Copyright Ken Fletcher 2004 Australian Computer Security Pty Ltd Printed: 26-Jun-15 08:50 1 Prepared for: Monash University Subj: CSE5806 Telecommunications.

Copyright Ken Fletcher 2004 Australian Computer Security Pty Ltd

Printed: Apr 18, 2023 21:49

1 Prepared for: Monash University Subj: CSE5806 Telecommunications Management

CSE5806

Telecommunications ManagementLecturer: Ken Fletcher

Lecture 4

Telecommunications Network

Strategy and Design Aspects

2Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49

Prepared for: Monash University Subj: CSE5806 Telecommunications Management

Network Planning Issues Internal factors

• current usage and forecast requirements

• constraints - – eg existing contracts, buildings, residual life of existing equipment

• technical needs of the applications - – eg mission criticality, hard or soft ‘real time’, timing variability

External factors:• technology available - now, future, costs involved (eg training)

• regulation - governments, codes of conduct etc

• labour and related issues:– skills needed, compared with those available– training - immediate, ongoing, future– surplus personnel - retrenchment, retraining etc

• financial appraisal of the proposal - including maintenance cost

• development and procurement plans



System Life Cycle - Conceptual

Ideas

Decision Design

Implement

System Operations

ReviewOperations

GO

NO-GO

ProgressClockwise

Strategy Studies



Network Strategy Development

Network Life Cycle is a sequence of:– Network Strategy Determination;

• Architectural Concepts

– Designing the network;– Implementing the network;– Operation and Maintenance of the network;

• (Maintenance = Approx 10% of initial cost per annum)

– Modification of network as needs change; – Upgrading equipment/software to remain current; and finally

– Closing Down, Dismantling, and Disposing of the equipment, documentation, circuits etc.

‘Technical Strategy’ should consider ALL of these steps

Initial costs

Costs approx equal to

Initial costs



Round the Loop, again and again… Most organisations have been around this loop several times

• Many larger organisations have had • computers since late 1960s

• communications networks of various kinds for many years:– telephones - from 1920s– telegraphic transfers via paper tape

(using pre-allocated time windows) since 1960– Telex and TWX (dial up messages) 1960s– internal computer links - LANS from 1970s– WANs for computer data from 1980s

• Yet people still have difficulty in realising that:• planning is required

• most network design work is enhancement or replacement of

existing networks. Few are ‘green fields’ design.



Strategy Revision

Strategy Study

• Suggested 6 stages:– Analysis of existing network(s)

– Identification of future network & facility requirements

– Definition & evaluation of options

– Strategy consolidation

– Reporting

– Recording the requirements and decisions



Stage 1 Analysis of Existing Network This stage provides information & insight into organisation:

• how the existing facilities work, and how well• Network topology and organisation• weaknesses & strengths – networks, applications, people• satisfaction or unhappiness of the user community

• traffic loads• now• in future, both existing systems (up/down) and future systems (really stage 2) • dispersal and characteristics of communications traffic• aggregated traffic collections• criticality

• working lives of existing equipments. It may be:• worn out – needs replacement• out of support - unmaintainable• out of capacity - overloaded

• contractual commitments/lease arrangements in place• Constraints?, can be bought out?, must live with?, need updating?



Stage 2 Future Network Requirements What is Required – (not how it will be achieved)

• Characteristics• loads & bandwidth

• switching requirements

• time profiles

• dispersion - centralised, distributed, remoted?

• growth pattern - application by application

• back-up & redundancy (service agreements)

• external access - other networks, databases

• interfaces, protocol converters, gateways

• Functions and capabilities required• Available buildings and environmental support

• eg is the company vacating buildings somewhere?



Stage 3 Consider Options Define and Evaluate Options and alternative solutions

– This is where you consider the questions:• ‘HOW to do it’ and

• ‘HOW MUCH would it cost if done this way’

A major creative effort• Can use brainstorming, think tanks, seminars, etc.

