Fore Systems forerunner series, Configuration Manual

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ForeRunner ATM Switch Network Configuration Manual
Glossary - 7
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Glossary
Cell -
an ATM Layer protocol data unit (PDU). The basic unit of information transported in
ATM technology, each 53-byte cell contains a 5-byte header and a 48-byte payload.
Cell Delay Variation (CDV) -
a quantification of cell clumping for a connection. The cell clump-
ing CDV (
yk
) is defined as the difference between a cell's expected reference arrival time (ck)
and its actual arrival time (ak). The expected reference arrival time (ck) of cell k of a specific
connection is max. T is the reciprocal of the negotiated peak cell rate.
Cell Delineation -
the protocol for recognizing the beginning and end of ATM cells within the
raw serial bit stream.
Cell Header -
ATM Layer protocol control information.
Cell Loss Priority (CLP) -
the last bit of byte four in an ATM cell header; indicates the eligibility
of the cell for discard by the network under congested conditions. If the bit is set to 1, the cell
may be discarded by the network depending on traffic conditions.
Cell Loss Ratio -
In a network, cell loss ratio is (1-x/y), where y is the number of cells that
arrive in an interval at an ingress of the network; and x is the number of these y cells that leave
at the egress of the network element.
Cell Loss Ratio (CLR) -
CLR is a negotiated QoS parameter and acceptable values are network
specific. The objective is to minimize CLR provided the end-system adapts the traffic to the
changing ATM layer transfer characteristics. The Cell Loss Ratio is defined for a connection as:
Lost Cells/Total Transmitted Cells. The CLR parameter is the value of CLR that the network
agrees to offer as an objective over the lifetime of the connection. It is expressed as an order of
magnitude, having a range of 10-1 to 10-15 and unspecified.
Cell Misinsertion Rate (CMR) -
the ratio of cells received at an endpoint that were not originally
transmitted by the source end in relation to the total number of cells properly transmitted.
Cell Rate Adaptation (CRA) -
a function performed by a protocol module in which empty cells
(known as unassigned cells) are added to the output stream. This is because there always must
be a fixed number of cells in the output direction; when there are not enough cells to transmit,
unassigned cells are added to the output data stream.
Cell Relay Service (CRS) -
a carrier service which supports the receipt and transmission of ATM
cells between end users in compliance with ATM standards and implementation specifications.
Cell Transfer Delay -
the transit delay of an ATM cell successfully passed between two desig-
nated boundaries. See CTD.
Cell Transfer Delay (CTD) -
This is defined as the elapsed time between a cell exit event at the
measurement point 1 (e.g., at the source UNI) and the corresponding cell entry event at the
measurement point 2 (e.g., the destination UNI) for a particular connection. The cell transfer
delay between two measurement points is the sum of the total inter-ATM node transmission
delay and the total ATM node processing delay.
Channel -
A path or circuit along which information flows.