3Com CoreBuilder 9000, Руководство пользователя

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436 A
PPENDIX
C: P
ROTOCOLS AND
I
NTERFACES
Cell Delineation: This function permits the identification of cell
boundaries in the payload. It uses the Header Error Control (HEC) field
in the cell header.
Path Signal Identification: An integrity check is performed on the
end-to-end signal.
Cell Mapping: This function maps ATM cells by aligning every cell
with the byte structure of the SONET STS-3c payload capacity. Because
the STS-3c payload capacity is not an integer multiple of the cell
length, a cell may cross a payload boundary.
Cell Scrambling/Descrambling: This function permits the
randomization of the cell payload to avoid continuous non-variable bit
patterns and improve the efficiency of the cell delineation algorithm.
Transmission Frame Generation and Recovery: This function
builds the frame, sends, and recovers it from the physical media.
Bit Timing and Line Coding: This function performs the
transmission and recovery of data to and from the serial line based on
physical line coding (NRZ).
The ATM SONET physical layer interface can be over UTP5. In addition,
numerous optical interfaces (for example, Multi Mode, Single Mode) can
be used.
The SDH-STM-1 is a physical layer similar to the SONET-STS-3c with some
differences in frame fields. The SDH-STM-1 is usually used in Europe.