Nortel Networks 8000 - Manual (Page 64)

Nortel Secure Router 8000 Series
Configuration -WAN Access 4 POS and CPOS interface configuration
Terms
The STM-N is in the block frame structure of 9 lines x 270 x N rows. The number N here is
consistent with that in STM-N. The value of N can be 1, 4, 16, and so on, which indicates that
the signal is multiplexed by N STM-1 signals.
The STM-N frame structure divides as follows:
• Section Overhead (SOH): It has Regenerator Section Overhead (RSOH) and Multiplex
Section Overhead (MSOH).
• Administration Unit Pointer (AU-PTR): AU-PTR is the pointer that specifies the location
of the first byte of payload in STM-N frame.
• Payload: The receiving end can properly extract payload according to the pointer.
Multiplex Unit are basic multiplex units of the SDH include several containers (C-n),
virtual containers (VC-n), tributary units (TU-n), tributary unit groups (TUG-n),
administrative units (AU-n) and administrative unit groups (AUG-n). Here, n is the
sequence number of unit level.
Container is the information structure unit of service signals used to load various rates.
The G.709 defines the criteria for the following five types of standard containers: C-11,
C-12, C-2, C-3, and C-4.
VC is the information structure unit which supports channel layer connection of the SDH.
It is the information terminal of the SDH channel. The VC is divided into lower order
and higher order VCs. The VC-4 and VC-3 in AU-3 are both higher order virtual
containers.
TU and TUG: The TU is the information structure which provides adaptation between
higher order and lower order channel layers. A set of one or more TUs is known as TUG.
This has fixed location in higher order VC payload.
AU and AUG: The AU is the information structure which provides adaptation between
higher order channel layer and multiplex section layer. A set of one or more AUs is
known as AUG. This has fixed location in the payload of STM-N.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 4-3