ITU-T G.707 155520 kbit/s (STM-1) interface
Frame formats, multiplexing, definitions
The following figure demonstrates the multiplexing structure and section layers of SDH. Structure provides the multiplexing and mapping of the ATM cells both the European (2..140 Mbit/s) (SDH), and American (1.5 .. 44 Mbit/s) (SONET) G.702 PDH signal stream of hierarchy:
ATM --->----+ SDH
+---+ | +----+ +----+ +---+ +-----+
|C-4| +-------------->-------------------|VC-4|-|AU-4|-|AUG|-|STM-N|->
140 >| |-|-------------->-------------------| | | |+| | | |
Mbit/s+---+ | +| | +----+|| | |STM-1|
| 3+----+ |+---+ +-----+
+---+ | +----+ +----+ +-----+| |
44 |C-3| +-|VC-3|-|TU-3|>-----------|TUG-3|+ 3
(34) >| |--+| | | | | | |
Mbit/s+---+ ||+----+ +----+ +-| | SONET |
|| 7 +-----+ +----+ +----+|
|+------------->---------|---------|VC-3|-|AU-3|+
+---+ | +----+ +----+ +-----+| +--7---| | +----+
|C-2| +-|VC-2|-|TU-2|>--|TUG-2|+ | +----+| + pointer |
6 >| |-|-| | | | | | | | | állítás |
Mbit/s+---+ | +----+ +----+ +-| |---+ | | |
| 3+| | | | |
+---+ | +----+ +----+ ||+-----+ | | |
|C12|---|VC12|-|TU12|>+| | |
E1 2 >| | +-| | | | | | | |
Mbit/s+---+ | +----+ +----+ 4 | | |
+---+ | +----+ +----+ | HOVC | |
DS1 |C11| +-|VC11|-|TU11|>-+ Higher | |
1.5 >| |---| | | | Order | |
Mbit/s+---+ +----+ +----+ Virtual | |
| | | | + pointer Container | |
circuit PDH | SDH állítás SDH Transmission
layer path | Lower Higher media (physical)
layer | Order Order layer
| Path Path
| layer layer
|
LOVC
Lower
Order
Virtual
Container
- Synchronous transport module level N (STM-N). STM-N= N x STM-1. (N=4,16,64,256)
- Synchronous Transport Module level 1 (STM-1). An information structure (frame) supporting the "section layer" connections in SDH.
STM-1 = AU-4 (European, SDH) vagy 3xAU-3 (American, SONET) + SOH (overhead) .
Section layers of SDH:
- circuit layer - (telecommunication services for end users)
- path layer - (delivery services for the circuit layer. E. g. DS3 vagy VC4)
- lower order path layer - (E.g. between VC-12 containers.)
In other words: pathes for the streams to be multiplexed.
Functions:
- Assembly and disassembly the Lower Order Virtual Container (LOVC) (e.g. VC-12)
- Path error monitoring,
- Signal label, path trace handling,
- insertion and extraction of the payload.
- higher order path layer - (E.g. between VC-4 containers.)
In other words: pathes for the multiplexed streams.
Functions:
- Assembly and disassembly the high order virtual container (HOVC) (e.g. VC-4)
- Path error monitoring,
- Signal label, path trace handling
- insertion and extraction of the payload.
- transmission media layer (physical layer) - (transport services for the higher order path layers)
- regenerator layer (section)
- multiplex layer (section)
- Adminisrative unit AU-n , AU = VC-n + (AU PTR - AU pointer) (n=3,4) adapts the layer of high order path layer to the multiplex layer
- Payload information to transmit in SDH
- Container C-n (n=1 to 4). Synchronized information structure of payload (rate equalization) (bitrates according to G.702)
- Virtual container VC-n. Information structure (frame) supporting "path layer" connections in SDH.
- Lower Order Virtual Container - LOVC (e.g. VC-12)
VC = C + POH (Path OverHead). Frame time: 500 us.
- Higher Order Virtual Container - HOVC (e.g. VC-4)
- Tributary unit TU-n (n=1 to 3) TU adapts the low order path layer to the high order path layer.
TU = VC + (TU PTR - TU pointer)
- Tributary unit group TUG-2, a frame consisting of multiple TU-1s, or one TU-2
- Tributary unit group TUG-3, a frame consisting of multiple TU-2s, or one TU-3
- Pointer (PTR) - an indicator showing offset between the begining of the frame and the begining of the payload:
- AU pointer
- TU-3 pointers
- TU-1/TU-2 pointers
- Mapping formats and multiplexing methods
- Mapping of tributaries into VCs (American system, SONET)
- Mapping of tributaries into VC-4 (European system, SDH)
SDH-PDH comparision:
PDH -> numerous hierarchy levels, numerous bit rates
multiplexing technique: rate equalization
Advantages of the synchronous digital multiplexing and the connecting synchronous digital hierarchy:
- more simple mutiplexing/demultiplexing technique
- indirect access to the tributaries with smaller rate
- enhanced Operations Administrations and Maintenance (OAM) capabilities.
- upgradeability towards higher bit rates