Traditional Network Design

• Based on a set of general rules– “80/20”– “Bridge when you can, route when you must”– Can’t deal with scalability & complexity

• Focused on capacity planning– Throw more bandwidth at the problem– No consideration to delay optimization– No guarantee of service quality– Less importance given to network RMA (Reliability,

Maintainability, and Availability) compared to throughput

Application Characteristics

Applications Message Length

Message arrival rate

Delay need Reliability need

Interactive terminals

Short Low Moderate Very high

File transfer Very long Very low Very low Very high

Hi-resolution graphics

Very long Low to moderate

High Low

Packetized voice

Very short Very high High Low

Application Bandwidths

Word Processing

File Transfers

Real-Time Imaging

100s Kbps Few Mbps

Few Mbps 10s Mbps

10s Mbps 100s Mbps

Transaction Processing 100 Bytes Few Kbps

A Look on Multimedia NetworkingVideo standard Bandwidth per

userWAN services

Digital video interactive

1.2 Mbps DS1 lines ISDN H11, Frame Relay, ATM

Motion JPEG 10 to 240 Mbps ATM 155 or 622 Mbps

MPEG-1 1.5 Mbps DS1 lines ISDN H11, Frame Relay, ATM

MPEG-2 4~6 Mbps DS2, DS3, ATM at DS3 rate

Some Networking Issues

• LAN, MAN and WAN• Switching and routing• Technologies: Ethernet, FDDI, ATM …• Wireless/Mobile networking• Internetworking• Applications• Service quality• Security concerns

Network Design: Achievable?

Response Time Cost

Business GrowthReliability

Where to begin?

WAN

CampusCampus

TrafficTrafficPatternsPatterns

Dial in Dial in UsersUsers

SecuritySecurity

WWW WWW AccessAccess

UsersUsers

NetworkNetworkManagementManagement

AddressingAddressing

• Performance– Depends on Network Elements– Measured in terms of Delay and Throughput

• Reliability– Failure rate of network components– Measured in terms of availability/robustness

• Security– Data protection against corruption/loss of data due to:

– Errors– Malicious users

Network Criteria

Traditional Network Design Methodology

• Many network design tools and methodologies that have been used resemble the “connect-the-dots” game

• These tools let you place internetworking devices on a palette and connect them with LAN or WAN media

• Problem with this methodology:– It skips the steps of analyzing a customer's requirements, and

selecting devices and media based on those requirements

Top-Down Network Design Methodology (1/2)

• Good network design– Recognizes that a customer’s requirements embody many

business and technical goals– May specify a required level of network performance, i.e.,

service level– Includes difficult network design choices and tradeoffs that

must be made when designing the logical network before any physical devices or media are selected

• When a customer expects a quick response to a network design request– A bottom-up (connect-the-dots) network design methodology

can be used, if the customer’s applications and goals are well known

Top-Down Network Design Methodology (2/2)

• Network designers often think they understand a customer’s applications and requirements.

• However, after the network installation, they may discover that:– They did not capture the customer's most important needs– Unexpected scalability and performance problems appear as

the number of network users increases

Top-Down Network Design Process (1/2)

• Begins at the upper layers of the OSI reference model before moving to the lower layers– Focuses on applications, sessions, and data transport before the

selection of routers, switches, and media that operate at the lower layers

• Explores divisional structures to find the people:– For whom the network will provide services, and– From whom to get valuable information to make the design

succeed

Top-Down Network Design Process (2/2)

• It is an iterative process:– It is important to first get an overall view of a customer's

requirements– More detail can be gathered later on protocol behavior,

scalability requirements, technology preferences, etc.• Recognizes that the logical model and the physical design may

change as more information is gathered• A top-down approach lets a network designer get “the big

picture” first and then spiral downward into detailed technical requirements and specifications

Network Development Life Cycle

Management

Analysis

Design

Simulation/Prototyping

Implementation

Monitoring

Network Design and Implementation Cycle

Network Design and Implementation Cycle (1/3)

• Analyze requirements:– Interviews with users and technical personnel– Understand business and technical goals for a new

or enhanced system– Characterize the existing network: logical and

physical topology, and network performance– Analyze current and future network traffic,

including traffic flow and load, protocol behavior, and QoS requirements

Network Design and Implementation Cycle (2/3)

• Develop the logical design:– Deals with a logical topology for the new or

enhanced network– Network layer addressing and naming– Switching and routing protocols– Security planning– Network management design– Initial investigation into which service providers

can meet WAN and remote access requirements

Network Design and Implementation Cycle (3/3)

• Develop the physical design:– Specific technologies and products to realize the logical design

are selected– The investigation into service providers must be completed

during this phase

• Test, optimize, and document the design:– Write and implement a test plan– Build a prototype or pilot– Optimize the network design– Document your work with a network design proposal

Another Perspective

• Data collection– Traffic– Costs– Constraints

• Design process• Performance analysis• Fine tuning• A painstaking iterative process

PDIOO Network Life Cycle (1/3)(Cisco)• Plan:

– Network requirements are identified in this phase– Analysis of areas where the network will be installed– Identification of users who will require network services

• Design:– Accomplish the logical and physical design, according to

requirements gathered during the Plan phase

• Implement:– Network is built according to the Design specifications– Implementation also serves to verify the design

PDIOO Network Life Cycle (2/3)(Cisco)• Operate:

– Operation is the final test of the effectiveness of the design– The network is monitored during this phase for performance

problems and any faults, to provide input into the Optimize phase

• Optimize:– Based on proactive network management which identifies and

resolves problems before network disruptions arise– The optimize phase may lead to a network redesign

