Content








Overview











Local-area network (LAN) design has
developed and changed over time. Network designers until very recently
used hubs and bridges to build networks. Now switches and routers are
the key components in LAN design, and the capabilities and performance
of these devices are continually improving.
This module returns to some of the roots of modern Ethernet LANs with a
discussion of the evolution of Ethernet/802.3, the most commonly
deployed LAN architecture. A look at the historical context of LAN
development and various networking devices that can be utilized at Layer
1, Layer 2, and Layer 3 of the OSI model will help provide a solid
understanding of the reasons why network devices have evolved as they
have.
Until recently, most
Ethernet networks were built using repeaters. When the performance of
these networks began to suffer because too many devices shared the same
segment, network engineers added bridges to create multiple collision
domains. As networks grew in size and complexity, the bridge evolved
into the modern switch, allowing microsegmentation of the network.
Todayłs networks typically are built using switches and routers, often
with the routing and switching function in the same device.
Many modern switches are capable of
performing varied and complex tasks in the network. This module will
provide an introduction to network segmentation and will describe the
basics of switch operation.
Switches and bridges perform much of the
heavy work in a LAN, making nearly instantaneous decisions when frames
are received. This module describes in detail how frames are transmitted
by switches, how frames are filtered, and how switches learn the
physical addresses of all network nodes. As an introduction to the use
of bridges and switches in LAN design, the principles of LAN
segmentation and collision domains are also covered.
Switches are Layer 2 devices that are
used to increase available bandwidth and reduce network congestion. A
switch can segment a LAN into microsegments, which are segments with
only a single host. Microsegmentation creates multiple collision-free
domains from one larger domain. As a Layer 2 device, the LAN switch
increases the number of collision domains, but all hosts connected to
the switch are still part of the same broadcast domain.
Students completing this module should be
able to:

Describe the history and function of
shared, half-duplex Ethernet
Define collision as it relates to
Ethernet networks
Define microsegmentation
Define CSMA/CD
Describe some of the key elements
affecting network performance
Describe the function of repeaters
Define network latency
Define transmission time
Describe the basic function of Fast
Ethernet
Define network segmentation using
routers, switches, and bridges
Describe the basic operations of a
switch
Define Ethernet switch latency
Explain the differences between Layer
2 and Layer 3 switching
Define symmetric and asymmetric
switching
Define memory buffering
Compare and contrast store-and-forward
and cut-through switching
Understand the differences between
hubs, bridges, and switches
Describe the main functions of
switches
List the major switch frame
transmission modes
Describe the process by which switches
learn addresses
Identify and define forwarding modes

Define LAN segmentation
Define microsegmentation using
switching
Describe the frame-filtering process
Compare and contrast collision and
broadcast domains
Identify the cables needed to connect
switches to workstations
Identify the cables needed to connect
switches to switches