Which statement about standard STS-1 SONET framing is true?

Question

Options

• A8 rows by 64 bytes
• B6 rows by 64 bytes
• C10 rows by 96 bytes
• D8 rows by 128 bytes
• E9 rows by 90 bytes

• A
  10% (5)
• B
  4% (2)
• C
  4% (2)
• D
  2% (1)
• E
  80% (40)

Explanation

In the case of an STS-1, the frame is 810 octets in size, while the STM-1/STS-3c frame is 2,430 For STS-1, the frame is transmitted as three octets of overhead, followed by 87 octets of payload. This is repeated nine times, until 810 octets have been transmitted, taking 125 s. In the case of an STS-3c/STM-1, which operates three times faster than an STS-1, nine octets of overhead are transmitted, followed by 261 octets of payload. This is also repeated nine times until 2,430 octets have been transmitted, also taking 125 s. For both SONET and SDH, this is often represented by displaying the frame graphically: as a block of 90 columns and nine rows for STS-1, and 270 columns and nine rows for STM1/STS-3c. This representation aligns all the overhead columns, so the overhead appears as a contiguous block, as does the payload.

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