• Essentially draws from:– existing installed base– information about current & emerging technology and techniques– bright ideas– future requirements

• to produce a short list of options (combination of evolution and revolution)



Stage 4 Strategy Consolidation

Determine preferred approach or approaches – This stage requires plenty of discussions with stakeholders,

covering:• Requirements to be implemented

• Timetables when these will be implemented

• Budgets - – money– time– people

• Benefits identified at each stage



Stages 5 and 6 Stage 5 - Report to Management

– Basically, keep management informed

Stage 6 - Record the Requirements and decisions– Even if the decision is not to proceed, the strategy study results

need to be recorded.– If decision is to proceed, then move along towards

implementation:• design

• install

• operate, support, maintain



Project Lifecycle - Eng’g Processes

SystemSpecifications

SystemSpecifications

System and Sub-System

Specifications

Detail Design

Ideas

Sub-system Testing

System Testing

Acceptance Testing

ProgressClockwise

Review Operations Strategy Studies

Operations

AnalysisArchitectural Design

User Requirements Specification

User Oriented Testing - Functional and Performance

System Oriented Testing- Technical Functionality, plusConnectivity and Interfacing

Acquire and ImplementSub-systems

Sub-system Oriented Testing- Detailed Functionality, plusConnectivity and Interfacing



General Design Approach Network design is a complex task -

– as much people-handling & political as technical issues– requires patience and endurance

Starting conditions:– Usually a request ‘to install a network’– Sometimes with written ‘brief’, such as the document from

Strategy Studies “Stage 6 - Recording Concept for Later”

Ending Conditions:– A detailed specification of the technical design, from which the

network could be built, tested, and implemented.

Frequently, the designer then also implements the network



Major Stakeholders & Roles

Customer Has:Money to pay for products & services

Business Needs & ExpectationsEmployees (Operators and Users)

Designer Has:Knowledge (education &training)

Wisdom (experience)

Vendors Have:Products & ServicesSkilled Workforce

All are needed to implement and support the network



Project Engineer/Designer Role

Network Implementation Tasks(build, install, test, train staff etc)

Project Engineer/Designer is Buffer between the (demanding) customer and the implementers

Customer (With Needs & Money)

Needs & Expectations

Money to pay costs

Specifications &

Requirements

CostsProblems

and Resolutions



Main Design Drivers Network Design driven by five main issues:

– Functionality Required– What is the network to do?

– Performance Required– How fast is to be?

– Reliability and Availability Required– When is it needed, and impact of not being available when needed

– Facilities and Capabilities Available - (sometimes a constraint)

– What buildings/rooms/equipment are available - must they be used?

– Price or Cost– If lucky, you get what you pay for, but rarely more than that



Components within Computer Network The computer communications network will essentially

consist of:– Processor(s) of all kinds;

– Mainframes, Servers, email servers, etc

– Node(s);– Hubs, Switching Centres, routers, bridges PABX

– Line(s) and possibly modems;– Communications circuits linking sites/hubs etc

– Terminal(s); – Desktop computers, printers, POS terminals, IVR units etc

– Miscellaneous Components– Crypto gear, firewalls, telemetry interfaces etc



Design Issues The design will need to comply with some constraints, and

answer some questions, including:

• How many nodes, and where? • logically and physically

• Which terminals and/or processors will connect to each node(s)?

• Eg where will the colour printer be placed and connected?

• Is this a centralised or distributed network?

• How will they be connected (within node)?• What configuration - star, daisy chain? One (or two) way loop?

• How will nodes connect to each other?• Leased lines, VPN, high speed links (eg ATM, fast Ethernet)?



Key Points The key points when approaching network design are:

• Proper definition & specification of the technical problem, AND

• Well specified evaluation criteria - eg• What is `good response'?

• What is à reliable system'?

• What constitutes àn expandable network'?

• Don't rely on intuition or assume that you know what is wanted, this is usually dangerous.

– Remember: ‘Assume’ makes an ass (donkey) out of you and me ( Ass / u / me )



Design is an Iterative Process

Design

ActivityGoals

Demand

Resources

Adjust Criteria

Review Results

NetworkDesign

Temper Design

Order Circuits Order Equip't

Iterative Design Process

Design DocumentsSpec’nsDrawingsPlans



Design Goals The major design goals are to:

– Deliver the functionality, performance and connectivity required

– Mininise costs

– Optimise performance• Speed

• Capacity

– Efficiently use the Facilities provided (efficient use of space etc)

– Meet Objectives in:• Implementation Ease

• Availability and Reliability

• Maintainability

• Servicing

• Flexibility

• Robustness


Printed: Apr 18, 2023 21:49


Performance Required

Performance requirements drive the ‘dimensioning’ of the network

ie number of circuits/components,

and the bandwidth required for their connection



Response Time

Response time is performance in interactive mode Typical User view:

– The time from pressing the key that `commits' the input command, and viewing the full output screen. (ie end-to-end delay)

Typical Specialist view:– Time from last input character going to line, and first output

character being received at the computer (ie transit delay).

