I.S. 4123
Introduction to
Telecommunication
in Business
Chapter 6 Network
Hardware Components
Dr. Jan Clark
FALL, 2002
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Repeaters
Provide both physical and electrical
connections
Function - regenerate and propagate a signal
Extend distance covered
Receives signal from one cable segment,
regenerates and transmits signal to one or
more cable segments
Source of propagation delay in a network
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Types of Hubs
Repeater hub - simplest connection
Switching hub - does not broadcast to
all nodes
Bridging hub - can connect dissimilar
networks
Stackable Repeater Hub - two or more
LANS daisy chained together
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Multislot Repeater Hub
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Stackable Hubs
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Repeater or Switch Hub?
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Which is Better?
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Bridge
Interconnects two or more LANs or LAN
segments
Operate at Data Link Layer
Physical Layer transparent
Usually connect like networks, but can bridge
unlike (e.g. Ethernet to Token Ring) - MAC
Layer bridge
Rely upon Data Link Layer address - monitor
messages and forward when appropriate
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The LAN user is often unaware that a
bridge exists. They do not experience
performance degradation and are
allowed access to any station on either
network (within security reasons)
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Broadcast Storms
Bridges pass broadcast frames from one
network to another.
Broadcast storm occurs when several
broadcasts are transmitted at the same
time - can cause a network to crash or
shut down.
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Bridges are Store-and-Forward
They capture an entire frame before
deciding whether to filter or forward the
frame
CRC computed by bridge - if invalid,
frame is dropped
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A user on one LAN can address
another LAN as though it were
another node in their network. This is
done without signing onto a
communication device, dialing
through a modem, or learning any
new software commands or menus
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"NEW" Bridge Definition
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Bridge Standards
Transparent - Broadcast, multicast frames
always forwarded. If not broadcast or
multicast, creates "learned" address table
when frames sent.
Source Routing (Token Ring only) - source
address must know if destination address is
on a different network. If so, provides routing
info with message
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When Does a Bridge
Forward Data?
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Source Routing Bridge
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Which Would You Select for
Interconnecting Networks Bridge or Repeater?
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Switches
Operate at the Data Link, Network, or
Transport Layers (depending upon type of
switch)
Connect two or more computers or network
segments.
Ethernet switch - Layer 2 (Data Link)
Designed for shared media LANs
Permits multiple, simultaneous data
transmission between different paths
Static switching
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Switch Types
Store-and-forward switches copy the incoming packet
into memory before processing the destination
address - may hold for longer periods if destination is
busy - performs CRC
Cut-through switches examine the destination of the
incoming packet and immediately connect the port
with the incoming message to the correct outgoing
port (hardware based). No waiting, no error checking
(great if not busy or error free, BUT…)
Hybrid - works either way. When error rates fall below
a certain range, switch act as cut-through. If above
the range, switch acts as store-and-forward.
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Store-and-Forward Switch
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Cut-Through Switch
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Cut-Through
Backplane Switch
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How Can Collisions Occur
on a Switched Ethernet Network?
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Latency
Amount of time a frame spends inside a
network device such as a bridge or a switch
The lower the latency, the faster a device
processes a data frame
Network can time out with high latency
Which has higher latency - store-and-forward,
or switch-through?
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