Switch
                       +--------+
Serial         3       |        |              Device
Source 1 <=====/======>+        |             +------+
                       |        |      3      |      |
                       |        +<=====/=====>+      |
Serial         3       |        |             |      |
Source 2 <=====/======>+        |             +------+
                       |        |
                       +--------+