CSE5806
Telecommunications Management
Lecturer: Ken Fletcher
Lecture 4
Telecommunications Network
Strategy and Design Aspects
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd
1 Prepared for: Monash University
Subj: CSE5806 Telecommunications Management
Printed: 26-Jan-12 11:35
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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 2 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
System Life Cycle - Conceptual
NO-GO
Strategy GO
Decision Design
Studies
Ideas
Progress
Review Clockwise
Implement
Operations
System Operations
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 3 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Network Strategy Development
Network Life Cycle is a sequence of:
– Network Strategy Determination;
Initial costs
• 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 Costs approx
equal to
equipment, documentation, circuits etc. Initial costs
‘Technical Strategy’ should consider ALL of these steps
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 4 Prepared for: Monash University
Printed 26-Jan-12 11:35 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.
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 5 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 6 Prepared for: Monash University
Printed 26-Jan-12 11:35 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?
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 7 Prepared for: Monash University
Printed 26-Jan-12 11:35 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?
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 8 Prepared for: Monash University
Printed 26-Jan-12 11:35 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)
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 9 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 10 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 11 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Project Lifecycle - Eng’g Processes
Review Operations Ideas Strategy Studies
Operations Progress
Clockwise
User Oriented Testing - Analysis
Functional and Performance Architectural Design
Acceptance Testing User Requirements Specification
System Oriented Testing-
Technical Functionality, plus
Connectivity and Interfacing
System Testing Detail Design
Sub-system Oriented Testing-
Detailed Functionality, plus System and
Connectivity and Interfacing Sub-System
System
Sub-system Testing System
Specifications
Acquire and Implement Specifications
Specifications
Copyright Ken Fletcher 2004
Sub-systems
Australian Computer Security Pty Ltd 12 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 13 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Major Stakeholders & Roles
Designer Has:
Customer Has:
Knowledge
Money to pay for products & services (education &training)
Business Needs & Expectations Wisdom
Employees (Operators and Users) (experience)
Vendors Have:
Products & Services
All are needed
Skilled Workforce
to implement
and support
the network
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 14 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Project Engineer/Designer Role
Customer (With Needs & Money)
Needs & Money to
Expectations pay costs
Project Engineer/Designer is Buffer between the
(demanding) customer and the implementers
Specifications Problems
and Costs
&
Resolutions
Requirements
Network Implementation Tasks
(build, install, test, train staff etc)
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 15 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 16 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 17 Prepared for: Monash University
Printed 26-Jan-12 11:35 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)?
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 18 Prepared for: Monash University
Printed 26-Jan-12 11:35 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 )
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 19 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Design is an Iterative Process
Demand
Resources Design
Goals
Activity
Network Design Documents
Design Spec’ns
Adjust Criteria Drawings
Plans
Review Results
Temper Design
Iterative Design Process
Order Circuits Order Equip't
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 20 Prepared for: Monash University
Printed 26-Jan-12 11:35 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 21 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd
22 Prepared for: Monash University
Subj: CSE5806 Telecommunications Management
Printed: 26-Jan-12 11:35
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?
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 23 Prepared for: Monash University
Printed 26-Jan-12 11:35 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.
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 24 Prepared for: Monash University
Printed 26-Jan-12 11:35 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’
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 25 Prepared for: Monash University
Printed 26-Jan-12 11:35 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.
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 26 Prepared for: Monash University
Printed 26-Jan-12 11:35 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.'
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 27 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 28 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 29 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 30 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 31 Prepared for: Monash University
Printed 26-Jan-12 11:35 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)
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 32 Prepared for: Monash University
Printed 26-Jan-12 11:35 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’
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 33 Prepared for: Monash University
Printed 26-Jan-12 11:35 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.
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 34 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 35 Prepared for: Monash University
Printed 26-Jan-12 11:35 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 36 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Message Volumes
Traffic 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
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 37 Prepared for: Monash University
Printed 26-Jan-12 11:35 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 38 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management
Network Delay and Response Times
A small example
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd
39 Prepared for: Monash University
Subj: CSE5806 Telecommunications Management
Printed: 26-Jan-12 11:35
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.
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 40 Prepared for: Monash University
Printed 26-Jan-12 11:35 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.
Copyright Ken Fletcher 2004
Australian Computer Security Pty Ltd 41 Prepared for: Monash University
Printed 26-Jan-12 11:35 Subj: CSE5806 Telecommunications Management