedure is illustrated in Figure 65 and Figure 66.
  PDP上下文二次激活流程只能在已经有一个active的PDP上下文并且具有相同PDP地址和APN的情况下，才能发起建立。这个流程在图例65和66中描述。
  

Figure 65 Secondary PDP Context Activation Procedure for A_Gb mode

Figure 66 Secondary PDP Context Activation Procedure for Iu mode

1）The MS sends an Activate Secondary PDP Context Request (Linked TI, NSAPI, TI, QoS Requested, TFT, Protocol Configuration Options) message to the SGSN. Linked TI indicates the TI value assigned to any one of the already activated PDP contexts for this PDP address and APN. QoS Requested indicates the desired QoS profile. TFT is sent transparently through the SGSN to the GGSN to enable packet classification for downlink data transfer. TI and NSAPI contain values not used by any other activated PDP context. Protocol Configuration Options may be used to transfer optional PDP parameters and/or requests to the GGSN (see GSM 29.060 [26] and 24.229 [75]). Protocol Configuration Options is sent transparently through the SGSN.
If the SGSN decides to establish Direct Tunnel between RNC and GGSN, the SGSN provides to the RNC the Direct Tunnel specific parameters in step 4 "RAB Assignment Procedure" and shall initiate PDP Context Update procedure in step 6 to update IP Address and TEID for Downlink data.
   1 MS发送Activate Secondary PDP Context Request (Linked TI, NSAPI, TI, QoS Requested, TFT, Protocol Configuration Options)消息给SGSN.Linked TI指示的TI值表明了这个PDP上下文是和一个已经建立的具有这个PDP地址和APN的PDP上下文进行关联。 QoS Requested 指明了期望的Qos profile。TFT通过SGSN透明传递给GGSN用于下行方向数据传递的包的分类。TI和NSAPI包含的值不用于任何其他的已经激活的PDP上下文。PCO用于传递可选的PDP参数和/或请求给GGSN（参考GSM 29060和24229)。PCO是通过SGSN透明传递的。

   如果SGSN决定要建立一个RNC和GGSN之间的直接隧道，SGSN给RNC提供建立直接隧道相关的参数（在步骤4的RAB分配流程中指明）并且应发起PDP上下文更新流程（在步骤6中）来更新下行方向用户面的IP地址和TEID。   

2) In A/Gb mode, security functions may be executed. These procedures are defined in clause "Security Function".

   2 在A/Gb模式，安全功能可以执行。这个流程在"安全功能"章节定义。
3) The SGSN validates the Activate Secondary PDP Context Request using the TI indicated by Linked TI. The same GGSN address is used by the SGSN as for the already-activated PDP context(s) for that TI and PDP address.
   The SGSN may restrict the requested QoS attributes given its capabilities and the current load, and it shall restrict the requested QoS attributes according to the subscribed QoS profile, which represents the maximum QoS per PDP context to the associated APN. The GGSN may restrict or increase, and negotiate the requested QoS as specified in clause "PDP Context Activation Procedure". The SGSN sends a Create PDP Context Request (QoS Negotiated, TEID, NSAPI, Primary NSAPI, TFT, Protocol Configuration Options, serving network identity, IMEISV, CGI/SAI, RAT type, S-CDR CAMEL information, CGI/SAI/RAI change support indication, Correlation-ID) message to the affected GGSN. The SGSN shall send the serving network identity to the GGSN. Primary NSAPI indicates the NSAPI value assigned to any one of the already activated PDP contexts for this PDP address and APN. TFT is included only if received in the Activate Secondary PDP Context Request message. Protocol Configuration Options is sent transparently through the SGSN if received in the Activate secondary PDP Context Request message. The Correlation-ID shall only be included if the Secondary PDP Context Activation is performed as part of the Network Requested Secondary PDP Context Activation Procedure (clause 9.2.2.3), and shall be linked to the TI as described in clause 9.2.2.3.
   The GGSN uses the same packet data network as used by the already-activated PDP context(s) for that PDP address, generates a new entry in its PDP context table, and stores the TFT. The new entry will allow the GGSN to route PDP PDUs via different GTP tunnels between the SGSN and the packet data network. The GGSN returns a Create PDP Context Response (TEID, QoS Negotiated, Cause, Protocol Configuration Options, Prohibit Payload Compression, APN Restriction, CGI/SAI/RAI change report required) message to the SGSN. Protocol Configuration Options may be used to transfer optional PDP parameters to the UE (see GSM 29.060 [26] and 24.229 [75]). The Prohibit Payload Compression indicates that the SGSN should negotiate no data compression for this PDP context. If an APN Restriction is received from the GGSN for this PDP Context, then the SGSN shall store this value for the PDP Context.
   If the CGI/SAI/RAI report required is received from the GGSN for this PDP context, then the SGSN shall store this for the PDP context and the SGSN shall report to that GGSN whenever a CGI/SAI/RAI change occurs that meets the GGSN request.
   The SGSN shall re-verify and may restrict the QoS Negotiated received from the GGSN against the subscribed QoS profile and additionally restrict the QoS negotiated based on its capabilities and current load. The SGSN shall use this updated QoS Negotiated for the subsequent steps.

