Download Basic Concepts

An Introduction
to Networking
Chapter 1
Panko’s
Business Data Networks and Telecommunications, 7th edition
© 2009 Pearson Education, Inc. Publishing as Prentice Hall
May only be used by adopters of the book
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Builds
2
• Slides with the blue mouse icon in the upper right
hand corner are “build” slides
• Not everything on the slide will appear at once
• Each time the mouse click icon is clicked, more
information on the slide will appear
• The number by the mouse icon gives the number
of builds on the slide (the number of mouse
clicks)
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1-1: Black Box View of Networks
• What Is a Network?
– Preliminary definition: A network is a communication
system that allows application programs on different
hosts to work together.
Application 1
Application 2
Network
Host A
Host B
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Hosts
• Hosts
– Any computer attached to a network is called a host
– Including client PCs, servers, mobile phones, etc.
Host
Host
Host
Host
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Networked Applications
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Application Standards
• Application standards govern communication
between application programs
– Allow products from different vendors cannot talk to one
another
• The Hypertext Transfer Protocol (HTTP) standardizes
communication between browsers and webservers
– Standards are also called protocols
– HTTP is an open standard (not controlled by any vendor)
• Open standards drive down product costs
• Vendor-controlled standards are called proprietary
standards
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1-2: Hypertext Transfer Protocol (HTTP)
1
• HTTP is a Client/Server Protocol
– The client is the browser; it sends a request
– The server is the webserver; it sends a response
– Most application standards are client/server protocols
Browser
Client Host
HTTP
Request Message
(Asks for File)
Webserver
Program
HTTP
Response Message
(Contains the Requested File)
Webserver
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1-3: The ARPANET and the Internet
• ARPANET
– Some of the first networked
applications were created for
the ARPANET
– Created by the Defense
Advanced Research
Projects Agency
(DARPA) around 1970
• Served researchers doing business with DARPA
• Connected many sites around the United States
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1-3: The ARPANET and the Internet
• Next, DARPA Created the Internet
in 1980 to Connect Networks
Together
– Initially, commercial activity
was forbidden
– Became commercial in 1995
– Today, the Internet is almost entirely commercial
– Almost no government money flowing in to run the
Internet
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1-4: Traditional Internet Applications
• File Transfer Protocol (FTP)
• E-Mail
• The World Wide Web (WWW)
• E-Commerce
– Buying and selling on the Internet
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1-5: The Internet versus the World Wide
Web (and Other Applications)
World Wide Web
E-Mail
FTP
(Application)
(Application)
(Application)
Other Applications
The Internet (Transmission System)
The Internet is a global transmission system. The WWW, e-mail, etc.
are applications that run over the Internet global transmission system.
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1-6: Newer Internet Applications
3
• Instant Messaging (IM)
• Streaming Audio and Video
– No need to wait until the entire file is
downloaded before beginning to see or hear it
• Voice over IP (VoIP)
– Telephony over the Internet or other IP networks
• Peer-to-Peer (P2P) Applications
– Growing processing power of PCs allows PCs to serve
other PCs directly
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1-6: Newer Internet Applications
• Web 2.0
– A hazy term that focuses on using the Internet to
facilitate communication among people
– Including the creation of communities
– In addition, the users themselves typically generate the
content
– Blogs, wikis, podcasts
– Community building sites such as MySpace and
Facebook, video sharing sites such as YouTube, virtual
worlds such as Second Life, and specific information
sharing sites, such as craigslist
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1-7: Corporate Network Applications
1
• Applications Specific to Businesses
– Can consume far more corporate network resources
than traditional and new Internet applications combined
• Transaction-Processing Applications
– Simple, high-volume repetitive clerical transaction
applications
– Accounting, payroll, billing, manufacturing, etc.
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1-7: Corporate Network Applications
• Enterprise Resource Planning (ERP) Applications
– Serve individual business functions while providing
integration between functional modules
Inter-Function
Transaction
Accounting
Billing
Sales
Manufacturing
Purchasing
Inter-Function
Transaction
Warehousing
Inter-Function
Transaction
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Shipping
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1-7: Corporate Network Applications
• Organizational Communication Applications
– E-mail, etc.
