Specifications

Chapter 1 Understanding Networking and IP Addressing
Introduction to Networking
Niagara Release 2.3
Niagara Networking & Connectivity Guide Revised: May 22, 2002
1–13
Protocol Bindings
Multiple protocols can be bound to the same network card. When more than one
protocol is bound to a particular adapter, the binding order becomes important. The
order in which protocols are bound determines the order in which the protocols are
used to attempt a successful connection.
In Windows NT, protocol bindings are made in the NT Control Panel. In the Network
folder, you can view and modify connections between the NIC cards, protocols, and
services that are installed on your computer.
Access Methods
In communications systems in which more than one transmitter has access to the
same communication channel, a standard procedure must be established to prevent
or handle instances where multiple transmitters attempt to send messages on the
media at the same time. Different methods exist to control access to a network.
Contention
Methods
Computers transmit data on a first-come, first-served basis. This can lead to a
situation where two or more computers transmit simultaneously, which results in a
collision. Collisions are detected by monitoring voltage levels on the wire. A voltage
level of two or more times higher than expected indicates a collision, since this means
there are multiple signals traveling along the backbone at the same time.
In an attempt to prevent this from happening, a contention-based protocol was
developed called carrier sense, multiple access (CSMA). A carrier is the presence of
any data transmission. CSMA operates like a two-way radio system—a computer
with a message to send listens to the network and if it does not hear the carrier signal
of another network device, the computer broadcasts its message. Since two devices
could theoretically listen, then transmit at the same time, thereby causing a collision,
various schemes have been developed to help detect and avoid collisions. The most
common methods are as follows:
CSMA/CD (Carrier Sense, Multiple Access with Collision Detection)—
When transmitting devices detect a collision on the network, they each wait a random
length of time before attempting to retransmit. The slim chance that both devices will
wait the exact same time almost assures that the next attempt will be successful. This
is the contention method used in Ethernet networks.
CSMA/CA (Carrier Sense, Multiple Access with Collision Avoidance)—
With collision avoidance, devices announce their intent to transmit. If the
announcement causes a collision, the offending station waits a pre-determined
period, then retries. This is the contention method used in wireless networks.
Token Passing Another access method used with a ring topology is token passing. With token
passing, network devices pass a token (a special sequence of bits) that grants the
device holding it permission to transmit a frame packet. If a station does not need to
transmit, it passes the token onto the next station on the network. If a station does
have data to transmit, it holds the token and transmits its data to the next station on