Avaya Configuring ATM DXI Services Uživatelský manuál stáhnout pdf (Strana 42)

Configuring ATM DXI Services

2-18 117375-A Rev. A

Data Transmission

Data transmission (also called cell switching) through the ATM network relies on

the establishment of logical connections between ATM entities. ATM is a

connection-oriented service. This means that an ATM entity cannot transmit

information until it establishes a connection with a receiving entity. These

connections consist of virtual channels, virtual paths, and transmission paths.

A virtual channel is a logical connection between two communicating ATM

entities. Each virtual channel may carry a different protocol or trafﬁc type. The

virtual channel transports cells that have a common identiﬁer. The identiﬁer is

called the virtual channel identiﬁer (VCI) and is part of the cell header. You can

establish virtual channels permanently or set them up dynamically, allowing the

network to adjust itself to the trafﬁc demand.

A virtual path is a set of virtual channels between a common source and

destination. The virtual channels in a virtual path logically associate to a common

identiﬁer. This identiﬁer is called the virtual path identiﬁer (VPI) and is part of the

cell header. You can base cell switching on either the VPI alone, or on a

combination of the VPI and VCI.

Virtual paths enable you to separate network transport functions into those related

to an individual logical connection (virtual channel) and those related to a group

of logical connections (virtual path).

A transmission path is a physical connection that comprises several virtual paths,

each virtual path containing several virtual channels. The transmission path may

support multiple virtual paths across a single connection to the network.

Figure 2-12 shows the relationships between the virtual channel, the virtual path,

and the transmission path.

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Avaya Configuring ATM DXI Services Uživatelský manuál Strana 42