– Groupware
• Integrate multiple types of communication, organize
communication for retrieval, and provide multiple
ways to disseminate and retrieve information
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1-8: File Service
2
File Server
1.
User saves data file
to file server, which is
backed up nightly
3.
Others can retrieve
the file and even
edit it if they are
given permission
2.
Later, user can
retrieve the
data file from
any other computer
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1-8: File Service
2.
A multiuser version
of the program is required
1.
A program is Installed
on the file server;
Less expensive
than installing it on
many individual PCs
3
File Server
3.
For execution,
a copy is downloaded
from the file server.
4.
Note that the program is
executed on the client PC,
not on the file server!
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Quality of Service (QoS)
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1-9: Network Quality of Service (QoS)
• Quality of Service (QoS)
– Indicators of network
performance
• Metrics
– Ways of measuring specific
network quality-of-service
variables
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1-10: Transmission Speed
• Measuring Transmission Speed
– Measured in bits per second (bps)
– In metric notation:
• Increasing factors of 1,000 …
– Not factors of 1,024
• Kilobits per second (kbps)-note the lowercase k
• Megabits per second (Mbps)
• Gigabits per second (Gbps)
• Terabits per second (Tbps)
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1-10: Transmission Speed
3
• Writing Transmission Speeds in Proper Form
– The rule for writing speeds (and metric numbers in
general) in proper form is that there should be 1 to 3
places before the decimal point
– 23.72 Mbps is correct (2 places before the decimal
point).
– 2,300 Mbps has four places before the decimal point, so
it should be rewritten as 2.3 Gbps (1 place).
– 0.5 Mbps has zero places to the left of the decimal point.
It should be written as 500 kbps (3 places).
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1-10: Transmission Speed
• Writing Transmission Speeds in Proper Form
– How to convert 1,200 Mbps to proper form, to 12.02
Gbps
Number
Suffix
12,020
Mbps
Divide by 1,000
Multiply by 1,000
12.02
Gbps
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1-10: Transmission Speed
• Writing Transmission Speeds in Proper Form
– How to convert .2346 Mbps to proper form, to 234.6 kbps
Number
Suffix
0.2346
Mbps
Multiply by 1,000
Divide by 1,000
234.6
kbps
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1-10: Transmission Speed
• Writing Transmission Speeds in Proper Form
– How should you write the following in proper form?
• 549.73 kbps
• 0.47 Gbps
• 11,200 Mbps
• .0021 Gbps
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1-10: Transmission Speed
• Rated Speed
– The speed in bits per second that you should get
(advertised or specified in the standard).
• Throughput
– The speed you actually get
– Almost always lower than the rated speed
• On Shared Transmission Lines
– Aggregate throughput—total throughput for all users
– Individual throughput—the individual user’s share of the
aggregate throughput
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1-11: Cost
• Network Demand, Budgets, and Decisions
– Figure 1-12 shows that network demand is growing
explosively, while network budgets are growing slowly
– This creates a cost squeeze that affects every decision
– Overspending in one area will result in the inability to
fund other projects
Figure 1-12
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1-11: Cost
• Systems Development Life Cycle Costs
– Hardware: Full price: advertised base price plus
necessary options
– Software: Full price: advertised base price plus
necessary options
– Labor costs: Networking staff and user costs
– Outsourcing development costs
– Total development investment
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1-13: Other Quality-of-Service Metrics
• We Have Already Seen Speed and Cost
• Availability
– The percentage of time a network is available for use
– “Our availability last year was 99.9%”
• Downtime is the amount of time a network is
unavailable
– Measured in minutes, hours, etc.
– “In July, we had five minutes of downtime.”
