IBM Turboways 155, Installation And User Manual

Page: 23 / 36

Chapter 4. Managing the Network
This chapter provides information to assist in creating and maintaining ATM
networks.
ATM Connections
ATM networks use a virtual path identifier (VPI) and a virtual channel identifier (VCI).
VPI and VCI together identify connections in the ATM network. A VPI:VCI pair
defines a path between two nodes in an ATM network. The VPI field occupies 1
byte in the ATM cell's 5-byte header while the VCI field occupies 2 bytes in the ATM
cell's 5-byte header.
For the TURBOWAYS 155 PCI UTP ATM Adapter, the value of VPI must be 0. VCI
can be between 0 and 127 decimal.
Although not required, VPI:VCI values are typically assigned symmetrically, that is,
the same values are reserved in both directions across the link. A link is the physical
medium of transmission, for example, a telephone wire or microwave beam. A link
connection includes the physical medium for transmission, the protocol, associated
devices and programming. A link connection is both logical and physical.
More than one virtual channel (VC) can be set up on the same link, but the VPI:VCI
must be different for each connection on the link. A permanent virtual channel (PVC)
is a static connection between two end stations and the ATM network. The PVC is
created by selecting a physical path from the end station through the switches to the
other end station. VPI:VCIs are assigned to establish the connection between the
two end stations. The PVC must be configured in each end station and in all
switches included in the connection.
An ATM switch performs the following functions automatically:
Ÿ
Recognizes the source of the cell.
Ÿ
Changes VPI:VCI.
Ÿ
Determines the destination of the cell.
Ÿ
Transmits the cell to its destination.
Chapter 4. Managing the Network
4-1