3Com MSR 50 Series, Руководство по настройке

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540 C
HAPTER
29: CPOS I
NTERFACE
C
ONFIGURATION
SDH Frame Structure The frame structure of SDH signal STM-N is described in the following part.
Low-speed tributary signals should distribute in one frame regularly and evenly for
the convenience of adding/dropping them in high-speed signal. ITU-T specifies
that STM-N frames adopt the structure of rectangle blocks in bytes, as illustrated
in the following figure:
Figure 150 STM-N frame structure
STM-N is a rectangle-block frame structure of 9 rows x 270 x N columns, where
the N in STM-N equals the N columns. N takes the value 1, 4, 16, and so on,
indicating the number of STM-1 signals that form SDH signal.
The STM-N frame structure consists of three parts: section overhead (SOH), which
includes regenerator section overhead (RSOH) and multiplex section overhead
(MSOH); administration unit pointer (AU-PTR); and payload. AU-PTR is the pointer
that indicates the location of the first byte of payload in an STM-N frame so that
the receiving end can correctly extract payload.
Terms
■
Multiplex Unit: A basic SDH multiplex unit includes multiple 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), where n is
the hierarchical sequence number of unit level.
■
Container: Information structure unit that carries service signals at different
rates. G.709 defines the criteria for five standard containers: C-11, C-12, C-2,
C-3 and C-4.
■
Virtual container (VC): Information structure unit supporting channel layer
connection of SDH. It terminates an SDH channel. VC is divided into
lower-order and higher-order VCs. VC-4 and VC-3 in AU-3 are higher-order
virtual containers.
■
Tributary unit (TU) and tributary unit group (TUG): TU is the information
structure that provides adaptation between higher-order and lower-order
channel layers. TUG is a set of one or more TUs whose location is fixed in
higher-order VC payload.
Regenerator
section
overhead
AU-PTR
Multiplex
section
overhead
Payload
1
2
3
4
5
6
7
8
9
9 x N 261 x N
9 x 270 x N (bytes)