【OpenAirInterface5g】RRC NR解析之RrcSetupRequest

作者柒号华仔个人主页欢迎访问我的主页个人信条星光不问赶路人,岁月不负有心人。个人方向专注于4G/5G领域同时兼顾其他网络协议编解码协议C/Clinux等感兴趣的小伙伴可以关注我一起交流。目录1. RrcSetupRequest介绍1.1 发起目的1.2 信令内容抓包1.3 gNB回复2. RrcSetupRequest解析处理流程3. 相关代码1. RrcSetupRequest介绍Rrc setup Request消息由UE发起携带RRC建立原因和UE标识用于UE向gNB请求建立RRC 连接传输信道为CCCH。1.1 发起目的建立SRB1无线承载发送NAS消息1.2 信令内容抓包信令抓包ue-Identity为终端标识类型为randomValuerandomValue是长度为39bit的随机值establishmentCause为建立原因mo-Signalling常见的有mt-Access、mo-Signalling以及mo-Data三种原因。1.3 gNB回复gNB进行准入判断若允许UE接入回复RRC Connection Setup继续接入流程若不允许回复RRC Connection Reject拒绝接入2. RrcSetupRequest解析处理流程OAI 调用nr_rrc_gNB_decode_ccch()函数解码CCCH pdu其解码rrcSetupRequest流程如下rrcSetupRequest处理流程对于主函数传过来的buffer调用uper_decode()进行per解码获得消息ID为rrcSetupRequest。根据rnti查找UE上下文rrc_gNB_get_ue_context()如果能够找到上下文说明该rnti已经注册释放掉该UE上下文rrc_gNB_free_mem_UE_context()一般正常情况UE是初次接入rnti也是唯一的在上下文中是无法查找到的。对ue_Identity类型进行判断分三种情况ue_Identity为NR_InitialUE_Identity_PR_randomValue 即随机值长度为39bitue_Identity为NR_InitialUE_Identity_PR_ng_5G_S_TMSI_Part1 5G_S_TMSI长度为48bitPart1为前39bit。以上两种均不是。对于randomValue或者5G_S_TMSI_Part1将为该UE创建上下文rrc_gNB_get_next_free_ue_context()然后生成RRCSetup回复UE调用函数rrc_gNB_generate_RRCSetup()。对于无法识别类型的ue_Identity将为该UE创建上下文rrc_gNB_get_next_free_ue_context()然后生成RRCReject拒绝该UE接入调用函数rrc_gNB_generate_RRCReject()。3. 相关代码switch(ul_ccch_msg-message.choice.c1-present){caseNR_UL_CCCH_MessageType__c1_PR_rrcSetupRequest:LOG_D(NR_RRC,Received RRCSetupRequest on UL-CCCH-Message (UE rnti %x)\n,ctxt_pP-rnti);ue_context_prrc_gNB_get_ue_context(gnb_rrc_inst,ctxt_pP-rnti);if(ue_context_p!NULL){rrc_gNB_free_mem_UE_context(ctxt_pP,ue_context_p);MSC_LOG_RX_DISCARDED_MESSAGE(MSC_RRC_GNB,MSC_RRC_UE,buffer,dec_rval.consumed,MSC_AS_TIME_FMT NR_RRCSetupRequest UE %x size %u (UE already in context),MSC_AS_TIME_ARGS(ctxt_pP),ue_context_p-ue_context.rnti,dec_rval.consumed);}else{rrcSetupRequestul_ccch_msg-message.choice.c1-choice.rrcSetupRequest-rrcSetupRequest;if(NR_InitialUE_Identity_PR_randomValuerrcSetupRequest-ue_Identity.present){/* randomValue BIT STRING (SIZE (39)) */if(rrcSetupRequest-ue_Identity.choice.randomValue.size!5){// 39-bit random valueLOG_E(NR_RRC,wrong InitialUE-Identity randomValue size, expected 5, provided %lu,(longunsignedint)rrcSetupRequest-ue_Identity.choice.randomValue.size);return-1;}memcpy(((uint8_t*)random_value)3,rrcSetupRequest-ue_Identity.choice.randomValue.buf,rrcSetupRequest-ue_Identity.choice.randomValue.size);/* if there is already a registered UE (with another RNTI) with this random_value, * the current one must be removed from MAC/PHY (zombie UE) */if((ue_context_prrc_gNB_ue_context_random_exist(RC.nrrrc[ctxt_pP-module_id],random_value))){LOG_W(NR_RRC,new UE rnti %x (coming with random value) is already there as UE %x, removing %x from