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Configuring ATM Services

2-4

ATM DXI Error Checking

The ATM DXI veriﬁes that the VPI/VCI is valid for the PVCs conﬁgured for that

ATM circuit. It also veriﬁes the header format as deﬁned by the value of the DXI

Mode parameter. Refer to the “ATM DXI Modes of Operation” section, later in

this chapter, for details.

ATM DXI also veriﬁes that the BTag ﬁeld in the CS_PDU header is equal to the

ETag ﬁeld in the CS_PDU trailer and ensures that the frame size is valid. If the

packet contains an invalid header, the router drops the packet, updates the

appropriate MIB statistic, and logs the appropriate event.

ATM DXI LMI Support

The router supports a proprietary version of the ATM DXI Local Management

Interface (LMI). This proprietary version of the LMI was a precursor to the

standardized ATM Forum version.

LMI uses an SNMP-like protocol to query network management statistics

maintained on the DSU/CSU MIB. The DSU/CSU may also send asynchronous

events in the form of trap messages to the router.

Simulated Multicast Packet Support

The ATM DXI interface supports multicast packets, enabling the router to take

advantage of multicast functionality, if it is available from the ATM network. ATM

multicasting reserves selected network-assigned VPIs/VCIs as multicast

addresses. The ATM network maps multiple recipients to a single VPI/VCI and

delivers copies of all ATM cells to each member of the address group. As a cell

passes through the ATM network, the network manipulates the cell to reveal the

actual source to the cell recipient.

Note: The ETag and BTag ﬁelds verify that the reassembled AAL3/4 Common

Part Convergence Sublayer (CPCS) frame is not just two frames concatenated

together. If these two ﬁelds do not match, then the frame is most likely the

concatenation of two frames.

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Avaya Configuring ATM Services Manual do Utilizador Página 40