diff --git a/contexthub/aidl/default/ContextHub.cpp b/contexthub/aidl/default/ContextHub.cpp
index a915191..4ae9c09 100644
--- a/contexthub/aidl/default/ContextHub.cpp
+++ b/contexthub/aidl/default/ContextHub.cpp
@@ -16,10 +16,54 @@
 
 #include "contexthub-impl/ContextHub.h"
 
-namespace aidl::android::hardware::contexthub {
+#ifndef LOG_TAG
+#define LOG_TAG "CHRE"
+#endif
+
+#include <inttypes.h>
+#include <log/log.h>
 
 using ::ndk::ScopedAStatus;
 
+namespace aidl::android::hardware::contexthub {
+
+namespace {
+
+constexpr uint64_t kMockVendorHubId = 0x1234567812345678;
+constexpr uint64_t kMockVendorHub2Id = 0x0EADBEEFDEADBEEF;
+
+// Mock endpoints for the default implementation.
+// These endpoints just echo back any messages sent to them.
+constexpr size_t kMockEndpointCount = 4;
+const EndpointInfo kMockEndpointInfos[kMockEndpointCount] = {
+        {
+                .id = {.hubId = kMockVendorHubId, .id = UINT64_C(0x1)},
+                .type = EndpointInfo::EndpointType::GENERIC,
+                .name = "Mock Endpoint 1",
+                .version = 1,
+        },
+        {
+                .id = {.hubId = kMockVendorHubId, .id = UINT64_C(0x2)},
+                .type = EndpointInfo::EndpointType::GENERIC,
+                .name = "Mock Endpoint 2",
+                .version = 2,
+        },
+        {
+                .id = {.hubId = kMockVendorHub2Id, .id = UINT64_C(0x1)},
+                .type = EndpointInfo::EndpointType::GENERIC,
+                .name = "Mock Endpoint 3",
+                .version = 1,
+        },
+        {
+                .id = {.hubId = kMockVendorHub2Id, .id = UINT64_C(0x2)},
+                .type = EndpointInfo::EndpointType::GENERIC,
+                .name = "Mock Endpoint 4",
+                .version = 2,
+        },
+};
+
+}  // anonymous namespace
+
 ScopedAStatus ContextHub::getContextHubs(std::vector<ContextHubInfo>* out_contextHubInfos) {
     ContextHubInfo hub = {};
     hub.name = "Mock Context Hub";
@@ -112,7 +156,13 @@
     }
 }
 
-ScopedAStatus ContextHub::setTestMode(bool /* enable */) {
+ScopedAStatus ContextHub::setTestMode(bool enable) {
+    if (enable) {
+        std::unique_lock<std::mutex> lock(mEndpointMutex);
+        mEndpoints.clear();
+        mEndpointSessions.clear();
+        mEndpointCallback = nullptr;
+    }
     return ScopedAStatus::ok();
 }
 
@@ -137,6 +187,10 @@
 }
 
 ScopedAStatus ContextHub::getHubs(std::vector<HubInfo>* _aidl_return) {
+    if (_aidl_return == nullptr) {
+        return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+    }
+
     ContextHubInfo hub = {};
     hub.name = "Mock Context Hub";
     hub.vendor = "AOSP";
@@ -158,61 +212,217 @@
     vendorHub.version = 42;
 
     HubInfo hubInfo2 = {};
-    hubInfo2.hubId = UINT64_C(0x1234567812345678);
+    hubInfo2.hubId = kMockVendorHubId;
     hubInfo2.hubDetails =
             HubInfo::HubDetails::make<HubInfo::HubDetails::Tag::vendorHubInfo>(vendorHub);
 
+    VendorHubInfo vendorHub2 = {};
+    vendorHub2.name = "Mock Vendor Hub 2";
+    vendorHub2.version = 24;
+
+    HubInfo hubInfo3 = {};
+    hubInfo3.hubId = kMockVendorHub2Id;
+    hubInfo3.hubDetails =
+            HubInfo::HubDetails::make<HubInfo::HubDetails::Tag::vendorHubInfo>(vendorHub2);
+
     _aidl_return->push_back(hubInfo1);
     _aidl_return->push_back(hubInfo2);
+    _aidl_return->push_back(hubInfo3);
 
     return ScopedAStatus::ok();
 };
 
