Agilent Technologies 622Vu Advisor, User Manual

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provide a smooth connection between the two devices. It doesn’t protect one device against
problems in the other, but rather assumes that the two devices function correctly according to
the rules of the public or private network. (In the case of NNI used on a provider network, it’s
assumed that the devices abide by current ATM standards.)
OAM
Operations, Administration, and Maintenance.
OC data rate
Optical Carrier data rate: a term referring to the rate of data transmission of a bit
stream after being converted to optical signals, specified in conformance with SONET
standards. Current OC transmission rates vary from 51.84 Mb/s, known as Optical Carrier
level 1 (OC-1), to 2,488.32 Mb/s, or OC-48. In between are OC-3, OC-12/STM-4, and OC-
24. The n designation specifies the number of level-1 (OC-1) circuits that could be at the data
rate: OC-12/STM-4 carries 622.08 Mb/s (51.84 x 12), for example. Visual Networks offers a
physical-interface option that supports OC-3 (155.52 Mb/s) and OC-12/STM-4, with future
plans to support OC-48 (although no ATM standards exist currently for OC-48 speeds). See
also STS data rate, STM data rate.
OLE
Object Linking and Embedding — A Microsoft term used to refer to the capability of one
piece of software (e.g., CellCommand) to create objects that you include (embed) in other
systems (e.g., Visual Basic, C++, Excel, or 622Vu Advisor).
OLE Automation
Capability that applications (such as 622Vu Advisor) use to expose their OLE
objects to development tools that support OLE Automation — container applications such as
Visual Basic or C++, for example, or macro languages. OLE Automation allows one program
to essentially operate another program; specifically, allowing it to dynamically discover and
use the interfaces to the other program at run time.
OLE object
Piece of code that makes its functions available (i.e., exposes its functions) through
distinct function groups known as interfaces.
OSI
Open Systems Interconnection — One of several protocols commonly used to communicate
over an internet. The OSI standard (an ISO standard itself) supports a seven-layer
communications protocol, where each layer is responsible for a specific type of activity (raw
signalling over the transmission media, data framing, placing on an internet, etc.). This is well
documented in most data communications material.
Payload Type
Three-bit cell-header field that serves primarily to distinguish between user and
operations traffic (where operations traffic includes administration and management —
OAM). The first bit is 0 for user data, 1 for OAM data.
•
For user data (bit 1 is zero), the second bit is used to indicate whether the cell encoun-
tered any network congestion during the last hop: 0 indicates no congestion, 1 indicates
congestion. The third bit is available to the user for any signalling purposes.
•
For OAM data (bit 1 is set), the specifics of use for the second and third bits are still not
finalized. (Exceptions are Payload Type 111, which is reserved for future use, and 110,
which is reserved for future traffic-control and resource management.)
Payload Type Indicator
See PTI.
PC
For purposes of Agilent Technologies' product line, any "C or newer" model of the Agilent
Advisor.
PDU Protocol Data Unit — The information unit of a particular communications protocol; in the
case of ATM traffic, the collection of cells that make up a packet. PDUs can be packaged
using any of several standard formats, as described under ATM Adaptation Layer. The format
used varies depending on the type of data being sent and the medium over which it’s being
transmitted.
Physical Media Dependent sublayer (PMD)
Sublayer, within the physical layer, that
defines the transmitter, receiver, timing recovery, and channel specifications that facilitate a
connection to appropriate transmission media.
A: Glossary
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