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SMDS Overview

114069 Rev. A 1-5

The router next prepares the Level-3 PDU for transmission to the DSU/CSU by

encapsulating it within a DXI header and trailer that provide control information.

Upon receiving the DXI packet, the DSU/CSU strips the DXI header/trailer and

divides the Level-3 PDU into ﬁxed-length (44-byte) units called cells. The

DSU/CSU encapsulates these cells within a 7-byte header and 2-byte trailer to

form Level-2 PDUs.

Finally, the DSU/CSU inserts an additional four bytes of framing information

between each Level-2 PDU and transmits the framed cells across a

Digital Service Level 1 (DS1) or DS3 connection to the SMDS network.

Figure

1-5 shows the assembly of SMDS cells as speciﬁed by the DXI.

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Avaya Configuring SMDS Manual do Utilizador Página 27