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12004
Network Analysis and Design
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22004
Computer Networks
do not of themselves
justify their existence
Networks exist to do something
It is what they do which justifies their existence
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32004
Computer Networks
exist
to support
Business, Government, Social, Educational ….
Functions
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42004
Computer Networks - New and Existing
• In the case of designing a NEW network ask:
What is the new network for ?
What are the specific functions that must be supported ?
etc
• In the case of upgrading an EXISTING network ask:
What is the existing network supposed to be doing, that it is not ?
Which transmission links need to be upgraded ?
etc
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52004
Business Factorsthat Influence Network Development and Expansion
• Expansion into NEW Geographic Areas
• Merger or Acquisition of companies
• Competition to provide service to customers
• Distribution of Centralised Functions
• Interface with other organisations’ computer systems
• Capture of transactions at point of origin to reduce errors
• On line sales of goods and services
• etc
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62004
Systems Analysis
Network Analysis and Design
should be seen as
“Systems Analysis”
within a
SDLC Model.
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72004
General Steps
• Feasibility Study
• Network Design Plan
• Assess geographic status\scope
• What are the business’ operations and procedures ?
• Link Speed to Handle Aggregate Data Rate ?
• Link Speed to Handle Response Time Requirements ?
• Review Estimates
• Network Configurations
• Derive Cost estimates by referring to available Telecommunications services
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82004
Feasibility Study
• Identify the Purpose of Network development or expansion
– to support point of sale transactions from discount stores
– to support timely submission of stock orders to suppliers etc
• Identify factors that indicate need for Network development or expansion - Needs Assessment Factors
• Preliminary Identification of COSTS
• Result should be either a GO or NO GO Decision
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92004
Network Design Plan• The Plan should take into account:
– Technical feasibility of network » Leading edge or stable technology ?» Is support available for ongoing operation ?
– Operational feasibility » For the users who conduct their daily business by using the
network» Identify users (managers, sales staff etc) and their requirements» Will security constraints make access difficult ?
– Economic feasibility» Need to keep the network within budgetary limitations
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102004
Network Design Plan
• Goals of Network Design
• Network Evaluation Criteria
– Used for measuring the success of the network at completion
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112004
Geographic Status\Scope
• Assess geographic status\scope of the projected network by identifying the sites to be (served) connected to the network
• International, worldwide network, WAN, can be variations in
– telecomms stds - ISDN primary service, Australia 30 B channels of 64kbps, US 23
– telecomms regulatory environment - Private vs Public Telcos
• Country, within boundaries and laws of a single country, WAN
• City, within boundaries of a specific city/state/province or local government jurisdiction, MAN
• Local facility, within a specific building or confined to a series of buildings located on the same contiguous property, LAN
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122004
What are the business operations and procedures ?
• By identifying the types of transaction generated by the organisation we can determine the business operations and procedures
• Create a Workload Table
– Shows the network traffic that will be generated by each site that is to be attached to the network
• Allow for:
– future growth eg Sales and Marketing Dept predict that sales will grow by 10% per annum over the next 5 years
– Protocol Overhead
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132004
Transactions
• For each site:
– Determine transaction types - Customer inquiry etc
– Determine volumes expected in the peak period (hour) for each transaction type:
TxVol of Customer inquiries = 400
By focusing on the peak period (hour) we ensure that sufficient resources will be available and response time will be adequate throughout the day.
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142004
Transactions
• For each site:
– Determine the size (total bytes exchanged - includes request and response) of the transaction in bytes
TxSize of Customer inquiry = 500 bytes
• We can derive this information by looking at the CURRENT or a SIMILAR system.