• if too many problems arise due to design errors, or• as network performance degrades over time as actual use and

capabilities diverge– Redesign may also be required when requirements change

significantly

PDIOO Network Life Cycle (3/3)(Cisco)

• Retire:– When the network, or a part of the network, is out-of-date, it may

be taken out of production– Although Retire is not incorporated into the name of the life cycle

(PDIOO), it is nonetheless an important phase

One More Look

Define Objectivesand Requirements

Create InitialSolution

Define DeploymentStrategy

DevelopArchitecture

Create BuildDocumentation

Develop DetailedDesign

Review and VerifyDesign

CreateImplementation Plan

Procure Resourcesand Facilities

Stage and Install

Certify and Hand-offto Operations

Develop OperationsPolicies andCapabilities

ConfigurationManagement

FaultManagement

ChangeManagement

PerformanceManagement

Review andApprove

BusinessBusinessPlanningPlanning

OperationsOperationsImplementImplementNetworkNetwork

Network Network DesignDesign

Information Flows between Network Analysis, Architecture, and Design

Network Analysis and Design Methodology- Overall Characteristics -

• Requirements (business, application, and data) definition is required prior to network design activities

• Expected compliance with requirements in a Request For Proposal (RFP) by both in-house personnel and outside consultants

• Activities from various stages often take place simultaneously and backtrack to previous activities is sometimes needed

• This methodology is an overall guideline to the network development process rather than “cookbook” instructions

Network Analysis and Design Methodology- Critical Success Factors of the NDLC (1/3) -

• Identification of all potential customers and constituencies– All groups must be consulted

• Political awareness:– Corporate culture: hierarchical, distributed, or open– Backroom politics can play a role in systems design– Find ways to ensure objectivity of the analysis and design process

(e.g., measurable goals)• Buy-in:

– Reach consensus on the acceptability of results of each stage– Approved results of one stage become the foundation or starting

point for the next stage– Makes the final presentation smoother

Network Analysis and Design Methodology- Critical Success Factors of the NDLC (2/3) -

• Communication:– With all groups– Write memos, communicate with key people in person, etc.

• Detailed project documentation:– Prepare agendas– Take meeting minutes– Action items– Use a project binder for all the above

Network Analysis and Design Methodology- Critical Success Factors of the NDLC (3/3) -

• Process/Product awareness:– Stay focused: what is the process/product at each stage?– Keep meeting on track: no off-subject discussions

• Be honest with yourself:– Be your own harshest critic (no one else knows the potential

weaknesses or areas for improvement in your proposal better than you)

– Use peer reviews– Not all weaknesses can be corrected (e.g., financial or time

constraints)

Network Analysis and Design Methodology - Overall Guidelines -

• Start with a clearly defined problem:– Identify affected parties and representatives– Held brainstorming sessions to define problems and

requirements of a solution• Understand strategic business objectives defined by senior

management• Collect baseline data from customer groups about the

current status of the system and network– This is used to measure eventual impact of the installed

network• Perform a feasibility study: problem definition and associated

alternative recommendations for further study

Customer’s Requirements- Understanding the Customer -

• A good network design must recognize the customer’s requirements - need to make sure your design meets THEIR needs and not just YOURS!

• The “Customer” may be your own firm, the “who” you are designing the network for

• Need an overview of a customer’s requirements• The best designed network will fail miserably without the

support of people

Customer’s Requirements- Users’ Needs -

What do the users want?– Services

What do the users need?What don’t they know but they need?Organize and Prioritize Requirement

Customer’s Requirements- How they are used -

• User Requirements Performance Requirements

• Timeliness• Interactivity• Reliability• Quality• Security• Affordability• User Numbers• User Locations• User Growth

Capacity

Reliability

Delay

Analysis and Design Processes

• Set and achieve goals– Maximizing performance– Minimizing cost

• Optimization with trade-offs– Recognizing trade-offs– No single ‘best’ answer

• Hierarchies– Provide structure in the network

• Redundancy – Provides availability & reliability

Approaches Used for Design

• Heuristic – by using various algorithms• Exact – by working out mathematical solutions

based on linear programming, etc., minimizing certain cost functions

• Simulation – often used when no exact analytical form exists. Experiments are conducted on simplified models to see the performance of a network

Design and Study of a System

Art or Science?

The Art of Network Design• Technology choices

• Relations to business goals

The Science of Network Design Understanding of network technologies

Analysis of capacity, redundancy, delay …

Types of Network Design

• New network design

• Re-engineering a network design

• Network expansion design

New Network Design

• Actually starting from scratch

• No legacy networks to accommodate

• Major driver is the budget, no compatibility issues to worry about

• Getting harder to find these situations

Re-engineering a Network Design

• Modifications to an existing network to compensate for original design problems

• Sometimes required when network users change existing applications or functionality

• More of the type of problems seen today

Network Expansion Design

• Network designs that expand network capacity

• Technology upgrades

• Adding more users or networked equipment

OAM&POperations, Administration, Maintenance, Provisioning

NetworkManagement

NetworkProvisioning

Network Operations

NetworkMaintenance

Planning

Design

Fault Management

Trouble TicketAdministration

Network Installation

Network Repairs

Facilities Installation& MaintenanceRoutine NetworkTests

Fault Management / Service Restoration

Configuration Management

Performance Management / Traffic Management

Security Management

Accounting Management

Reports Management

Inventory Management

Data Gathering & Analyses

Figure 1.21 Network Management Functional Groupings

Functional Flow Chart

Engineering Group

- Network Planning &Design

Operations GroupNOC

- Network Operations

I & M Group

-Network Installation &Maintenance

Fault TT

Configuration Data

TT RestorationPerformance & Traffic Data

Installation

Figure 1.22. Network Management Functional Flow Chart

NewTechnology

Network

Users

ManagementDecision