12004

Network Analysis and Design

22004

Computer Networks

do not of themselves

justify their existence

Networks exist to do something

It is what they do which justifies their existence

32004

Computer Networks

exist

to support

Business, Government, Social, Educational ….

Functions

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

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

62004

Systems Analysis

Network Analysis and Design

should be seen as

“Systems Analysis”

within a

SDLC Model.

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

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

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

102004

Network Design Plan

• Goals of Network Design

• Network Evaluation Criteria

– Used for measuring the success of the network at completion

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

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

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.

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.

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

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

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.

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

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 ?

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

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

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

232004

Telstra - ISDN

• Charging Principles

» Access

• Installation Charge

• Annual Rental

» Usage

• Connect Time

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

252004

Telstra - Austpac

• Charging Principles

– X.28 Dial-Up

» Usage

• Zone Based

• Connect Time/Time of day

• Volume

• Charging Zones

– Metro

– Country

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

272004

Other Issues

• Though cost minimisation is a major factor you must not forget:

– Backup

– Recovery

– Maintenance

– Training

– Security

etc

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

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