How to use the google-gax.CallSettings function in google-gax

listFieldsStream(request, options) {
        request = request || {};
        const callSettings = new gax.CallSettings(options);
        return this._descriptors.page.listFields.createStream(this._innerApiCalls.listFields, request, callSettings);
    }
    // --------------------

listDocumentsStream(request, options) {
        request = request || {};
        const callSettings = new gax.CallSettings(options);
        return this._descriptors.page.listDocuments.createStream(this._innerApiCalls.listDocuments, request, callSettings);
    }
    /**

listIndexesStream(request, options) {
        request = request || {};
        const callSettings = new gax.CallSettings(options);
        return this._descriptors.page.listIndexes.createStream(this._innerApiCalls.listIndexes, request, callSettings);
    }
    /**

listCollectionIdsStream(request, options) {
        request = request || {};
        const callSettings = new gax.CallSettings(options);
        return this._descriptors.page.listCollectionIds.createStream(this._innerApiCalls.listCollectionIds, request, callSettings);
    }
    /**

listDocumentsStream(request, options) {
        request = request || {};
        const callSettings = new gax.CallSettings(options);
        return this._descriptors.page.listDocuments.createStream(this._innerApiCalls.listDocuments, request, callSettings);
    }
    /**

listCollectionIdsStream(request, options) {
        request = request || {};
        const callSettings = new gax.CallSettings(options);
        return this._descriptors.page.listCollectionIds.createStream(this._innerApiCalls.listCollectionIds, request, callSettings);
    }
    /**