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1-13: Other Quality-of-Service Metrics
• Error Rates
– Packet error rate: the percentage of packets lost or
damaged
– Bit error rate: the percentage of bits lost or damaged
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1-13: Other Quality-of-Service Metrics
• Latency and Jitter
– Latency
• Delivery delay, measured in milliseconds
– For instance, 250 ms is a quarter of a second
• Bad for real-time applications
– Voice and video
– Network control messages
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1-13: Other Quality-of-Service Metrics
• Latency and Jitter
– Jitter
• Variation in latency between successive packets
• Makes voice sound jittery
Figure 1-14
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1-13: Other Quality-of-Service Metrics
• Service Level Agreements
– Customers want guarantees
for performance
– Provider pays penalties if the network does not meet its
service metrics guarantees
– Often specified on a percentage basis
• At least 100 Mbps 99.5% of the time
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1-13: Other Quality-of-Service Metrics
• Service Level Agreements
– Specify a worst case
– Speed SLAs
• Low speed is the worst case
• So an SLA would guarantee a lowest speed
• E.g., no worse than 1 Mbps)
• Customer would like higher speeds
• But wants no less than 1 Mbps
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1-15: Network Security
• Security
– Security attacks can be extremely expensive
– Companies need to install defenses against attacks
– Chapter 9 discusses network security in depth
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1-15: Network Security
• Authentication
– Goal is to stop impostors
– Supplicant attempts to prove its identity to a verifier
– Example: user logging into a server is a supplicant; the
server is a verifier
– Proofs of identity are called credentials
Supplicant:
True User?
Credentials:
Password
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Verifier:
Server
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1-15: Network Security
2
• Cryptographic Protections
– Eavesdroppers may intercept your messages
• Read and even change messages
• Send new messages impersonating the other side
– Cryptography is the use of mathematics to protect
information in storage or in transit
– Encryption for confidentiality
• An eavesdropper cannot read encrypted messages
• Legitimate receiver, however, can decrypt the
message
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1-15: Network Security
• Firewall
– Examines each packet passing through it
– Drops and logs provable attack packets
– It lets other packets get through, even if suspicious
Passes
Other
Packets
Drops
Arriving
Packet
Provable
Attack Packet
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1-15: Network Security
• Host Hardening
– Some attacks will inevitably get
past safeguards and reach hosts
– Hosts must be “hardened” to withstand attacks
– Hardening is a set of protections we will see in Chapter 9
• Example: installing antivirus software on the host
• Example: downloading security updates
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Switched Networks
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Figure 1-16: Ethernet Switch Operation
In switched networks,
Messages are called frames
Ethernet Switch
Host A1-… wishes to send
a frame to Host C3.
The frame must pass
Through the switch
A1-44-D5-1F-AA-4C
D4-47-55-C4-B6-9F
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
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Figure 1-16: Ethernet Switch Operation
Ethernet Switch
UTP
Host A1-… sends the
frame to the switch
D4-47-55-C4-B6-9F
Frame To C3…
A1-44-D5-1F-AA-4C
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
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Figure 1-16: Ethernet Switch Operation
Switching Table
Port Host
10
A1-44-D5-1F-AA-4C
13
B2-CD-13-5B-E4-65
15
C3-2D-55-3B-A9-4F
16
D4-47-55-C4-B6-9F
Ethernet Switch
Frame To C3…
UTP
D4-47-55-C4-B6-9F
A1-44-D5-1F-AA-4C
The switch reads the destination
address in the frame.
It looks up the address (C3-…)
in the switching table.
It reads the port number (15)
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
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Figure 1-16: Ethernet Switch Operation
Switching Table
Port Host
10
A1-44-D5-1F-AA-4C
13
B2-CD-13-5B-E4-65
15
C3-2D-55-3B-A9-4F
16
D4-47-55-C4-B6-9F
The switch sends the
Ethernet Switch
D4-47-55-C4-B6-9F
frame out Port 15,
to the destination host.
Frame To C3…
A1-44-D5-1F-AA-4C
C3-2D-55-3B-A9-4F
B2-CD-13-5B-E4-65
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1-17: Switched Network in a Multistory Building
On each floor, hosts
connect to a
workgroup switch via
wire or wireless
transmission
A core switch connects
the workgroup
switches to each other
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1-17: Switched Network in a Multistory Building
3
Client
Server
Wall Jack
Workgroup Switch 2
Workgroup Switch 1
Wall Jack
To
WAN
Router
Core Switch
Frames from the client to the server go through Workgroup Switch 2,
through the Core Switch, through Workgroup Switch 1, and then to the
server
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Figure 1-18: Four-Pair Unshielded Twisted Pair
(UTP) Copper Wiring
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1-19: Packet Switching and Multiplexing
In packet switching, the sending host breaks
each message into many smaller packets
Sends these packets out one at a time
Packets are routed to the destination host
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1-19: Packet Switching and Multiplexing
Multiplexing reduces cost. Each conversation only has to pay
For its share of the trunk lines it uses.
