Altera Corporation 15
AN 46: ATM Packet Scheduler in FLEX 8000 Devices
Glossary
The following definitions are from the
“Glossary of ATM Terms,” provided by 3Com
in conjunction with Technology Transfer
Institute, Business Communications Review,
and McQuillan Consulting.
ABR (Available Bit Rate) One of five ATM
Forum-defined service types. Supports variable
bit rate data traffic with flow control, a
minimum guaranteed data transmission rate,
and specified performance parameters.
BISDN (Broadband Integrated Services Digital
Network) ITU-TSS name for the application of
ISDN concepts to the high-speed (above
1.544 Mbps) broadband area. Primarily
identifies SONET as the transmission sub-
system and ATM as the transport protocol of
choice.
cell Unit of transmission in ATM. A fixed-
size frame consisting of a 5-octet header and a
48-octet payload.
concentrator A network device used in FDDI
and token ring networks, which provides
connections for multiple stations, so they can
communicate with other stations on the
network.
frame A bundle of data, usually in binary
form, organized in a specific way for
transmission. Three principal elements are
included in the frame: control information
(destination, origin, length of frame); the data
to be transmitted; and the error detection and
correction bits. The data and control elements
and error-control information are arranged in a
specified format. A frame is the basic data
transmission unit employed in bit-oriented
protocols.
FR (Frame Relay) A network technology based
on virtual circuits and supporting variable-
length frame transmission between end users.
port The entrance or physical access point to a
repeater, computer, multiplexer, device, or
network where signals may be supplied,
extracted, or observed.
routing (1) The assignment of a path by which
a message will reach its destination. (2) The
forwarding of a message unit along a particular
path as determined by the parameters carried
in the message. (3) Routing may also include
the translation of messages between LAN
segments that use different LLC protocols.
SONET (Synchronous Optical Network) ANSI
standard for transmission over optical fiber.
Used in the U.S. and Canada. A variation of the
SDH international standard.
token In token-passing networks, the token
gives the “holding” queue the right to transmit
on the shared medium. The token circulates
sequentially through the stations on the ring.
FDDI specifically uses two classes of tokens:
restricted and non-restricted.
VC (Virtual Channel) Each physical circuit in
an ATM network is pre-configured with some
number of virtual paths. Each virtual path may
support many virtual channels. VCs are not
assigned any dedicated bandwidth. Bandwidth
is allocated on demand by the network as users
have traffic to transmit.
VCI (Virtual Channel Identifier) The 16-bit
number in an ATM cell header identifying the
specific virtual channel on which the cell is
traversing on the current physical circuit.