Download - CIS 460CH 2
-
8/7/2019 CIS 460CH 2
1/22
CIS 460 - Network Analysis and
Design
Chapter 2
Analyzing Technical Goals and
Constraints
-
8/7/2019 CIS 460CH 2
2/22
Analyzing Technical Goals
and Constraints Goals include:
scalability
availability
performance
security
manageability
usability
adaptability
affordability
Tradeoffs associated with these goals
Provides terminology to discuss technical goals
with customer
-
8/7/2019 CIS 460CH 2
3/22
Scalability
How much growth a network design must support
maybe a prime goal for some
Proposed design should be able to adapt to increase inusage/scope
Planning for Expansion
How many sites to add
How extensive the networks for each new site How many more users to access the corporate network
How many more servers or hosts to add to theinternetwork
-
8/7/2019 CIS 460CH 2
4/22
Scalability (Contd)
Expanding the Data Available to Users
Empowered employees make strategic
decisions that require access to sales,marketing, engineering and financial data
The 80/20 rule is no longer valid (80 % stays inlocal LANs, 20% destine for other places)
Increasing access to WWW servers Increasing intranet usage
Strategic alliances with suppliers/customers
-
8/7/2019 CIS 460CH 2
5/22
Scalability (Contd) Technical goals for scaling/upgrading enterprise
networks:
Connect separate department LANs in corporateinternetworks
Solve LAN/WAN bottleneck problems Provide centralized servers that reside on server farms
Merge an independent SNA network w/enterprise IPnetwork
Add new sites to support field offices & telecommuters
Add new sites to support communication withcustomers, suppliers, resellers, and other businesspartners
Constraints
There are impediments to scalability due to incorrect
-
8/7/2019 CIS 460CH 2
6/22
Availability
Refers to the amount of time a network isavailable to users and is often a critical goal
Can be expressed as a percent uptime per year,
month, week, day, or hour Also lined to reliability but has a more specificmeaning (percent uptime) than reliability.Reliability refers to a variety of issues, includingaccuracy, error rates, stability and TBF.
Also associated with resiliency - how much stressa network can handle and how quickly a networkcan rebound from problem.
Disaster recovery. Disaster recovery plan
-
8/7/2019 CIS 460CH 2
7/22
Availability (Contd)
Specifying Availability Requirements
Specify with precision (% uptime), timeframe(day or nightdowntime), time unit (day, week, etc.)
Cost of Downtime
For critical applications document how much lost per hour
Also helps to determine whether in-service upgrades must besupported
MTBF/MTR
Define as mean time between failures and mean time to repair
They can be used to calculate availability goals
4000 hours MTBF is a common goal
Good idea to identify for specific applications in addition tonetwork as a whole
Can usually use data supplied by manufacturer for equipment
-
8/7/2019 CIS 460CH 2
8/22
Network Performance
Criteria for accepting network performance
throughput, accuracy, efficiency, delay, and response
time Tightly tied to analyzing the existing network to
determine what changes need to be made to meetperformance goals.
Also tightly linked to scalability goals Definitions
capacity (bandwidth), utilization, optimum utilization,throughput, offered load, accuracy, efficiency, delay(latency), delay variation, response time
-
8/7/2019 CIS 460CH 2
9/22
Network Performance
(Contd)
Optimum Network Utilization
measure of how much bandwidth is used during aspecific time period. Commonly specified as apercentage of capacity
Various tools 7used to measure usage and averaging theusage over elapsed time.