Need agreed definition– Either view is valid - but

remember the golden rule, and who has the gold.

– Try for peak or busy hour definition • EG. “95% of traffic items shall be handled within ‘n’ seconds”

• What should ‘n’ be?



Throughput

Related to response time figure but effect is quite different. Throughput is a `batch' type of concept

• Inevitably difficult to define • Inevitably difficult to specify meaningfully• Interrelates with response time -

• good response times imply good throughput

• TRY:– “Throughput is the bulk traffic able to be handled by the network.”

• eg 1000K file transfer in one minute.

• NOTE:– If no priority system for traffic, a bulk file transfer will cause the

communications link loading to approach 100% utilisation for short periods, thereby creating significant delays for interactive traffic.



End-to-End Delay

The total time for an item to transit the network - including all:

• communications transit times –(usually negligible, except for satellite links)

• queuing times at intermediate nodes

• error recovery delays

• etc

• and sometimes includes processing times

Ensure that you know whether ‘allowable delay’ includes processing times.

It is often included in the ‘perceived comms delay’



Busy Rate Goal

Usually related to `LOSS' aspects• ie. those situations like a busy line on a telephone, where

the request is lost if unable to be satisfied immediately.– Dial up circuits– Port Selection– Virtual Circuits

Usually set to an acceptable criteria

(`grade of service’ or ‘degree of congestion’) – say 1% in busy hour is a typical rate for congestion of outgoing

telephone calls being unable to be completed due to circuit/switch congestion.



Maintenance Goal How much effort is management prepared to expend

on Hardware and on Software for both – fault correction, and – environmental maintenance

• (keeping up with technology)

• eg Should they buy high reliability equipment, even though it costs much more than commercial grade equipment?

Mean Time Between Failures (MTBF)– concept

• For each critical component

• For the communication carrier's circuits

Needs to be specified carefully– eg Òver six months, the MTBF shall be greater than xxx hours.'



Servicing Goal Mean Time to Restore (MTTR) concept

– Central or Capital City installations• Service personnel are less than an hours drive away• Spares warehouses are close to hand

– Remote Installations• Service personnel may have to fly in• Consider holding extended spares stocks on site

– Communications Carrier's MTTR (probably very high, but …)

Needs to be specified carefully– Define whether MTTR is to respond, repair, restart or RESTORE;– EG Òver six months, the MTTR shall not exceed three hours on

average, nor five hours for any single incident.’

NOTE: Many other terms apply to these concepts - eg– Inherent availability, mean down time, etc



Implementation Ease Goal The ease or difficulty of implementation -

– closely related to ‘Technical Risk’

How long to achieve implementation? How much upheaval in the organisation? What is the risk of project failure:

– equipment inadequate– supplier/vendor failure to deliver– traffic estimates grossly inappropriate – facilities not available on time– Training– state-of-the-art equipment on a par with kindergarten art

Leading Edge technology is BLEEDING edge for managers



Robustness Goal

How well the network stands up to stress and shocks Electrical and installation aspects

• Over/Under Temperatures• Uninterruptable/No-Break Power Supplies

Circuit aspects• Overloads• Zero Loads• Circuit transients - `hits' and `failures'• Circuit major outages

Application Dependencies• Peaky interactive loads• Unexpected large batch loadings

MUST BE COST_JUSTIFIED - no system can be perfect

– Many people demand high robustness, but cost is 200% to 500% more



Security Goals

ALWAYS treat security as exercise in RISK MANAGEMENT– (AS/NZS 4444 of 1999 “Information Security Management”

and AS/NZS ISO/IEC 17799:2001 “Code of Practice”)

Base security on impact assessments and costs

Avoid knee jerk reactions and quick fixes

Match network security to application/installation security



Performance Issues Regarding performance issues, concentrate on:

– Network and Line Capacity• Line BPS or Char/Sec

• Nodes Packets etc per second

– Delays • Waiting in queues for service

• Service Times

For all lines, actual throughput is always less than the theoretical maximum possible throughput due to:

• polling

• error block retransmissions

• synch frames and overheads

• effect of random traffic patterns

• Line utilisation = (Actual Load handled / Maximum Possible)



Traffic Characteristics

Design is significantly affected by

• Type of traffic activity being handled

• Volume of traffic to be handled

– eg average transaction (packet) size

– eg average number of packets/second during the busy hour

Strange as it may seem, you will spend more time determining and analysing these issues than actually ‘designing’ the network.

