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 upgraded to 100
megabits/second over twisted-pair cable or multimode fiber. Fast
Ethernet devices support 10 and 100 megabit/second operation over
twisted-pair media.
Gigabit Ethernet -- Ethernet upgraded to
1000 megabits/second over twisted-pair cable or multimode fiber.
Gigabit Ethernet devices support 10, 100, and 1000megabit/second
operation over twisted-pair media.
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 transfered 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 plus 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 Electical
and Electronics Engineers, an organization that, among other activities, develops
and maintains standards for the computer and electronics industries,
including the 802 standards that cover local area networking.
ANSI -- American
Natioanl 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 Ethernet networks to resolve contention between nodes competing
for access to the network medium.
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 the system board. A combo adapter
consists of multiple adapters on one card, so, for example, a quad
Ethernet NIC may be referred to as a 4-port card.
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, EISA, ISA, XMI, TurboChannelTurboChannel,
each of which typically has multiple slots to accomodate several
I/O devices.
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 specific 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 exchange valid link pulses, 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 valid link pulses from the other end of the link, the link
is considered 'down' and the device will not transmit or receive
over the network communications path. For Fast Ethernet and Gigabit Ethernet,
the link connection state is determined by the presence of a carrier
signal, for both twisted-pair and fiber cabling.
Ring Available/Unavailable -- Network
connection state, for FDDI, Token Ring, or ATM devices.
Open Systems Interconnect
(OSI)
Model - Defines seven layers in a networking framework consisting
of:
(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
UDP port.
In this chapter, applications open
a port to the LAN driver to communicate over a particular LAN device.
In VMS 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.