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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
3Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
System Life Cycle - Conceptual
Ideas
Decision Design
Implement
System Operations
ReviewOperations
GO
NO-GO
ProgressClockwise
Strategy Studies
4Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
5Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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.
6Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
7Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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?
8Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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?
9Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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)
10Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
11Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
12Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
13Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
14Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
15Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
16Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
17Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
18Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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)?
19Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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 `a reliable system'?
• What constitutes `an 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 )
20Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
21Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
Copyright Ken Fletcher 2004 Australian Computer Security Pty Ltd
Printed: Apr 18, 2023 21:49
22 Prepared for: Monash University Subj: CSE5806 Telecommunications Management
Performance Required
Performance requirements drive the ‘dimensioning’ of the network
ie number of circuits/components,
and the bandwidth required for their connection
23Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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?
24Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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.
25Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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’
26Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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.
27Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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 `Over six months, the MTBF shall be greater than xxx hours.'
28Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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 `Over 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
29Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
30Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
31Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
32Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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)
33Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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’
34Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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.
35Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
36Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
37Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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
38Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
`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"
Copyright Ken Fletcher 2004 Australian Computer Security Pty Ltd
Printed: Apr 18, 2023 21:49
39 Prepared for: Monash University Subj: CSE5806 Telecommunications Management
Network Delay and Response Times
A small example
40Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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.
41Copyright Ken Fletcher 2004 Australian Computer Security Pty LtdPrinted Apr 18, 2023 21:49
Prepared for: Monash University Subj: CSE5806 Telecommunications Management
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.