Customer may have a network design goal for themaximum average network utilization allowed on
shared segments. For shared Ethernet should not exceed 37 percent else
collision rate becomes excessive
Toke Ring/FDDI typical goal is 70 percent
For WANs optimum is also about 70 percent
-
8/7/2019 CIS 460CH 2
10/22
Network Performance
(Contd)
Throughput
the quantity of error -free data that is transmitted perunit of time
Ideally should be the same as capacity, however noutusually
Capacity depends on the physical-layer technologies inuse
Depends on the access method
Throughput of Internetworking Devices
Some specify goals as Number of packets per second
The maximum rate the device can forward packets
without dropping
-
8/7/2019 CIS 460CH 2
11/22
Network Performance
(Contd)
Application layer throughput
a measure of good and relevant application-layer datatransmitted per unit of time (also called goodput)
Can increase throughput not goodput because extra datatransmitted is overhead data
Usually measure in kilobytes or megabytes per second
Constraints
end-to-end error rates
protocol functions such as handshaking, windows, &acknowledgments protocol parameters such as frame size
protocol parameters such as frame size and retransmissiontimers
PPS or CPS rate of internetworking devices
Lost packets or cells at internetworking devices Workstation and server performance factors
-
8/7/2019 CIS 460CH 2
12/22
Network Performance
(Contd) Accuracy
goal is that data received at the destination must be the
same as the data sent by the source. Typical causesinclude power surges or spikes, failing devices, noise,impedance mismatch, poor physical connection
Accuracy goals can be specified as a bit error rate(BER)
On shared Ethernet errors are often result of collisions Collision that happens beyond the first 64 bits of a
frame is a late collision which are illegal and shouldnever happen
In token rings accuracy goals sometimes include goals
for minimizing media-access control error reports
-
8/7/2019 CIS 460CH 2
13/22
Network Performance
(Contd) Efficiency
measurement of how effective an 0operation is in comparison tothe cost in effort, energy, time, or money
Provides a useful way to talk about network performance
Large frame headers are an obvious cause for inefficiency
Goal is to minimize the amount of bandwidth used by headers
Delay and Delay Variation
Users of interactive applications expect minimal delay inreceiving feedback
Multimedia applications require a minimal variation in theamount of delay that packets experience
Telnet protocol applications are also sensitive to delay because
of echo feedback
-
8/7/2019 CIS 460CH 2
14/22
Network Performance
(Contd) Causes of Delay
delay is relevant to all data transmission technologies, butparticularly satellite links and long terrest4rial cables. Alsotime required to put digital data on a transmission line. Packet
switching delay, router delay, queuing delay
Delay Variation
Digital voice and video applications are effected with jitter, ordisrupted communications. Can be minimized using a buffer
to minimize jitter Response Time
the network performance goal that users care about most. Theyrecognize small changes in the expected response time. If lessthan 100 ms most users do not notice
-
8/7/2019 CIS 460CH 2
15/22
Security
Overall goal is that security problems should not
disrupt the companys ability to conduct business.
Have protection so that business data and otherresources are not lost or damaged
First task is planning which involves analyzing
risks and developing requirements.
Hackers, financial costs, sensitive of customer data
-
8/7/2019 CIS 460CH 2
16/22
Security (Contd)
Security Requirements
protect resources from being incapacitated, stolen,
altered, or harmed. Let outsiders access data on public web but not internal
data
authorize/authenticate branch-office users, mobile users& telecommuters
detect intruders physically secure hosts and internetworking devices
protect applications and data from viruses
train network users and network managers on security
risks
-
8/7/2019 CIS 460CH 2
17/22
Manageability
Includes the following network management
functions
performance management
fault management
configuration management
security management accounting management
-
8/7/2019 CIS 460CH 2
18/22
Usability
Refers to the ease-of-use with which
network users can access the network and
services
some network design components can have
a negative effect on usability
-
8/7/2019 CIS 460CH 2
19/22
-
8/7/2019 CIS 460CH 2
20/22
Affordability
Sometimes called cost-effectiveness
Primary goal is to carry the maximum amount oftraffic for a given financial cost
In a campus network low cost of often the primarygoal
For enterprise networks availability is usuallymore important than low cost
Minimizing hiring, training, and maintainingpersonnel to operate and manage the network is
also an important goal
-
8/7/2019 CIS 460CH 2
21/22
Affordability (Contd)
Making Network Design Tradeoffs
Need to know how important affordability is to other
goals Availability often requires Redundant componentswhich raises costs
To implement affordability might mean availabilitymust suffer
Your customer should identify a single driving networkdesign goal
Sometimes making tradeoffs is more complex thanwhat has been described because goals can differ
for various parts of an internetwork
-
8/7/2019 CIS 460CH 2
22/22
Technical Goals Checklist
You should use a technical goals checklist
and Table 2-3 to determine if all the
clients technical objectives and concerns
are addressed.