In a Nokia Hierarchical VPLS (H-VPLS) architecture, frames from a customer-facing I-VPLS are encapsulated before being transported across the provider backbone B-VPLS. This encapsulation adds overhead. The service-mtu of the B-VPLS must be large enough to accommodate the maximum frame size from the I-VPLS plus this overhead. The overhead consists of a 4-byte Service Delimiting Tag (S-tag) and a 4-byte control word, totaling 8 bytes. Therefore, the maximum service-mtu for any attached I-VPLS is the B-VPLS service-mtu minus 8 bytes.

Calculation: 9108 bytes (B-VPLS MTU) - 8 bytes (overhead) = 9100 bytes.

B. 9104 bytes: This incorrectly accounts for only the 4-byte S-tag overhead and omits the 4-byte control word.

C. 9108 bytes: This is incorrect as it fails to account for the necessary 8-byte encapsulation overhead required by the B-VPLS.

D. 9118 bytes: This is incorrect because the I-VPLS MTU cannot be larger than the B-VPLS MTU that must transport its frames.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "VPLS Services" Section: In the subsection on "Hierarchical VPLS (H-VPLS)", under "MTU Considerations in H-VPLS", the documentation states: "The B-VPLS service MTU must be at least 8 bytes larger than the I-VPLS service MTU to accommodate the S-tag and control word." This directly supports the calculation of 9108 - 8 = 9100. (Document ID: 3HE 17196 AAAD TQZZA, Page 457).

2. Nokia Data Center and Cloud-Native VPLS and EVPN Services Courseware (4A0-105 Student Guide): Module 3, "Hierarchical VPLS (H-VPLS)", discusses the MTU relationship between I-VPLS and B-VPLS. It explicitly details the addition of a 4-byte S-tag and a 4-byte control word when an I-VPLS frame is passed to the B-VPLS, requiring the B-VPLS MTU to be at least 8 bytes greater than the I-VPLS MTU.