Determining New Requirements


Background.  Now that we have looked at the current network infrastructure, we will start to look towards the future of the firm to help determine how the network can be improved.  Again, the Teare book presents a series of steps that will first be presented summarily and then described in more detail.
  1. Identify business constraints
  2. Identify security requirements
  3. Identify manageability requirements
  4. Determine application requirements
  5. Characterize new network traffic
  6. Identify performance requirements
  7. Create a customer needs specification document (optional)

Now we will go into much more detail about each of these steps.

Step 1 - Identify Business Constraints.  The following outlines three major aspects of performing this identification.

  • Document the budget and resources available for this project.
  • Document the time line for this project.
  • Identify the staffing requirements, such as hiring or training.

Step 2 - Identify Security Requirements.  The following outlines five major aspects of performing this identification.

  • Appraise security risks and determine how much and what types of security will be needed.
  • Determine requirements for outside users to access data.
  • Determine the authorization and authentication requirements for branch offices, mobile users and telecommuters.
  • Identify any requirements for authenticating routes received from access routers or other routers.
  • Identify any requirements for host security, such as physical security of the devices, user accounts, dated software, access rights on data and etceteras.

One of the standard ways to help identify security requirements is to develop an Authorization Matrix.  Such a matrix is going to list the services that users may need authorizations across the top.  It is going to list the users and user groups and the sorts of authorizations they will need for these services down the side.  Then the elements of the matrix are filled in with appropriate abbreviations to denoted things like read access, write access, administrative rights, report access and on and on.  The following is a small example matrix for a small e-commerce firm.




  Online Store Store
General Employees RU X W X  
Developers RWEU RWEU W X  
Product Managers   RWE W X  
Personnel       RWEU  

R - read access
W - write access
E - execute access
U - use access
X - no access

Step 3 - Identify Manageability Requirements.  The following outlines five major aspects of performing this identification.
  • Isolate any requirements for fault management.
  • Isolate any requirements for accounting management.
  • Isolate any requirements for configuration management.
  • Isolate any requirements for performance management.
  • Isolate any requirements for security management.

Step 4 - Determine Application Requirements.  The following outlines five major aspects of performing this identification.

  • Document the names and types of new applications.
  • Document the names and types of new protocols.
  • Document the number of users who will use new applications and protocols.
  • Document the flow of information when new applications are introduced.
  • Identify the peak hours of usage of new applications.

Step 5 - Characterize New Network Traffic.  The following outlines three major aspects of performing this characterization.  Two of these aspects have a sizable number of sub-aspects that will be outlined also.  Since this entire step will often get more technical and involved than the other steps, we will dedicate an entire subsequent web page to this step.

  • Characterize traffic load.
  • Characterize traffic behavior including, 
    • Broadcast/multicast behavior
    • Frame size(s) supported
    • Windowing and flow control
    • Error recovery mechanisms
  • Use tools such as the following used previously when characterizing the existing network.
    • Cisco's NETSYS and NETSYS Baseliner Tools.
    • Cisco's NetFlow switching traffic management.
    • CiscoWorks.
    • Protocol analyzers such as Network Associate's Sniffer network analyzer.
    • The Scion software package, developed by Merit Network, Incorporated.

Step 6 - Identify Performance Requirements.  The following outlines seven major aspects of identifying performance requirements.  

  • Response Time - the amount of time to receive a response to a request for a service from the network system.
  • Accuracy - the percentage of useful traffic that is correctly transmitted on the system, relative to total traffic, including transmission errors
  • Availability - the amount of time the network is operational, sometimes expressed as MTBF - mean time between failure
  • Maximum Network Utilization - the maximum percentage of the total capacity (bandwidth) of a network segment that can be used before the network is considered to be saturated
  • Throughput - the quantity of data successfully transferred between nodes per unit of time, usually in bits per second.
  • Efficiency - the measure of how much effort is required to produce a certain amount of data throughput
  • Latency - the time between a frame being ready for transmission from a node and the successful completion of the transmission.

Step 7 - Create  Customer Needs Specification Document (Optional).  To create a customer needs document you need to record the customer's requirements and constraints, and the characteristics of the existing network.  The goal of this document is to record the

  • characterization of the existing network
  • requirements for the new network
  • constraints under which the new network must be constructed

The information from this page's process and the steps completed in the previous two webs are agglutinated and organized in one place.

This document can also serve as the basis of the agreement between you and your customer on the network design requirements.  It is also an excellent start for the document you will produce when you complete the implementation of your design.