Chapter 9 Network Design Networking in the Internet Age by Alan Dennis 1 Copyright 2002 John Wiley Sons Inc Copyright John Wiley Sons Inc All rights reserved Reproduction or translation of this work beyond that named in Section 117 of the United States Copyright Act without the express written consent of the copyright owner is unlawful Requests for further information should be addressed to the Permissions Department John Wiley Sons Inc Adopters of the textbook are granted permission to make back up copies for their own use only to make copies for distribution to students of the course the textbook is used in and to modify this material to best suit their instructional needs Under no circumstances can copies be made for resale The Publisher assumes no responsibility for errors omissions or damages caused by the use of these programs or from the use of the information contained herein 2 Chapter 9 Learning Objectives Be familiar with the overall process of design and implementing a network Be familiar with techniques for developing a logical network design Be familiar with techniques for developing a physical network design Be familiar with network design principles 3 Chapter 9 Outline Introduction Traditional Network Design Building Block Network Design Needs Analysis Geographic Scope Application Systems Network Users Categorizing Network Needs Deliverables Technology Design Designing Clients and Servers Designing Circuits and Devices Network Design Tools Deliverables Cost Assessment Request for Proposal Selling the Proposal to Management Deliverables Designing for Network Performance Managed Networks Network Circuits Network Devices Minimizing Network Traffic 4 Introduction 5 Traditional Network Design The traditional network design approach follows a structured systems analysis and design process similar to that used to build application systems The network analyst meets with users to determine the needs and applications The analyst estimates data traffic on each part of the network The analyst designs circuits needed to support this traffic and obtains cost estimates Finally a year or two later the network is implemented 6 Traditional Network Design Three forces are making the traditional design approach less appropriate for many of today s networks 1 The underlying technologies used in computers networking devices and network circuits are rapidly changing 2 Network traffic is growing rapidly 3 The balance of costs has changed dramatically over the last 10 years 7 Building Block Network Design Figure 9 1 While some organizations still use the traditional approach many others use a simpler approach to network design the building block approach This approach involves three phases needs analysis technology design and cost assessment When the cost assessment is initially completed the design process returns to the needs analysis phase and cycles through all three phases again refining the outcome of each phase The process of cycling through all three design phases is repeated until a final design is decided on Figure 9 2 8 Figure 9 1 Network Design 9 Fig 9 2 The cyclical nature of network design 10 Needs Analysis 11 Needs Analysis The first step is to analyze the needs of network users along with the requirements of network applications Most efforts today involve upgrades and not new network designs so most needs may already be understood LAN and BN design issues include improving performance upgrading or replacing unreliable or aging equipment or standardizing network components to simplify network management At the MAN WAN level circuits are leased and upgrades involve determining if capacity increases are needed The object of needs analysis is to produce a logical network design which describes what network elements will be needed to meet the organization s needs 12 Geographic Scope Figure 9 3 Needs analysis begins by breaking the network into three layers based on their geographic and logical scope The access layer which lies closest to the user The distribution layer which connects the access layer to the rest of the network The core layer which connects the different parts of the distribution layer together 13 Figure 9 3 Geographic Scope 14 Application Systems The designers must review the applications currently used on the network and identify their location so they can be connected to the planned network baselining Next applications expected to be added to the network are included It is also helpful to identify the hardware and software requirements and protocol type for each application 15 Network Users In the past application systems accounted for the majority of network traffic Today much network traffic comes from Internet use i e e mail and WWW The number and type of users that will generate network traffic may thus need to be reassessed Future network upgrades will require understanding how the use of new applications such as video will effect network traffic 16 Categorizing Network Needs The next step is to assess the traffic generated in each segment based on an estimate of the relative magnitude of network needs i e typical vs high volume This can be problematic but the goal is a relative understanding of network needs Once identified network requirements should be organized into mandatory requirements desirable requirements and wish list requirements 17 Deliverables The key deliverable for the needs assessment stage is a set of network maps showing the applications and the circuits clients and severs in the proposed network categorized as typical or high volume 18 Figure 9 4 Sample needs assessment 19 Technology Design 20 Technology Design After needs assessment has been completed the next design phase is to develop a technology design or set of possible designs for the network 21 Designing Clients and Servers In the building block approach the technology design is specified by using standard computer units Typical users are allocated base level client computers as are servers supporting typical applications High volume users and servers are assigned advanced computers The definition for a standard unit however keeps changing as hardware costs continue to fall 22 Designing Circuits and Devices Two interrelated decisions in designing network circuits and devices are 1 deciding on the fundamental technology and protocols and 2 choosing the capacity each circuit will operate at Capacity planning means estimating the size and type of the standard and advanced