H35-210_V2.5 · Question #350
In the 10G GPON system, the XGEM frame is used to encapsulate data. How many bits of PORT ID are defined in the XGEM header?
The correct answer is A. 16. In the XGEM header defined by ITU-T G.987.3 (XG-PON / 10G GPON), the PORT ID field is 16 bits wide, supporting up to 65,536 (2¹⁶) distinct logical connections between the OLT and ONUs - option A is correct. Options B (14 bits) and C (12 bits) are too narrow and would severely…
Question
In the 10G GPON system, the XGEM frame is used to encapsulate data. How many bits of PORT ID are defined in the XGEM header?
Options
- A16
- B14
- C12
- D18
How the community answered
(44 responses)- A73% (32)
- B7% (3)
- C5% (2)
- D16% (7)
Explanation
In the XGEM header defined by ITU-T G.987.3 (XG-PON / 10G GPON), the PORT ID field is 16 bits wide, supporting up to 65,536 (2¹⁶) distinct logical connections between the OLT and ONUs - option A is correct. Options B (14 bits) and C (12 bits) are too narrow and would severely limit the number of addressable connections the system could support. Option D (18 bits) exceeds the actual field width specified in the standard and does not correspond to any real XGEM header field. The 8-byte XGEM header allocates exactly 16 bits to the Port ID, which aligns with common networking conventions of using full 2-byte (word-sized) fields for identifiers.
Memory tip: Think "16 = 2 bytes = one full network word" - standards bodies favor clean byte-aligned field sizes, and 16 bits is the natural choice for a port identifier that needs to scale to tens of thousands of subscribers on a single PON.
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