Transcript CCNA 3 v3.0 Module 4 Switching Concepts © 2003, Cisco Systems, Inc.

CCNA 3 v3.0 Module 4
Switching Concepts
© 2003, Cisco Systems, Inc. All rights reserved.
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Objectives
• Introduction to Ethernet 802.3 LANs
• Introduction to LAN switching
• Switch operation
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802.3 LAN Development: Today’s LANs
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Devices Function at Layers
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Factors that Impact Network Performance
• Network traffic (congestion).
• Multitasking desktop operating systems
(Windows, UNIX, and Mac) allow
simultaneous network transactions.
• Faster desktop operating systems
(Windows, UNIX, and Mac) can initiate
faster network activity.
• Increased number of client/server
applications using shared network data.
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Typical Causes of Network Congestion
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Ethernet 802.3
• Performance of a shared-medium Ethernet/802.3
LANs is negatively affected by factors such as
the following:
The broadcast delivery nature of Ethernet.
Carrier sense multiple access collision detect
(CSMA/CD) access method allows only one host to
transmit at a time.
Multimedia applications with higher bandwidth
demand such as video and the Internet.
The latency of additional devices added by the
extension of LANs by using repeaters.
The distance added by using Layer 1 repeaters.
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Half-Duplex Ethernet Design
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Network Congestion
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Network Latency
Latency, or delay, is the time a frame or a
packet takes to travel from the source
station to the final destination.
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Ethernet 10BASE-T Transmission Times
• Bit time (or slot time) — The basic unit of time in which 1
bit can be sent. For electronic or optical devices to
recognize a binary 1 or 0, there is a minimum duration
during which the bit is "on" or "off. "
• Transmission time — Equals the number of bits being sent
times the bit time for a given technology. Another way to
think about transmission time is as the time it takes a
frame to actually be transmitted. (Small frames take a
shorter amount of time, large frames take a longer amount
of time to be transmitted.)
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Benefits of Using Repeaters
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Full-Duplex Transmitting
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LAN Segmentation
Segmentation allows network congestion to
be significantly reduced within each
segment.
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LAN Segmentation with Bridges
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LAN Segmentation with Routers
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LAN Segmentation with Switches
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LAN Switch Operation
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Ethernet Switch Latency
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Layer 2 Switching
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Layer 3 Switching
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Symmetric Switching
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Asymmetric Switching
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Memory Buffering
• Port-based memory buffering
Packets are stored in queues that are linked to
specific incoming ports.
It is possible for a single packet to block all other
packets because its destination port is busy (even
if the other packets could be delivered).
• Shared-memory buffering
All packets use a common memory buffer.
Packets in the buffer are then linked (mapped)
dynamically to the appropriate destination port.
Helps balance between 10- and 100-Mbps ports.
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Two Switching Methods
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Store and Forward
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Cut Through
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Functions of Ethernet Switches
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Frame Transmission Modes
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Network Switch Using CAM
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How Switches and Bridges Filter Frames
• Bridges and switches only forward frames,
which need to travel from one LAN
segment to another.
• To accomplish this task, they must learn
which devices are connected to which
LAN segment.
• Bridges are capable of filtering frames
based on any Layer 2 fields.
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LAN Segmentation Using Bridges
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Microsegmentation of the Network
A switch employs “microsegmentation” to
reduce the collision domain on a LAN. The
switch does this by creating dedicated network
segments, or point-to-point connections.
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Switches and Collision Domains
The network area where frames originate and
collide is called the collision domain. All shared
media environments are collision domains.
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Three Methods of Communication
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Switches and Broadcast Domains
• Broadcasting is when one transmitter tries
to reach all the receivers in the network.
The server station sends out one
message, and everyone on that segment
receives the message.
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Communication Between Switches and
Workstations
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