Informal studies have indicated that actual network loads experienced within a short time of commissioning the new system are often 100% above the ‘design load’



BATCH Traffic These types of traffic flows were the norm before interactive

terminals became common. Still in widespread use today.

Examples: Overnight backups, End of Day POS dump. One major direction of flow at any time

– Usually very asymmetrical at any point in time

Many records - size & number determinable (more or less) Performance objectives `hours’ rather than seconds

– Usually this traffic type is ‘overnight’

Impacts N/W performance badly– Line and switch gear utilisations approach maximums during

large batch flows - thus there is little capacity left for other network users at that time.



Transaction Oriented Traffic

This traffic type is a cross between Batch and Interactive

It has become very common via the internet

Bursty - Random Traffic patterns

Performance objectives `minutes’ (or tens of seconds)– Consider the delays caused by downloading the ‘pretty effects’ of

many web pages -

• the authors may not realise it, but the psychological impact from to the ‘pretty effects’ is drastically reduced due to the slow nature of the transactions. Impact is frequently negative due to the excessive delays.

One major direction of flow

Variable record sizes and numbers



Interactive (eg Query/Response)

This type of traffic normally appears as Query/Response situations, where the response is required within one or seconds of the query. Typically, the traffic volumes are very asymmetrical (short query, large response)

Bursty - Random Traffic patterns

Two way flow, (although one predominates)

Performance objectives `seconds’

Variable sizes and numbers of records



Message VolumesTraffic volumes are critical to response time/throughput.

`Communication item' sizes• Average size - best by application if available• Statistical distribution of sizes• Are these figures constant throughout the day/week/month?

Totals in-out for each application• Volumes of traffic - by application if available

Peak Times • (NOTE: WA is 2-3 hours later)• Special Days (Holidays, Religious festivals)

• Identifying the peak times for each application may be very useful

NEED TO UNDERSTAND BUSINESS / LOCAL

PEAKS

First Tuesday in November = holiday for many, peak for TAB



`Turnpike Effect' and Growth

(AKA as `Suppressed Demand’, Freeway Effect, etc)

Well designed systems encourage greater use - • especially enquiry systems

Need to add a contingency allowance for the unknown suppressed demand

Martin 1968:– "If terminals provide a useful service, their utilisation will

expand to fill the system capacity"


Printed: Apr 18, 2023 21:49


Network Delay and Response Times

A small example



Network Delays What is involved in the delay?

• Node delays:• Usually small (and consistent)

– Specialised processors etc used in switches and hubs

• Delays Affected by CPU and buffer numbers– Low processor CPU power means less nominal ‘packets per second’– Low memory size means lower capability for switching (buffer overflows

etc)

• Line Delays• Trunk Lines and Branch Lines

• Generally, Comms lines are the bottle neck points in a network aa they are the slowest

• Note: These delays are for each node and line transited.



Response Times example Query (1000 bytes) / response (10,000 bytes) using a mainframe / 10Mbps LAN Response Time = the SUM of:

– Inbound Terminal Delay (usually small - say 50 milliseconds)

– Inbound Queuing Delay (queued traffic held in terminal waiting for LAN access. Time delayed depends on other terminals & traffic - say 20 milliseconds)

– Inbound Service Time (time to transmit a packet on the network) • (depends on line speed and message size - say 10 milliseconds)

– Front End Processor (FEP) Delays (should be small - say 10 milliseconds)

– Mainframe delays (could be comparatively large - say 1000 milliseconds)

– FEP Delays on output (say 100 milliseconds)

– Outbound Queuing (held in FEP while waiting for LAN access - 1000 ms)

– Outbound Service Time (say 50 milliseconds)

– Outbound Terminal Delay (say 50 milliseconds)

Total time - 2290 milliseconds - of which 60 can be assigned directly to ‘network’ (the inbound and outbound service times). Most of the rest is waiting times.

Copyright Ken Fletcher 2004 Australian Computer Security Pty Ltd Printed: 26-Jun-15 08:50 1 Prepared for: Monash University Subj: CSE5806 Telecommunications.

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