STM-1

Frame structure

• : Multiplex Section Overhead
• : Regeneration Section Overhead
• : AU-4 Pointers

• : Path Overhead

  Frame characteristic

• Length: 270 column × 9 row = 2430 bytes
• Byte: 1-byte = 8 bit
• Duration : 125 μs i.e. 8000 frame/s
• Rate : 2430 × 8 × 8000 = 155.5200 Mbit/s
• Payload = 2349bytes × 8bits × 8000frames/sec = 150.336 Mbit/s

  RSOH (regenerator section overhead)

• 1st row = Unscrambled bytes. Their contents should therefore be monitored
• X = Bytes reserved for national use
• D = Bytes depending on the medium

• A1, A2 The Frame Alignment Word is used to recognize the beginning of an STM-N frame
• A1: 1111 0110 = F6
• A2: 0010 1000 = 28
• J0: Path Trace. It is used to give a path through an SDH Network a "Name". This message enables the receiver to check the continuity of its connection with the desired transmitter
• B1: Bit Error Monitoring. The B1 Byte contains the result of the parity check of the previous STM frame, after scrambling of the actual STM frame. This check is carried out with a Bit Interleaved Parity check.
• E1 Engineering Orderwire. It can be used to transmit speech signals between Regenerator Sections for operating and maintenance purposes
• F1 User Channel. It is used to transmit data and speech for service and maintenance
• D1 to D3 Data Communication Channel at 192 kbit/s. This channel is used to transmit management information via the STM-N frames

  MSOH (multiplex section overhead)

• B2 : Bit Error Monitoring. The B2 Bytes contains the result of the parity check of the previous STM frame, except the RSOH, before scrambling of the actual STM frame. This check is carried out with a Bit Interleaved Parity check
• K1, K2 Automatic Protection Switching. In case of a failure, the STM frames can be routed new with the help of the K1, K2 Bytes through the SDH Network. Assigned to the multiplexing section protection protocol
• K2 MS_RDI: Multiplex Section Remote Defect Indication
• D4 to D12 Data Communication Channel at 576 kbit/s.
• S1 Synchronisation quality level:
• * 0000 Quality unknown
• * 0010 G.811 10-11/day frequency drift
• * 0100 G.812T transit 10-9 /day frequency drift
• * 1000 G.812L local 2*10-8/day frequency drift
• * 1011 G.813 5*10-7/day frequency drift
• * 1111 Not to be used for synchronisation
• E2 Engineering Order wire. Same function as E1 in RSOH
• M1 MS_REI: Multiplex Section Remote Error Indicator, number of interleaved bits which have been detected to be erroneous in the received B2 bytes.
• Z1, Z2 Spare bytes