anotherim/src/main/res/layout/activity_rtp_session.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.AppBarLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingLeft="16dp"
            android:paddingTop="32dp"
            android:paddingRight="16dp"
            android:paddingBottom="32dp">

            <TextView
                android:id="@+id/status"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="@style/TextAppearance.Conversations.Title"
                android:textColor="@color/white"
                tools:text="Incoming call" />

            <TextView
                android:id="@+id/with"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@id/status"
                android:textAppearance="@style/TextAppearance.Conversations.Display2"
                android:textColor="@color/white"
                tools:text="Juliet Capulet" />

        </android.support.design.widget.AppBarLayout>


        <RelativeLayout
            android:layout_width="288dp"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"
            android:layout_marginBottom="24dp">

            <android.support.design.widget.FloatingActionButton
                android:id="@+id/reject_call"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentStart="true"
                android:layout_alignParentLeft="true"
                android:layout_centerVertical="true"
                android:layout_margin="16dp"
                android:src="@drawable/ic_call_end_white_48dp"
                android:visibility="gone"
                app:backgroundTint="@color/red700"
                app:elevation="4dp"
                app:fabCustomSize="72dp"
                app:maxImageSize="36dp"
                tools:visibility="visible" />

            <android.support.design.widget.FloatingActionButton
                android:id="@+id/end_call"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerInParent="true"
                android:layout_margin="16dp"
                android:src="@drawable/ic_call_end_white_48dp"
                android:visibility="gone"
                app:backgroundTint="@color/red700"
                app:elevation="4dp"
                app:fabCustomSize="72dp"
                app:maxImageSize="36dp" />

            <android.support.design.widget.FloatingActionButton
                android:id="@+id/accept_call"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentEnd="true"
                android:layout_alignParentRight="true"
                android:layout_centerVertical="true"
                android:layout_margin="16dp"
                android:src="@drawable/ic_call_white_48dp"
                android:visibility="gone"
                app:backgroundTint="@color/green700"
                app:elevation="4dp"
                app:fabCustomSize="72dp"
                app:maxImageSize="36dp"
                tools:visibility="visible" />
        </RelativeLayout>

    </RelativeLayout>
</layout>