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Routed Networks
(Internets)
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1-20: Routed Networks
• The 1980s: A Switched Tower of Babel
– At first, there were only switched networks
– Soon, there were many incompatible switched networks
– Users on different switched networks could not
communicate with each other
Switched Network 1
SW
SW
SW
Switched Network 2
SW
SW
SW
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1-20: Routed Networks
• Routers and Routed Networks
– Routers were created connect different switched
networks together
– Routed networks are also called internets
Routed Network (Internet)
Switched Network 1
SW
SW
SW
Router
Switched Network 2
SW
Router
SW
SW
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1-20: Routed Networks
• Routers and Routed Networks
– Routers are more complex (and expensive) than
switches
• Designed to work no matter how complex the internet
• Require more hands-on administration than switches
Routed Network (Internet)
Switched Network 1
SW
SW
SW
Router
Switched Network 2
SW
Router
SW
SW
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Terminology
• Capitalization of “Internet”
– “Internet” with a capital “I” is used for the global Internet
we all use each day
– “internet” with a lower-case “i” is used when talking about
a smaller internet or about internets in general
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1-20: Routed Networks
• Hosts Have Two Addresses
• IP Address
– This is the host’s unique official address on its internet
– Used by routers to forward the packet
– 32 bits long
– Expressed for people in dotted decimal notation (e.g.,
128, 171, 17.13)
• Single Switched Network Addresses
– This is the host’s address on its single network
– Used by switches to forward the frame
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1-20: Routed Networks
• Packets and Frames
– Packets are called frames in switched networks
– Packets are called packets in routed networks
– A packet is carried in a frame within each switched
network
Packet
Frame
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Routers, Frames, and Packets
• A frame arrives at a router
– The frame contains a packet
• The router takes the packet out of the frame
– The router puts the packet into a new frame appropriate
for the next network and sends it out
Packet
Frame 1
Packet
Frame 2
Router
Packet
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1-21: Routed Network (Internet)
2
2. Packet travels through
three switched networks
1. When a packet is sent,
the packet travels all the
way from the source host
to the destination host
3. The packet travels in
three frames—one in
each switched network
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4
1-22: The Global Internet
1.
User PC
Host
Computer
Access
Line
1.
Webserver
Host
Computer
3.
Internet Backbone
(Multiple ISP Carriers)
Access
Line
Router
NAP
ISP
NAP
ISP
NAP
ISP
ISP
2.
User PC’s
Internet Service
Provider
4.
NAPs = Network Access Points
Connect ISPs
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2.
Webserver’s
Internet Service
Provider
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1-22: The Global Internet
• How is the Internet Financed?
– Through ISP subscriber payments
• Residences typically pay $10 to $50 per month
• Business typically pay thousands or tens of
thousands of dollars per month
– Like the telephone network
• The telephone network is supported by customer
payments to telephone carriers
– Almost no government money involved
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1-22: The Internet
• The TCP/IP Standards
– The set of protocols that governs the Internet
– Standards for both applications and packet delivery
– Created by the Internet Engineering Task Force (IETF)
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1-23: Domain Name System (DNS)
• Domain Name System (DNS)
– IP addresses are official addresses on the Internet and
other internets
– Hosts can also have host names (e.g., cnn.com)
• Not official—like nicknames
– If you only know the host name of a host that you want to
reach, your computer must learn its IP address
• DNS servers tell our computer the IP address of a
target host whose name you know
– Like looking up someone’s name in a telephone directory
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1-23: Domain Name System (DNS)
1
1.
Client Host
wishes to reach
Voyager.cba.hawaii.edu;
Needs to know
its IP Address
DNS Table
Host Name
IP Address
…
…
…
…
Voyager.cba.hawaii.edu 128.171.17.13
…
…
2. Sends DNS Request Message
“The host name is Voyager.cba.hawaii.edu”
Voyager.cba.hawaii.edu
128.171.17.13
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Local
DNS
Host
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1-23: Domain Name System (DNS)
2
DNS Table
3.
