Avaya Configuring ATM Half-Bridge Services Manual de usuario descargar pdf (Pagina 85)

Understanding ATM Concepts

308611-14.00 Rev 00

B-5

Permanent Virtual Connections

Virtual channels and virtual paths allow you to establish virtual channel links

(VCLs). To use the ATM Half-Bridge protocol, you must create VCLs as

permanent virtual circuits (PVCs). Once you establish a PVC, you can transfer

information over it at any time.

Service Records and Virtual Circuits

ATM devices communicate using virtual circuits (VCs). These VCs transmit and

receive ATM cells containing upper-layer protocols. Nortel Networks ATM

routers use service records to provide a way of creating logical interfaces (within

the physical ATM interface) for these upper-layer protocols. In essence, these

service records allow you to:

• Organize multiple VCs into logical groups.

• Create direct, point-to-point connections.

• Assign, delete, and modify upper-layer protocols for just one PVC, or for a

group of VCs, at any given time.

Data Encapsulation

Nortel Networks ATM routers support multiprotocol encapsulation (as defined in

RFC 1483), enabling the router to multiplex (combine) and demultiplex (separate)

bridged or routed protocol data units (PDUs).

For transmission, the encapsulation process adds a header between 2 and 8 octets

in length to the PDU to allow decoding. The decoding process determines the

proper service access point (SAP).

When receiving information, the encapsulation method evaluates the header to

determine whether the PDU is a valid routed or bridged cell. If it is valid, the

encapsulation method then strips the header from the cell and passes it to the

appropriate SAP for routing or bridging.

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Avaya Configuring ATM Half-Bridge Services Manual de usuario Pagina 85