   3)SGSN使用Linked TI里面指明的TI值来验证Activate Secondary PDP Context Request。SGSN将使用和关联的PDP上下文相同的GGSN地址来进行二次PDP上下文的激活。

   SGSN可以根据自己的能力和当前的负荷来限制请求的Qos属性，它应根据签约的Qos profile所描述的和相关APN关联的每个PDP上下文的最大Qos来对请求的Qos进行限制。SGSN发送Create PDP Context Request (QoS Negotiated, TEID, NSAPI, Primary NSAPI, TFT, Protocol Configuration Options, serving network identity, IMEISV, CGI/SAI, RAT type, S-CDR CAMEL information, CGI/SAI/RAI change support indication, Correlation-ID) 消息给相应的GGSN。SGSN应发送serving network identity给GGSN。Primary NSAPI指示了关联的已经激活的PDP上下文的NSAPI值。TFT只有从Activate secondary PDP Context Request消息里收到了以后才会携带。Correlation-ID仅当是网络侧发起的二次PDP激活请求时才被携带，参考9.2.2.3.

   GGSN将为这个PDP上下文使用相同的PDN网络和相同的PDP地址，并在它的PDP上下文表中生成一个新条目，并存储TFT。这个新条目将允许GGSN通过不同的GTP隧道来在SGSN和PDN网络之间路由PDP PDUs。GGSN返回一个Create PDP Context Response (TEID, QoS Negotiated, Cause, Protocol Configuration Options, Prohibit Payload Compression, APN Restriction, CGI/SAI/RAI change report required)消息给SGSN。PCO可用于传输一些可选的PDP参数给UE（参考GSM29060和24229）。Prohibit Payload Compression指示SGSN不应为这个PDP上下文来协商进行数据压缩。如果从GGSN那里收到了关于这个PDP上下文的APN限制，那SGSN应存储用于这个PDP上下文的这个值。
   如果从GGSN收到了，要求对这个PDP上下文进行CGI/SAI/RAI报告，那SGSN应存储起来并在CGI/SAI/RAI发生变化的情况下报告给GGSN来满足GGSN的请求。

   SGSN应重新验证并且限制从GGSN收到的协商的Qos，可以根据签约的Qos profile和它当前的能力和负荷情况。SGSN将应用这个更新后的Qos协商值在后续的步骤中。

4) In Iu mode, RAB setup is done by the RAB Assignment procedure.
5) In A/Gb mode, BSS packet flow context procedures may be executed. These procedures are defined in clause "BSS Context".
6) The SGSN sends an Update PDP Context Request message to the GGSN, including the QoS attributes that have been accepted by the RAN. In case the QoS attributes have been downgraded in step 5 for A/Gb mode or in step 4 for Iu mode, the SGSN may inform the GGSN about the downgraded QoS. The GGSN shall not attempt to renegotiate the QoS attributes. A RAN Procedures Ready flag is included in the Update PDP Context Request. A GGSN that receives an Update PDP Context Request with a RAN Procedures Ready flag set, should start to route downlink PDP PDUs immediately. The No QoS negotiation indication is set in Update PDP Context Request to indicate to the GGSN that the SGSN does not upgrade the previously negotiated QoS attributes and that the GGSN shall accept the provided QoS attributes without negotiation. The GGSN confirms the reception of the message and the potentially downgraded QoS attributes by sending an Update PDP Context Response to the SGSN. If the SGSN established Direct Tunnel in step 4 it shall send Update PDP Context Request and include the RNC's Address for User Plane and downlink TEID for data, the No QoS negotiation indication and DTI. DTI is used to instruct the GGSN to apply Direct Tunnel specific error handling as described in clause 13.8.

