Network Design Principles

CP3397 Network Design and SecurityLecture 2

Contents

Design goalsDesign choicesDesign approachesThe design processCapacity planning

Design goals

Good designs should: Deliver services requested by users Deliver acceptable throughput and response

times Be within budget and maximise cost efficiencies Be reliable Be expandable without major redesign Be manageable by maintenance and support

staff Be well documented

Design Choices

Balance of distributionLevel of transparencySecurityConnectivity technology

Design approaches

Two typical methods Traditional analytic design Building block approach

Both use a similar iterative approach

The traditional design process

A g r e e r e q u i r e m e n t s

I n f o r m a t i o n g a t h e r i n g

D e s i g n p r o c e s s

D e p l o y m e n t

C o m m i s s i o n i n g

M o d i f y

M e e t s c o n s t r a i n t s ?

Y e s

N o

Design Stages - Agree requirements

Engage end usersTranslate requirements Business objectives –> technical

specification

Phasing the requirements Right level of detail at each design

stage

Designing the requirements

Design Stages - Designing the requirements

Aim for completenessPrioritise with a hierarchical system such as

[M] - Mandatory [H] – Highly desirable [D] - Desirable [N] - Note

Design Stages - Assessing requirements

Consider all aspects E.g. support & maintenance, depreciation,

commissioning costs, project management fees, h/w & s/w upgrade costs, b/w/ costs, consultancy charges – over the lifetime of the network

Weighted matrix multipliers M=100, H=10, D=1, N=0 Produce scores and rank suppliers

Design Stages - Information gathering

Need to find details of user behaviour, application use and location information for example:

User: location, numbers, services used, typical access Sites: number, location, constraints on traffic (security, political

or cost) Servers and services: location, level of distribution WAN/backbone predicted link traffic Protocol support: bridged, routed or switched – Gateways

needed? Legacy support: equipment, protocols or services Specific availability needs? 24-hour/backup links etc Five-year plan – changes to population or business

requirements Budgetary constraints Greenfield or existing site

Information is refined and leads to a requirements database and capacity plan

Design Stages - Site constraints

Greenfield or Greenfield sites have no legacy constraints but… It is difficult to determine the real network loads and

stresses Needs more detail of application use and underlying

protocols Could use simulation to predict performance

Existing site Limited access Access to live network could be restricted but… Bottlenecks more obvious Can use traffic/network analysis tools

Design Stages - Planning

Uses information on Hosts, users, services, and their

internetworking needs

Iterative process of Conceptual design Analysis Refinement

Involving Brainstorming, design reviews, modelling

tools

Leading to final draft design

Design Stages - Design specification

Detailed document of the design Acts as a benchmark for design

changes Final design choices and changes

need justification and documenting Should include change history to aid

maintenance Used for the implementation

Design Stages - Implementation

Needs a project plan to include Phased introduction of new technology Educating the users (what to expect) Pilot installation (test for possible

problems) Acceptance testing (to prove

performance meets requirements) Deployment (provide support on going

live and provide fallback position)

Connectivity options

Technology choices LANs (Ethernet, Token ring, ATM) MANs (FDDI, SMDS, ATM, SONET/SDH) WANS (Frame relay, ATM, ISDN, X.25,

PDCs, Satellite) Wireless (802.11, Bluetooth, GPRS, GSM) Dial-up lines Serial links

Connectivity option determinants

Packet, cell or circuit switchingWired or wirelessDistancePerformanceBandwidthQuality of ServiceAvailability

Media and bandwidth choices

Capacity Planning - Outline

Concerned with User response times Application behaviour and performance

characteristics Network utilisation

Needed to Minimise downtime Maximise service to customers Minimise costs of procurement and

maintenance Avoid unscheduled maintenance or re-design Avoid costly upgrades and bad publicity

Capacity Planning - Stages

Form a discussion group (involve users etc.)Quantify user behaviourQuantify Application behaviourBaseline existing network Traffic profiles

Make traffic projectionsSummarize input data for design processAssess other data (environmental, location restrictions, deployment constraints etc)

Capacity Planning – Step 1

Form a discussion group (involve users etc.) Needs wide representation Users, network managers, application groups

To elicit What uses find acceptable and unacceptable Map of services and users and details of user behaviour

Quantify items using User and service sizing data Snapshots from data capture and network management

tools Traces of key services using protocol analysers Pilot network implementation

Capacity Planning – Step 2

Quantify user behaviour Need to know population and and

location of users Summary of major user groups Application use by user group Site location data (country, grid ref.,

town, postcode, telephone exchange) Planned changes

Capacity Planning – Step 3

Quantify Application behaviour Need to identify

Applications that could affect performance Location and performance of servers and clients Key constraints on performance (response times, buffer

sizes etc And define

Application behaviour under fault conditions (lost data) Addressing mechanisms( broad/multi/unicast) Packet characteristics (frame sizes and direction) Routable and non-routable services (IP, NETBIOS)

Undefined applications allow choice of distribution balance

Capacity Planning – Step 4

Baseline existing network Baselining – a behavioural profile of the network obtained

from Packet traces, transaction rates, event logs and stats Router ACLs, firewall rulebases Inventory of H/W and S/W revisions

Traffic profiles -Capture data for a stable working network with details of

B/w utilization by packet type and protocol Packet/frame size distribution Background error rates Collision rates

Various tools can be used Network and protocol analysers, SNMP data, RMON probes, OS

tools, traceroute, ping etc

Capacity Planning – Step 5

Make traffic projections using some, or all of: Hand calculation Commercial analytical tools to project

network utilisation Simulation tools (most detail)

Capacity Planning – Step 6

Summarize input data for design process Budget Database of sites, user populations, List of key applications and their behaviour Traffic matrix

Need to consider Static or dynamic bandwidth allocation Max. Delay and Max. hops between sites Resilience, Availability, degree of meshing Design constraints and trade-off

(e.g. delay v cost)

The building-block design process (an alternative)

NeedsAnalysis

Technologydesign

CostAssessment

Summary

Good design Is an iterative process of continuous

refinement Is logical and consistent Should deliver acceptable performance

and cost metrics (trade-off) Is more than choosing the technology!