MAC/PHY\n,ctxt_pP-rnti,ue_context_p-ue_context.rnti,ue_context_p-ue_context.rnti);ue_context_p-ue_context.ul_failure_timer20000;}ue_context_prrc_gNB_get_next_free_ue_context(ctxt_pP,RC.nrrrc[ctxt_pP-module_id],random_value);ue_context_p-ue_context.Srb0.Srb_id0;ue_context_p-ue_context.Srb0.Active1;memcpy(ue_context_p-ue_context.Srb0.Rx_buffer.Payload,buffer,buffer_length);ue_context_p-ue_context.Srb0.Rx_buffer.payload_sizebuffer_length;}elseif(NR_InitialUE_Identity_PR_ng_5G_S_TMSI_Part1rrcSetupRequest-ue_Identity.present){/* TODO *//* 5G-S-TMSI AMF Set IDAMF Pointer5G-TMSI 48-bit *//* ng-5G-S-TMSI-Part1 BIT STRING (SIZE (39)) */if(rrcSetupRequest-ue_Identity.choice.ng_5G_S_TMSI_Part1.size!5){LOG_E(NR_RRC,wrong ng_5G_S_TMSI_Part1 size, expected 5, provided %lu \n,(longunsignedint)rrcSetupRequest-ue_Identity.choice.ng_5G_S_TMSI_Part1.size);return-1;}uint64_ts_tmsi_part1bitStr_to_uint64(rrcSetupRequest-ue_Identity.choice.ng_5G_S_TMSI_Part1);if((ue_context_prrc_gNB_ue_context_5g_s_tmsi_exist(RC.nrrrc[ctxt_pP-module_id],s_tmsi_part1))){LOG_I(NR_RRC, 5G-S-TMSI-Part1 exists, ue_context_p %p, old rnti %x %x\n,ue_context_p,ue_context_p-ue_context.rnti,ctxt_pP-rnti);nr_rrc_mac_remove_ue(ctxt_pP-module_id,ue_context_p-ue_context.rnti);RB_REMOVE(rrc_nr_ue_tree_s,RC.nrrrc[ctxt_pP-module_id]-rrc_ue_head,ue_context_p);/* and insert again, after changing rnti everywhere it has to be changed */ue_context_p-ue_id_rntictxt_pP-rnti;ue_context_p-ue_context.rntictxt_pP-rnti;RB_INSERT(rrc_nr_ue_tree_s,RC.nrrrc[ctxt_pP-module_id]-rrc_ue_head,ue_context_p);/* reset timers */ue_context_p-ue_context.ul_failure_timer0;ue_context_p-ue_context.ue_release_timer0;ue_context_p-ue_context.ue_reestablishment_timer0;ue_context_p-ue_context.ue_release_timer_s10;ue_context_p-ue_context.ue_release_timer_rrc0;}else{LOG_I(NR_RRC, 5G-S-TMSI-Part1 doesnt exist, setting ng_5G_S_TMSI_Part1 to %p %ld\n,ue_context_p,s_tmsi_part1);ue_context_prrc_gNB_get_next_free_ue_context(ctxt_pP,RC.nrrrc[ctxt_pP-module_id],s_tmsi_part1);if(ue_context_pNULL){LOG_E(RRC,%s:%d:%s: rrc_gNB_get_next_free_ue_context returned NULL\n,__FILE__,__LINE__,__FUNCTION__);}if(ue_context_p!NULL){ue_context_p-ue_context.Initialue_identity_5g_s_TMSI.presenceTRUE;ue_context_p-ue_context.ng_5G_S_TMSI_Part1s_tmsi_part1;}}}else{memcpy(((uint8_t*)random_value)3,rrcSetupRequest-ue_Identity.choice.randomValue.buf,rrcSetupRequest-ue_Identity.choice.randomValue.size);rrc_gNB_get_next_free_ue_context(ctxt_pP,RC.nrrrc[ctxt_pP-module_id],random_value);LOG_E(NR_RRC,PROTOCOL_NR_RRC_CTXT_UE_FMT RRCSetupRequest without random UE identity or S-TMSI not supported, lets reject the UE\n,PROTOCOL_NR_RRC_CTXT_UE_ARGS(ctxt_pP));rrc_gNB_generate_RRCReject(ctxt_pP,rrc_gNB_get_ue_context(gnb_rrc_inst,ctxt_pP-rnti),CC_id);break;}ue_context_p-ue_context.establishment_causerrcSetupRequest-establishmentCause;rrc_gNB_generate_RRCSetup(ctxt_pP,rrc_gNB_get_ue_context(gnb_rrc_inst,ctxt_pP-rnti),du_to_cu_rrc_container,gnb_rrc_inst-carrier.servingcellconfigcommon,CC_id);}break;}