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virtual path identifier (ATM) (VPI)

The Virtual Path Identifier (VPI) is an identification number for the logical connection hierarchy, the virtual path( VP), in B-ISDN.

The VPI field is an 8-bit long data field in the header of the ATM cell at the User Network Interface( UNI) or a 12-bit long data field at the Network to Network Interface( NNI) and at B-ICI. Together with the 16-bit Virtual Channel Identifier( VCI), the Payload Type( PT) and the data fields for the Cell Loss Priority (CLP) and the Header Error Control( HEC) it forms the NNI header.

ATM header

ATM header

It is not used in the DQDB header because there are no logical connections that are multiplexed. Instead, the data fields for the segment type( ST) and the message identifier( MID) are used.

Informations:
Englisch: virtual path identifier (ATM) - VPI
Updated at: 28.11.2011
#Words: 124
Links: identification number (ID), connection, hierarchy, virtual, path
Translations: DE
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