Lecture 7: Network Design Principles

1. Lecture 7: Network Design Principles CP3397 Network Design and Security

2. Contents • Design goals • Design choices • Design approaches • The design process • Capacity planning

3. 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

4. Design Choices • Balance of distribution • Level of transparency • Security • Connectivity technology

5. Design approaches • Two typical methods • Traditional analytic design • Building block approach • Both use a similar iterative approach

6. The traditional design process

7. Design Stages - Agree requirements • Engage end users • Translate requirements • Business objectives –> technical specification • Phasing the requirements • Right level of detail at each design stage • Designing the requirements

8. Design Stages - Designing the requirements • Aim for completeness • Prioritise with a hierarchical system such as • [M] - Mandatory • [H] – Highly desirable • [D] - Desirable • [N] - Note

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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)

15. 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

16. Connectivity option determinants • Packet, cell or circuit switching • Wired or wireless • Distance • Performance • Bandwidth • Quality of Service • Availability

17. 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

18. Capacity Planning - Stages • Form a discussion group (involve users etc.) • Quantify user behaviour • Quantify Application behaviour • Baseline existing network • Traffic profiles • Make traffic projections • Summarize input data for design process • Assess other data (environmental, location restrictions, deployment constraints etc)

19. 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

20. 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

21. 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

22. 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

23. 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)

24. 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)

25. The building-block design process (an alternative)

26. 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!