-ScopedAStatus ContextHub::getEndpoints(std::vector<EndpointInfo>* /* _aidl_return */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+ScopedAStatus ContextHub::getEndpoints(std::vector<EndpointInfo>* _aidl_return) {
+    if (_aidl_return == nullptr) {
+        return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+    }
+
+    Service echoService;
+    echoService.format = Service::RpcFormat::CUSTOM;
+    echoService.serviceDescriptor = "ECHO";
+    echoService.majorVersion = 1;
+    echoService.minorVersion = 0;
+
+    for (const EndpointInfo& endpoint : kMockEndpointInfos) {
+        EndpointInfo endpointWithService(endpoint);
+        endpointWithService.services.push_back(echoService);
+        _aidl_return->push_back(std::move(endpointWithService));
+    }
+
+    return ScopedAStatus::ok();
 };
 
-ScopedAStatus ContextHub::registerEndpoint(const EndpointInfo& /* in_endpoint */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+ScopedAStatus ContextHub::registerEndpoint(const EndpointInfo& in_endpoint) {
+    std::unique_lock<std::mutex> lock(mEndpointMutex);
+
+    for (const EndpointInfo& endpoint : mEndpoints) {
+        if ((endpoint.id.id == in_endpoint.id.id && endpoint.id.hubId == in_endpoint.id.hubId) ||
+            endpoint.name == in_endpoint.name) {
+            return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+        }
+    }
+    mEndpoints.push_back(in_endpoint);
+    return ScopedAStatus::ok();
 };
 
-ScopedAStatus ContextHub::unregisterEndpoint(const EndpointInfo& /* in_endpoint */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+ScopedAStatus ContextHub::unregisterEndpoint(const EndpointInfo& in_endpoint) {
+    std::unique_lock<std::mutex> lock(mEndpointMutex);
+
+    for (auto it = mEndpoints.begin(); it != mEndpoints.end(); ++it) {
+        if (it->id.id == in_endpoint.id.id && it->id.hubId == in_endpoint.id.hubId) {
+            mEndpoints.erase(it);
+            return ScopedAStatus::ok();
+        }
+    }
+    return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
 };
 
 ScopedAStatus ContextHub::registerEndpointCallback(
-        const std::shared_ptr<IEndpointCallback>& /* in_callback */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+        const std::shared_ptr<IEndpointCallback>& in_callback) {
+    std::unique_lock<std::mutex> lock(mEndpointMutex);
+
+    mEndpointCallback = in_callback;
+    return ScopedAStatus::ok();
 };
 
-ScopedAStatus ContextHub::requestSessionIdRange(int32_t /* in_size */,
-                                                std::vector<int32_t>* /* _aidl_return */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+ScopedAStatus ContextHub::requestSessionIdRange(int32_t in_size,
+                                                std::vector<int32_t>* _aidl_return) {
+    constexpr int32_t kMaxSize = 1024;
+    if (in_size > kMaxSize || _aidl_return == nullptr) {
+        return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+    }
+
+    {
+        std::lock_guard<std::mutex> lock(mEndpointMutex);
+        mMaxValidSessionId = in_size;
+    }
+
+    _aidl_return->push_back(0);
+    _aidl_return->push_back(in_size);
+    return ScopedAStatus::ok();
 };
 