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152004
Link Speed to handle Aggregate Data Rate - ADR
• The Aggregate Data Rate is the amount of data generated by a site in the peak hour of business
• For each site:
– Calculate the message volume in bytes for each transaction type: Customer Enquiry - TxVol x TxSize = 400 x 500 = 200,000 bytes
– Allow for protocol overhead
– Allow for growth in transaction volume
– Aggregate volume across transaction types to obtain estimate of Aggregate Data Rate:
ADR = Sum of (TxVol x TxSize + Protocol
Overhead + Growth) bytes
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162004
Link Speed to handle Aggregate Data Rate - ADR
• For each site:
– The Link Speed needed to handle ADR in peak hour
= ((ADR x bits per byte)/secs per hour) bps
eg Headquarters [(1,267,125 x 11bits/byte)/3600] = 3872 bps
• Refer Workload Table
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172004
Link Speed to HandleTransaction Response Time Requirements
• Check Link Speed chosen to handle ADR will satisfy Response Time (R/T) requirements for each transaction
• (R/T) has two components - Transmission time (T/T) and Processing time (P/T).
• Suppose the design objective for the Customer Inquiry transaction is a R/T of 3 secs.
• If P/T is 1 sec, then T/T must be <= 2 secs.
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182004
Link Speed to HandleTransaction Response Time Requirements
• As the Customer Inquiry transaction involves the exchange of 500 bytes then the Link Speed can be calculated as:
size in bytes / link speed in bytes <= 2 secs 500bytes/[ x bytes/sec] <= 2 secs hence x >= 500bytes /2 secs >= 250bytes/sec
• This can be converted to bps: (250 x 8bits/byte)/sec = 2000 ~ 2400bps
hence a 2400bps link is needed to satisfy R/T requirements of the Customer Inquiry Transaction
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192004
Review Estimates
• Review estimates with users to make sure the volumes make business sense and are representative
• Should there be six times as many inquiries on Inventory as compared to those on Orders ?
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202004
Network Configurations and Costs
• Propose alternative network configurations:
– Point-to-Point
– Multipoint
• Derive cost estimates for the WAN by referring to Telco Services
– ATM
– DDS
– Austpac
– ISDN
– Frame Relay
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212004
Telestra’s Charging Principles
– Line Access Charges
» Once Only Installation
» Access - Annual Rental
– Transmission Charges - can be based on:
» Connect Time - STD, Mobiles
» Time of day
» Volume of data - Austpac
» Distance
» Zones
» Area within a zone
» Link Speed
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222004
Telstra - ISDN
• Provides Integrated Services - voice, data, video
• Microlink
– Basic Rate access for small business/residential
– Two Full Duplex 64kbps B channels for data
– One “ 16kbps D channel for control signalling
• Macrolink
– Primary Rate access for large organisations with high volume requirements
– 30 B channels
– One D channel at 64kbps
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232004
Telstra - ISDN
• Charging Principles
» Access
• Installation Charge
• Annual Rental
» Usage
• Connect Time
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242004
Telstra - Austpac
• X.25 Packet Switching Network for Data transmission, up to 128kbps
• Charging Principles
– X.25 Dedicated
» Access - Zone Based
• Installation Charge
• Annual Rental
» Usage
• Volume of packets sent
• Time of day
• Volume Capping
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252004
Telstra - Austpac
• Charging Principles
– X.28 Dial-Up
» Usage
• Zone Based
• Connect Time/Time of day
• Volume
• Charging Zones
– Metro
– Country
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262004
Telstra - DDS
• Digital Data Service - up to 48kbps
• Charging Principles
– Zone Based, 9 Zones
– Area Based, within each zone have Primary, Secondary and Tertiary Areas
– Access
» Installation
» Annual Rental
– Transmission Fees - depend on distance, Areas and Zones
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272004
Other Issues
• Though cost minimisation is a major factor you must not forget:
– Backup
– Recovery
– Maintenance
– Training
– Security
etc
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282004
Staged Approach
• Recommend staged approach to implementation
• High Priority/Low Priority sites can be selected and linked first
• Later sites will benefit from experience gained
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292004
Deliverables
• Estimation of traffic load on network including future growth
• Estimation of transmission requirements between any two sites to be connected
• Identification of hardware needed at each site.
• Interface issues - WAN to WAN etc
• Support required once network operational
• Costing of alternative network configurations
• Security and Reliability issues