5G RRC Java Sample Code Using OSS ASN.1 Tools

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/* THIS SAMPLE PROGRAM IS PROVIDED AS IS. THE SAMPLE PROGRAM AND ANY RESULTS */
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/*
 * $Id: 5G-rrc-java.html 3327 2026-01-06 10:07:48Z macra $
 */

/*
 * Demonstrates part of RRC protocol layer of an 5G UE stack.
 */

import java.io.*;

import com.oss.asn1.*;
import com.oss.util.*;

import rrc.*;
import rrc.oss_rrc_nr_rrc_definitions.*;

public class Trrc {

    static Coder coder;
    static String border = "-------------------------------------------------------";

    /*
     * Decodes and prints the input messages; creates, encodes and prints
     * the output (response) messages.
     */
    public static void main(String[] args)
    {
	// Initialize the project
	try {
	    Rrc.initialize();
	} catch (Exception e) {
	    System.out.println("Initialization exception: " + e);
	    System.exit(1);
	}

	coder = Rrc.getPERUnalignedCoder();
	coder.enableAutomaticEncoding();
	coder.enableAutomaticDecoding();
	coder.enableEncoderDebugging();
	coder.enableDecoderDebugging();

	// An optional parameter includes the path to all the files that are used by
	// the program.
	String path = (args.length > 0) ? args[0] : null;

	try {
	    testDL_DCCH_Message(path, "RRCRelease.uper");
	} catch (Exception e) {
	    System.out.println(e);
	}

	try {
	    testDL_DCCH_Message(path, "SecurityModeCommand.uper");
	} catch (Exception e) {
	    System.out.println(e);
	}
	System.out.println("\nTesting successful");
    }

    /*
     * Represents am imcomplete implementation of UE-side function processing
     * a downlink DCCH message. It decodes the message, prints it, and creates
     * a response for some particular alternatives. The function can be used
     * to implement a complete 5G RRC UE-side dispatcher.
     */
    static void testDL_DCCH_Message(String path, String filename) throws IOException, Exception
    {
	OSS_RRC_DL_DCCH_Message 	request;
	OSS_RRC_UL_DCCH_Message 	response;

	File file = new File(path, filename);
	if (!file.exists()) {
	    throw new IOException("Failed to open the " + file.toString() + " file. " +
		"Restart the sample program using as input parameter the name of the directory " +
		"where the '" + file.getName() + "' file is located.\n");
	}
	FileInputStream source = new FileInputStream(file);

	System.out.println("============================================================================");
	System.out.println("Read encoding from file: " + filename + "\n");
	System.out.println("Decoding the input downlink DCCH message");
	System.out.println(border);
	/* Deserialize input message */
        request = (OSS_RRC_DL_DCCH_Message)coder.decode(
    			    source, new OSS_RRC_DL_DCCH_Message());
	source.close();
	System.out.println("\nPDU decoded");

	if (!request.getMessage().hasC1()) {
	    throw new Exception("Incorrect message");
	}

	OSS_RRC_DL_DCCH_MessageType.C1 msg_typ = request.getMessage().getC1();
	System.out.println(border);
	switch (msg_typ.getChosenFlag()) {
	    /* You can take unimplemented CHOICE alternatives one by
	     * one and add support for them */
	    case OSS_RRC_DL_DCCH_MessageType.C1.rrcReconfiguration_chosen:
		System.out.println("Unimplemented");
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.rrcResume_chosen:
		System.out.println("Unimplemented");
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.rrcRelease_chosen:
		System.out.println(request);
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.rrcReestablishment_chosen:
		System.out.println("Unimplemented");
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.securityModeCommand_chosen:
		/* Print deserialized message */
		System.out.println(request);
		System.out.println("Creating response");
		System.out.println(border);
		/* Create response */
		response = createSecurityModeCommandResponse(request);

		System.out.println();
		System.out.println("Response created successfully");
		System.out.println(border);
		/* Print outcome message */
		System.out.println(response);
		System.out.println("Encoding response");
		System.out.println(border);
		/* Serialize outcome message */
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		try {
		    coder.encode(response, out);
		    out.close();
		} catch (Exception e) {
		    System.out.println("Encoding failed: " + e);
		    System.exit(1);
		}

