The following is a list
of terms relevant to local area networks:
Ethernet — A network communications technology using coaxial or twisted-pair
cable, originally developed by Intel, Xerox, and Digital. It has
a data transmission rate of 10 megabits/second. It is characterized
by the use of the CSMA/CD network access method. It is described
by the IEEE 802.3 standard. Ethernet is also used as an adjective
to describe Ethernet characteristics, such as an Ethernet address,
or an Ethernet application.
Fast Ethernet —
Ethernet operating at 100 megabits/second over twisted-pair cable
or multimode fiber. Fast Ethernet devices support 10 and 100 megabits/second
operation over twisted-pair media or 100 megabits/second over multimode
Gigabit Ethernet —
Ethernet operating at 1000 megabits/second over twisted-pair cable
or multimode fiber. Gigabit Ethernet devices support 10, 100, and
1000 megabits/second operation over twisted-pair media or 1000 megabits/second
over multimode fiber.
FDDI — Fiber Distributed Data Interface, a token-passing network
communications technology characterized by use of a dual ring configuration
to improve availability upon failure of a node or connection. It
has a data transmission rate of 100 megabits/second. It operates
over multimode fiber or twisted-pair cable. It is described by the
American National Standards Institute (ANSI) standard X3T9.5.
Token Ring — A token-passing network communications technology characterized
by a star topology in most implementations. It has a data transmission
rate of 4 or 16 megabits/second. It operates over twisted-pair cable.
It is described by the IEEE 802.5 standard.
ATM — Asynchronous
Transfer Mode, a cell-based network communications technology, where
network data is divided into 48-byte chunks and transferred across
the network with a 5-byte header that contains addressing and control
information. The ATM Forum describes the communications protocol,
and specifies how it is to be used to interoperate with Ethernet networks,
in the LAN Emulation (LANE) standard. To interoperate with Ethernet,
the ATM device hardware transparently breaks transmit packets into
48-byte chunks and adds a 5-byte header and transmits the cells onto
the ATM network. On receive, it transparently re-assembles the 48-byte
chunks to construct each receive packet.
IEEE — Institute of Electrical and Electronics Engineers, an
organization that, among other activities, develops and maintains
standards for the computer and electronics industries, including the
802 standards that define local area networking.
ANSI — American
National Standards Institute, an organization that develops and maintains
standards for the computer and communications industries
802.3 — The IEEE
standard for Ethernet network technology, including 802.3u for Fast
Ethernet, and 802.3z for Gigabit Ethernet.
802.5 — The IEEE
standard for Token Ring network technology.
CSMA/CD — Carrier Sense Multiple Access with Collision Detection,
the network access protocol used on half-duplex Ethernet networks
to resolve contention between nodes competing for access to the network
NIC — Network Interface
Card. Other terms that may be used interchangeably include Adapter,
Controller, Device, Card, Port. LAN On Motherboard (LOM) is a variant
where the NIC hardware is included on a system board. A multiport
adapter consists of multiple adapters on one card, so, for example,
a quad Ethernet NIC may be referred to as a 4-port card. A combo
adapter consists of multiple adapters, some Ethernet and some storage,
SCSI or Fibre Channel.
Bus — Data and
control paths that connect the functional units of a computer. In
relation to LAN devices, it refers to the hardware interface between
the CPU and the I/O devices. Each LAN device connects to a particular
type of bus, such as PCI, PCI-X, PCI-Express, EISA, ISA, XMI, TurboChannel,
each of which typically has multiple slots to accommodate several
Duplex — A characteristic
of a 2-way communication channel that indicates whether the channel
can allow transmission in both directions at the same time (full-duplex)
or not (half-duplex).
Flow Control —
A technique where the flow of data along a communications channel
is adjusted to ensure that the receiving side can handle incoming
data without loss. Many network applications implement flow control
techniques in software. Here, this term refers to the implementation
of flow control in hardware independent of the network application
or protocol, as specified by the IEEE 802.3x standard. The receiver
side hardware sends special packets, called pause frames, that asks
the transmitting side to stop transmitting for a certain amount of
time. When the receiver has caught up, it sends a pause frame with
a zero time to re-enable the transmitter.
Packet — A unit
of data transmission on the network, also called frame. It consists
of a header, body of data, and a Cyclic Redundancy Check (CRC). The
frame may be encapsulated by additional data needed for the particular
network technology. Note that LAN Emulation over ATM imposes packet
concepts over the underlying cell-based network technology.
Jumbo Frames — Oversize Ethernet packets, where
the range of sizes on Ethernet is from 64-1518 bytes, jumbo frames
are packets ranging in size from 1519 to 9216 bytes depending on the
hardware and software implementation.
Link Up/Down —
Network connection state, for Ethernet devices. Most Ethernet devices
that connect to twisted-pair cables have the ability to detect if
an active link connection exists. When both ends of the network connection
can detect a valid connection, the link is considered to be 'up'
and the Ethernet device is capable of using the network channel to
transmit and receive packets. When the Ethernet device cannot detect
a valid connection, the link is considered 'down' and the
device will not transmit or receive over the network communications
— Network connection state, for FDDI, Token Ring, or ATM devices.
Open Systems Interconnect
(OSI) Model — Defines the following seven layers
in a networking framework:
(7) Application Layer
(6) Presentation Layer
(5) Session Layer
(4) Transport Layer
(3) Network Layer
(2) Data Link Layer
(1) Physical Layer
Port — One end
of a communications channel, or the channel itself. When correlated
to the OSI Model, port may refer to a communications channel at various
layers. At the physical layer, a port is a LAN device, so a quad
Ethernet device is said to be a 4-port card. At the data link layer,
the LAN drivers allow multiple applications to run on one LAN device.
Each application will have opened a port to the LAN driver. At the
application layer, an application may allow multiple ports to be opened
to it, with the application itself doing the multiplexing of the ports
through itself to the underlying network. An example of this would
be a network application written to send and receive data over a TCP/IP
In this chapter, applications open
a port to the LAN driver to communicate over a particular LAN device.
In OpenVMS terms, opening a port is done by assigning a channel.
User — Refers to
the application that has opened a port to the LAN driver. A LAN device
may be described as having a number of different users. Each user
would have opened a port to the LAN device. Examples of users are
LAT, TCP/IP, DECnet, Clusters (NISCA).
In this chapter,
the terms application and user may be used interchangeably.