 ScopedAStatus ContextHub::openEndpointSession(
-        int32_t /* in_sessionId */, const EndpointId& /* in_destination */,
-        const EndpointId& /* in_initiator */,
-        const std::optional<std::string>& /* in_serviceDescriptor */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+        int32_t in_sessionId, const EndpointId& in_destination, const EndpointId& in_initiator,
+        const std::optional<std::string>& in_serviceDescriptor) {
+    // We are not calling onCloseEndpointSession on failure because the remote endpoints (our
+    // mock endpoints) always accept the session.
+
+    std::shared_ptr<IEndpointCallback> callback = nullptr;
+    {
+        std::unique_lock<std::mutex> lock(mEndpointMutex);
+        if (in_sessionId > mMaxValidSessionId) {
+            ALOGE("openEndpointSession: session ID %" PRId32 " is invalid", in_sessionId);
+            return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+        }
+
+        for (const EndpointSession& session : mEndpointSessions) {
+            bool sessionAlreadyExists =
+                    (session.initiator == in_destination && session.peer == in_initiator) ||
+                    (session.peer == in_destination && session.initiator == in_initiator);
+            if (sessionAlreadyExists) {
+                ALOGD("openEndpointSession: session ID %" PRId32 " already exists", in_sessionId);
+                return (session.sessionId == in_sessionId &&
+                        session.serviceDescriptor == in_serviceDescriptor)
+                               ? ScopedAStatus::ok()
+                               : ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+            } else if (session.sessionId == in_sessionId) {
+                ALOGE("openEndpointSession: session ID %" PRId32 " is invalid: endpoint mismatch",
+                      in_sessionId);
+                return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+            }
+        }
+
+        // Verify the initiator and destination are valid endpoints
+        bool initiatorIsValid = findEndpoint(in_initiator, mEndpoints.begin(), mEndpoints.end());
+        if (!initiatorIsValid) {
+            ALOGE("openEndpointSession: initiator %" PRIu64 ":%" PRIu64 " is invalid",
+                  in_initiator.id, in_initiator.hubId);
+            return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+        }
+        bool destinationIsValid = findEndpoint(in_destination, &kMockEndpointInfos[0],
+                                               &kMockEndpointInfos[kMockEndpointCount]);
+        if (!destinationIsValid) {
+            ALOGE("openEndpointSession: destination %" PRIu64 ":%" PRIu64 " is invalid",
+                  in_destination.id, in_destination.hubId);
+            return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+        }
+
+        mEndpointSessions.push_back({
+                .sessionId = in_sessionId,
+                .initiator = in_initiator,
+                .peer = in_destination,
+                .serviceDescriptor = in_serviceDescriptor,
+        });
+
+        if (mEndpointCallback != nullptr) {
+            callback = mEndpointCallback;
+        }
+    }
+
+    if (callback != nullptr) {
+        callback->onEndpointSessionOpenComplete(in_sessionId);
+    }
+    return ScopedAStatus::ok();
 };
 
-ScopedAStatus ContextHub::sendMessageToEndpoint(int32_t /* in_sessionId */,
-                                                const Message& /* in_msg */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+ScopedAStatus ContextHub::sendMessageToEndpoint(int32_t in_sessionId, const Message& in_msg) {
+    bool foundSession = false;
+    std::shared_ptr<IEndpointCallback> callback = nullptr;
+    {
+        std::unique_lock<std::mutex> lock(mEndpointMutex);
+
+        for (const EndpointSession& session : mEndpointSessions) {
+            if (session.sessionId == in_sessionId) {
+                foundSession = true;
+                break;
+            }
+        }
+
+        if (mEndpointCallback != nullptr) {
+            callback = mEndpointCallback;
+        }
+    }
+
+    if (!foundSession) {
+        ALOGE("sendMessageToEndpoint: session ID %" PRId32 " is invalid", in_sessionId);
+        return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
+    }
+
+    if (callback != nullptr) {
+        if (in_msg.flags & Message::FLAG_REQUIRES_DELIVERY_STATUS) {
+            MessageDeliveryStatus msgStatus = {};
+            msgStatus.messageSequenceNumber = in_msg.sequenceNumber;
+            msgStatus.errorCode = ErrorCode::OK;
+            callback->onMessageDeliveryStatusReceived(in_sessionId, msgStatus);
+        }
+
+        // Echo the message back
+        callback->onMessageReceived(in_sessionId, in_msg);
+    }
+    return ScopedAStatus::ok();
 };
 
 ScopedAStatus ContextHub::sendMessageDeliveryStatusToEndpoint(
         int32_t /* in_sessionId */, const MessageDeliveryStatus& /* in_msgStatus */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+    return ScopedAStatus::ok();
 };
 
-ScopedAStatus ContextHub::closeEndpointSession(int32_t /* in_sessionId */, Reason /* in_reason */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+ScopedAStatus ContextHub::closeEndpointSession(int32_t in_sessionId, Reason /* in_reason */) {
+    std::unique_lock<std::mutex> lock(mEndpointMutex);
+
+    for (auto it = mEndpointSessions.begin(); it != mEndpointSessions.end(); ++it) {
+        if (it->sessionId == in_sessionId) {
+            mEndpointSessions.erase(it);
+            return ScopedAStatus::ok();
+        }
+    }
+    ALOGE("closeEndpointSession: session ID %" PRId32 " is invalid", in_sessionId);
+    return ScopedAStatus::fromExceptionCode(EX_ILLEGAL_ARGUMENT);
 };
 
 ScopedAStatus ContextHub::endpointSessionOpenComplete(int32_t /* in_sessionId */) {
-    return ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+    return ScopedAStatus::ok();
 };
 
 }  // namespace aidl::android::hardware::contexthub