   4 在Iu模式，RAB建立通过RAB Assignment流程来完成。

   5 在A/Gb模式，BSS packet flow context流程可以被执行。请参考章节"BSS Context"。

   6 SGSN发送Update PDP Context Request消息给GGSN，包括被RAN接受的Qos属性。一旦在A/Gb模式的步骤5或Iu模式的步骤4中的Qos被降级，SGSN应通知GGSN关于这个降级的Qos。GGSN不应尝试来重新协商Qos属性。在Update PDP Context Request会携带RAN Procedures Ready flag。当GGSN收到的请求中带有这个flag，就应立即开始发送下行的PDP PDUs。No QoS negotiation也在Update PDP Context Request消息中被指示，用来告诉GGSN，说名SGSN不能升级到之前协商好的Qos属性，GGSN应使用在这个请求消息里提供的Qos属性，并且不能再协商。GGSN发送Update PDP Context Response给SGSN来确认，并且潜在的降低Qos。如果SGSN在步骤4中建立了直接隧道，它应发送Update PDP Context Request并且包含RNC的用户面地址和TEID已经No QoS negotiation指示和DTI。DTI用于指示GGSN要应用直接隧道，在13.8章节中列出的特别错误处理事件除外。
7) The SGSN selects Radio Priority and Packet Flow Id based on QoS Negotiated, and returns an Activate Secondary PDP Context Accept (TI, QoS Negotiated, Radio Priority, Packet Flow Id, Protocol Configuration Options) message to the MS. If the MS indicated in the MS Network Capability it does not support BSS packet flow procedures, then the SGSN shall not include the Packet Flow Id. In A/Gb mode, the QoS Negotiated shall take into account the Aggregate BSS QoS Profile, if any, returned from the BSS. Protocol Configuration Options is sent transparently through the SGSN if received in the Create PDP Context Response message. The SGSN is now able to route PDP PDUs between the GGSN and the MS via different GTP tunnels and possibly different LLC links.
   If the MS is incapable of accepting the new QoS Negotiated, the MS should initiate application level signalling to lower the QoS requirements for the concerned application(s). If this is not possible then the MS shall instead de-activate the PDP context with the PDP Context Deactivation Initiated by the MS procedure.
For each additionally activated PDP context a QoS profile and TFT may be requested.
   If the secondary PDP context activation procedure fails or if the SGSN returns an Activate Secondary PDP Context Reject (Cause, Protocol Configuration Options) message, the MS may attempt another activation with a different TFT, depending on the cause.

   7 SGSN根据协商的Qos来选择无线优先级和Packet Flow Id，并且返回一个Activate Secondary PDP Context Accept (TI, QoS Negotiated, Radio Priority, Packet Flow Id, Protocol Configuration Options)消息给MS。如果MS在MS Network Capability中曾经指示过它不支持BSS packet flow流程，那么SGSN不应包含Packet Flow Id。在A/Gb模式，协商的Qos应用于考虑Aggregate BSS QoS Profile。PCO是在Create PDP Context Response消息里收到透明传递给手机的。SGSN现在可以通过不同的GTP隧道和可能不同的LLC链路来在MS和GGSN之间路由PDP PDUs了。

   如果MS没有能力接受新的协商的Qos，MS应发起应用层的信令（例如HTTP层）来降低Qos要求。如果不行的话，那么MS将发起PDP Context Deactivation来将这个PDP上下文去激活。对每个额外的激活的PDP上下文，都可能需要提供一个Qos profile和TFT。

   如果PDP上下文二次激活流程失败或者SGSN返回了一个Activate Secondary PDP Context Reject (Cause, Protocol Configuration Options)消息，那MS根据cause code的不同，可以尝试用另一个不同的TFT来进行激活。

小林子爱学习

爱老板，请教一下二次激活当中TI、TFT、radio priority和packet flow ID有什么作用啊？还有在二次激活的请求消息中协议里面讲会携带linked TI,但在消息里面没有这个参数，有一个linked NSAPI的参数，请问一下这是做什么用的啊？

爱卫生

简单来说，TI可以看成是Gb接口的NSAPI，用于标识PDP上下文。TFT用于描述二次激活中对应的应用类型。radio priority这个顾名思义，和Qos有关，无线优先级。PFI可以参考这个帖子http://www.gprshome.com/forum.php?mod=viewthread&tid=440。Linked TI是有的，在Gb口抓包是能够抓到的，代表依附的primary pdp context对应的TI值是多少，作用和Linked NSAPI类似。

iscehsj

Hi 爱总，

请问一个问题，在关于PDP context activation procedure和secondary PDP context activation procedure当中，为什么2G可能要执行security function，而3G不需要执行这个过程？

2) In A/Gb mode, security functions may be executed. These procedures are defined in clause "Security Function".

谢谢！

galaxy

要好好学习一下

爱卫生

回复 iscehsj 的帖子

很好的问题，也很难的问题感觉。找了好久，才找到一个勉强能说服自己的答案。仅供参考。不一定对。

关于Iu模式，如果MS要发送一个Activate PDP Context Request给网络侧，那他只能在PMM-IDLE或PMM-CONNETED状态发，如果是后者，则已经在附着阶段做过鉴权，因此PDP激活不需要重复做。关键是前者，如果用户在PMM-IDLE状态下如果要做PDP上下文的激活，那这时候Iu信令连接已经释放了，所以UE在发送PDP激活请求之前，首先要发送一个Service Request流程重建Iu连接，而针对Service Request流程，协议在6.12.1章节规定：“The SGSN shall perform the security functions if the MS in PMM-IDLE state initiated the service request.“。也就是说，在这个业务请求流程中，SGSN会对MS做一个鉴权。这样Iu连接建立好后，MS的PDP激活请求就可以发送了，就没必要重新鉴权了。

