This object indicates the sub type of the optical transceiver.
Options:
1. unknown(1) - Unknown
2. classbplus(101) - CLASS B+
3. classcplus(102) - CLASS C+
4. classb(103) - CLASS B
5. px20(201) - PX20
6. px20plus(202) - PX20+
7. pr30(301) - PR30
8. pr20(302) - PR20
9. prx30(303) - PRX30
10. prx20(304) - PRX20
11. invalid(-1) - Indicates that the query fails or no information is detected