		/* Print serialized outcome message */
		System.out.println("\nEncoded response "
				+ "(" + out.size() + " bytes):");
		System.out.println(HexTool.getHex(out.toByteArray()));
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.dlInformationTransfer_chosen:
		/* Print deserialized message */
		System.out.println(request);
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.ueCapabilityEnquiry_chosen:
		System.out.println("");
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.counterCheck_chosen:
		System.out.println("Unimplemented");
		break;
	    case OSS_RRC_DL_DCCH_MessageType.C1.mobilityFromNRCommand_chosen:
		System.out.println("Unimplemented");
		break;
	    default:
		System.out.println("Unknown CHOICE alternative selected");
		break;
	}
    }

    /*
     * Creates an OSS_RRC_UL_DCCH_Message PDU (security mode complete)
     * for given OSS_RRC_DL_DCCH_Message PDU (security mode command).
     */
    static OSS_RRC_UL_DCCH_Message createSecurityModeCommandResponse(
				OSS_RRC_DL_DCCH_Message request)
    throws IOException, Exception
    {
	OSS_RRC_IntegrityProtAlgorithm ipalg;
	OSS_RRC_CipheringAlgorithm calg;

	if (!request.getMessage().hasC1()
	    || !request.getMessage().getC1().hasSecurityModeCommand()
	    || !request.getMessage().getC1().getSecurityModeCommand()
                                             .getCriticalExtensions()
                                             .hasSecurityModeCommand())
	    throw new Exception("cannot handle ASN.1 data");



	ipalg = request.getMessage()
                        .getC1()
                        .getSecurityModeCommand()
                        .getCriticalExtensions()
                        .getSecurityModeCommand()
                        .getSecurityConfigSMC()
                        .getSecurityAlgorithmConfig()
                        .getIntegrityProtAlgorithm();

	calg = request.getMessage()
                       .getC1()
                       .getSecurityModeCommand()
                       .getCriticalExtensions()
                       .getSecurityModeCommand()
                       .getSecurityConfigSMC()
                       .getSecurityAlgorithmConfig()
                       .getCipheringAlgorithm();

	if (ipalg != OSS_RRC_IntegrityProtAlgorithm.nia0
		&& ipalg != OSS_RRC_IntegrityProtAlgorithm.nia1
		&& ipalg != OSS_RRC_IntegrityProtAlgorithm.nia2)
	    throw new Exception("unknown integrity protection");

	if (calg != OSS_RRC_CipheringAlgorithm.nea0
		&& calg != OSS_RRC_CipheringAlgorithm.nea1
		&& calg != OSS_RRC_CipheringAlgorithm.nea2)
	    throw new Exception("unknown ciphering");

	OSS_RRC_RRC_TransactionIdentifier transactionIdentifier =
		request.getMessage()
                        .getC1()
                        .getSecurityModeCommand()
                        .getRrc_TransactionIdentifier();
	OSS_RRC_SecurityModeComplete.CriticalExtensions criticalExtensions =
	    OSS_RRC_SecurityModeComplete.CriticalExtensions.
		createCriticalExtensionsWithSecurityModeComplete(
		    new OSS_RRC_SecurityModeComplete_IEs());
	OSS_RRC_SecurityModeComplete securityModeComplete =
	    new OSS_RRC_SecurityModeComplete(transactionIdentifier, criticalExtensions);
	OSS_RRC_UL_DCCH_MessageType.C1 c1 =
	    OSS_RRC_UL_DCCH_MessageType.C1.createC1WithSecurityModeComplete(securityModeComplete);
	OSS_RRC_UL_DCCH_MessageType message =
	    OSS_RRC_UL_DCCH_MessageType.createOSS_RRC_UL_DCCH_MessageTypeWithC1(c1);
	OSS_RRC_UL_DCCH_Message response = new OSS_RRC_UL_DCCH_Message(message);

	return response;
    }
}