STM-1

ITU-T G.707 STM-1 frame format

We forward information on STM-1 interface framed. Build-up of the basic frame structure used for connecting "section-layers" of the European SDH is demonstrated on the following figure:

        1       9                                                   270
      1+---------+---------------------------------------------------+byte
       | RSOH    |                                                   |
       |         |                                                   |
      3|---------|                                                   |
       | AU-4 PTR|                    STM-1 payload (VC-4)           |
      5|---------+                                                   |
       | MSOH    |                                                   |
       |         |                                                   |
      9+----|----+---------------------------------------------------+
         overhead

Main parts of the frame:

payload information to be forwarded, which has a VC-4 frame.
overhead - SOH Section Overhead - header of the frame. It can be split into further three parts:
- RSOH - regenerator section overhead - Functions:
  The RSOH processing block handles frame alignment, scrambling and supervision of the transmission line, including regenerator section error monitoring.
- MSOH - multiplexer section overhead - Functions:
  The MSOH processing block supervises the transmission between points where the AUG (e.g. AU-4) is assembled and disassembled. It handles multiplex section error monitoring and synchronisation status communication.
- AU-4 (Administrative Unit) pointer - payload (VC-4) is not in a fitted phase situation compared to the frame (dynamic framing), and the pointer gives situation of the payload compared to the frame. We can equalize the difference of phase and rate between VC and payload with changing the pointer.
  AU-4 PTR points to the first byte of the VC-4 frame (VC-4 POH J1 byte).

Main parameters of the frame:

Frame time: 125 us
Frame consists of 9 rows, and 270 bytes by rows. 
              9 x 270 x 8 x 8000 = 155 520 000 bit/s
              |    |    +    + frame/sec (frame time: 125 us)
              |    |    |
              |    |    + one byte = 8 bits
              |    there are + 270 bytes in a row
              + number of rows in the frame

Frame consists of 2430 bytes (octets)
Payload consists of 2349 bytes (octets)
Overhead consists of 81 bytes (octets)

Section OverHead (SOH)
Build-up of header of the frame - Section overhead (SOH):
(Header consists of 9 rows, and 9 bytes by rows)

            1  2  3  4  5  6  7  8  9
 RSOH  1   A1 A1 A1 A2 A2 A2 J0 xx xx
       2   B1       E1       F1
       3   D1       D2       D3
AU PTR 4   H1 H1 H1 H2 H2 H2 H3 H3 H3
 MSOH  5   B2 B2 B2 K1       K2
       6   D4       D5       D6
       7   D7       D8       D9
       8   D10      D11      D12
       9   S1 Z1 Z1 Z2 Z2 M1 E2




RSOH:

Label Length Description Values
A1 3 bytes Framing - frame sync 11110110
A2 3 bytes Framing - frame sync 00101000
J0 old:C1 1 byte RS trace (section access point identifier) 00000001
B1 1 byte BIP-8  (bit error monitor) parity check ---
E1 1 byte Orderwire - Service speech channel 0
F1 1 byte User channel 0
D1-D3 3 bytes Data communication channel (for management) 0,0,0

AU-4 PTR:

Label Length Description Values
H1 3 bytes Tx:xxxx10xx (e.g. H1/H2 pointer value: 98)
Rx: 01101000
H2 3 bytes Tx:--- Rx: 00010001
H3 3 bytes Tx:---

MSOH:

Label Length Description Values
B2   3 bytes BIP-24: B2 x 3(bit error monitor bit interleaved parity) ---
K1,K2 2 bytes APS-channel: K1, K2  Automatic protection switching signaling
D4-D12 9 bytes Data communication channel (for management) 
S1 1 byte 
M1 1 byte for transmission of MS-REI
Z1, Z2 2 bytes Spare
E2 1 byte Orderwire - Service speech channel



A  VC-4 framed payload

      1                                                  261
      +-+-------------------------------------------------+byte
      |V|                                                 |
      |C|                                                 |
      |4|                                                 |
    9 | |                  STM-1 payload (VC-4)           |
      |P|                                                 |
      |O|                                                 |
      |H|                                                 |
      +-+-------------------------------------------------+
       |
       +-- VC-4 Path Overhead



mapping of a PDH signal stream of 140 Mbit/s

A PDH signal stream of 140 Mbit/s mappeable directly to the VC-4 frame.

 mapping of ATM cells into a VC-4 container

We put ATM cells with a byte synchronous mode into the container. 
Since VC-4 container is not an integer multiple of the ATM cell, 
the ATM cells may reach over to the next VC-4 container.

Multiplexing of the different components with a lower rate will happen according to the multiplexing plan.


Example:

Location of a TU-12 component with a (1,1,1) 
(TUG-3, TUG-2, TU-12) identifier in the VC-4 frame is the following:
      1                                                  261
      +-+-------------------------------------------------+byte
      |V|   | |        | |          | |          | |      |
      |C|   | |        | |          | |          | |      |
      |4|   | |        | |          | |          | |      |
    9 | |   | |        | | STM-1 payload (VC-4)  | |      |
      |P|   | |        | |          | |          | |      |
      |O|   | |        | |          | |          | |      |
      |H|   | |        | |          | |          | |      |
      +-+-------------------------------------------------+
            10         73          136          199


Bytes of the TU-12 frame are multiplexed into the 10,99,136 and 199. columns 
of the VC-4 frame, according to the multiplexing plan. We forward 9x4=36 bytes 
in a VC-4 frame from 144, and forwarding of a whole TU-12 frame will happen in 
the 4 VC-4 frame.

VC-4 Path OverHead (POH)

HOVC POH (VC-4 POH):

Label Description Values
J1 az AU-4 PTR PATH trace points here (high order path access point identifier) 
B3 BIP-8  (bit error monitor)  parity check
C2 Signal label (Payload type) 
G1 Path status (bit 1-4: REI, bit 5: RDI) 
F2 User communication channel 
H4 multiframe indicator 
F3 User communication channel 
K3 
N1

Label	Length	Description	Values
A1	3 bytes	Framing - frame sync	11110110
A2	3 bytes	Framing - frame sync	00101000
J0 old:C1	1 byte	RS trace (section access point identifier)	00000001
B1	1 byte	BIP-8 (bit error monitor) parity check	---
E1	1 byte	Orderwire - Service speech channel	0
F1	1 byte	User channel	0
D1-D3	3 bytes	Data communication channel (for management)	0,0,0

Label	Length	Description
H1	3 bytes	Tx:xxxx10xx (e.g. H1/H2 pointer value: 98) Rx: 01101000
H2	3 bytes	Tx:--- Rx: 00010001
H3	3 bytes	Tx:---

Label	Length	Description	Values
B2	3 bytes	BIP-24: B2 x 3(bit error monitor bit interleaved parity)	---
K1,K2	2 bytes		APS-channel: K1, K2 Automatic protection switching signaling
D4-D12	9 bytes	Data communication channel (for management)
S1	1 byte
M1	1 byte	for transmission of MS-REI
Z1, Z2	2 bytes	Spare
E2	1 byte	Orderwire - Service speech channel

Label	Description	Values
J1	az AU-4 PTR PATH trace points here (high order path access point identifier)
B3	BIP-8 (bit error monitor) parity check
C2	Signal label (Payload type)
G1	Path status (bit 1-4: REI, bit 5: RDI)
F2	User communication channel
H4	multiframe indicator
F3	User communication channel
K3
N1