但A/Gb模式不一样，如果MS在standby状态下发PDP激活请求的话，不需要重建信令连接（没这个概念），并且MS从standby到idle状态的切换时间可能是很长的，要经过T3312、可达计时器、隐式去附着计时器查不过1个多小时的时间，SGSN才将用户的状态从standby切换到idle。因此，从安全性角度出发，SGSN当然有权利要求对用户重新做鉴权。

iscehsj

回复 爱卫生 的帖子

谢谢爱总的回复！

个人觉得，在协议中关于PDP context activation的流程描述中，当MS/UE发出Activate PDP Context Request之时，其前提应该是该MS/UE已经处于Ready或者PMM-Connected状态了。
在Iu Mode中，处于PMM-IDLE状态的UE发起service request，核心网侧对其进行鉴权的目的应该是为了建立security context，也就是重新协商Ciphering和Integrity的算法，因为RRC连接之前已经断了现在需要重建。
在A/Gb Mode中，用户在Ready状态下发起PDP context的激活，确实不需要重建信令连接；但感觉以此来说明A/Gb Mode下“ security functions may be executed”，还不是很充分。

是否能从2G、3G在security方面的特点解释呢？{:soso_e132:}
2G系统的加密机制是针对空中接口的，只有在无线接入部分的信息被加密，而在网络内的传输链路和网间链路上的信息仍然使用明文传送。
3G系统不仅加长了密钥长度，而且引入了加密算法协商机制。3G系统加强了消息在网络内的传送安全，采用了以交换设备为核心的安全机制，加密链路延伸到交换设备，并提供基于端到端的全网范围内的加密。在3G系统中采用了消息认证来保护用户和网络间的信令消息没有被篡改，保护了消息的完整性。

2G：
用户鉴权
无线接口通信的加密
使用临时标识符
3G：
用户和网络的鉴权
使用临时标识
无线接入网加密
UTRAN内部的信令完整性保护

爱卫生

回复 iscehsj 的帖子

我的理解和你的还是有一些分歧。主要体现在

1 你提到的“当MS/UE发出Activate PDP Context Request之时，其前提应该是该MS/UE已经处于Ready或者PMM-Connected状态了。”这个感觉不一定。首先，从流程上来讲。MS/UE在Standby和PMM-IDLE状态下都是可以触发PDP激活流程的。特别是Standby状态可以直接发，而PMM-IDLE要发的话，会首先发起一个Service Request流程将PMM状态切换到PMM-CONNECTED，然后再发PDP激活流程。这个在规范里是这么说的：“The PDP state ACTIVE is permitted only when the mobility management state of the subscriber is STANDBY, READY, PMM IDLE, or PMM CONNECTED. ”，以及在6.9章PDP激活流程中提到“If the MS is in PMM IDLE state, it needs to perform a service request procedure to enter the PMM CONNECTED state before initiating these procedures.”。所以，Iu模式下，正如你所说，发出PDP激活请求时的UE，移动是在PMM-CONNECTED状态了，已经经过鉴权了，所以在Iu模式下的PDP激活不需要鉴权。这点我们的观点应该是一致的。 而2G下不一样，也是我们的分歧所在，我认为MS在Standby状态下是可以直接发起PDP激活请求的，而不用先将MM状态切换到Ready。这和3G是不一样的。因为根据23060中6.1.1.4的MM状态切换图说明：Standby到Ready状态的切换条件是上行PDU的传递，而PDP激活请求就是一个PDU消息的传递。因此在MS发出PDP激活请求的那时刻，可能是Ready也可能是Standby状态。而正像我前面提到的，由于MS停留在Standby的时间很长，可能1个多小时。网络侧当然可能要求MS进行重新鉴权。

2 规范中提到的都是"Security Function"，在后续的信令流程中也都用Security Function替代。Security Function包括鉴权和加密两个方面。但实际上在应用时是有偏向的。规范里提到的Security Function应该更关注的是鉴权的功能，而加密的功能是可选的。因为首先要防止的是用户假冒，而安全性从来都是一个可选功能，不应该以此来作为判断规范信令流程中是必选还是可选流程的依据。

爱卫生

回复 爱卫生 的帖子

或者这么说吧。假设有一种极端情况，在gsm/edge模式下，手机附着成功后，由于无线环境不好。一直处于standby状态，而网络测则在约两小时后将用户隐式去附着了，并没有也无法通知ms,这时网络侧可能已经把用户mm上下文删除了。这时无线环境又恢复了。手机在standby状态发起pdp激活。那网络侧当然要执行可选鉴权。

iscehsj

谢谢爱总的细心回复！
今天又学到新的知识了，谢谢！：）