# ================================================================================== # Copyright (c) 2020 HCL Technologies Limited. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. # ================================================================================== ============================================================================================ Bouncer xAPP (C++) ============================================================================================ -------------------------------------------------------------------------------------------- User's Guide -------------------------------------------------------------------------------------------- Introduction ============================================================================================ The RIC platform provides set of functions that the xAPPs can use to accomplish their tasks. The Bouncer xAPP is envisioned to provide xAPP developers, examples of implementing these sets of functions. Bouncer xAPP Features ============================================================================================ RIC Platform provides many APIs and libraries to aid the development of xAPPs. All xAPPs will have some custom processing functional logic core to the xApp and some additional non-functional platform related processing using these APIs and libraries. Bouncer xAPP attempts to show the usage of such additional platform processing using RIC platform APIs and libraries. The Bouncer xApp demonstrates how an xApp uses E2 interfaces and near-ric platform for the RIC Benchmarking implementation. The following paragraphs cover the various steps involved to create an Bouncer xApp instance, setting its configuration, retrieving R-NIB data, sending subscription, connecting SDL, and usage of "Bouncer SM" Bouncer Creation ============================================================================================ The creation of the xApp instance is as simple as invoking the object's constructor with two required parameters: Bouncer xAPP, may choose to create following objects for obtaining desired set of functionalities provided under xapp-utils: XappRmr -------------------------------------------------------------------------------------------- An xAPP can have the capability of receiving and sending rmr messages. This is achieved by creating an XappRmr object. The constructor of xAPPRMR object requires xAPP developer to provide xAPP's listening port and developer configurable number of attempts need to be made to send the message. The key functionalities of the class being : 1. Setting RMR initial context: ...xapp_rmr_init(...) 2. Sending RMR message: ...xapp_rmr_send(xapp_rmr_header, void*) 3. Receiving RMR message: ...xapp_rmr_receive(msghandler,...) The RMR Header can be defined using xapp_rmr_header : :: typedef struct{ struct timespec ts; int32_t message_type; //mandatory int32_t state; int32_t payload_length; //mandatory unsigned char sid[RMR_MAX_SID]; unsigned char src[RMR_MAX_SRC]; unsigned char meid[RMR_MAX_MEID]; } xapp_rmr_header; Except for message type and payload length, its developers prerogative to use remaining header information. The XappMsgHandler (msghandler) instance in xapp_rmr_receive function handles received messages. The handling of messages is based on the usecase catered by a xAPP. Hence, XappMsgHandler class used in Bouncer xAPP is not very comprehensive and addresses only Healthcheck Messages. XappSettings ------------------------------------------------------------------------------------------- An xAPP has the capability to use environment variables or xapp-descriptor information as its configuration settings creating XappSettings object, whose key functions being : 1. Loading Default Settings: ...loadDefaultSettings() 2. Loading Environment Variables: ...loadEnvVarSettings() 3. Loading Command Line Settings: ...loadCmdlineSettings(argc, argv) Bouncer E2 Message Handling ============================================================================================ Helper Objects -------------------------------------------------------------------------------------------- Bouncer xAPP creates wrapper datastructures mirroring ASN and JSON messages. These datastructures facilitate processing of E2 messages in the xAPP. A sample helper object for Health Check message being: :: struct a1_policy_helper{ std::string operation; std::string policy_type_id; std::string policy_instance_id; std::string handler_id; std::string status; }; And a sample E2AP Control datastructure: :: struct ric_control_helper{ ric_control_helper(void):req_id(1), req_seq_no(1), func_id(0), action_id(1), control_ack(-1), cause(0), sub_cause(0), control_status(1), control_msg(0), control_msg_size(0), control_header(0), control_header_size(0), call_process_id(0), call_process_id_size(0){}; long int req_id, req_seq_no, func_id, action_id, control_ack, cause, sub_cause, control_status; unsigned char* control_msg; size_t control_msg_size; unsigned char* control_header; size_t control_header_size; unsigned char *call_process_id; size_t call_process_id_size; }; As mentioned, these datastructures are very much tied to the message specifications. ASN Encoding/Decoding -------------------------------------------------------------------------------------------- RIC platform provided ASN1C (modified) library is used for processing ASN1 messages. Bouncer xAPP, for each ASN message type, uses a class which is responsible for handling a particular message type. The class encapsulates, the APIs and datastructures used in ASN1C using helper objects. For example: :: class ric_control_response{ ... bool encode_e2ap_control_response(..., ric_control_helper &); bool set_fields(..., ric_control_helper &); bool get_fields(..., ric_control_helper &); ... } Note, the helper objects and message type processing classes can be found under xapp-asn subdirectories. E2AP Subscription -------------------------------------------------------------------------------------------- In Bouncer xAPP, we consider sunny-side scenario, in which for a E2AP subscription request sent, it is assumed, that Bouncer xAPP will be receiving E2AP subscription response. Handling advanced subscription (class SubscriptionHandler) flows is out of the scope of Bouncer xAPP. Current form of class SubscriptionHandler has following key functionalities: 1. manage_subscription_request(...) 2. manage_subscription_response(...) The manage_subscription_request function waits for the response for a specified time for subscription response and if no response is received within a specified time, gives a time out error message. A subscription message is created using ASN Encodong/Decoding and Helper classes. (Refer test_sub.h). Bouncer xAPP sends the subscriptions based on the gNodeB IDs received from RNIB. Please refer following function in xapp.* for RNIB transactions: set_rnib_gnblist(...) E2SM Subscription, Indication, Control -------------------------------------------------------------------------------------------- Bouncer E2SM (e2sm-Bouncer-v001.asn) is an example E2SM available in the docs directory. The Helper and encoding/decoding classes are in xapp-asn/e2sm. Sample code for control message E2SM: :: //ControlHeader unsigned char header_buf[128]; size_t header_buf_len = 128; //ControlMessage unsigned char msg_buf[128]; size_t msg_buf_len = 128; bool res; e2sm_control_helper e2sm_cntrldata; //helper object e2sm_control e2sm_cntrl; //encoding/decoding object unsigned char msg[20] = "Bouncer"; e2sm_cntrldata.header = 1001; e2sm_cntrldata.message = msg; e2sm_cntrldata.message_len = strlen((const char*)e2sm_cntrldata.message); // Encode the control header res = e2sm_cntrl.encode_control_header(&header_buf[0], &header_buf_len, e2sm_cntrldata); if(!res) std::cout << e2sm_cntrl.get_error() << std::endl; // Encode the control message res = e2sm_cntrl.encode_control_message(&msg_buf[0], &msg_buf_len, e2sm_cntrldata); if(!res) std::cout << e2sm_cntrl.get_error() << std::endl;