DNS Host
looks up the
target host’s
IP address
Host Name
IP Address
…
…
…
…
Voyager.cba.hawaii.edu 128.171.17.13
…
…
4. DNS Response Message
“The IP address is 128.171.17.13”
5.
Client sends packets to
128.171.17.13
DNS
Host
Voyager.cba.hawaii.edu
128.171.17.13
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LANs and WANs
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1-25: LANs and WANs (Study Figure)
Category
Local Area Networks
Wide Area Networks
Abbreviation
LAN
WAN
Distance Span
Customer premises
(apartment, office,
building, campus, etc.)
Between sites within a
corporation or between
different corporations
Wide Area
Network
Building
LAN
Campus
LAN
Home
LAN
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1-25: LANs and WANs
Category
Local Area Networks
Cost per bit transmitted Low
Therefore, typical
transmission speed
Wide Area Networks
High with arbitrary
Changes unrelated
to costs
Usually 100 Mbps to 10 About 256 kbps to 50
Gbps
Mbps
In economics, you learned that when unit price goes up, people will
purchase less of the product
Because WANs cost much more per bit, companies learn to live with
fewer bits per second
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Network Management
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1-26: Network Management
• Strategic Network Management
– As far as possible, build a coherent roadmap
– Pay special attention to decisions that lock you in
for long periods of time
– Legacy technologies are technologies selected
previously that limit services today
• For upgrading, service benefits must exceed
update costs
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1-26: Network Management
• Product Selection with Multicriteria Decision
Making
– The entire systems development life cycle (SDLC) must
be followed
– For network products, corporations buy instead of make
network elements
• Must use multicriteria decision making (Figure 1-26)
• Select purchasing criteria (speed, cost, etc.)
• Give each criterion an importance weight
• Rate each product on each purchasing criteria
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1-27: Multicriteria Decision Making in Purchase Decisions
Criterion
Functionality
Product A
Product B
Criterion Criterion Criterion Product Criterion
Weight Rating
Score
Rating
Score
(Max: 5) (Max:
(Max: 10)
10)
5
9
45
7
35
Availability
2
7
14
7
14
Cost
Ease of
Management
Electrical
Efficiency
Total Score
5
4
20
9
45
4
8
32
6
24
1
9
9
8
8
120
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1-28: Network Management
• Ongoing Management
– After the SDLC ends
– The most important (and
expensive) part of the
systems life cycle
– Often discussed in terms of
OAM&P
– Operations, administration,
maintenance, and
provisioning
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1-28: Network Management
• Ongoing Management (OAM&P)
– Operations
• Moment-by-moment traffic management
• Network operations center (NOC) using SNMP (see
Figure 1-29)
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1-28: Network Management
• Ongoing Management (OAM&P)
– Maintenance
• Fixing things that go wrong
• Conducting preventative maintenance
• Should be separate from the operations staff
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1-28: Network Management
• Ongoing Management (OAM&P)
– Provisioning (Providing Service)
• Includes physical installation
• Includes setting up user accounts
and services
• Reprovisioning when things
change
• Deprovisioning when accounts
and services are no longer
permitted
• Collectively extremely expensive
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Simple Network
Management Protocol
(SNMP)
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1-29: Simple Network Management Protocol
(SNMP)
Network Management
Software (Manager)
The manager manages multiple
managed devices from a
central location
Managed
Device
Managed
Device
Collects information about
each managed device
Can sometimes reconfigure
managed devices remotely
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Figure 10-13: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Network
Management
Agent (Agent),
Objects
Managed
Device
Manager talks to a network
management agent on each
managed device—not to the
managed device directly.
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Figure 10-13: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
Data
Management
Information
Base (MIB)
Data
Manager collects data about
each device; stores the data
in a Management
Information Base (MIB)
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Figure 10-13: Simple Network Management
Protocol (SNMP)
Network Management
Software (Manager)
1.
Command (Get, Set, etc.)
2.
Response
3.
Trap (Alarm) Initiated by
a Managed Device
Simple Network
Management Protocol (SNMP)
Messages
Managed Device
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