chapter 7b pp
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Chapter 7b 04/10/23 1
Ethernet (IEEE 802.3)Ethernet (IEEE 802.3) Developed in 1973 by David Boggs and Bob
Metcalfe of Xerox Corporation Xerox, DEC, and Intel worked jointly to
establish the Ethernet standard 70 % of the Worldwide base of LANs uses
Ethernet technology Formalized as the IEEE 802.3 LAN standard
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Chapter 7b 04/10/23 2
First Ethernet System DrawingFirst Ethernet System Drawing
By Bob Metcalfe: http://wwwhost.ots.utexas.edu/ethernet
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Chapter 7b 04/10/23 3
TopologyTopology
Topology is the basic geometric layout of the network -- the way in which the computers on the network are interconnected.
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Chapter 7b 04/10/23 4
IEEE 802.3 Logical TopologyIEEE 802.3 Logical Topology
T-terminator
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Chapter 7b 04/10/23 5
IEEE 802.3 Physical TopologyIEEE 802.3 Physical Topology
HUB (MAU)
Bus cable
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Chapter 7b 04/10/23 6
CSMA/CD -1CSMA/CD -1
Carrier Sense (CS) Any node can detect
the presence of a carrier signal on the cable
If no signal is present, any node having data to send may access the cable
This gives rise to the term Multiple Access (MA)
Y N
N Y
CS?
Send Data
Send Jam
Random#Generated
Wait
CD?
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Chapter 7b 04/10/23 7
CSMA/CD -2CSMA/CD -2
Collision Detect (CD) Added so that
collisions could be detected
When a collision is detected, a JAM signal is sent out telling all stations to ignore the garbled transmission
Y N
N Y
CS?
Send Data
Send Jam
Random#Generated
Wait
CD?
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Chapter 7b 04/10/23 8
CSMA/CD -3 CSMA/CD -3
Backoff The transmitting
stations involved in the collision generate random numbers and wait that amount of time before trying again
Y N
N Y
CS?
Send Data
Send Jam
Random#Generated
Wait
CD?
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Chapter 7b 04/10/23 9
Ethernet CablesEthernet Cables
Called “10Base5” meaning 10 Mbps, baseband transmission, maximum distance of 500 meters between hubs
Using heavy, thick coax cable, it is often called “Thick Ethernet”
Difficult/expensive to install
10Base5 10Base2 10BaseT 10Broad36
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Chapter 7b 04/10/23 10
Ethernet CablesEthernet Cables
Uses a smaller coaxial cable Often called “Thin Ethernet” or “Cheapernet” Makes use of a T-connector mounted directly
into the NIC Real problems if something happens to one
system in the line
10Base5 10Base2 10BaseT 10Broad36
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Chapter 7b 04/10/23 11
Ethernet CablesEthernet Cables
The most common type of Ethernet The “T” means twisted-pair wiring Unshielded twisted Pair (UTP) Very low cost Also uses the T-connector
10Base5 10Base2 10BaseT 10Broad36
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Chapter 7b 04/10/23 12
Ethernet CablesEthernet Cables
Called “10Broad36” meaning 10 Mbps, broadband transmission, maximum distance of 3600 meters between hubs
Most commonly used in BN Allows an intermix of voice, data, and images
10Base5 10Base2 10BaseT 10Broad36
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Chapter 7b 04/10/23 13
Ethernet (IEEE 802.3)Ethernet (IEEE 802.3) Uses bus topology Computers receive messages intended for all
computers Bus - high speed circuit/limited distance Requires repeaters & terminators Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) Baseband (digital) or Broadband (analog) 10Base5 (thick) 10Base2 (thin) 10BaseT
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Chapter 7b 04/10/23 14
Token Ring (IEEE 802.5)Token Ring (IEEE 802.5) This is the second most popular type of LAN,
25% worldwide installations Originally developed by IBM in 1985 and
known as the IBM Token Ring LAN Exists in both 4 Mbps and 16 Mbps versions Normally uses twisted-pair, either STP or UTP All wiring is done at a HUB
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Chapter 7b 04/10/23 15
IEEE 802.5 Logical TopologyIEEE 802.5 Logical Topology
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IEEE 802.5 Physical TopologyIEEE 802.5 Physical Topology
HUB (MAU)
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Token Passing Access Token Passing Access
Access Method The sending station
waits for a “free” token.
1
S
D
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Token Passing Access Token Passing Access
Access Method Adds data,
addresses, and sets token as “busy”.
2
S
D
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Token Passing Access Token Passing Access
Access Method Receiving station
copies data, adds the ACK, and sets “copied bit” on the token. 3
S
D
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Token Passing Access Token Passing Access
Access Method Sending station
verifies the acknowledgement and generates “free” token. 4
S
D
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Token Passing Access Token Passing Access
Problems One station in the ring
is designated as “token monitor” to deal with lost tokens.
The free token moves between the computers in a predetermined sequence.
Maximum number of messages that a computer can send before issuing a free token.
