Communication System Chapter 9
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Transcript of Communication System Chapter 9
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2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.0
Ethernet
Network Fundamentals
Chapter 9
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Objectives Identify the basic characteristics of network media used in
Ethernet.
Describe the physical and data link features of Ethernet.
Describe the function and characteristics of the media accesscontrol method used by Ethernet protocol.
Explain the importance of Layer 2 addressing used for datatransmission and determine how the different types ofaddressing impacts network operation and performance.
Compare and contrast the application and benefits of using
Ethernet switches in a LAN as apposed to using hubs.
Explain the ARP process.
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Physical and Data Link Features of Ethernet
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Physical and Data Link Features of Ethernet
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Ethernet: Layer 1 and Layer 2
Ethernet defines these Layer 1 elements:
Signals
Bit streams
Physical component
Various topologies
At data link layer addresses these requirements:
Provides interface
Provides address
Uses frames to organize bits into meaningful groups
Controls transmission of data from sources
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Physical and Data Link Features of Ethernet Logic Link Control Connecting the Upper Layers
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Physical and Data Link Features of Ethernet Media Access Control (MAC)
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Physical and Data Link Features of Ethernet
Physical Implementations of the Ethernet
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Why Ethernet is successful?
Simple and easy to maintain
Ability to incorporate to new technology
Reliable
Low cost
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Characteristics of Network Media used in Ethernet
Historic Ethernet:1. Coaxial cable2. Bus topology3. CSMA/CD4. Thicknet (10BASE5) and
Thinnet (10BASE2)
Legacy Ethernet:1. 10BASET2. Star with hub as central
point
3. CSMA/CD4. Half duplex
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Current Ethernet
10Mbps and 100Mbps
Physical star with switch in the middle or P2P
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Moving to 1Gbps and beyond
UTP full duplex
Increased cabling distance
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Layer 2 Addressing and Its Impact on NetworkOperation and Performance
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Layer 2 Addressing and Its Impact on NetworkOperation and Performance
Hexadecimal Numbering and Addressing
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Another layer of addressing
Layer 2
Enables packet tobe carried by thelocal media
across eachsegment
Physical address
Layer 3
Enables packet tobe forwardedtoward itsdestination
Logical address
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Layer 2 Addressing and Its Impact on NetworkOperation and Performance
The Ethernet MAC Address
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Ethernet Unicast, Multicast and Broadcast
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Carrier Sense Multiple Access with Collision Detection
Collision happens in shared medium
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Carrier Sense Multiple Access with Collision Detection
Steps in CSMA/CD: Listen before sending
Detecting a collision
Jam signal and random backoff
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Hubs and collision domains
Conditions that cause collisions:
More devices connected to the network
More frequent access to media
Increased cable distances between devices
Hubs does not operate in higher level network, socollision occurs
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Ethernet Timing
Preamble: timing synchronization information
Timing information is not required in synchronizecommunication
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Ethernet timing
Bit time = period of time required for a bit to be placedand sensed on media
Slot time
How many devices can share a network
Used to establish minimum size of Ethernet frame and limiton maximum size of networks segment
Includes time it takes to travel through cables and hubs
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Interframe spacing and backoff
Interframe spacing
Minimum spacing between 2 noncolliding frames
To give media time to stabilize after transmission of
previous frame for the device to process frame
Jam signal length
32 bit jam signal that will enforce collision
Repeating 1010 pattern
Backoff timing
Waiting period after collision
Random so that 2 stations do not delay for same amounntof time before transmitting
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4 different data rates 10Mbps
10BASE-T Ethernet
Physical star
Manchester encoding
100Mbps
Fast Ethernet
Implemented using UTP or fiber
100BASE-TX AND 100BASE-FX
1000Mbps
Gigabit Ethernet Signals occurring in less time
1000BASE-T, 1000BASE-SX and 1000BASE-LX
10Gbps
10Gigabit Ethernet
CSMA/CD not necessary
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Compare and Contrast the Use of Ethernet Switchesversus Hubs in a LAN
Using Hubs Does not perform filtering
Share bandwidth of media
High level of collisions
Issues: Lack of scalability
Increase latency
More network failure
More collisions
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Compare and Contrast the Use of Ethernet Switchesversus Hubs in a LAN
Using Switches Allow segmentation of LAN into separate collision domains
Throughput increases because:
Dedicated bandwidth to each port
Collision free environment Full duplex environment
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Compare and Contrast the Use of Ethernet Switchesversus Hubs in a LAN
Describe how a switch can eliminate collisions,backoffs and retransmissions, the leading factors inreduced throughput on a hub-based Ethernet network
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Why not using switches instead of hubs?
Availability
Economics
Requirements
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Switch
MAC table: maps destination MAC address with portsused to connect to each node
MAC table = switch table = bridge table
Bridge: device used in early days to connect to physicalnetwork segments.
Operations:
Learning
Aging
Flooding
Selective forwarding
Filtering
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Address Resolution Protocol (ARP)
2 functions
Resolving IPv4 address to MAC
Maintaining a cache of mappings
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Explain the Address Resolution Protocol (ARP) Process
Mapping IP to MAC Addresses
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Maintaining a cache of mappings
Different process is required to provide IP to MACaddress:
Adding entries to ARP table
Getting the map for a frame
Mapping destination outside local network
Removing address mappings
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Explain the Address Resolution Protocol (ARP) ProcessARP Destinations Outside the Local Network
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Explain the Address Resolution Protocol (ARP) ProcessARP Removing Address Mappings
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Explain the Address Resolution Protocol (ARP) ProcessARP Broadcasts - Issues
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Summary
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