Nortel Networks Passport Module 8672A - Manual (Page 32)

32 Chapter 2 Passport 8672ATM Module technology overview
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• VC: Virtual circuit. This is a network service that provides
connection-oriented service regardless of the underlying network structure.
• VP: Virtual path. A virtual path is a set of virtual channels between a common
source and destination. The virtual channels in a virtual path are logically
associated with a common identifier, the virtual path identifier.
• VPI: Virtual path identifier. Identifier contained in the ATM cell header to
designate the virtual path on the physical ATM link.
• VCI: Virtual circuit identifier. Address or label contained in the ATM cell
header to designate the virtual circuit within the virtual path on the physical
ATM link
• ELAN: Emulated LAN. Following the ATM Forum specification, ELANs
make connection-oriented ATM networks look like connectionless LANs.
• UBR: Unspecified bit rate. UBR is an ATM service category that does not
specify traffic-related service guarantees. No numerical commitments are
made with respect to the cell loss ratio or to the cell transfer delay.
• VBR: Variable bit rate. VBR is an ATM Forum-defined service category that
supports variable bit rate data traffic with average and peak traffic parameters.
• PCR: Peak cell rate. The PCR, in cells/second, is the maximum cell rate.
• SCR: Sustainable cell rate. The SCR is an upper bound on the cell rate that is
long relative to that of the PCR. Enforcement of this bound by the Usage
Parameter Control allows the network to allocate sufficient resources, but less
than those for the PCR, to ensure that the specified cell loss ratio can be
achieved.
• MBS: Maximum burst size. The signaling method determines the MBS,
which is coded as a number of cells, that can be transmitted at peak rate and
still conform to the overall algorithm.
Data transmission (also called cell switching) through the ATM network relies on
establishing logical connections between ATM devices. ATM is a
connection-oriented service, which means that an ATM device cannot transmit
information until it establishes a connection with a receiving device.