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Chapter 7b 04/10/23 22
Token Ring (IEEE 802.5)Token Ring (IEEE 802.5) Uses ring topology Messages pass to each computer in turn Token passing (short electronic message)
turn taken when has possession of free token changes free token to busy token and attaches
message token passed up the line to receiving computer
Requires a token monitor for lost tokens Token-ring-4 and Token-ring-16 (TR-100)
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Chapter 7b 04/10/23 23
Token Bus (IEEE 802.4)Token Bus (IEEE 802.4) May be either baseband or broadband in its
architecture baseband bus has only one token on the network
at any given time broadband bus has multiple tokens, one for each
channel, using FDM
MAP (Manufacturing Automation Protocol) uses IEEE 802.4 Token Bus
Supports factory automation where real-time, guaranteed response is a necessity (robotics)
Exists in 1, 5, 10 and 20 Mbps
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Chapter 7b 04/10/23 24
IEEE 802.4 Token BusIEEE 802.4 Token Bus The network maintains a table of addresses
for each node Addresses indicate the order in which nodes
receive the token Any node requiring priority is simply listed
more frequently in the table
A B C D E
1 2 345
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Chapter 7b 04/10/23 25
Arcnet - Attached Resource Arcnet - Attached Resource Computing Network Computing Network
Developed by Datapoint Corporation in 1977 Peer-to-Peer Low-cost PC LAN Baseband Token-passing Bus or star architecture ANSI 878.1 Coaxial cable 2.5 Mbps/Arcnet Plus 20Mbps 1000 feet between computers
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Apple TalkApple Talk Macintosh computers w/built-in network
hardware Apple cabling system (LocalTalk) 230 Kbps 32 computers / 1000 feet between computers Carrier Sense Multiple Access/Collision
Avoidance (CSMA/CA) LLAP - LocalTalk Link Access Protocol Slow data transmission rate Non-standard
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Wireless LANs (IEEE 802.11)Wireless LANs (IEEE 802.11) Transmit through the air rather than by cable Useful in old building where wiring is difficult
and costly NICs installed in the computer are attached to
external infrared or radio transmitters Increasingly used by laptop computers to
provide mobile workgroup computing
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Wireless LANs (IEEE 802.11)Wireless LANs (IEEE 802.11) There are three commonly used types of
wireless LANs: Infrared Direct-sequence spread spectrum radio Frequency hopping spread spectrum radio.
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Infrared Wireless LANsInfrared Wireless LANs Most require direct-line-of-sight Diffuse infrared -- bounces light around the
room Extremely short range (50-75 feet) Operate only within a room
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Radio Wireless LANsRadio Wireless LANs Travel in all directions and penetrates non-
metallic objects Larger range - 100 to 500 feet DSSS (Direct Spread Spectrum System)
transmit signals through a wide spectrum of radio frequencies simultaneously
FHSS (Frequency Hopping Spread Spectrum) minimizes eavesdropping by changing quickly from
one frequency to another
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Wireless LANs (IEEE 802.11)Wireless LANs (IEEE 802.11) Transmit through the air rather than by cable Use same protocols as other LANs NIC is connected to an external infrared or
radio transmitter low cost - no or little wiring noise disrupts transmissions slower data transmission rates lack of security
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Chapter 7b 04/10/23 32
LAN PerformanceLAN Performance
Throughput and Bottlenecks Software
NOS disk caching - storing commonly used data in memory disk elevatoring - order data is accessed
Hardware Server CPU Server memory Number and speed of hard disks NIC Cards
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Improving LAN PerformanceImproving LAN PerformancePerformance Checklist
Increase Server Performance Software
Upgrade to a faster network operating system Fine-tune the network operating system settings
Hardware Add more servers and spread the network applications across the servers
to balance the load Upgrade to a faster computer Increase the server’s memory Increase the number and speed of the server’s hard disk(s) Upgrade to a faster NIC
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Improving Server PerformanceImproving Server Performance
Software: Faster NOS Disk caching Disk elevatoring NOS software settings
Hardware Second server Upgrade server (CPU
speed, Memory) Number and speed of hard
drives in the server. NIC
Improving server performance can be approached from two directions simultaneously:
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Improving LAN Performance Improving LAN Performance
Performance Checklist (cont’d.)
Increase Circuit Capacity Upgrade to a faster circuit Change protocols Segment the network
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Circuit CapacityCircuit Capacity Increase capacity
4 Mbps --> 16Mbps --> 100Mbps
LAN Protocol Ethernet -vs- TokenRing
TokenRing supports higher data transmission CSMA/CD faster than token passing on smaller networks Token passing faster on larger networks Token ring response time more consistent Ethernet allows one computer to monopolize network
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Network SegmentationNetwork Segmentation Increasing circuit capacity by network
segmentation Breaking up the network into smaller
segments The more computers and NICs on the
segment the slower the performance
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Improving LAN Performance Improving LAN Performance
Performance Checklist (cont’d.)
Reduce Network Demand Move files from the server to the client computers Increase the use of disk caching on client computers Change user behavior
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Reducing Network DemandReducing Network Demand
Performance can also be improved by reducing network demand: Moving files from the server to clients. Using disk caching software on the client
machines, to reduce the client’s need for to access disk files stored on the server.
Attempting to move user demands from peak times to off-peak times.
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Selecting a LANSelecting a LAN
Start with basic questions: How many users are expected? How much data will be stored and
transmitted? How easy will it be to add workstations? What cabling is needed? Whose software should be selected? How much security is needed?
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LAN Selection ChecklistLAN Selection Checklist
Network Needs Number of client computers Number of dedicated servers Distance between computers Internetworking requirements Specific application needs User training, documentation, and network policies Future growth
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LAN Selection ChecklistLAN Selection ChecklistTechnology
Protocols Cabling/Wireless Network Operating System
Reliability Ease of use Performance
LAN management software LAN backup software and hardware
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LAN Selection ChecklistLAN Selection ChecklistVendor
Experience with network hardware and software Experience with your network application Vendor service and support
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Selecting a LAN Selecting a LAN
expected usage what cabling is required token ring or ethernet baseband or broadband NOS configuration topology vendor support print features
number of computers expected growth type of server distance (LAN or WAN) NIC cards backup and recovery legal issues privacy and security expertise